U.S. patent application number 13/442720 was filed with the patent office on 2013-03-28 for ammonia nanosensors, and environmental control system.
This patent application is currently assigned to NANOMIX, INC.. The applicant listed for this patent is Mikhail Briman, Craig Bryant, Ying-Lan Chang, Jean-Christophe P. Gabriel, Shripal C. Gandhi, Bradley N. Johnson, Willem-Jan Ouborg, John Loren Passmore, Kastooriranganathan Ramakrishnan, Sergei Skarupo, Alexander Star, Christian Valcke. Invention is credited to Mikhail Briman, Craig Bryant, Ying-Lan Chang, Jean-Christophe P. Gabriel, Shripal C. Gandhi, Bradley N. Johnson, Willem-Jan Ouborg, John Loren Passmore, Kastooriranganathan Ramakrishnan, Sergei Skarupo, Alexander Star, Christian Valcke.
Application Number | 20130075690 13/442720 |
Document ID | / |
Family ID | 39316886 |
Filed Date | 2013-03-28 |
United States Patent
Application |
20130075690 |
Kind Code |
A1 |
Briman; Mikhail ; et
al. |
March 28, 2013 |
Ammonia Nanosensors, and Environmental Control System
Abstract
Embodiments of nanoelectronic sensors are described, including
sensors for detecting analytes such ammonia. An environmental
control system employing nanoelectronic sensors is described. A
personnel safety system configured as a disposable badge employing
nanoelectronic sensors is described. A method of dynamic sampling
and exposure of a sensor providing a number of operational
advantages is described.
Inventors: |
Briman; Mikhail;
(Emeryville, CA) ; Bryant; Craig; (Alameda,
CA) ; Chang; Ying-Lan; (Cupertino, CA) ;
Gabriel; Jean-Christophe P.; (Pinole, CA) ; Gandhi;
Shripal C.; (Los Angeles, CA) ; Johnson; Bradley
N.; (Berkeley, CA) ; Ouborg; Willem-Jan;
(Moraga, CA) ; Passmore; John Loren; (Berkeley,
CA) ; Ramakrishnan; Kastooriranganathan; (San Rafael,
CA) ; Skarupo; Sergei; (Berkeley, CA) ; Star;
Alexander; (Pittsburgh, PA) ; Valcke; Christian;
(Orinda, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Briman; Mikhail
Bryant; Craig
Chang; Ying-Lan
Gabriel; Jean-Christophe P.
Gandhi; Shripal C.
Johnson; Bradley N.
Ouborg; Willem-Jan
Passmore; John Loren
Ramakrishnan; Kastooriranganathan
Skarupo; Sergei
Star; Alexander
Valcke; Christian |
Emeryville
Alameda
Cupertino
Pinole
Los Angeles
Berkeley
Moraga
Berkeley
San Rafael
Berkeley
Pittsburgh
Orinda |
CA
CA
CA
CA
CA
CA
CA
CA
CA
CA
PA
CA |
US
US
US
US
US
US
US
US
US
US
US
US |
|
|
Assignee: |
NANOMIX, INC.
Emeryville
CA
|
Family ID: |
39316886 |
Appl. No.: |
13/442720 |
Filed: |
April 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11636360 |
Dec 8, 2006 |
8152991 |
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13442720 |
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11588845 |
Oct 26, 2006 |
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11636360 |
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60748834 |
Dec 9, 2005 |
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60730905 |
Oct 27, 2005 |
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60773138 |
Feb 13, 2006 |
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60850217 |
Oct 6, 2006 |
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Current U.S.
Class: |
257/9 ;
977/957 |
Current CPC
Class: |
G01N 27/127 20130101;
G01N 27/4146 20130101; G01N 33/0062 20130101; Y10S 977/957
20130101; G01N 27/129 20130101; B82Y 15/00 20130101; G01N 33/0054
20130101; H01L 29/0669 20130101; G01N 2033/0068 20130101 |
Class at
Publication: |
257/9 ;
977/957 |
International
Class: |
H01L 29/06 20060101
H01L029/06 |
Claims
1. A nanostructure sensor for sensing an analyte of interest in a
sample, comprising: a substrate; a nanostructured element disposed
adjacent the substrate; one or more conducting elements in
electrical communication with the first nanostructure; and at least
one functionalization operatively associated with the
nanostructured element, the at least one functionalization
configured to provide sensitivity for the analyte of interest.
2. A sensor as in claim 1, wherein the nanostructured element
includes a network of carbon nanotubes disposed adjacent the
substrate.
3. A sensor as in claim 2, wherein the analyte of interest includes
ammonia.
4. A sensor as in claim 2, wherein the at least one
functionalization includes an organic recognition material.
5. A sensor as in claim 4, wherein the organic recognition material
includes a polymer.
6. A sensor as in claim 5, wherein the polymer includes at least
one of a conductive polymer and a semi-conductive polymer.
7. A sensor as in claim 4, wherein the organic recognition material
includes PABS.
8. A sensor as in claim 4, wherein the organic recognition material
includes a nonionic surfactant.
9. A sensor as in claim 4, wherein the organic recognition material
includes glycerol.
10. A sensor as in claim 4, wherein the network includes at least
one SWNTs which is stably associated with the organic recognition
material prior to formation of the network.
11. A sensor as in claim 2, wherein the at least one
functionalization includes an inorganic recognition material.
12. A sensor as in claim 2, wherein the one or more conducting
elements includes a spaced-apart pair of conducting elements
defining a conduction path through at least a portion of the
network.
13. A sensor as in claim 12, wherein the conduction path includes
electrical interconnections between carbon nanotubes.
14. A sensor as in claim 13, wherein substantially none of the
nanotubes are in contact with both of the spaced-apart pair of
conducting elements.
15. A sensor as in claim 1, further comprising a gate electrode
configured to electrically influence the nanostructured
element.
16. A nanostructure sensor for sensing an analyte of interest,
comprising: a substrate, the substrate including a generally
sheet-like base material and at least one conductor formed on a
surface of the substrate; a network of nanostructures deposited on
the substrate so as to contact the at least one conductor
formation, the network being deposited on the substrate subsequent
to the forming of the at least one conductor; a recognition
material disposed in associated with the network of nanostructures,
the recognition material configured to interact with the analyte of
interest.
17. A sensor as in claim 16, wherein the substrate comprises a
flexible polymeric material, and wherein the network of
nanostructures includes carbon nanotubes deposited upon the
substrate from a liquid suspension.
18. A sensor as in claim 17, wherein the substrate comprises a
flexible polymeric material, and wherein the network of
nanostructures includes carbon nanotubes deposited upon the
substrate from a liquid suspension.
19. A sensor as in claim 18, wherein the recognition material is
associated with the nanotubes prior to the deposition of the
nanotubes from liquid suspension.
20. A sensor as in claim 18, wherein the sensor includes at least a
pair of conductors formed on the substrate in a spaced-apart
arrangement, the network of nanotubes configured to electrically
communicate between the pair of conductors, and the recognition
material configured so that the interaction of the recognition
material with the analyte of interest produces a change in the
conductivity of the network between the pair of conductors.
21.-37. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority pursuant to 35 USC.
.sctn.119(e) to the following US Provisional applications, each of
which applications are incorporated by reference: [0002] No.
60/748,834 filed Dec. 9, 2005 entitled "Nanoelectronic Sensors
Having Substrates With Pre-Patterned Electrodes, And Environmental
Ammonia Control System".
[0003] This application is a continuation-in-part of and claims
priority to U.S. patent application Ser. No. 11/588,845, filed Oct.
26, 2006 (Attorney Docket No. 612, 407-098; published 2006-______),
entitled "Anesthesia Monitor, Capacitance Nanosensors and Dynamic
Sensor Sampling Method", which is incorporated by reference; and
which in turn claims the priority to the following US provisional
and non-provisional patent applications, each of which applications
are incorporated by reference: [0004] No. 11/488,456 filed Jul. 18,
2006 (published 2006-______) entitled "Improved Carbon Dioxide
Nanosensor, And Respiratory CO.sub.2 Monitors", [0005] No.
11/437,275 filed May 18, 2006 (published 2006-______) entitled
"Nanoelectronic Breath Analyzer and Asthma Monitor", [0006] No.
11/390,493 filed Mar. 27, 2006 (published 2006-______) entitled
"Nanoelectronic Measurement System For Physiologic Gases, And
Improved Nanosensor For Carbon Dioxide", [0007] No. 11/111,121
filed Apr. 20, 2005 (published 2006-0055,392) entitled "Remotely
communicating, battery-powered nanostructure sensor devices",
[0008] No. 11/019,792 filed Dec. 18, 2004 (published 2005-0245,836)
entitled "Nanoelectronic capnometer adapter", [0009] No. 10/940,324
filed Sep. 13, 2004 (published 2005-0129,573) entitled "Carbon
Dioxide Nanoelectronic Sensor", [0010] No. 10/656,898 filed Sep. 5,
2003 (published 2005-0279,987) entitled "Polymer Recognition Layers
For Nanostructure Sensor Devices", [0011] No. 60/730,905 filed Oct.
27, 2005, [0012] No. 60/850,217 filed Oct. 6, 2006, [0013] No.
60/773,138 filed Feb. 13, 2006, [0014] No. 60/700,944 filed Jul.
20, 2005, [0015] No. 60/683,460 filed May 19, 2005, [0016] No.
60/665,153 filed Mar. 25, 2005, [0017] No. 60/564,248, filed Apr.
20, 2004, [0018] No. 60/531,079 filed Dec. 18, 2003, [0019] No.
60/502,485 filed Sep. 12, 2003, and [0020] No. 60/408,547 filed
Sep. 5, 2002.
[0021] This application is related in subject matter to U.S. patent
application Ser. No. 11/090,550 filed Mar. 25, 2005 entitled
"Sensitivity Control For Nanotube Sensors", which is a divisional
of No. 10/280,265 filed Oct. 26, 2002 (U.S. Pat. No. 6,894,359),
which claims priority to U.S. No. 60/408,412 filed Sep. 4, 2002;
each of which applications are incorporated by reference.
[0022] This application is related in subject matter to U.S. patent
application Ser. No. 10/846,072 filed May 14, 2004 (published
2005-0184,641) entitled "Flexible Nanotube Transistors", which
claims priority to U.S. No. 60/471,243 filed May 16, 2003; each of
which applications are incorporated by reference.
[0023] This application is related in subject matter to U.S. patent
application Ser. No. 10/177,929 filed Jun. 21, 2002 entitled
"Dispersed Growth Of Nanotubes On A Substrate" (equivalent
published as WO04-040,671); each of which applications are
incorporated by reference.
[0024] This application is related in subject matter to U.S. patent
application Ser. No. 11/139,184 filed May 27, 2005 entitled
"Modification Of Selectivity For Sensing For Nanostructure Device
Arrays", which is a continuation of No. 10/388,701 filed Mar. 14,
2003 (U.S. Pat. No. 6,905,655), which claims the priority of U.S.
No. 60/366,566 filed Mar. 22, 2002, and which also is a
continuation-in-part of U.S. Ser. No. 10/099,664 filed Mar. 15,
2002; each of which applications are incorporated by reference.
BACKGROUND OF THE INVENTION
[0025] 1. Field of the Invention
[0026] The present invention relates to nanoelectronic devices, and
in particular to nanostructured sensor systems for measurement of
environmental gases, such as ammonia. Nanostructured sensor
embodiments having aspects of the invention have utility in
industrial, medical, and personal safety applications, including
refrigeration leak detection, environmental management of poultry
houses, and the like.
[0027] 2. Description of Related Art
[0028] Ammonia has known toxic effects on both humans and animals
even at low exposure levels. For example, occupational health
regulations typically set upper limits for acceptable ammonia
concentrations for human exposure. The limit in the UK is 25 ppm,
in Sweden and Germany the limit is 25 and 20, respectively, for an
8-hour working day. Sweden also has a second limit of 50 ppm for a
maximum of 5 minutes exposure.
[0029] In addition, ammonia is a common environmental contaminant
in poultry houses with important consequences to poultry
production. See, for example, I. Estevez, "Ammonia And Poultry
Welfare", Poultry Perspectives, Univ. of Maryland, Spring 2002
volume 4, issue 1, which publication is incorporated by
reference.
[0030] Ammonia in poultry houses is difficult to avoid. Uric acid
is excreted by poultry and, unless immediately removed, is
decomposed by bacteria growing in the warm, moist conditions
present in the poultry house litter. Under these conditions, uric
acid is readily oxidized (enzymatic oxidative hydrolysis) to form
urea as follows:
C.sub.2(NH).sub.4(CO).sub.3+2H.sub.2O+1.5O.sub.2.fwdarw.2(NH.sub.2).sub.-
2CO+3CO.sub.2 (1)
Urea in turn is readily decomposed to form ammonia (hydrolysis by
urease) as follows:
(NH.sub.2).sub.2CO+H.sub.2O.fwdarw.2NH.sub.3+CO.sub.2 (2)
[0031] The combination of ammonia and wet litter is responsible for
a large number of health- and density-related welfare problems in
poultry, for example, the occurrence of ascites, gastrointestinal
irritation, and respiratory diseases is correlated with high levels
of ammonia, as shown in TABLE 1.
TABLE-US-00001 TABLE 1 Effect of ammonia levels on poultry health
Level (ppm) Effects 10 Trachea irritation, susceptible to bacterial
infections. 20 Increased rate of infection by Newcastle disease.
25-75 Impaired growth rate and feed conversion, reduced final body
weight. 25-50 Air sac inflammation 50 Increased levels of
keratoconjunctivitis. 100 Increased chick mortality.
[0032] In addition to the animal welfare consequences of the pain
and stress of ammonia related pathologies, ammonia levels above
about 25-50 ppm have an important, affect on growth rate and feed
conversion performance. See B. Lott, "Will ammonia really hurt
broiler performance?", Chicken Talk, Mississippi State University
Extension, Information sheet No. 1639, 2003, which publication is
incorporated, by reference. It is believed that ammonia levels have
a greater impact than behavioral factors in depressing poultry
growth at high rearing densities (TABLE 2).
TABLE-US-00002 TABLE 2 Effect of ammonia on average body weight of
males at 7 weeks age. Ammonia (ppm) 4 weeks (lb) 7 weeks (lb) 0
2.99 6.74 25 2.95 6.55 50 2.41 6.24 75 2.47 6.23
[0033] Note that the effects of ammonia are highly dependent on
exposure time. Therefore any effect demonstrated at rather high
concentrations is likely to be present at much lower concentrations
with longer exposure times. The cumulative effect of reduction in
poultry growth and feed conversion due to environmental ammonia is
a major economic burden on the poultry industry.
[0034] While ammonia levels may be partially controlled by
attention to poultry diet, watering equipment, absorbent litter,
and the like, adequate ventilation control is a necessary component
of ammonia level management, as well as for temperature and
humidity control. U.S. Pat. No. 5,407,129 issued to Carey et al.
describes systems and methods for environmental control of poultry
houses, and suggests that ammonia sensors may be included in such
systems, which patent is incorporated by reference. However, in
practice, systems have not been introduced into the poultry
industry that use measurement of ammonia as a primary control
variable, and instead typically seek to control ammonia indirectly
by monitoring and controlling humidity and temperature.
[0035] A variety of different techniques for ammonia sensing are
available for sensing ammonia, but generally suffer from one
disadvantage or another. Colorimetric indicators or sensing paper
do not provide an electronic signal suitable for feedback control
systems. Metal-oxide and catalytic metal detectors have generally
low selectivity, drift and a high operating temperatures
(.about.400-600 C). Optical gas sensors are generally large,
expensive, and slow in response. Conducting polymer detectors have
irreversible reactions, limiting their utility.
[0036] Current electrochemical sensors for ammonia have an
electrolyte component that is consumed as the sensor is exposed to
ammonia, thereby limiting service life, except in very low level
exposure. The sensor life rating is thus in terms of "exposure time
at concentration". For example, for a sensor rating of 1000
ppm-day, an exposure to 50 ppm of ammonia (realistic level for
poultry houses) for 20 days will completely exhaust the
electrolyte.
[0037] What is needed is a low-cost, compact electronic sensor with
dependable service life, stable calibration and high selectivity,
to provide a practical ammonia sensor for medical, industrial and
personal safety applications. In particular, there is a need for
such sensors for environmental management of poultry houses and
other livestock enclosures.
SUMMARY OF THE INVENTION
[0038] Exemplary embodiments of nanoelectronic sensors having
aspects of the invention have a conductive (e.g., semiconducting)
nanostructured element, the nanostructured element comprising a
nanostructured material or "nanostructure". As used herein, the
terms "nanostructure" or "nanostructured material" include a
particulate or macromolecular entities having at least one
dimension less than about 100 nm. The nanostructured material or
nanostructure may include single or multiple-wall carbon nanotubes,
nanoparticles, nanowires, nanofibers, nanorods, nanospheres,
nanohorns or the like, or mixtures of these. Additionally,
nanostructures may self-assemble to form composite structures, such
as ropes, bundles, or other stable aggregations. Although the
principal examples include one or more carbon nanotubes, the
nanostructures may comprise boron, boron nitride, and carbon boron
nitride, silicon, germanium, gallium nitride, zinc oxide, indium
phosphide, molybdenum disulphide, silver, or other suitable
materials.
[0039] A preferred nanostructured material for employment in
nanoelectronic sensors is the carbon nanotube. Nanotubes were first
reported in 1993 by S Iijima and have been, the subject of intense
research since. Single walled nanotubes (SWNTs) are characterized
by strong covalent bonding, a unique one-dimensional structure, and
exceptionally high tensile strength, high resilience, metallic to
semiconducting electronic properties, high current carrying
capacity, and extreme sensitivity to perturbations caused by
charged species in proximity to the nanotube surface. Elements
based on nanostructures such carbon nanotubes (CNT) have unique
electrical characteristics, and their sensitivity to environmental
changes can modulate the surface energies of the CNT, and can
measurably change electrical properties, such as resistance,
conductivity, transistor characteristics, capacitance or impedance,
and the like. Certain exemplary embodiments having aspects of the
invention include single-walled carbon nanotubes (SWNTs) as
semiconducting or conducting elements.
[0040] Embodiments of sensors may comprise a substrate and a
nanostructured element disposed adjacent the substrate. Such
nanostructured elements may comprise single or pluralities of
discrete parallel elements (e.g. CNTs). For many applications,
however, it is advantageous to employ nanostructured elements
comprising a film, mat, array or network of semiconducting or
conducting nanotubes (or other nanostructures) substantially
randomly distributed adjacent a substrate, conductivity being
maintained by interconnections between nanotubes. In examples
including a substrate configured to have a generally planar form,
the nanostructured element may comprise a generally planar layer or
coating arranged parallel to the substrate surface. In alternative
examples including a substrate configured to have a curved surface
shape, such as a rod, or tube-like form, the nanostructured element
may comprise a layer or coating arranged to have a similar shape
adjacent the substrate.
[0041] One or more conductive elements, contacts or electrodes may
be disposed adjacent to the nanostructured element so as to
communicate electrically with the nanostructured element.
[0042] Nanostructured materials comprising a nanostructured element
may be non-functionalized, or may functionalized to alter
properties. In some embodiments, a nanoelectronic sensor may
include a recognition material, layer or coating disposed in
association with the nanostructured element, wherein the
recognition material may be configured to influence the response of
the sensor to an analyte of interest (e.g., increase sensitivity,
response rate, or the like) and/or may be configured to influence
the response of the sensor to the operating environment (e.g.,
increase selectivity, reduce interference or contamination, or the
like).
[0043] For example, functionalization material reactive with
NH.sub.3 may be disposed on a sensor, for example, on a nanotube.
Recognition layers that preserve the semi-conductive or conductive
properties may be selected from noncovalent materials, for example,
polymer coatings. In certain examples, a recognition material may
be isolated from the nanostructure by an insulating coating, such
as an ALD dialectic material. Gate electrodes, reference electrodes
or other counter electrodes may be included, e.g., for transistor
measurements or capacitance measurements of sensor properties.
[0044] Certain exemplary embodiments of sensors including
nanostructured elements (nanoelectronic sensor or nanosensor) are
described in parent application Ser. No. 10/940,324 (published US
2005-0129,573), which is incorporated by reference. Nanosensors
having aspects of the invention may be configured for the
measurement of analytes, for example ammonia (NH.sub.3) present in
environmental air. An NH.sub.3 sensor may be connected to an
electrical circuit, which will respond to changes in NH.sub.3
concentration in the ambient sensor environment.
[0045] In certain examples, a single substrate sheet, surface or
chip may include a plurality of sensors, capable of one or more
analytes. Much of the signal processing may be built into the
sensor board, requiring only simple and inexpensive external
instrumentation for display and data logging, so as to provide a
fully calibrated, packaged gas sensor. Alternative embodiments
having aspects of the invention include systems configured to
include multiplexed assays on a single sensor platform or chip,
microprocessors and/or wireless transceivers, permitting convenient
recordation and analysis of measurement histories and/or remote
monitoring. The output is digital so electronic filtering and post
processing may be used to eliminate extraneous noise, if need be.
See, for example, U.S. patent application Ser. No. 11/111,121 filed
Apr. 20, 2005 entitled "Remotely communicating, battery-powered
nanostructure sensor devices"; which is incorporated by
reference.
[0046] Alternative embodiments having aspects of the invention are
configured for detection of analytes employing nanostructured
sensor elements configured as one or more alternative types of
electronic devices, such as capacitive sensors, resistive sensors,
impedance sensors, field effect transistor sensors, and the like,
or combinations thereof. Two or more such measurement strategies in
a may be included in a sensor device so as to provide orthogonal
measurements that increase accuracy and/or sensitivity. Alternative
embodiments have functionalization groups or material associated
with the nanostructured element so as to provide sensitive,
selective analyte response.
[0047] One embodiment of a nanosensor having aspects of the
invention comprises: a substrate; a nanostructured element disposed
adjacent the substrate; one or more conducting elements in
electrical communication with the first nanostructure; and at least
one functionalization operatively associated with the
nanostructured element, the at least one functionalization
configured to provide sensitivity for the analyte of interest.
Alternative functionalization materials include a range of organic
and inorganic materials. A preferred embodiment includes a network
of carbon nanotubes disposed adjacent the substrate and
functionalized for sensitivity to ammonia. A number of alternative
structures and functionalization schemes are described more
particularly in the description below and the claims herein.
[0048] An alternative embodiment of a nanosensor having aspects of
the invention comprises: a substrate, the substrate including a
generally sheet-like base material and at least one conductor
formed on a surface of the substrate; a network of nanostructures
deposited on the substrate so as to contact the at least one
conductor formation, the network being deposited on the substrate
subsequent to the forming of the at least one conductor; and a
recognition material disposed in associated with the network of
nanostructures, the recognition material configured to interact
with the analyte of interest. In certain examples, the substrate
comprises a flexible polymeric material, and wherein the network of
nanostructures includes carbon nanotubes deposited upon the
substrate from a liquid suspension. In other examples, a
recognition material is associated with the nanotubes prior to the
deposition of the nanotubes from liquid suspension. A number of
alternative structures and functionalization schemes are described
more particularly in the description below and the claims
herein.
[0049] An embodiment of an integrated sensor system having aspects
of the invention comprises: a nanosensor as described above and
configured to expose at least a portion of the network and
associated functionalization to a sample, and further comprising a
contact in communication with the at least one conducting element,
the contact exposed on the sensor surface. The embodiment further
comprises a sensor socket, including: a body configured to engage
and mount the sensor; at least one pin configured to electrically
communicate with at least the contact when the sensor is mounted in
the socket, the pin configured to communicate at least one signal
to measurement circuitry; and an opening configured to provide that
the portion of the network and associated functionalization
communicates with the sample. In preferred alternatives the sensor
is functionalized for sensitivity to ammonia and may be disposable.
A number of alternative structures and functionalization schemes
are described more particularly in the description below and the
claims herein.
[0050] One embodiment of a control system for regulating the
internal environment having aspects of the invention comprises a
sensor as described above; and a processor in communication with
the sensor so as to receive at least one signal indicative of a
concentration of the analyte of interest, the processor configured
to send at least a command signal to an environmental actuator in
response to the at least one signal, the command suited to cause
the environmental actuator to control the concentration of the
analyte of interest in the enclosed volume. In preferred
alternatives the sensor is functionalized for sensitivity to
ammonia and may be disposable. A number of alternative structures
and functionalization schemes are described more particularly in
the description below and the claims herein.
[0051] One embodiment of a personnel safety badge having aspects of
the invention comprises: a badge body, configured to be worn by the
user; a sensor as described above disposed adjacent to the body and
configured to measure the analyte of interest; a processor disposed
adjacent to the body and in communication with the sensor so as to
receive at least one signal indicative of a concentration of the
analyte of interest; a power source disposed adjacent to the body
and in communication with the processor; and at least one warning
output device disposed adjacent to the body, in communication with
the processor, and produce at least one communication to the user
in response to a concentration of the analyte of interest in the
environment of a user.
[0052] One method embodiment for dynamic sensor operation having
aspects of the invention comprises: (a) selectively exposing at
least a portion of a sensor to the environment so that the sensor
portion is exposed only intermittently; and (b) dynamically
sampling a response signal output from the sensor so as to
determine the presence or concentration of the analyte of by
analysis of the dynamically sampled signal. A number of alternative
operational steps are described more particularly in the
description below and the claims herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] The following is a list which summarizes the drawings and
figures herein:
[0054] FIG. 1 is a cross-sectional diagram which illustrates an
exemplary electronic sensing device for detecting an analyte,
configured in this example as a NTFET.
[0055] FIG. 2 are photographic views of a sensor system such as
shown in FIG. 1, wherein views (a-c) include SEM images showing (a)
showing the layout of interdigitated source and drain contacts S,D,
(b) showing an enlarged detail of a nanotube network N and the
contacts 5, D, and (c) showing an enlarged detail of the margin of
network N. View (d) shows an example of a sensor device mounted in
a conventional electronic device package.
[0056] FIG. 3A shows the device characteristics for a transistor
device (NTFET) embodiment without additional functionalization
(bare nanotubes) to a pulse of 200 ppm ammonia.
[0057] FIG. 3B shows exemplary response of a nanotube device that
is not coated with a recognition layer to fluctuating levels of NH3
in a test environment.
[0058] FIG. 3C shows exemplary improved response of a nanotube
device coated with a PEI recognition layer to NH3 in the same test
environment.
[0059] FIG. 4 is a cross-sectional diagram which illustrates an
exemplary electronic sensing device, similar in a number of
respects to the device of FIG. 1, configured in this example
configured for measurement of capacitance and related properties as
a signal for detecting an analyte.
[0060] FIG. 5A shows the response of both capacitance signals and
resistance signals to samples of isoflurane in air.
[0061] FIG. 5B shows the response of both capacitance signals and
resistance signals to samples of halothane in air.
[0062] FIG. 6 is a flow diagram showing exemplary steps of a method
according to the invention for producing a device including a CVD
deposited CNT network and having a polymer substrate;
[0063] FIG. 7 is a plot showing the response to ammonia of the
sensor of FIG. 6.
[0064] FIGS. 8A-8C illustrate alternative embodiments of sensors
having solution deposited nanotube networks, wherein:
[0065] FIG. 8A shows a sensor in which a recognition layer is
applied following deposition of nanotube film;
[0066] FIG. 8B shows a sensor in which a layer of recognition
material is deposited upon the substrate prior to application of a
nanotube film 2; and
[0067] FIG. 8C shows a sensor which includes a layer of
pre-functionalized nanotubes without a distinct recognition
layer.
[0068] FIG. 9 shows an exemplary embodiment of a sensor device 50
having aspects of the invention and including a nanotube networks
fabricated by deposition of a solution of pre-functionalized
nanotubes upon a substrate.
[0069] FIG. 10 shows the response of the sensor of FIG. 8 to
repeated exposures of 50 ppm of ammonia.
[0070] FIG. 11 shows the response of the sensor of FIG. 8 to
ammonia exposures through a dynamic range spanning 50 ppm to 500
ppm.
[0071] FIG. 12 is a schematic layout diagram of an exemplary
environmental control system including a nanoelectronic ammonia
sensor having aspects of the invention.
[0072] FIGS. 13A-13E illustrate alternative embodiments of sensors
having aspects of the invention and including nanotube networks
fabricated by deposition of a solution upon flexible substrates
with pre-patterned conductor traces, wherein:
[0073] FIG. 13A shows an alternative sensor including a gate
dielectric and gate electrode;
[0074] FIG. 13B shows a sensor including a plurality of distinct
pairs of pre-patterned traces having differently functionalized
nanotube networks;
[0075] FIG. 13C shows a sensor generally similar to that shown in
FIG. 9, and having additional layers for conditioning the
sample;
[0076] FIG. 13D shows a sensor configured as a capacitance sensor;
and
[0077] FIG. 13E shows alternative embodiment of a capacitance
sensor.
[0078] FIGS. 14A-14E illustrate an exemplary embodiment of a sensor
system having aspects of the invention, wherein:
[0079] FIG. 14A shows a sensor generally similar to the embodiment
of FIG. 9 configured as a disposable sensor;
[0080] FIG. 14B shows a sensor mounting socket suitable for the
sensor of FIG. 14A;
[0081] FIG. 14C shows the sensor of FIG. 14A as sealed in a
"blister pack" package; and
[0082] FIG. 14D shows the sensor of FIG. 14A as mounted in the
socket of FIG. 14C.
[0083] FIG. 15 shows an exemplary embodiment of a control system
employing the disposable sensor and socket of FIGS. 14A-14D.
[0084] FIG. 16 shows an exemplary embodiment of a personnel safety
badge having aspects of the invention.
[0085] FIG. 17 shows an exemplary embodiment of a sensor having a
network suspended apart from a substrate.
[0086] FIG. 18 is a schematic plot illustrating principles of a
dynamic sensor sampling method having aspects of the invention.
[0087] FIG. 19 is a schematic plot an example of dynamic sensor
sampling for a step change in analyte concentration, having a fixed
response cut-off values and recovery interval.
[0088] FIG. 20 is a schematic plot an example of dynamic sensor
sampling for a step change in analyte concentration, having both
fixed maximum and minimum values.
[0089] FIG. 21 is a schematic plot an example of dynamic sensor
sampling for a step change in analyte concentration, having a both
fixed measurement and recovery intervals.
[0090] FIG. 22 is a schematic diagram of an exemplary sensor system
configured for employing a dynamic sampling method.
[0091] FIG. 23 illustrates the structure of a sensor adapted for
measuring NH3, for example in a system such as is shown in FIG.
22.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A. Exemplary Nanosensor Architecture
[0092] FIG. 1. shows an exemplary electronic sensing device 100
having aspects of the invention, for detecting an analyte 101
(e.g., inorganic species such as NH.sub.3, CO.sub.2, H.sub.2S, NO
and the like; organic compounds such as glucose, ethanol and the
like; biomolecules such as DNA, globular proteins and the like). A
number of alternative sensor device architectures and operating
modes are possible, and may be employed alone or in combinations
without departing from the spirit of the invention. In the example
of FIG. 1, sensing device 100 includes a nanostructure sensor 102
configured for convenient transconductance measurements, as well as
other properties. Sensor 102 comprises a substrate 104.
[0093] Sensor 102 comprises a conductive (e.g., semiconductive)
nanostructured element configured to include a channel, coating or
layer 106 and comprising a nanostructured material (e.g., one or
more conducting or semiconducting nanotubes, nanorods, nanowires
and/or nanoparticles; a film, mat or network of nanotubes;
combinations of these; or the like). The nanostructured element
(layer or channel 106) may be disposed adjacent the substrate 104.
Channel or layer 106 may contact the substrate as shown, or in the
alternative, may be spaced a distance away from the substrate, with
or without a layer of intervening material. In a preferred
embodiment, layer 106 comprises an interconnecting network
including a plurality of semiconducting single-walled carbon
nanotubes (SWNTs).
[0094] One or more conductor elements, contacts or electrodes 110,
112 may be disposed over the substrate and electrically connected
to channel or layer 106. In the example shown in FIG. 1, the device
100 is configured to facilitate measurements of transconductance
properties of channel 106 as influenced or modulated by a constant
or variable gate voltage Vg, in this case by employment of
substrate 104 as a gate electrode. However, alternative
configurations are useful (see discussion of FIG. 3).
[0095] Elements 110, 112 may comprise metal electrodes in contact
with conducting channel 106. In the alternative, a conductive or
semi-conducting material (not shown) may be interposed between
contacts 110, 112 and conducting channel 106. Contacts 110, 112 may
comprise source and drain electrodes, respectively, upon
application of a source-drain voltage Vsd. The voltage or polarity,
of source 110 relative to drain 112 may be variable, e.g., the
applied voltage may be DC, AC, pulsed, or variable. In an
embodiment of the invention, the applied voltage is a DC
voltage.
[0096] In an embodiment of the invention, conducting channel 106
may comprise a plurality of carbon nanotubes forming a mesh, film
or network. Such a network may be formed by various suitable
methods. One suitable approach may comprise forming an
interconnecting network of single-wall carbon nanotubes directly
upon the substrate, such as by reacting vapors in the presence of a
catalyst or growth promoter disposed upon the substrate. For
example, single-walled nanotube networks can be grown on silicon or
other substrates by chemical vapor deposition from iron-containing
catalyst nanoparticles with methane/hydrogen gas mixture at about
900 deg. C. Advantageously, the use of highly dispersed catalyst or
growth-promoter for nanostructures permits a network of nanotubes
of controlled diameter and wall structure to be formed in a
substantially random and unclumped orientation with respect to one
another, distributed substantially evenly at a selected mean
density over a selected portion of the substrate.
[0097] Alternatively, a nanotube network may be deposited on a
device substrate by spray deposition and the like. For example,
single wall carbon nanotubes (SWNTs) and/or other nanoparticles may
be suspended in a suitable fluid solvent, and sprayed, printed or
otherwise deposited in a substrate. The SWNTs or other
nanoparticles may optionally have additional functionalization
groups, purification and/or other pre-deposition processing. For
example SWNTs functionalized with poly m-aminobenzene sulfonic acid
(PABS) show hydrophilic properties and may be dispersed in aqueous
solutions.
[0098] One or more conductive traces or electrodes may be deposited
after deposition, or alternatively, the substrate may include
pre-patterned electrodes or traces exposed on the substrate
surface. Similarly, alternative embodiments may have a gate
electrode and a source electrode supported on a single substrate.
The substrate may include a flat, sheet-like portion, although one
skilled in the art will appreciate that geometric variations of
substrate configurations (rods, tubes or the like) may be employed
without departing from the spirit of the inventions.
[0099] The density of a network of nanotubes (or other
nanostructure elements) may be adjusted to achieve a selected
conductivity in an electrically continuous network via
interconnections between adjacent nanotubes (e.g., a CNT film of
density close to but greater than the percolation limit). For
example, this may be achieved through controlled CVD conditions
(e.g., catalyst particle density, deposition environment, duration,
or the like); by controlled flow through a filter membrane (see L.
Hu et al., "Percolation in Transparent and Conducting Carbon
Nanotube Networks", Nano Letters (2004), 4, 12, 2513-17, which is
incorporated by reference), by controlled deposition from a fluid
carrier (e.g., spray deposition); or the like.
[0100] In a spray-deposition example, multiple light, uniform spray
steps may be performed (e.g., with drying and resistance testing
between spray steps) until the network sheet resistance reaches a
target value (implying a target network density and conductivity).
In one example, P2-SWNTs produced by Carbon Solutions, Inc of
Riverside, Calif. were spray-deposited on a portion of a PET sheet
substrate with pre-patterned traces until a sheet resistance about
1 k.OMEGA. was reached.
[0101] See also the methods for making nanotube networks as well as
additional device and substrate alternatives as described the
following patent applications, each of which is incorporated by
reference: U.S. patent application Ser. No. 10/177,929 filed Jun.
21, 2002 entitled "Dispersed Growth Of Nanotubes On A Substrate",
(PCT equivalent published as WO04-040,671); U.S. application Ser.
No. 10/846,072 filed May 14, 2004, entitled "Flexible nanotube
transistors" (Publication 2005-0184,641); U.S. patent application
Ser. No. 11/274,747 filed Nov. 14, 2006 entitled "Nanoelectronic
Glucose Sensors"; and U.S. Patent Application No. 60/748,834, filed
Dec. 9, 2005, entitled "Nanoelectronic Sensors Having Substrates
With Pre-Patterned Electrodes, And Environmental Ammonia Control
System".
[0102] Similar methods of making and depositing alternative
nanostructures may be employed, so as to configure a nanostructured
elements comprising a networks or film of, for example,
nanospheres, nanocages, nanococoons, nanofibers, nanowires,
nanoropes and nanorods, or mixtures thereof, having compositions
including carbon, boron, boron nitride, and carbon boron nitride,
silicon, germanium, gallium nitride, zinc oxide, indium phosphide,
molybdenum disulphide, and silver.
[0103] In the example of FIG. 1, the device 100 may be operated as
a gate-controlled field effect transistor, with sensor 102 further
comprising a gate electrode 114. Such a device is referred to
herein as a nanotube field effect transistor or NTFET. Gate 114 may
comprise a base portion of substrate 104, such as a doped-silicon
wafer material isolated from contacts 110, 112 and channel 106 by a
dielectric layer 116, so as to permit a capacitance to be created
by an applied gate voltage V.sub.g. For example, the substrate 104
may comprise a silicon back gate 114, isolated by a dielectric
layer 116 comprising SiO.sub.2. Alternatively gate 114 may include
a separate counter electrode, liquid gate or the like.
[0104] Sensor 102 may further comprise a layer of inhibiting or
passivation material 118 covering regions adjacent to the
connections between the conductive elements 110, 112 and conducting
channel 106. The inhibiting material may be impermeable to at least
one chemical species, such as to the analyte 101 or to
environmental materials such as water or other solvents, oxygen,
nitrogen, and the like. The inhibiting material 118 may comprise a
passivation material as known in the art, such as silicon dioxide,
aluminum oxide, silicon nitride, or other suitable material.
Further details concerning the use of inhibiting materials in a
NTFET are described in prior co-invented U.S. Pat. No. 6,894,359
entitled "Sensitivity Control For Nanotube Sensors" which is
incorporated by reference herein.
[0105] Device 100 may further comprise suitable circuitry in
communication with sensor elements to perform electrical
measurements. For example, a conventional power source may supply a
source drain voltage V.sub.sd (113) between contacts 110, 112.
Measurements via the sensor device 100 may be carried out by
suitable measurement circuitry represented schematically by meter
122 connected between contacts 110, 112. In embodiments including a
gate electrode 114, a conventional power source 124 may be
connected to provide a selected or controllable gate voltage
V.sub.g. Device 100 may include one or more electrical supplies
and/or a signal control and processing unit (not shown) as known in
the art, in communication with the sensor 102.
[0106] Optionally, device 100 may comprise a plurality of sensors
like sensor 102 disposed in a pattern or array, such as described
in prior application Ser. No. 10/388,701 filed Mar. 14, 2003
entitled "Modification Of Selectivity For Sensing For Nanostructure
Device Arrays" (now published as US 2003-0175161), which is
incorporated by reference herein. Each device in the array may be
functionalized with identical or different functionalization.
Identical device in an array can be useful in order to multiplex
the measurement to improve the signal/noise ratio or increase the
robustness of the device by making redundancy. Different
functionalization may be useful for providing differential
sensitivity so as to permit measurement of a profile of different
responses to analytes.
[0107] The substrate 104 may be insulating, or on the alternative,
may comprise a layered structure, having a base 114 and a separate
dielectric layer 116 disposed to isolate the contacts 110, 112 and
channel 106 from the substrate base 114. The substrate 104 may
comprise a rigid or flexible material, which may be conducting,
semiconducting or dielectric. Substrate 104 may comprise a
monolithic structure, or a multilayer or other composite structure
having constituents of different properties and compositions. For
example, in an embodiment of the invention, the substrate 104 may
comprise a silicon wafer doped so as to function as a back gate
electrode 114. The wafer being coated with intermediate diffusion
barrier of Si.sub.3N.sub.4 and an upper dielectric layer of
SiO.sub.2. Optionally, additional electronic elements may be
integrated into the substrate for various purposes, such as
thermistors, heating elements, integrated circuit elements or other
elements.
[0108] In certain alternative embodiments, the substrate may
comprise a flexible insulating polymer, optionally having an
underlying gate conductor (such as a flexible conductive polymer
composition), as described in application Ser. No. 10/846,072 filed
May 14, 2004, which application is incorporated by reference. In
further alternative embodiments, the substrate may comprise a
polymeric substance coated with nanotube or other nanostructure
particles in the in the manner described in U.S. application Ser.
No. 11/274,747 filed Nov. 14, 2005, which application is
incorporated by reference.
[0109] The conducting channel 106 (e.g., a carbon nanotube layer)
may be functionalized to produce a sensitivity to one or more
target analytes 101. Although nanostructures such as carbon
nanotubes may respond to a target analyte through charge transfer
or other interaction between the device and the analyte, more
generally a sensitivity can be achieved by employing a recognition
material 120, also called a functionalization material, that
induces a measurable change in the device characteristics upon
interaction with a target analyte. In addition or in substitution
to the metallic nanoparticle functionalization, of the exemplary
embodiments described in detail herein, the functionalization may
alternatively include metal oxides, metal salts, polymers, and the
like. Likewise, functionalization may include composite
nanoparticles, mixtures of materials or the like.
[0110] In the exemplary embodiments described in detail herein, the
recognition material disposed upon the channel 106 comprises on or
more metallic materials. In particular, alternative embodiments of
arrays of sensors such as shown in FIG. 1 may be functionalized
with a range of materials different catalytic metals to produce
cross-sensitive NTFET sensor elements.
[0111] FIG. 2 are photographic views (a-d) of a sensor system 100
such as shown in FIG. 1, wherein views (a-c) include SEM images
showing (a) showing the layout of interdigitated source and drain
contacts S 110 and D 112, (b) showing an enlarged detail of a
nanotube network N 106 and the contacts S 110 and D 112, and (c)
showing an enlarged detail of the margin of network N 106. View (d)
shows an example of a sensor device 100 mounted in a conventional
electronic device package 130. Note that the extent of a carbon
nanotube network may be conveniently controlled by selective or
masked oxidation of nanotubes from peripheral regions of the
substrate 104 ("ashing").
[0112] The conducting channel 106 (e.g., a carbon nanotube layer)
may be functionalized to produce a sensitivity to one or more
target analytes 101. Although nanostructures such as carbon
nanotubes may respond to a target analyte through charge transfer
or other interaction between the device and the analyte, a specific
sensitivity may be achieved by employing a recognition material
120, also called a functionalization material, that induces a
measurable change in the device characteristics upon interaction
with a target analyte.
[0113] Device 100 may be packaged in a conventional manner to
conveniently permit connection to operating circuitry. FIG. 2, view
(d) is a photograph of a sensor device 100 generally similar to
that of views (a-c), fabricated on a die of a wafer, and mounted as
a chip in a conventional 40 pin CERDIP package using wirebonding
techniques. Device 100 may further comprise suitable circuitry in
communication with sensor elements to perform electrical
measurements. For example, a conventional power source may supply a
source-drain voltage (Vsd) between contacts 110, 112. Measurements
via the sensor device 100 may be carried out by circuitry
represented schematically by meter 122 connected between contacts
110, 112. In embodiments including a gate electrode 114, a
conventional power source 124 may be connected to provide a
selected or controllable gate voltage (Vg). Device 100 may include
one or more electrical supplies and/or a signal control.
[0114] Ammonia detection. A nanotube network device such as is
shown in FIG. 2 may be functionalized as an ammonia detector having
aspects of the invention, as described in U.S. patent application
Ser. No. 10/656,898 filed Sep. 5, 2003 (published 2005-0279,987)
entitled "Polymer Recognition Layers For Nanostructure Sensor
Devices"; and U.S. patent application Ser. No. 11/541,794, filed
Oct. 2, 2006 entitled "Nanosensor Array For Electronic Olfaction",
incorporated by reference herein.
[0115] A recognition layer (corresponding to 120 in FIG. 1) may be
applied to the nanotube network 106 using any suitable method. For
example, in an embodiment of the invention, the substrate 104,
electrodes 110, 112 and nanotube network 106 were submerged in a
solution of poly(ethylene imine) (PEI, average molecular weight
.about.25,000, Aldrich) at about 20% by weight in methanol. After
soaking overnight, they were removed and rinsed with methanol. A
thin layer, such as less than 10 nm of PEI coated the exposed
portion of nanotube 106 after rinsing. Other suitable polymers, or
combinations of polymers, may be substituted for PEI. Other
solvents and rinse agents may also be suitable.
[0116] FIG. 3A shows the device characteristics for a transistor
device (NTFET) embodiment without additional functionalization
(bare nanotubes). The left hand plot of FIG. 3A shows the ammonia
concentration in ppm and the conductance at initial zero NH3
concentration (i-ii), a sustained pulse of 200 ppm (ii-iii) having
a loss of conductance, followed by a recover period of zero ppm
(iii-iv). The right hand plot of FIG. 3A shows the variation of
conductance as a function of gate voltage (note hysteresis during
sweep), the upper curve set representing point (i) prior to ammonia
pulse, and the lower curve set representing point (iii) after full
response to ammonia pulse, but before recovery. Note that the shape
of the device characteristic curve set is generally similar, the
response to ammonia being an overall reduction in conductance at
both positive and negative gate voltages.
[0117] FIGS. 3B and 3C show the response of the non-functionalized
device and the PEI functionalized device, respectively, to exposure
to pure ammonia gas. It may be seen that functionalization with PEI
improved the response of the semiconducting nanostructure device
for NH3. As seen in FIG. 3B, the non-functionalized device responds
with a modest reduction in current, followed by comparatively slow
recovery. In contrast, the response and recovery of the
PEI-functionalized ammonia sensor (FIG. 3C) is remarkably fast, and
the device responds with a substantial increase in current. Upon
exposure to pure ammonia gas the current increases from 400 nA to
800 nA. The measured change in current is dependent on ammonia
concentration. When the device was exposed to different
concentrations of ammonia in argon, a change in the device
conductivity was found to be proportional to ammonia concentration.
The response to ammonia is also dependent on a gate voltage. At
positive gate, measured current through the PEI-functionalized
device is increasing significantly. This is true with or without
the functionalization material.
[0118] Alternative Nanosensor Architectures.
[0119] FIG. 4 shows one example of a an exemplary electronic
sensing device 130 having aspects of the invention, similar in a
number of respects to the device of FIG. 1, configured in this
example as a capacitance sensor for detecting an analyte, as
further described in commonly invented and assigned U.S.
Provisional Applications No. 60/773,138 filed Feb. 13, 2006; No.
60/660,441, filed Mar. 10, 2005; and No. 60/669,126, filed Apr. 6,
2005, each of which is incorporated by reference. Where
appropriate, the same reference numerals are used to denote
elements which may have commonality of function with respect to
FIG. 1. Nanostructured capacitance sensors may be used in
conjunction with transconductance sensor modalities, so as to
increase specificity, reduce cross sensitivity, and to provide an
additional means of sensor calibration.
[0120] As shown in FIG. 4, Sensor device 130 includes a
nanostructure sensor 131 which includes a conductive nanostructured
element configured to include a channel, coating or layer 106
comprising a nanostructured material (see description of example of
FIG. 1). In an exemplary embodiment, the nanostructured material
includes a carbon nanotube network 106, disposed upon a substrate
comprising a dielectric isolation layer 116 disposed upon a base
114, in this example a doped silicon wafer back gate.
[0121] The nanotube network 106 is contacted by at least one
conductive electrode 110 (in this case having optional passivation
on the electrode-nanotube contact region). A
conditioning/recognition structure 138 may be included, disposed
adjacent network 106 and may included functionalization or
recognition material, analyte conditioners (e.g., a filter,
selectively permeable polymer, etc.) and the like.
[0122] The sensor device 130 further includes at least a
capacitance measurement circuit 136 in electrical communication
with contact 110 and back gate 114, so as to permit the capacitance
and/or impedance of the spaced apart nanotube network/back gate
assembly to be readily measured (i.e., the total charge required to
be placed on either conductor to create a given voltage potential
between conductors, C=Q/V).
[0123] It should be understood that other capacitor conductors may
be substituted for back gate 114 or added to the device 1300
without departing from the spirit of the invention, such as a top
gate, liquid gate, a second spaced-apart nanotube network
conductor, and the like. Additionally, many alternative functional
arrangements of the respective conductors are possible. The
capacitance C of the sensor 131 may be calibrated, and compared
analytically with the capacitance during exposure to analyte of
interest 110. In particular, species having significant dipole
moments may act to change the capacitance upon interaction with the
nanotube network 106. As shown in FIG. 4, additional
functionalization 138 may be included in sensor 131 (e.g., an
absorbent filter, a selectively permeable polymer layer, a
selectively reactive or binding species, etc., to enhance
selectivity, sensitivity and/or signal strength).
[0124] Combined conductance and capacitance measurements.
Simultaneous conductance and capacitance measurements on a
nanostructure sensor element (e.g., a single-walled carbon nanotube
(SWNT) network may be used to extract an intrinsic property of
molecular adsorbates. From a comparison of FIG. 1 and FIG. 4, it
may seen that a single sensor configuration may be combined with
circuitry permitting measurements in several modalities from a
single sensor. Alternatively, a plurality of differently configured
sensors may be employed. Measurements may be made of related
properties as well, such as impedance of a sensor having a
capacitive circuit architecture below).
[0125] For example, adsorbed analytes produce a rapid response in
both the capacitance and the conductance of a SWNT network. These
responses are caused by a combination of two distinct
physiochemical properties of the adsorbates: charge transfer and
polarizability. It has been shown that the ratio of the conductance
(or resistance) response to the capacitance response is a
concentration-independent intrinsic property of a chemical vapor
that can assist in its identification. See Eric S. Snow and F.
Keith Perkins, "Capacitance and Conductance of Single-Walled Carbon
Nanotubes in the Presence of Chemical Vapors", Nano Lett (2005) 5
(12), 2414-2417, which publication is incorporated by
reference.
[0126] Thus, a sensor system may produce a response which
characterizes analyte identity in one output or signal analysis
mode, and produce a response which characterizes analyte
concentration in another output or signal analysis mode. In one
exemplary embodiment having aspects of the invention, a sensor
system may include capacitance and resistance
measurement/processing circuitry communicating with a nanosensor
(e.g., such as in FIG. 1) to determine the identity of an analyte
employing a ratio of the resistance and capacitance change upon
exposure to an analyte sample, and then determine a concentration
of the thus-identified analyte from the capacitance change based on
analyte-specific calibration data.
[0127] FIGS. 5A and 5B are plots illustrating one example of the
use of multiple measurement modalities for analyte detection and
discrimination. The measurements represent the response of a sensor
having aspects of both FIGS. 1 and 4. In each case, the sensor was
exposed to a sequential set of samples of an analyte gas in air,
through a graded series of concentrations. The samples are
administered in timed pulses of approximately 60 second duration
each. The overlay dashed line at each concentration is not a
measured value, but an approximated mean level, shown for clarity
and convenience. The sensors employed in the examples of FIGS.
5A-5B included a directly-exposed nanotube network, although
various functionalization and conditioning layers or materials may
optionally be included (see FIG. 4). In each plot, a capacitance
response to an exemplary analyte species is shown superimposed upon
a signal measuring the simultaneous source-drain resistance, the
capacitance units being shown on the left-hand axis, and the
resistance units on the right-hand axis.
[0128] FIG. 5A shows the response of both capacitance signal
resistance signals to samples of an exemplary analyte in air, in
this example the anesthetic agent, isoflurane. The response of the
device to the analyte in both the capacitance and resistance
signals can be seen to be very rapid, with a rapid recovery. The
relation of capacitance to isoflurane concentration can be seen to
be in the opposite direction, each generally proportional in
magnitude to the other. The arrows to the right of the plot
illustrate the magnitude and ratios of the respective measurements
at a 5% analyte concentration.
[0129] FIG. 5B shows the comparable responses of both capacitance
signal resistance signals to samples of halothane in air;
respectively, plotted in the same manner as FIG. 5A. The arrows to
the right of the plot illustrate the magnitude and ratios of the
respective measurements at a 5% analyte concentration.
[0130] Halothane and isoflurane are chemically similar, have
similar properties, but may be distinguished based on the relative
magnitude of the responses (e.g., a ratio of .about.185 for
isoflurane vs. .about.169 for halothane). The this ratio may be
used to confirm or distinguish the identity of an analyte, and
advantageously this may be done in conjunction with the
simultaneous measurement of the agent's concentration. Where Vg is
the voltage of a substrate gate such as is shown in FIG. 1, the
signals of capacitance and conductance (or resistance) may be
converted for comparison (e.g., ratio calculation) to normalized
values in units of .DELTA.Vg that represent the change in the
substrate gate electrode (counter electrode) voltage required to
produce an equivalent change in capacitance .DELTA.C (or change in
resistance .DELTA.R), i.e. .DELTA.C*=.DELTA.C/(dC/dVg) and
.DELTA.G*=.DELTA.R/(dR/dVg) where the derivatives are evaluated at
Vg=0.
[0131] Optional Device Elements. Optionally, a nanosensor device
having aspects of the invention may include integrated temperature
control elements. Temperature control may be used to control sensor
sensitivity, selectivity, and/or recovery time. Thermal control may
also be used to carry out analyte-related processes, such as
polynucleotide hybridization and denaturization, stringency
conditions, PCR, biomolecule conformation changes and the like.
[0132] For example, a nanosensor may include ohmic thermal
regulation of the nanotubes of the channel, as described in U.S.
patent application Ser. No. 10/655,529 filed Sep. 4, 2003 entitled
"Improved Sensor Device With Heated Nanostructure", which is
incorporated by reference.
[0133] In another alternative embodiment, the sensor device may
include a microfabricated heater element and a thermal isolation
structure, such as a substrate bridge or a suspended membrane. Such
components may include temperature feedback sensors, such as
thermistors, to assist in automated thermal control, e.g., using a
microprocessor, as further described in commonly invented and
assigned U.S. application Ser. No. 11/488,465 60/700,953, filed
Jul. 18, 2006, entitled "Nanoelectronic Sensor With Integral
Suspended Micro-Heaterr", which is incorporated by reference. See
also C. Tsamis et al, "Fabrication of suspended porous silicon
micro-hotplates for thermal sensor applications", Physica Status
Solidi (a), Vol 197 (2), pp 539-543 (2003); A Tserepi et al,
"Fabrication of suspended thermally insulating membranes using
front-side micromachining of the Si substrate: characterization of
the etching process", J of Micromech. and Microeng, Vol 13, pp
323-329 (2003); A Tserepi et al, "Dry etching of Porous Silicon in
High Density Plasmas", Physica Status Solidi (a), Vol 197 (1), pp
163-167 (2003), each of which is incorporated by reference.
B. Exemplary Flexible Substrate Nanosensors
[0134] A number of alternative methods of forming a nanostructure
network channel (e.g., N in FIG. 1C) may be employed without
altering the underlying principal of operation of nanosensors
having aspects of the invention. In certain embodiments (e.g., for
fabrication condition compatibility), it is advantageous to form a
nanotube (or other nanostructure) network on an initial substrate,
and subsequently transfer the network to a final device substrate.
See for example, the methods described in U.S. patent application
Ser. No. 10/846,072, filed May 14, 2004 (published 2005-0184,641),
entitled "Flexible Nanotube Transistors", which is incorporated by
reference.
[0135] As shown in FIG. 6 (corresponding to FIG. 2 of the above
referenced application Ser. No. 10/846,072) in one alternative
method, flexible nanostructure electronic device 200 is formed as
follows: Step 201 includes depositing or growing (for example, by
chemical vapor deposition) a nanotube film 208 on a rigid substrate
220. Substrate 220 may comprise, for example a silicon material 222
covered by a layer of silicon oxide 221. Optionally, contacts 224,
226 may be formed on the substrate, either before or after the
nanotube film is formed. At step 202, nanotube film 208 and
substrate 220 may be coated with a flexible substrate layer 210.
Flexible substrate layer 210 may comprise any suitable material
capable of forming a coating film, for example, a liquid polymer.
Other polymers that may be used to effect a conductivity change in
nanotubes in response to absorption of target species. Alternative
materials for layer 210 may include, for example, those identified
in TABLE 3. Such materials may be included in sensors such as are
describe herein, alone or in combination, without departing from
the spirit of the invention.
TABLE-US-00003 TABLE 3 Examples of alternative recognition
materials Polyacrylic acid Polyurethane resin Poly(acrylic
acid-co-isooctylacrylate) Polycarbazole poly(ethylene imine), "PEI"
poly(sulfone) poly(4-vinylphenol) poly(vinyl acetate) poly(alkyl
methacrylate) poly(vinyl alcohol) poly(a-methylstyrene) poly(vinyl
butyral) poly(caprolactone) polyacrylamide poly(carbonate bisphenol
A) polyacrylonitrile poly(dimethylsiloxane) polyaniline
poly(ethylene glycol) polybutadiene poly(ethylene oxide)
polycarbonate poly(ethylenimine) polyethylene poly(methyl vinyl
ether-co-maleic polyoxyethylene anhydride) poly(N-vinylpyrrolidone)
polypyrrole poly(propylene) polytetrafluoroethylene poly(styrene)
polythiophene polyvinyl-methyl-amine Polyvinyl pyridine
polyaminostyrene chitosan chitosan HCL polyallylamine
polyallylamine HCL poly(diallylamine) poly(diallylamine) HCL
poly(entylene-co-vinyl acetate), poly-(m-aminobenzene sulfonic
acid), ~82% ethylene "PABS" poly(styrene-co-allyl alcohol),
poly(vinyl chloride-co-vinyl acetate), ~5.7% hydroxyl ~10% vinyl
acetate poly(styrene-co-maleic anhydride), poly(vinylidene
chloride-co-acrylonitrile), ~50% styrene ~80% vinylidene chloride
metalloporphyrin (M-porph) Poly-L-lysine Alpha-fetoprotein Profile
Four (AFP4) glycerol Poly methyl methacrylate (PMMA) polyglycerol
Nafion NR 50 Triton 100 and similar surfactants or amphiphilic
species metal coatings and nanoparticles, and Fe, V, Au, Pt, Pd,
Ag, Ni, Ti, Cr, Cu, Mg, Al, alloys or mixtures of these: Co,, Zn,
Mo, Rh, Sn, W, Pb, Ir, Ru, Os inorganic coatings and/or
nanoparticles: V.sub.2O.sub.5 WO.sub.3 Cu(SO.sub.4) Boric/Boronic
acid ZnO Boron Trichloride Al.sub.2O.sub.3 ZrO.sub.2
Fe.sub.2O.sub.3 CaCl.sub.2
[0136] Materials in the functionalization layer may be deposited on
the NTFET using various different methods, depending on the
material to be deposited. It should be understood that mixtures,
alloys and composites of the materials may also be included. For
many materials, ALD methodology is known which is suitable for
depositing thin, uniform layers or coatings, which may be
controlled to deposit on selected portions of a device, and which
may be employed to produce mixtures or multi-layer coatings also.
Other methods may be employed. For example, inorganic materials,
such as sodium carbonate, may be deposited by drop casting from 1
mM solution in light alcohols. The functionalized sensor may then
be dried by blowing with nitrogen or other suitable drying agent.
Polymeric materials may be deposited by dip coating. A typical
procedure may involve soaking of the chip with the carbon nanotube
device in 10% polymeric solution in water for 24 hours, rinsing
with water several times, and blowing the chip dry with nitrogen.
Polymers which are not soluble in aqueous solutions may be spin
coated on the chip from their solutions in organic solvents. Values
of polymer concentrations and the spin coater's rotation speeds may
be optimized for each polymer.
[0137] Polymers such as the foregoing may be dissolved and coated
on nanostructures in a manner similar to that described for PEI
above. Polymer and non-polymer materials other than those listed
above may also be useful. It is possible that the exemplary polymer
layer acts to cause a selective response by the nanostructure to
target species that are selectively absorbed or otherwise
interacted with by the polymer layer on the nanostructure. This
suggests that a nanostructure sensor may be made to respond
selectively to a particular material, by coating it with a polymer
or material having a known selective affinity for the desired
target. Also, more than one material may be included in a target
group by combining polymers with different affinities. The polymer
layer may be modified to produce different effects. For example,
part of the nanotube or other nanostructure may be masked during a
coating process for the polymer layer. After the polymer layer is
applied, the masking layer may be stripped away, leaving a
discontinuous polymer layer on the nanotube. Using a similar
process, different polymers may be deposited at different places
along a nanostructure.
[0138] The polymer or other recognition material should be selected
to provide the electrical and mechanical properties that are
desired for the substrate of the device to be formed. The polymer
210 may be deposited as a liquid layer, and then cured, hardened,
or otherwise solidified to provide the desired substrate
material.
[0139] At step 203, rigid substrate 220 is removed from substrate
210, for example, by dissolving the substrate in a suitable etching
agent. Optionally, one or more electrodes (not shown) may be formed
on the exposed surface of substrate layer 210, either before or
after it is removed from the rigid substrate. For example, a gate
electrode (not shown at 203) may be placed opposite to the nanotube
film 208. Turning substrate 210 over should yield a device 230 as
shown at the lower left of FIG. 6 (shown rotated 180 degrees
relative to its position at 201). The device 230 may comprise
source and drain electrodes 224, 226, nanotube network 208
connecting the source and drain, and a gate electrode 228 on the
opposite side of dielectric flexible substrate layer 210.
[0140] A nanotube network was grown by chemical vapor deposition on
a silicon substrate with a 200 nm silicon oxide coating, as
described in U.S. patent application Ser. No. 10/177,929, filed
Jun. 21, 2002 by Gabriel et al., which is hereby incorporated by
reference, in its entirety. Then the silicon substrate with the
network was patterned with optical lithography, and a liftoff
process, to form 100 .mum square metal contacts. The metal contacts
comprised a 3.5 nm thick titanium film covered by a 50 nm thick
gold film. After liftoff, the silicon substrate with network and
metal contacts was spin-coated with polyimide (HD 2610, 500 rpm).
The silicon substrate was heated at 90 deg C. for 10 minutes, 120
deg C. for 5 minutes, and 200 deg C. for 30 minutes to cure the
polyimide. Finally, the silicon substrate was immersed in 10%
hydrofluoric acid (HF) for 8 hours. The polyimide films, floating
freely in the HF solution, were removed and rinsed with deionized
water.
[0141] FIG. 7 shows the NH3 sensing capabilities of a nanosensor
embodiment having aspects of the invention, in this case a sensor
constructed by the method of FIG. 6 Introduction of NH3 to a test
chamber caused a rapid and easily measured change in conductivity
of the device.
C. Exemplary Solution Deposition Nanosensors
[0142] Solution Deposition Nanoparticle Network. In an alternative,
the nanostructure conducting layer comprising an interconnecting
network of nanostructures may be formed by deposition from a
solution or suspension of nanostructures, such as a solution of
dispersed carbon nanotubes. See for example, the methods described
in U.S. patent application Ser. No. 10/846,072, filed May 14, 2004
(published 2005-0184,641), entitled "Flexible Nanotube
Transistors", which is incorporated by reference. Such methods as
spin coating, spray deposition, dip coating and ink-jet printing
may be employed to deposit the solution or suspension of
nanostructures.
[0143] In certain embodiments, a micro-porous filter, membrane or
substrate may be employed in deposition of a nanotube (or other
nanoparticle) network channel from suspension or solution. A porous
substrate can accelerate deposition by removing solvent so as to
minimize "clumping", and can assist in controlling deposition
density. The deposition may be carried out by capillary absorption,
or using suction or vacuum deposition across the porous substrate
or membrane, as described in the above referenced application Ser.
No. 10/846,072 (e.g., see description of FIG. 3 and Example B of
that application); in U.S. Provisional Application No. 60/639,954
filed Dec. 28, 2004 entitled "Nanotube Network-On-Top Architecture
For Biosensor"; and in L. Hu et al., Percolation in Transparent and
Conducting Carbon Nanotube Networks, Nano Letters (2004), 4, 12,
2513-17, each of which application and publication is incorporated
herein by reference. The network thus formed may be separated from
the deposition membrane using a method such as membrane dissolution
or transfer bonding, and included in a sensor device structure as a
conducting channel (e.g., disposed on a device substrate, contact
grid, or the like).
[0144] Alternatively, a nanotube (or other nanoparticle) network
deposited on a micro-porous substrate may be included in a sensor
device as disposed upon the deposition substrate or membrane. This
arrangement may simplify fabrication, and has the advantage of
permitting analyte media flow perpendicularly through the pores of
the device substrate, as further described in commonly invented and
assigned U.S. Provisional Application No. 60/669,126, filed Apr. 6,
2005, entitled "Systems Having Integrated Cell Membranes And
Nanoelectronics Devices, And Nano-Capacitive Biomolecule Sensors,
which is incorporated by reference.
[0145] FIG. 8A is a diagram of an alternative exemplary embodiment
of a nanosensor 20 having aspects to the invention, including a
network of carbon nanotubes. Sensor 20 comprises a substrate 9,
which may comprise a flexible sheet-like material such a polyester
polymer (e.g., PET sheet). One or more electrodes (3a and 3b are
shown) are arranged on the substrate. The electrode 3 may comprise
a metal, or may be formed from a paste or ink-like composition,
such as carbon, graphite, conductive polymer, metallic ink
compositions, and the like.
[0146] A nanostructure layer 2 (in this example a film including
SWNTs) is deposited contacting the electrodes 3a (and 3b in this
example). Preferably the nanostructure layer 2 is formed by
spraying or otherwise coating the patterned substrate with an
liquid suspension of nanotubes, as is described in detail herein
and in the incorporated references. For example, SWNTs or MWNTs may
be conveniently dispersed in aqueous suspension at a desired
concentration, particularly where functionalization treatment of
the SWNTs assist in making the nanotubes hydrophilic. Alternative
organic solvents may likewise be used to disperse and apply the
nanotube film 2. See for example, U.S. patent application Ser. No.
10/846,072 entitled "Flexible Nanotube Transistors"; and L. Hu et
al., Percolation in Transparent and Conducting Carbon Nanotube
Networks, Nano Letters (2004), 4, 12, 2513-17, each of which
application and publication is incorporated herein by
reference.
[0147] In the example of FIG. 8A, the electrodes 3a, 3b are shown
deposited upon substrate 9 beneath the SWNT film 2, as this
advantageously permits the use of substrates having pre-printed or
pre-patterned electrode material, which permits substantial costs
savings in volume production. However, other electrode
configurations are possible without departing from the spirit of
the invention.
[0148] In the example shown in FIG. 8A, an optional
functionalization or recognition layer 7 is included in association
with the layer 2. This applied following deposition of SWNT film 2.
In the example shown in FIG. 8B, a layer of recognition material 7'
is deposited upon the substrate prior to application of the
nanotube film 2, and is disposed underneath film 2. In either of
the examples of FIGS. 8A and 8B, a recognition material may
penetrate the nanotube network 2 so as to be incorporated as a
mixture.
[0149] FIG. 8A shows an optional additional passivation, protective
or inhibiting layer 8 may cover electrodes 3 and all or a portion
of layers 2 and 7.
[0150] In certain embodiments, recognition or detection material is
deposited, reacted or bound to the nanotubes (or alternative
nanostructures) prior to deposition of layer 2. Depending on the
selected detection chemistry and analyte target, such
pre-functionalization may eliminate the need for any distinct
recognition layer 7. In the example shown in FIG. 8C, a layer of
pre-functionalized nanotubes 12 is deposited upon the substrate,
without any separate application of a recognition or
functionalization material.
[0151] The nanostructure layer 2 may be deposited stepwise, with
intermediate drying, to permit the density and conductivity of the
layer 2 to be accurately controlled, such as by probe-testing the
layer resistance or conductance between deposition steps, until a
selected layer conductivity or resistance is achieved.
[0152] Suitable measurement circuitry is included in communication
with electrodes 3a and 3b (and any optional additional electrodes),
here represented by meter 6 and source-drain power source Vsd.
D. Exemplary Sensor Having a Pre-Functionalized Nanotube
Network
[0153] Sensor fabrication. FIG. 9 shows an exemplary embodiment of
a sensor device 50 having aspects of the invention and including a
nanotube networks fabricated by deposition of a solution or
dispersion of nanotubes upon a substrate 9 to form a nanotube film
12. In an exemplary embodiment shown in FIG. 9, the nanotubes (or
other nanostructures) are dispersed in a volatile solvent which
evaporates following deposition to leave the nanotubes configured
as an open network 12.
[0154] Although electrical contacts may be deposited or applied
subsequent to nanotube deposition, it is convenient and
advantageous to pattern desired electrode or contact material 3
upon the substrate 9 prior to nanotube deposition (four contacts
3a-3d are shown). For example, substrates (e.g., polymer sheets
such as PET, polystyrene, polycarbonate and the like) are
commercially made having printable conductor material applied in a
selected pattern (e.g., carbon, silver, gold, silver/silver
chloride, mixtures and the like). A suitable flexible PET
substrates with a pattern of printed conductive carbon traces may
purchased from Conductive Technologies, Inc., of York, Pa., for
example, a flexible PET substrate with screen-printed carbon paste
electrodes, with spacing between the conductive traces of about 1
mm. A plurality of devices may conveniently be fabricated on a
sheet of substrate material, and may subsequently be partitioned
and packaged as desired, either as single sensor devices, or as
arrays of sensors, and the like.
[0155] In an exemplary embodiment having aspects of the invention,
the nanotube network was formed from SWNTs which were
functionalized by covalently bonded poly-(m-aminobenzene sulfonic
acid ("PABS"). Carbon nanotubes, preferably SWNTs, may be reacted
and treated with PABS (composite referred to as "SWNT-PABS") by the
methods as described in B Zhao et al, "Synthesis and Properties of
a Water-Soluble Single-Walled Carbon Nanotube-Poly(m-aminobenzene
sulfonic acid) Graft Copolymer", Adv Funct Mater (2004) Vol 14, No
1 pp 71-76, which article is incorporated by reference. A suitable
nanotube composite material ("SWNT-PABS") may be obtained from
Carbon Solutions, Inc. of Riverside, Calif. in the form of a dry
powder.
[0156] A variety of alternative functionalization species may be
included, such as conductive polymeric materials, polyaniline
(PANI), polypyrrole, polyaniline derivatives, and the alternative
materials described above in TABLE 3. See, for example, the
electrochemical treatments described in T Zhang et al, "Nanonose:
Electrochemically Functionalized Single-Walled Carbon Nanotube Gas
Sensor Array", Proc. 208th Meeting of Electrochemical Society (Los
Angeles, Calif. Oct. 16-21, 2005), which is incorporated by
reference.
[0157] A suitable aqueous deposition solution may be made by
suspending SWNT-PABS powder in water (preferably at a concentration
of about 1 mg/mL), and ultrasonication may be employed to assist in
making a homogeneous dispersion. The carbon nanotube dispersion may
be sprayed with an air brush to coat the substrate.
[0158] Preferably the deposition is done in several light coating
steps with intermediate drying (for example on a hotplate with the
temperature of about 55 to 75 degree C). The film resistance may be
measured between steps until the selected resistance is obtained
(the measurement may be between printed traces, or may be by pin
probes on the network coating. For example, the deposition may be
continued until resistance with a half-inch pin probe spacing is
about 15 K Ohm.
[0159] Ammonia Detection. FIGS. 10 and 11 are plots showing the
response of the sensor described above with respect to FIG. 8 to
ammonia in an automated gas test station. The selected ammonia
concentrations were obtained by dilution with nitrogen in a
computerized gas dilution system. Prior to measurements, the
sensors were purged with nitrogen for 30 min followed by exposure
to ammonia for 15 min. The ammonia gas was switched to nitrogen for
5 min between successive test experiments.
[0160] FIG. 10 shows the response of the sensor to repeated
exposures and recovery at 50 ppm of ammonia. The response may be
seen to be repeatable and consistent.
[0161] FIG. 11 shows the response of the sensor to repeated
exposures and intermediate recoveries throughout a 10 fold dynamic
range, beginning at 50 ppm, grading upwards to 500 ppm, and grading
downward back to 50 ppm. The response may be seen to be generally
repeatable and consistent throughout this range. The exemplary
sensors rapidly recover their resistance when NH3 is replaced with
argon.
[0162] The forgoing embodiments provide advanced chemical sensors
based on chemically functionalized single-walled carbon nanotubes
(SWNTs). The inclusion of conductive or semiconductive polymeric
functionalization material may improve sensor performance for
detection of NH3 (e.g., covalently attached poly-(m-aminobenzene
sulfonic acid forming a SWNT-PABS composite). The exemplary sensors
have ppm sensitive, rapid response, and rapidly recover when NH3
exposure ceases.
E. Exemplary Environmental Control and Actuator System
[0163] FIG. 12 is a schematic layout diagram of an exemplary
environmental control and actuator system including a
nanoelectronic ammonia sensor having aspects of the invention.
Preferably a plurality of sensing modalities are employed to
optimize environmental conditions in an enclosure, such as a
poultry house, by controlling ventilation, heating and optionally
air cooling. In the example shown, the control system includes at
least one ammonia sensor, and optionally a humidity sensor, a
temperature sensor, and a sensor specific to an additional
environmental gas, contaminant vapor or other species, such as CO2,
NOx, O3, CH4, H2S, CO, allergens, pathogens, or the like.
[0164] The sensors may be powered by any convenient method, such as
line power, batteries, solar cells, and the like. The sensors
communicate with a computer processor or microprocessor which
includes memory. The processor is preferably is in communication
with a user input and output/display device, such as a monitor and
keyboard. Either wired or wireless communication (or a combination
of these) may be employed, for example including conventional
network hardware, to connect sensors the processor. Alternative the
system may be integrated into a single control module.
[0165] For example, it may be advantageous to have a particular
sensor (e.g., ammonia) mounted in a wireless remote module, such as
is described in U.S. patent application Ser. No. 11/111,121 filed
Apr. 20, 2005 (publication 2006-0055,392) entitled "Remotely
communicating, battery-powered nanostructure sensor devices"; which
is incorporated by reference. The described nanosensors having
aspects of the invention have very low power dissipation, and
therefore lend themselves to compact remote installations powered,
for example, by a small battery and/or photovoltaic cell. The
described remotely communicating sensor devices can be interrogated
as needed by a processor located at another convenient
location.
[0166] Remote sensor modules permit monitoring an environmental
variable at a plurality of locations, and determining ventilation
or other control response based on a composition of sensor outputs.
Additionally, reliability and accuracy may be improved by including
redundant sensors for a particular environmental variable, such as
humidity or ammonia, and analyzing sensor outputs to determine a
most reliable value for the variable based on statistical or
quality control algorithms. See for example the methods described
in the above referenced U.S. Pat. No. 5,407,129 issued to Carey et
al.
[0167] The processor, memory and user I/O devices permit a user to
set control points, review measurement histories, track quality
control variables, and/or determine sensor status or maintenance
histories, and the like. The processor may also be configured to
monitor heater and ventilator fan performance. Conventional
feedback control algorithms may be employed to optimize
environmental control.
[0168] An environmental actuator system communicates with and
responds to commands of the control system, so as to maintain
ammonia, humidity and temperature (and optionally an additional
analyte) within programmed limits. The actuator system includes
such devices as ventilation fans, heaters, and optionally air
coolers. The actuator system may also include scrubbers, filters,
particle removers and the like to condition air quality. Generally,
ventilation and heater units dissipate power at a higher order of
magnitude than the control system sensor and processor functions,
and the actuators may conveniently be operated by relays and other
conventional power controls, in response to processor commands.
[0169] One of ordinary skill in the art may combine elements of
FIG. 12 in alternative ways without departing from the spirit of
the invention. For example, it may be advantageous in industrial
applications of the control system of FIG. 12 to integrate the
control system with a particular actuator modality as a modular
control-actuator system. This may be done to simplify installation
and maintenance, and to facilitate the economical retrofitting of
poultry houses as existing ventilation and heating equipment
reaches its service life. Thus, a ventilation unit may be supplied
with an integrated environmental control system, and a separate
heater unit may be supplied with a separate integrated
environmental control system.
F. Alternative Sensor Configurations
[0170] It should be understood that the embodiment shown in FIG. 8
is exemplary, and a number of alternative configurations are
possible without departing from the spirit of the invention. Some
examples are shown in FIGS. 13A-13E, including alternative
embodiments of sensors having aspects of the invention and
including nanotube networks fabricated by deposition of a solution
upon flexible substrates with pre-patterned conductor traces. It
should be understood that the vertical dimension is generally
highly exaggerated for clarity, and that thin sheets of substrates,
such a PET, may be printed or coated to very small tolerances with
conventional conducting materials. Where the embodiments include
generally similar elements, these are numbered the same.
[0171] FIG. 13A shows a NTFET alternative sensor 60 having
space-apart source and drain traces 3a and 3b disposed on substrate
9. An additional intermediate trace 14 is coated with a thin layer
of dielectric material 15 (organic film or inorganic deposit) prior
to deposition of nanotube layer 12, so as to form a gate
electrode.
[0172] FIG. 13B shows a sensor 65, generally similar in
configuration to that of FIGS. 8-9, and including a plurality of
distinct pairs of space-apart patterned source and drain traces on
a single substrate are coated with differently functionalized
nanotube networks (e.g., traces 3a, 3b coated with nanotube layer
12a, and traces 3c, 3d coated with nanotube layer 12b), so as to
have different sensing properties. A gap 17 between nanotube layer
portions may be provided (by masking, scoring, and the like) so as
to provide electrical isolation between nanotube layers 12a and
12b. Note that this configuration may also be employed to provide
reference sensors or calibration sensors in an array format.
[0173] FIG. 13C shows a sensor 70 generally similar to that shown
in FIGS. 8-9, and having additional layers of encapsulation or
covering material which functions to filter or condition the
ambient medium so as to improve selectivity or to protect the
sensor. In this example, nanotube layer 12 is covered by either or
both of an encapsulation layer 18, and a filter lamination layer
(fixed, e.g. by adhesive or taped edges 20). These additional
layers 18, 19 can provide a low-cost integrated sensor unit which
is protected by the layers (e.g., hydrophobic coatings permeable to
the analyte of interest) and with reduced cross-sensitivity
(filters selectively absorbing a cross-contaminant, such as NOx).
Such layers 18, 19 may cover all or only a portion of the sensor
surface, for example, to isolate a reference sensor from the
environment while leaving a measurement sensor exposed. The 18, 19
may also provide abrasion resistance to protect delicate nanotube
films, to permit convenient user handling, such as in a disposable
sensor.
[0174] FIG. 13D shows a sensor 75 configured as a capacitance
sensor in which a nanotube network 12 connects to at least one
trace 3, and is separated from at least one other counter-electrode
trace 17 by a defined gap 16 (e.g., gap made by masking, scoring,
or the like). Conventional circuitry may be used to measure the
change in capacitance of the nanotube layer 12 with respect to the
counter electrode 17 in response to an analyte.
[0175] FIG. 13E shows alternative embodiment 80 of a capacitance
sensor in which a second substrate 9b having a counter-electrode
trace 17' is laminated to a first substrate 9a having a nanotube
network 12, the counter electrode being maintained in a spaced
apart arrangement from the nanotube network by spacers to maintain
gap 16'. The spacers may include edge spacers 18 which do not
contact the nanotube layer 12 in the region of gap 16'.
Alternatively or additional, the device may include a thin porous
sandwich spacer 20 which provides a dielectric separation between
electrode 17' and layer 12 while permitting the diffusion of
analyte. Alternatively, a non-porous dielectric intermediate spacer
21 may be interposed between a portion of counter electrode 17' and
layer 12 to control the dimension of gap 16', while leaving other
portions of electrode 17' and layer 12 exposed to analyte.
[0176] It should be noted that spacer-controlled lamination of
substrates similar to that shown in FIG. 13E may be included in
sensor embodiments such as those of FIG. 13A-13D, so as to create
an enclosed lumen or volume for analyte medium, suitable for
microfluidic sensors and the like.
[0177] FIGS. 14A-14E illustrate an exemplary embodiment of a sensor
system having aspects of the invention, including a disposable
sensor generally similar to the embodiment of FIGS. 8-9, and
including a sensor mounting socket suitable for integration into an
instrumentation module, such as an environmental control
system.
[0178] It should be noted that while sensors generally similar to
that shown in FIGS. 8-9 may have a long service life, the low cost,
low power properties of the sensor embodiments having aspects of
the invention lend themselves elf to a disposable or easily
replaceable sensor module. In many applications, it may be
advantageous to replace a low-cost sensor at regular intervals,
simplifying calibration and quality control procedures. In
addition, a "generic" sensor socket may be configured to accept
sensors for different analytes or different concentration ranges,
making the control module conveniently re-configurable or
upgradable.
[0179] FIG. 14A shows, in cross section and longitudinal section
view, an exemplary embodiment of a disposable sensor device 50
having aspects of the invention and including a nanotube network 12
arranged on substrate 9. Nanotube network 12 connects with one or
more conductive traces or contacts 3 disposed on substrate 9. As
may be seen in the left-hand cross section view of FIG. 14A, in
this example the contacts 3 include a spaced-apart source-drain
pair of traces 3a and 3b. The layer 12 is functionalized for
sensitivity to an analyte of interest, for example ammonia. As may
be seen in the right-hand longitudinal section view of FIG. 14A, in
this example the contacts 3a and 3b extend beyond the network layer
12 to be exposed adjacent the end of substrate 9. A sealant portion
13 (e.g., an elastomer material) is disposed on substrate 9 at the
end opposite the exposed contacts.
[0180] FIG. 14B shows in longitudinal section view an exemplary
embodiment of a sensor mounting socket 51 having aspects of the
invention and suited to mounting the sensor 50 of FIG. 13A. The
socket 51 includes a body 52 having a central slot 53b terminating
at one end in opening 53a. At the opposite end of slot 53a, the
body 52 mounts one or more conductive pins 54b which have a spring
contact portion 54a protruding into slot 53b. On one side of body
52 is mounted a sensor orifice/filter 55.
[0181] FIG. 14C shows, in longitudinal section view, the disposable
sensor 50 of FIG. 14A as sealed in a conventional "blister pack"
type protective package 56 having a peelable backing. The package
56 may be hermetically sealed, pre-sterilized, and/or protects the
sensor 50, for example from abrasion, humidity and contamination,
while providing the sensor ready for immediate use.
[0182] FIG. 14D shows the disposable sensor 50 of FIG. 14A as
mounted in the sensor mounting socket 51 of FIG. 14B. Note in this
example (although not shown in side section), pins 54 include an
electrically isolated parallel pair of pins 54b and spring contacts
54a corresponding and communicating with traces 3a and 3b
respectively of sensor 50. Note also that nanotube layer 12 of the
mounted sensor 50 lies adjacent orifice/filter 55, which is
permeable to at least the analyte of interest. The sealant portion
13 contacts the opening 53a of slot 53b, so as to seal the opening
when the sensor is mounted. The sensor 50 in this example may be
held firmly in place by friction applied by one or both of sealant
13 and spring contacts 54a (additional or alternative closures and
the like may be included).
[0183] FIG. 15 shows an exemplary embodiment of a control system
unit 165 employing a sensor having aspects of the invention, such
as the disposable sensor 50 and socket 51 of FIGS. 14A-14E. The
unit 165 may include many or all of the functional elements shown
in the control system of FIG. 12, packaged in a convenient product
configuration, such as a battery-powered wall-mounted unit
accepting disposable analyte sensors. In this example, unit 165
includes a circuit board 175 for mounting power supply 177, A/D
converter 178, microprocessor/memory module 176, wireless or wired
I/O connections 168, thermistor 166, RH sensor 167, and the like.
The processor board is shown connected to one or more sensor
sockets 51 mounting disposable sensors 50 and 50'. The unit 165
also includes a display 180 and a keypad 181.
G. Sensor Arrays, and Low Cost Safety Badge Example
[0184] Optionally, The various embodiments of nanoelectronic
sensors describe in the above examples may comprise a plurality of
sensors disposed in a pattern or array, such as described in prior
application Ser. No. 10/388,701, entitled "Modification Of
Selectivity For Sensing For Nanostructure Device Arrays" (now U.S.
Pat. No. 6,905,655), which is incorporated by reference herein. A
sensor array embodiment may provide for a number of advantageous
measurement alternatives, methods and benefits according to the
invention, for example: [0185] a. multiple analytes detected by a
plurality of specifically functionalized sensors, [0186] b. improve
the signal/noise ratio or increase the robustness of the device.
[0187] c. increased precision and dynamic range by a plurality of
sensors each of which is optimized for a different range, [0188] d.
increased analyte specificity and flexibility by detecting a
characteristic "profile" of responses of a target analyte to a
plurality of differently-functionalized sensors, [0189] e. self
calibration systems and isolated reference sensors, [0190] f.
multiple-use array having a plurality of deployable one-time-use
sensor sub-units, or [0191] g. ultra-low-cost,
direct-digital-output sensor arrays, including a plurality of
sensors, each producing a binary signal, and collectively having a
range of response thresholds covering a selected analyte
concentration range.
[0192] Low cost substrate sensors having aspects of the invention
generally similar to the embodiments shown in FIGS. 8-9 and FIGS.
13A-13E are well suited to applications such as industrial safety
badges and similar equipment.
[0193] FIG. 15 shows an exemplary embodiment of an industrial
personnel safety badge 190 having aspects of the invention,
comprising a card mount or badge body 191 supported by a swivel
clip 192 suitable for attaching the card 190 to a pocket, shirt
lapel, jacket or article of clothing (a cord or necklace may also
be employed). The badge 190 may includes compact, low-cost
electronic components generally similar to those found in
inexpensive electronic watches, musical gift cards, and the like.
Badge 190 is shown including a battery 194, an integrated
microprocessor 192 and an user-readable display such as LCD 195. At
least one sensor, and preferably a multi-analyte sensor array (see
FIG. 12B) having aspects of the invention is mounted to the card
191, arranged so as to sample air next to the card surface, and is
connected to processor 192. The display 195 in this example is
simple a bar graph showing levels of one or more toxic analytes,
such as NH3, CO, and H2S, organic vapors and the like.
[0194] Additionally or alternatively to display 195, badge 190 may
include sound alerts such as beeper 196 to alert to hazardous
analyte levels. Light alerts such as flashing LED 197 may be
pre-programmed to alert to hazardous levels also. In additional
alternatives, badge 190 may include active or passive RFID-type
elements or other wireless communication components (not shown) to
provide for remote monitoring of personnel exposure to toxic
analytes. The processor may also include memory configured to
maintain analyte-specific exposure history, downloadable to
permanent record computers.
H. Suspended Network Sensor
[0195] FIG. 17 shows an additional exemplary embodiment of a sensor
device 200 having aspects of the invention and including a nanotube
network 12 arranged so as to be suspended above and spaced apart
from substrate 9. In this example, each of contacts 3a and 3b
support a plurality of pillar-like conductors 20a and 20b
respectively. Network 12 is supported by, and electrically
communicates with, the pillars 20a, 20b. The network 12 may be
deposited by a number of methods described herein, such as by CVD
growth (e.g., catalyst on pillars), by solution deposition, or by
network transfer (e.g., from a vacuum deposited network on a porous
substrate, rafted or transferred to adhere to the pillars). This
embodiment permits the network 12 and any recognition material
associated with it, to interact with analyte species isolated from
substrate influence. Alternative embodiments are possible (such as
a capacitive sensor) without departing from the spirit of the
invention.
I. Method of Dynamic Sensor Sampling
[0196] In one inventive aspect, a method of dynamic sensor sampling
is provided, which permits measurement of analyte concentration
over time, while avoiding exposure of the sensor to a sample medium
on a continuous basis. For example, a valve or fluidic circulation
system may be included to selectively expose a sensor having
aspects of the invention to a sample medium. In certain
embodiments, a dynamic sampling method permits minimizing exposure
of a sensor to corrosive or life-limiting environmental conditions.
In other embodiments (e.g., and electrochemical sensor), a dynamic
sampling method may conserve reagent supply and extend service
life. In yet other embodiments, a dynamic sampling method may avoid
irreversible or persistent changes in sensor properties. In still
other embodiments a dynamic sampling method may permit more rapid
sensor response to changes in analyte conditions and reduce
recovery time. A dynamic sampling method may also be employed to
reduce cross-sensitivity, where response to a cross-reactant is
slower than to a target analyte.
[0197] FIG. 18 is a schematic plot illustrating principles of a
dynamic sensor sampling method having aspects of the invention. The
vertical axis represents a nominal sensor response magnitude. In
the example shown, this is an electrical current I (e.g., across a
channel element of a transconductance sensor) but the response may
represent any one of a number different sensor properties, such as
a conductance, resistance, capacitance, impedance or the like. The
response may also represent a complex or derived property, such as
a ratio, modulation, time constant, exponent or other relationship
associated with measured properties. The response may alternatively
represent a statistical property in relation to multiple sensors of
a sensor array, such as a mean value or the like.
[0198] As may be seen in FIG. 18, the unexposed sensor is initially
at an response level (I.sub.0). Exposure of the sensor to a first
analyte concentration (concentration 1) produces a sensor response
that increases over time so as to asymptotically approach (dotted
curve) a steady-state response magnitude (I.sub.asym1). If the
sensor is isolated from exposure to a sample (or otherwise
prevented from responding to an analyte, such as by a controllable
inhibitor) at a point when the response reaches a selected cut-off
magnitude (I.sub.max), a recovery trend is begun, the response
value declining so as to asymptotically approach the initial value
I.sub.0. If the sensor is again exposed to the analyte sample after
a recovery interval (delta t), the sensor response again increases
("rise profile") in a similar manner until the cut-off value
I.sub.max is reached.
[0199] A second curve in FIG. 18 represents the response of the
sensor to an analyte sample of a differing concentration (heavy
dashed line--concentration 2), such that the response that
increases over time so as to asymptotically approach (dotted curve)
a different steady-state response magnitude I.sub.asym2). If the
exposure is interrupted at a cut-off value (I.sub.max), and the
sensor is permitted to recover for a selected interval (delta t),
the response curve of concentration 2 is similar to that of
concentration 1, but having a differing rise profile (rise profile
1 vs. rise profile 2). Analytical comparison of the rise profiles
may be employed to characterized the analyte concentrations,
without monitoring the sensor response until a steady-state
response magnitude is reached or approached.
[0200] FIG. 19 is a schematic plot an example of dynamic sensor
sampling for a step change in analyte concentration. As in FIG. 18,
the sampling method in this example applies a fixed maximum
response cut-off value I.sub.max and a fixed recovery interval
delta t. The curve of sensor response shows a change in rise
profile following the change in analyte concentration (rise profile
1 vs. rise profile 2). It should be understood that in the example
shown, the sensor recovery is consistent, independent of analyte
concentration, and approaches (I.sub.0) without a persistent
off-set. However, this may not be so, and methods of dynamic
sampling may be applied effectively to sensors which do not exhibit
these characteristics. For example, accumulated drift in sensor
response may be compensated for. A number of alternative analytical
algorithms may be applied to correlate rise profile with analyte
concentration.
[0201] FIG. 20 is a schematic plot an alternative example of
dynamic sensor sampling for a step change in analyte concentration,
having both fixed maximum and minimum response cut-off values. As
may be seen, the measurement and recovery phases (analyte exposure
and isolation) are triggered by a response magnitude reached a
maximum and minimum value (I.sub.max and I.sub.min).
[0202] FIG. 21 is a schematic plot an example of dynamic sensor
sampling for a step change in analyte concentration, having a both
fixed measurement and recovery intervals. As may be seen, the
measurement and recovery phases are triggered by the passage of a
determined measurement interval (dt.sub.M) and recovery interval
(dt.sub.R).
[0203] It should be understood that a sensor system may employ the
sampling modes of FIGS. 18-21 alone, in sequence or in combination.
For example, a sensor system may be programmed to apply a certain
sampling mode for analyte concentrations in a certain range and
another sampling mode for another range of analyte concentrations.
for a stand-by or active mode, or the like. Additional alternative
modes of sampling may be employed without departing from the spirit
of the invention.
[0204] In like fashion to that described in the example above,
alternative functionalization materials and alternative device
architectures may be included (e.g., alternative electrode elements
and nanostructures, such as nanowires, MWNTs, non-carbon or hetero
nanotubes other known nanoparticles, and the like). Such
alternatives may include measurements of other device properties,
such as capacitance, impedance and the like.
[0205] FIG. 22 is a schematic diagram of an exemplary embodiment of
a sensor system 250 having aspects of the invention, and configured
for employing a dynamic sampling method. System 250 includes a
controllable selector valve 252 which interconnects to a sampling
fluid path 253, to a purge fluid path 254, and to a measurement
fluid path 255.
[0206] System 250 comprises a sensor 251 disposed on measurement
fluid path 255, which may include one or more of any of the
nanoelectronic sensor embodiments described herein. Sensor 251 may
alternatively or additionally comprise any one of a number of
alternative sensor types, such as electrochemical sensors, SAW
sensors, optical sensors, CMOS sensors and the like.
[0207] In an example system 250 for the monitoring and/or control
of an ambient environment, such as ammonia (NH.sub.3) content of
the air within a poultry house, sampling path 253 may comprise an
inlet 256 from an environmental space which preferably connects to
a filter 257 configured to remove particulates from the sample air.
Additional treatment or filter component 258 may be included to
remove interferents or contaminants, for example H.sub.2S, from the
sample, or may additionally or alternatively include a
de-humidifier, such as a cold-trap.
[0208] Purge path 254 may comprise purge gas source 259, such as a
source of purified air, dry N.sub.2, and the like. In one example,
purge source 259 comprises sample air having additional filtering
or treatment to remove the analyte of interest (e.g., NH.sub.3
absorbent), fed in this example from the sampling path 253 by
bypass 260.
[0209] Measurement path 255 receives a multiplexed flow provided by
selector valve 252 sequentially comprising sample air and purge
air. In this example the selector valve is controlled by processor
261 which is in communication with sensor 251, and may be
configured for sampling/purge (measurement/recovery) sequences such
as are illustrated in FIGS. 18-21. Alternatively, the multiplexing
sequence may be controlled by other mechanisms, such as fixed
timers and the like.
[0210] The multiplexing sequence may be selected to apply a duty
cycle for sensor measurement, such as on the order of a few percent
or less. For certain types of sensor with finite measurement life
due to factors such as reagent exhaustion (e.g., many
electrochemical sensors), a fractional duty cycle can extend
effective sensor life by orders of magnitude.
[0211] Air flow is induced by pump 262 which connects to optional
temperature controller 263 (heater and/or cooler), which in turn
supplies multiplexed flow (at a selected temperature) to expose
sensor 251. Following sensor exposure, the multiplexed flow is
emitted at exhaust 264.
[0212] It should be understood that a number of alternative
arrangements of system 250 are possible without departing from
spirit of the invention, and that the system may be configured for
measurement of a broad range of different analytes in different
sample mediums (i.e., dissolved analytes in aqueous media). For
example, the pump may be provided downstream (262') from sensor
251, and/or may be provided upstream of selector valve 252 (not
illustrated). In certain measurement applications the pump may be
omitted, as where sample and/or purge flow is provided by other
means (e.g., natural convection, fans for space ventilation,
gravity flow, pressurized environmental spaces, and the like).
[0213] FIG. 23 illustrates the structure of an exemplary sensing
device 251 having aspects of the invention and adapted for
measuring an analyte, such as NH.sub.3, contained in measurement
medium 255, for example in a system such as is shown in FIG. 22.
The architecture of sensor 251 is generally similar to that shown
in FIG. 1. Sensing device 251 includes a nanostructure sensor 302
configured as a field effect transistor, comprising a substrate 304
having a dielectric surface layer 316. Substrate 304 may be
comprise a conductive material, such as doped silicon, permitting
it to function as a gate electrode. A spaced-apart pair of contacts
310, 312 (e.g., Ti/Au layers) are disposed in communication with
SWNT channel 306. Circuitry 322 preferably includes controllable
voltage sources 313 and 324 to regulate Vsd between contacts 31-312
and Vg applied at 314 to control the voltage of the substrate/back
gate. As in the case of the sensor of FIG. 1, a number of
alternative configurations are possible without departing from the
spirit of the invention.
[0214] In the example shown, SWNT channel 306 is covered or
passivated with thin a dielectric coating 318 which may comprise
Al2O3, ZrO2 or the like, either alone, in mixtures, or in a
multilayer coating. Coating 318 is preferably deposited by ALD and
may be only a few nanometer in thickness (e.g., between about 10
and about 100 nm). A functionalization layer 320 is deposited above
coating 318, and may comprise one or more of the materials listed
in Table 3 above. In a preferred example, layer 320 may comprise
glycerol, alone or in combination with a surfactant such as Triton
100.
[0215] A number of different measurement schemes may be
advantageously applied in ammonia detection using sensor device
251. For example, temperature and humidity dependence of the device
may be reduced by heating sample 255 to a temperature above the
ambient (e.g. between about 60 and about 70.degree. C.).
[0216] In one exemplary measurement protocol, the substrate gate or
"back gate" 304 is grounded and a DC bias-voltage Vsd is applied
between the source 310 and drain 312, so as to generate a
measurable current through channel 306, permitting the determine of
conductance or resistance as a function of exposure to medium 255
and/or as a function of time.
[0217] In an alternative measurement protocol, the Vg of the
backgate 304 is modulated with a voltage waveform produced by
circuitry 322. This waveform may have a particular shape (e.g., sin
wave, triangle wave, square wave, etc), a particular amplitude
(e.g., 1 mV peak-to-peak, 1 V peak-to-peak, 10 V peak-to peak,
etc), a particular offset (e.g., -1 V, 0V, +1 V, etc), and/or a
particular frequency (e.g., 0.1 Hz, 1 Hz, 10 Hz, etc). The
conductance or other properties may then be measured at one point,
or at multiple points during the gate-waveform. This protocol may
produce measurements with increased stablility.
[0218] In an additional alternative measurement protocol, the AC
gate voltage is applied to gate 304 as described above, and in
addition a waveform AC-bias Vsd is applied between the source 310
and drain 312, and measurements of conductance or other properties
is likewise taken at selected points within the Vsd waveform.
[0219] The employment of AC waveforms for Vg and/or Vsd can permit
much faster response and recovery of sensor response. Such
measurement protocols may stabilize the device and also reduce such
effects as charge migration, electrochemical reactions, or other
phenomena. Such AC measurement protocols can permit other
parameters to be measured simultaneously (e.g., RH, temperature,
and the like) which can then used in compensation algorithms to
improve measurements of analyte concentrations
[0220] In addition, global changes of the conductance response to
Vg ("I/Vg") may be tracked. For example, 1) electron transfer
shifts the I/Vg left or right along the gate-voltage axis, 2)
charge-carrier scattering scales the I/Vg in the "conducting"
region, 3) changes at any ohmic contact shifts the I/Vg up or down
along the conductance axis. There are likely to be many more global
changes than those listed here. A number of analog, digital, and/or
software algorithms may be used to track such global changes. This
information may be employed to increase the accuracy and precision
of measurements, among other things.
[0221] Having thus described a preferred embodiment of
nanostructures with electrodeposited nanoparticles, and methods of
making them, it should be apparent to those skilled in the art that
certain advantages of the within system have been achieved. It
should also be appreciated that various modifications, adaptations,
and alternative embodiments thereof may be made within the scope
and spirit of the present invention. For example, specific examples
have been illustrated for nanotube film nanostructures, but it
should be apparent that the inventive concepts described above
would be equally applicable to other types of nanostructures. The
invention is further defined by the following claims.
* * * * *