U.S. patent application number 12/977568 was filed with the patent office on 2012-06-28 for highly selective chemical and biological sensors.
This patent application is currently assigned to General Electric Company. Invention is credited to Binil Kandapallil, Radislav Alexandrovich Potyrailo, Cheryl Margaret Surman.
Application Number | 20120166095 12/977568 |
Document ID | / |
Family ID | 46318091 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120166095 |
Kind Code |
A1 |
Potyrailo; Radislav Alexandrovich ;
et al. |
June 28, 2012 |
HIGHLY SELECTIVE CHEMICAL AND BIOLOGICAL SENSORS
Abstract
Methods and sensors for selective fluid sensing are provided. A
sensor includes a resonant inductor-capacitor-resistor (LCR)
circuit and a sensing material disposed over the LCR circuit. The
sensing material includes a coordination compound of a ligand and a
metal nanoparticle. The coordination compound has the formula:
(X).sub.n-M, where X includes an alkylamine group having the
formula (R--NH.sub.2), an alkylphosphine having the formula
(R.sub.3--P), an alkylphosphine oxide having the formula
(R.sub.3P.dbd.O), an alkyldithiocarbamate having the formula
(R.sub.2NCS.sub.2), an alkylxanthate having the formula
(ROCS.sub.2), or any combination thereof, R includes an alkyl
group, n is 1, 2, or 3, and M includes the metal nanoparticle of
gold, silver, platinum, palladium, alloys thereof, highly
conductive metal nanoparticles, or any combination thereof. The
sensing material is configured to allow selective detection of at
least six different analyte fluids from an analyzed fluid
mixture.
Inventors: |
Potyrailo; Radislav
Alexandrovich; (Niskayuna, NY) ; Surman; Cheryl
Margaret; (Albany, NY) ; Kandapallil; Binil;
(Mechanicville, NY) |
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
46318091 |
Appl. No.: |
12/977568 |
Filed: |
December 23, 2010 |
Current U.S.
Class: |
702/23 ; 324/675;
977/773; 977/957 |
Current CPC
Class: |
G01N 27/3278 20130101;
G01N 33/48792 20130101; G01N 27/025 20130101 |
Class at
Publication: |
702/23 ; 324/675;
977/773; 977/957 |
International
Class: |
G06F 19/00 20110101
G06F019/00; G01R 27/26 20060101 G01R027/26 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &
DEVELOPMENT
[0001] This invention was made with Government support and funded
in part by the National Institute of Environmental Health Sciences
under Grant No. 1R01ES016569-01A1. The Government has certain
rights in the invention.
Claims
1. A sensor, comprising: a resonant inductor-capacitor-resistor
(LCR) circuit; and a sensing material disposed over the LCR
circuit, wherein the sensing material comprises a coordination
compound of a ligand and a metal nanoparticle, wherein: the
coordination compound has the formula: (X).sub.n-M, wherein: X
comprises an alkylamine group having the formula (R--NH.sub.2), an
alkylphosphine having the formula (R.sub.3--P), an alkylphosphine
oxide having the formula (R.sub.3P.dbd.O), an alkyldithiocarbamate
having the formula (R.sub.2NCS.sub.2), an alkylxanthate having the
formula (ROCS.sub.2), or any combination thereof; R comprises an
alkyl group; n is 1, 2, or 3; and M comprises the metal
nanoparticle, wherein the sensing material is configured to allow
selective detection of at least six different analyte fluids from
an analyzed fluid mixture.
2. The sensor, as set forth in claim 1, wherein the alkyl group has
the formula: C.sub.yH.sub.2y+1, wherein y=1 to 18.
3. The sensor, as set forth in claim 1, wherein the metal
nanoparticle comprises gold, silver, platinum, palladium, alloys
thereof, highly conductive metal nanoparticles, or any combination
thereof.
4. The sensor, as set forth in claim 1, comprising a memory
chip.
5. The sensor, as set forth in claim 1, wherein the sensor
comprises an RFID sensor.
6. The sensor, as set forth in claim 1, comprising a coil.
7. The sensor, as set forth in claim 1, wherein the sensing
material is disposed between electrodes of the LCR circuit.
8. The sensor, as set forth in claim 1, wherein the sensor is
configured to sense a first fluid in the analyzed fluid in the
presence of a second fluid in the analyzed fluid, wherein a
concentration of the second fluid is at least ten times greater
than a concentration of the first fluid.
9. A method of detecting chemical or biological species in a fluid,
comprising: measuring a real part and an imaginary part of an
impedance spectrum of a resonant sensor antenna coated with a
coordination compound of a ligand and a metal nanoparticle, wherein
the ligand comprises a primary alkyl amine, trialkylphosphine,
trialkylphosphine oxide, alkyldithiocarbamate, alkylxanthate or any
combination thereof; calculating at least six spectral parameters
of the resonant sensor antenna coated with the coordination
compound; reducing the impedance spectrum to a single data point
using multivariate analysis to selectively identify an analyte; and
determining one or more environmental parameters from the impedance
spectrum.
10. The method, as set forth in claim 9, wherein the coordination
compound has the formula: (X).sub.n-M, wherein: X comprises an
alkylamine group having the formula (R--NH.sub.2), an
alkylphosphine having the formula (R.sub.3--P), an alkylphosphine
oxide having the formula (R.sub.3P.dbd.O), an alkyldithiocarbamate
having the formula (R.sub.2NCS.sub.2), an alkylxanthate having the
formula (ROCS.sub.2), or any combination thereof; R comprises an
alkyl group, wherein the alkyl group has the formula
C.sub.yH.sub.2y+1, wherein y=1 to 18; n is 1, 2, or 3; and M
comprises the metal nanoparticle of gold, silver, platinum,
palladium, alloys thereof, highly conductive metal nanoparticles,
or any combination thereof.
11. The method, as set forth in claim 9, wherein measuring the
impedance spectrum and calculating at least six spectral parameters
comprises measuring over a resonant frequency range of the resonant
sensor.
12. The method, as set forth in claim 9, wherein calculating at
least six spectral parameters comprises calculating a frequency
position of the real part of the impedance spectrum, and a
magnitude of the real part of the impedance spectrum.
13. The method, as set forth in claim 9, wherein calculating at
least six spectral parameters comprises calculating a resonant
frequency of the imaginary part of the impedance spectrum, and an
anti-resonant frequency of the imaginary part of the impedance
spectrum.
14. The method, as set forth in claim 9, wherein determining
comprises determining a resistance and a capacitance of the
resonant sensor coated with the coordination compound.
15. The method, as set forth in claim 9, wherein reducing the
impedance spectrum to a single data point comprises calculating a
multivariate signature.
16. A sensor, comprising: a transducer having a multivariate output
to independently detect effects of different environmental
parameters on the sensor; and a coordination compound of a ligand
and a metal nanoparticle disposed on the transducer and having a
preserved magnitude of response to an analyte over a broad
concentration range of an interferent, wherein: the coordination
compound has the formula: (X).sub.n-M, wherein: X comprises an
alkylamine group having the formula (R--NH.sub.2), an
alkylphosphine having the formula (R.sub.3--P), an alkylphosphine
oxide having the formula (R.sub.3P.dbd.O), an alkyldithiocarbamate
having the formula (R.sub.2NCS.sub.2), an alkylxanthate having the
formula (ROCS.sub.2), or any combination thereof; R comprises an
alkyl group; n is 1, 2, or 3; and M comprises the metal
nanoparticle of gold, silver, platinum, palladium, alloys thereof,
highly conductive metal nanoparticles, or any combination
thereof.
17. The sensor, as set forth in claim 16, wherein the coordination
compound has multiple response mechanisms to analytes and
interferents.
18. The sensor, as set forth in claim 17, wherein the response
mechanisms of the sensing material are related to the changes of
dielectric constant, resistance, and swelling of the coordination
compound where these changes are not fully correlated with each
other and produce different patterns upon exposure to individual
fluids and their mixtures.
19. The sensor, as set forth in claim 16, wherein the transducer
comprises an inductor-capacitor-resistor (LCR) transducer.
20. The sensor, as set forth in claim 19, wherein the LCR
transducer comprises an RFID transducer with an integrated circuit
chip.
21. The sensor, as set forth in claim 19, wherein the sensor has
multiple components of LCR response from the LCR transducer,
wherein the multiple components of LCR response originate from one
or more factors affecting the LCR transducer.
22. The sensor, as set forth in claim 21, wherein the one or more
factors comprise resistance and capacitance of the sensing
material, resistance and capacitance between the transducer and the
sensing material, and resistance and capacitance between a
transducer substrate and the sensing material.
Description
BACKGROUND
[0002] The subject matter disclosed herein relates to chemical and
biological sensors, and more particularly, to highly selective
chemical and biological sensors.
[0003] Chemical and biological sensors are often employed in a
number of applications where the detection of various vapors may be
used to discern useful information. For instance, measuring the
presence of vapors by discerning a change in certain environmental
variables within or surrounding a sensor may be particularly useful
in monitoring changes in biopharmaceutical products, food or
beverages, monitoring industrial areas for chemical or physical
hazards, as well as in security applications, such as residential
home monitoring, home land security in airports, in different
environmental and clinical settings, and other public venues
wherein detection of certain harmful and/or toxic vapors may be
particularly useful.
[0004] One technique for sensing such environmental changes is by
employing a sensor, such as an RFID sensor, coated with a
particular sensing material. In addition, sensors may be arranged
in an array of individual transducers, which are coated with one or
more sensing materials. Many sensor arrays include a number of
identical sensors. However, while using identical sensors
simplifies fabrication of the sensor array, such an array may have
limited capabilities for sensing only a single response (e.g.
resistance, current, capacitance, work function, mass, optical
thickness, light intensity, etc). In certain applications multiple
responses or changes in multiple properties may occur. In such
applications, it may be beneficial to include an array of sensors
wherein different transducers in the array employ the same or
different responses (e.g. resistance, current, capacitance, work
function, mass, optical thickness, light intensity, etc.) and are
coated with different sensing materials such that more than one
property can be measured. Disadvantageously, fabricating a sensor
array having individual sensors uniquely fabricated to sense a
particular response, complicates fabrication of the array.
[0005] Further, in many practical applications, it is beneficial to
use highly selective chemical and biological sensors. That is, it
is often desirable to provide a sensor array capable of sensing
multiple vapors and vapor mixtures in the presence of other vapors
and mixtures. The greater the number of vapors and vapor mixtures
that may be present, the more difficult it may be to accurately
sense and discern a specific type of vapor or vapor mixture being
sensed. This may be particularly true when one or more vapors are
present at levels of magnitude greater than the other vapors of
interest for detection. For instance, high humidity environments
often interfere with the ability of traditional sensors to detect
selected vapors.
[0006] Various embodiments disclosed herein may address one or more
of the challenges set forth above.
BRIEF DESCRIPTION
[0007] In accordance with one embodiment, there is provided a
sensor that includes a resonant inductor-capacitor-resistor (LCR)
circuit and a sensing material disposed over the LCR circuit. The
sensing material includes a coordination compound of a ligand and a
metal nanoparticle. The coordination compound has the formula:
(X).sub.n-M, where X includes an alkylamine group having the
formula (R--NH.sub.2), an alkylphosphine having the formula
(R.sub.3--P), an alkylphosphine oxide having the formula
(R.sub.3P.dbd.O), an alkyldithiocarbamate having the formula
(R.sub.2NCS.sub.2), an alkylxanthate having the formula
(ROCS.sub.2), or any combination thereof, R includes an alkyl
group, n is 1, 2, or 3, and M includes the metal nanoparticle of
gold, silver, platinum, palladium, alloys thereof, highly
conductive metal nanoparticles, or any combination thereof. The
sensing material is configured to allow selective detection of at
least six different analyte fluids from an analyzed fluid
mixture.
[0008] In accordance with another embodiment, there is provided a
method of detecting chemical or biological species in a fluid. The
method includes measuring a real part and an imaginary part of an
impedance spectrum of a resonant sensor antenna coated with a
coordination compound of a ligand and a metal nanoparticle. The
ligand includes a primary alkyl amine, trialkylphosphine,
trialkylphosphine oxide, alkyldithiocarbamate, alkylxanthate or any
combination thereof. The method further includes calculating at
least six spectral parameters of the resonant sensor antenna coated
with the coordination compound. The method further includes
reducing the impedance spectrum to a single data point using
multivariate analysis to selectively identify an analyte. The
method further includes determining one or more environmental
parameters from the impedance spectrum.
[0009] In accordance with another embodiment, there is provided a
sensor that includes a transducer and a coordination compound of a
ligand and a metal nanoparticle disposed on the transducer. The
transducer has a multivariate output to independently detect
effects of different environmental parameters on the sensor. The
coordination compound has a preserved magnitude of response to an
analyte over a broad concentration range of an interferent. In
addition, the coordination compound has the formula: (X).sub.n-M,
where X includes an alkylamine group having the formula
(R--NH.sub.2), an alkylphosphine having the formula (R.sub.3--P),
an alkylphosphine oxide having the formula (R.sub.3P.dbd.O), an
alkyldithiocarbamate having the formula (R.sub.2NCS.sub.2), an
alkylxanthate having the formula (ROCS.sub.2), or any combination
thereof, R includes an alkyl group, n is 1, 2, or 3, and M includes
the metal nanoparticle of gold, silver, platinum, palladium, alloys
thereof, highly conductive metal nanoparticles, or any combination
thereof.
DRAWINGS
[0010] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0011] FIG. 1 illustrates a sensing system, in accordance with
embodiments of the invention;
[0012] FIG. 2 illustrates an RFID sensor, in accordance with
embodiments of the invention;
[0013] FIG. 3 illustrates an RFID sensor, in accordance with
alternate embodiments of the invention;
[0014] FIG. 4 illustrates measured responses of an RFID sensor, in
accordance with embodiments of the invention;
[0015] FIG. 5 illustrates a sensing material, in accordance with
embodiments of the invention; and
[0016] FIGS. 6 and 7 illustrate test data demonstrating a single
sensor capable of discriminating between water vapor and nine
individual alcohol vapors from their homologous series, in
accordance with embodiments of the invention.
DETAILED DESCRIPTION
[0017] Embodiments disclosed herein provide methods and systems for
selective vapor sensing wherein a single sensor is provided and is
capable of detecting multiple vapors and/or mixtures of vapors
alone, or in the presence of one another. Examples of such methods
and sensors are described in U.S. patent application Ser. No.
12/942,732 entitled "Highly Selective Chemical and Biological
Sensors," which is incorporated herein by reference. The disclosed
sensors are capable of detecting different vapors and mixtures even
in a high humidity environment or an environment wherein one or
more vapors has a substantially higher concentration (e.g.
10.times.) compared to other components in the mixture. Each sensor
includes a resonant inductor-capacitor-resistor (LCR) sensor that
is coated with a sensing material, namely a coordination compound
of a primary alkyl amine and a metal nanoparticle, as further
described below. Sensing materials that include exemplary
coordination compounds may provide improved ability for selective
vapor sensing and improved stability of response compared to the
performance of other sensing materials, such as sensing materials
that include thiol groups. Non-limiting examples of LCR sensors
include RFID sensors with an integrated circuit (IC) memory chip,
RFID sensors with an IC chip, and RFID sensors without an IC memory
chip (chipless RFID sensors). LCR sensors can be wireless or wired.
In order to collect data, an impedance spectrum is acquired over a
relatively narrow frequency range, such as the resonant frequency
range of the LCR circuit. The technique further includes
calculating the multivariate signature from the acquired spectrum
and manipulating the data to discern the presence of certain vapors
and/or vapor mixtures. The presence of vapors is detected by
measuring the changes in dielectric, dimensional, charge transfer,
and other changes in the properties of the materials employed by
observing the changes in the resonant electronic properties of the
circuit. By using a mathematical procedure, such as principal
component analysis (PCA) and others, multiple vapors and mixtures
can be detected in the presence of one another and in the presence
of an interferent as further described below. Embodiments disclosed
herein provide methods and systems for selective fluid sensing
wherein a single sensor is provided and is capable of detecting
multiple fluids and/or mixtures of fluids alone, or in the presence
of one another.
[0018] To more clearly and concisely describe the subject matter of
the claimed invention, the following definitions are provided for
specific terms, which are used in the following description and the
appended claims.
[0019] The term "fluids" includes gases, vapors, liquids, and
solids.
[0020] The term "digital ID" includes all data stored in a memory
chip of the RFID sensor. Non-limiting examples of this data are
manufacturer identification, electronic pedigree data, user data,
and calibration data for the sensor.
[0021] The term "monitoring process" includes, but is not limited
to, measuring physical changes that occur around the sensor. For
example, monitoring processes including monitoring changes in a
biopharmaceutical, food or beverage manufacturing process related
to changes in physical, chemical, and/or biological properties of
an environment around the sensor. Monitoring processes may also
include those industry processes that monitor physical changes as
well as changes in a component's composition or position.
Non-limiting examples include homeland security monitoring,
residential home protection monitoring, environmental monitoring,
clinical or bedside patient monitoring, airport security
monitoring, admission ticketing, and other public events.
Monitoring can be performed when the sensor signal has reached an
appreciably steady state response and/or when the sensor has a
dynamic response. The steady state sensor response is a response
from the sensor over a determined period of time, where the
response does not appreciably change over the measurement time.
Thus, measurements of steady state sensor response over time
produce similar values. The dynamic sensor response is a response
from the sensor upon a change in the measured environmental
parameter (temperature, pressure, chemical concentration,
biological concentration, etc.). Thus, the dynamic sensor response
significantly changes over the measurement time to produce a
dynamic signature of response toward the environmental parameter or
parameters measured. Non-limiting examples of the dynamic signature
of the response include average response slope, average response
magnitude, largest positive slope of signal response, largest
negative slope of signal response, average change in signal
response, maximum positive change in signal response, and maximum
negative change in signal response. The produced dynamic signature
of response can be used to further enhance the selectivity of the
sensor in dynamic measurements of individual vapors and their
mixtures. The produced dynamic signature of response can also be
used to further optimize the combination of sensing material and
transducer geometry to enhance the selectivity of the sensor in
dynamic and steady state measurements of individual vapors and
their mixtures.
[0022] The term "environmental parameters" is used to refer to
measurable environmental variables within or surrounding a
manufacturing or monitoring system. The measurable environmental
variables comprise at least one of physical, chemical, and
biological properties and include, but are not limited to,
measurement of temperature, pressure, material concentration,
conductivity, dielectric property, number of dielectric, metallic,
chemical, or biological particles in the proximity or in contact
with the sensor, dose of ionizing radiation, and light
intensity.
[0023] The term "analyte" includes any desired measured
environmental parameter.
[0024] The term "interference" includes any undesired environmental
parameter that undesirably affects the accuracy and precision of
measurements with the sensor. The term "interferent" refers to a
fluid or an environmental parameter (that includes, but is not
limited to temperature, pressure, light, etc.) that potentially may
produce an interference response by the sensor.
[0025] The term "multivariate analysis" refers to a mathematical
procedure that is used to analyze more than one variable from the
sensor response and to provide the information about the type of at
least one environmental parameter from the measured sensor spectral
parameters and/or to quantitative information about the level of at
least one environmental parameter from the measured sensor spectral
parameters. The term "principal components analysis (PCA)" refers
to a mathematical procedure that is used to reduce multidimensional
data sets to lower dimensions for analysis. Principal component
analysis is a part of eigenanalysis methods of statistical analysis
of multivariate data and may be performed using a covariance matrix
or correlation matrix. Non-limiting examples of multivariate
analysis tools include canonical correlation analysis, regression
analysis, nonlinear regression analysis, principal components
analysis, discriminate function analysis, multidimensional scaling,
linear discriminate analysis, logistic regression, or neural
network analysis.
[0026] The term "spectral parameters" is used to refer to
measurable variables of the sensor response. The sensor response is
the impedance spectrum of the resonance sensor circuit of the LCR
or RFID sensor. In addition to measuring the impedance spectrum in
the form of Z-parameters, S-parameters, and other parameters, the
impedance spectrum (its both real and imaginary parts) may be
analyzed simultaneously using various parameters for analysis, such
as, the frequency of the maximum of the real part of the impedance
(F.sub.p), the magnitude of the real part of the impedance
(Z.sub.p), the resonant frequency of the imaginary part of the
impedance (F.sub.1), and the anti-resonant frequency of the
imaginary part of the impedance (F.sub.2), signal magnitude
(Z.sub.1) at the resonant frequency of the imaginary part of the
impedance (F.sub.1), signal magnitude (Z.sub.2) at the
anti-resonant frequency of the imaginary part of the impedance
(F.sub.2), and zero-reactance frequency (F.sub.z, frequency at
which the imaginary portion of impedance is zero). Other spectral
parameters may be simultaneously measured using the entire
impedance spectra, for example, quality factor of resonance, phase
angle, and magnitude of impedance. Collectively, "spectral
parameters" calculated from the impedance spectra, are called here
"features" or "descriptors." The appropriate selection of features
is performed from all potential features that can be calculated
from spectra. Multivariable spectral parameters are described in
U.S. patent application Ser. No. 12/118,950 entitled "Methods and
systems for calibration of RFID sensors," which is incorporated
herein by reference.
[0027] The term "resonance impedance" or "impedance" refers to
measured sensor frequency response around the resonance of the
sensor from which the sensor "spectral parameters" are
extracted.
[0028] The term "protecting material" includes, but is not limited
to, materials on the LCR or RFID sensor that protect the sensor
from an unintended mechanical, physical or chemical effect while
still permitting the anticipated measurements to be performed. For
example, an anticipated measurement may include solution
conductivity measurement wherein a protecting film separates the
sensor from the liquid solution yet allows an electromagnetic field
to penetrate into solution. An example of a protecting material is
a paper film that is applied on top of the sensor to protect the
sensor from mechanical damage and abrasion. Another non-limiting
example of a protecting material is a polymer film that is applied
on top of the sensor to protect the sensor from corrosion when
placed in a liquid for measurements. A protecting material may also
be a polymer film that is applied on top of the sensor for
protection from shortening of the sensor's antenna circuit when
placed in a conducting liquid for measurements. Non-limiting
examples of protecting films are paper, polymeric, and inorganic
films such as polyesters, polypropylene, polyethylene, polyethers,
polycarbonate, polyethylene terepthalate, zeolites, metal-organic
frameworks, and cavitands. The protecting material can be arranged
between the transducer and sensing film to protect the transducer.
The protecting material can be arranged on top of the sensing film
which is itself is on top of the transducer to protect the sensing
film and transducer. The protecting material on top of the sensing
film which is itself is on top of the transducer can serve to as a
filter material to protect the sensing film from exposure to
gaseous or ionic interferences. Non-limiting examples of filter
materials include zeolites, metal-organic frameworks, and
cavitands.
[0029] As used herein the term "sensing materials and sensing
films" includes, but is not limited to, materials deposited onto a
transducer's electronics module, such as LCR circuit components or
an RFID tag, to perform the function of predictably and
reproducibly affecting the impedance sensor response upon
interaction with the environment. In order to prevent the material
in the sensor film from leaching into the liquid environment, the
sensing materials are attached to the sensor surface using standard
techniques, such as covalent bonding, electrostatic bonding, and
other standard techniques known to those of ordinary skill in the
art.
[0030] The terms "transducer and sensor" are used to refer to
electronic devices such as RFID devices intended for sensing.
"Transducer" is a device before it is coated with a sensing or
protecting film or before it is calibrated for a sensing
application. "Sensor" is a device typically after it is coated with
a sensing or protecting film and after being calibrated for the
sensing application.
[0031] As used herein the term "RFID tag" refers to an
identification and reporting technology that uses electronic tags
for identifying and/or tracking articles to which the RFID tag may
be attached. An RFID tag typically includes at least two components
where the first component is an integrated circuit (IC) memory chip
for storing and processing information and modulating and
demodulating a radio frequency signal. This memory chip can also be
used for other specialized functions, for example, it can contain a
capacitor. It can also contain at least one input for an analog
signal such as resistance input, capacitance input, or inductance
input. In the case of a chipless RFID tag, the RFID tag may not
include an IC memory chip. This type of RFID tag may be useful in
applications where a specific RFID tag does not need to be
identified, but rather a signal merely indicating the presence of
the tag provides useful information (e.g., product security
applications). The second component of the RFID tag is an antenna
for receiving and transmitting the radio frequency signal.
[0032] The term "RFID sensor" is an RFID tag with an added sensing
function as, for example, when an antenna of the RFID tag also
performs sensing functions by changing its impedance parameters as
a function of environmental changes. The accurate determinations of
environmental changes with such RFID sensors are performed by
analysis of resonance impedance. For example, RFID tags may be
converted into RFID sensors by coating the RFID tag with a sensing
film. By coating the RFID tag with a sensing film, the electrical
response of the film is translated into simultaneous changes to the
impedance response, resonance peak position, peak width, peak
height and peak symmetry of the impedance response of the sensor
antenna, magnitude of the real part of the impedance, resonant
frequency of the imaginary part of the impedance, anti-resonant
frequency of the imaginary part of the impedance, zero-reactance
frequency, phase angle, and magnitude of impedance, and others as
described in the definition of the term sensor "spectral
parameters." The "RFID sensor" can have an integrated circuit (IC)
memory chip attached to the antenna or can have no IC memory chip.
An RFID sensor without an IC memory chip is an LCR sensor. An LCR
sensor is comprised of known components, such as at least one
inductor (L), at least one capacitor (C), and at least one resistor
(R) to form an LCR circuit.
[0033] The term "single-use container" includes, but is not limited
to, manufacturing or monitoring equipment, and packaging, which may
be disposed of after use or reconditioned for reuse. Single-use
packaging in the food industry includes, but is not limited to,
food and drinks packaging, and candy and confection boxes.
Single-use monitoring components include, but are not limited to,
single-use cartridges, dosimeters, and collectors. Single use
manufacturing containers include, but are not limited to,
single-use vessels, bags, chambers, tubing, connectors, and
columns.
[0034] The term "writer/reader" includes, but is not limited to, a
combination of devices to write and read data into the memory of
the memory chip and to read impedance of the antenna. Another term
for "writer/reader" is "interrogator."
[0035] In accordance with embodiments disclosed herein, an LCR or
an RFID sensor for sensing vapors, vapor mixtures, and biological
species is described. As previously described, the RFID sensor
includes an RFID tag coated with the coordination compound of a
primary alkyl amine and a metal nanoparticle. In one embodiment, a
passive RFID tag may be employed. As will be appreciated, an RFID
tag may include an IC memory chip, which is connected to an antenna
coil for communication with a writer/reader. The IC memory chip can
be read by illuminating the tag by a radio frequency (RF) and/or
microwave carrier signal sent by the writer/reader. When the RF
and/or microwave field passes through the antenna coil, an AC
voltage is generated across the coil. The voltage is rectified in
the microchip to result in a DC voltage for the microchip
operation. The IC memory chip becomes functional when the DC
voltage reaches a predetermined level. By detecting the RF and/or
microwave signal backscattered from the microchip, the information
stored in the microchip can be fully identified. The distance
between the RFID tag/sensor and the writer/reader is governed by
the design parameters that include operating frequency, RF and/or
microwave power level, the receiving sensitivity of the
reader/writer, antenna dimensions, data rate, communication
protocol, and microchip power requirements. The distance between
the "RFID sensor" without an IC memory chip (chipless RFID sensor
or LCR sensor or LCR transducer) and the sensor reader is governed
by the design parameters that include operating frequency, RF or
microwave power level, the receiving sensitivity of the sensor
reader, and antenna dimensions.
[0036] In one embodiment a passive RFID tag with or without an IC
memory chip may be employed. Advantageously, a passive RFID tag
does not rely on a battery for operation. However, the
communication distance between the writer/reader and RFID tag is
typically limited within a proximity distance because the passive
tag operates with only microwatts of RF power from the
writer/reader. For passive tags operating at 13.56 MHz, the read
distance is typically not more than several centimeters. The
typical frequency range of operation of 13.56 MHz passive RFID tags
for digital ID writing/reading is from 13.553 to 13.567 MHz. The
typical frequency range of operation of 13.56-MHz passive RFID
sensors for sensing of environmental changes around the RFID sensor
is from about 5 MHz to about 20 MHz, more preferably from 10 to 15
MHz. The requirement for this frequency range is to be able to
recognize the tag with a writer/reader that operates at 13.56 MHz
while the sensor portion of the RFID tag operates from 5 to 20
MHz.
[0037] Depositing sensing films onto passive RFID tags creates RFID
chemical or biological sensors. RFID sensing is performed by
measuring changes in the RFID sensor's impedance as a function of
environmental changes around the sensor, as described further
below. If the frequency response of the antenna coil, after
deposition of the sensing film, does not exceed the frequency range
of operation of the tag, the information stored in the microchip
can be identified with a conventional RFID writer/reader. An
impedance or network analyzer (sensor reader) can read the
impedance of the antenna coil to correlate the changes in impedance
to the chemical and biological species of interest and to physical,
chemical, or/and biological changes of environmental parameters
around the sensor.
[0038] In operation, after coating of the RFID tag with a
chemically sensitive film, both the digital tag ID and the
impedance of the tag antenna may be measured. The measured digital
ID provides information about the identity of the tag itself, such
as an object onto which this tag is attached, and the properties of
the sensor (e.g. calibration curves for different conditions,
manufacturing parameters, expiration date, etc.). For
multi-component detection, multiple properties from the measured
real and imaginary portions of the impedance of a single RFID
sensor may be determined, as described further below.
[0039] In summary, and in accordance with the embodiments described
herein, in order to achieve high selectivity detection of analytes
in the presence of high levels of interferences, the sensor should
exhibit a number of characteristics. First, the selected transducer
should include a multivariate output to independently detect the
effects of different environmental parameters on the sensor.
Second, the sensing material should have a preserved magnitude of
response to an analyte over a wide concentration range of an
interferent. The response to the relatively small analyte
concentrations should not be fully suppressed by the presence of
the relatively high concentrations of the interferents. Third, the
response of the sensing material to interference species is allowed
and may exist but should not compete with the response to the
analyte and should be in a different direction of the multivariate
output response of the transducer.
[0040] To achieve these characteristics, in one embodiment, the
sensing material has multiple response mechanisms to vapors where
these response mechanisms are related to the changes of dielectric
constant, resistance, and swelling of the sensing material where
these changes are not fully correlated with each other and produce
different patterns upon exposure to individual vapors and their
mixtures. Further, the LCR transducer can have multiple components
of LCR response from the LCR circuit where these multiple
components of LCR response originate from the different factors
affecting the transducer circuit with the non-limiting examples
that include material resistance and capacitance, contact
resistance and capacitance between the transducer and sensing
material, and resistance and capacitance between the transducer
substrate and sensing material. Further, the LCR transducer can
have multiple conditions of LCR circuit operation where an
integrated circuit chip is a part of the sensor circuit.
[0041] Thus, one method for controlling the selectivity of the
sensor response involves powering of the integrated circuit chip to
affect the impedance spectral profile. The different impedance
spectral profiles change the selectivity of sensor response upon
interactions with different vapors. The IC chip or IC memory chip
on the resonant antenna contains a rectifier diode and it can be
powered at different power levels to influence the impedance
spectral profile of the sensor. The differences in spectral
profiles at different power levels are pronounced in different
values of F.sub.p, F.sub.1, F.sub.2, F.sub.z, Z.sub.p, Z.sub.1,
Z.sub.2, and calculated values of C and R. In one embodiment, the
enhanced sensor selectivity is achieved through the appropriate
selection of at least one power level of the IC chip or IC memory
chip operation. In another embodiment, the enhanced sensor
selectivity is achieved through the appropriate selection of at
least two power levels of the IC chip or IC memory chip operation
and analyzing the combined impedance spectral profiles of the
sensor under different power levels. Powering of the sensor with at
least two power levels is performed in the alternating fashion
between a relatively low and relatively high power. The alternating
powering of the sensor with at least two power levels is performed
on the time scale that is at least 5 times faster than the dynamic
changes in the measured environmental parameters. In all these
embodiments, powering at different power levels is in the range
from -50 dBm to +40 dBm and provides the ability to detect more
selectively more analytes and/or to reject more selectively more
interferences.
[0042] Another method of controlling the selectivity of the sensor
response involves applying different powers to the LCR or to RFID
sensor to affect the dipole moment, the dielectric constant, and/or
temperature of the material in proximity to the sensor. The
material in proximity to the sensor refers to the sensing material
deposited onto the sensor and/or the fluid under investigation.
These changes in the dipole moment, the dielectric constant, and/or
temperature of the material in proximity to the sensor when exposed
to different power levels of LCR or RFID sensor operation originate
from the interactions of the electromagnetic field with these
materials. Powering of the sensor with at least two power levels is
performed in the alternating fashion between a relatively low and
relatively high power. The alternating powering of the sensor with
at least two power levels is performed on the time scale that is at
least 5 times faster than the dynamic changes in the measured
environmental parameters. In all these embodiments, powering at
different power levels is in the range from -50 dBm to +40 dBm and
provides the ability to detect more selectively more analytes
and/or to reject more selectively more interferences.
[0043] Turning now to the figures and referring initially to FIG.
1, a sensing system 10 is provided to illustrate the principle of
selective vapor sensing utilizing an RFID sensor 12 having a
sensing material 14, namely the coordination compound of a primary
alkyl amine and a metal nanoparticle, coated thereon. Referring
briefly to FIG. 2, the sensor 12 is a resonant circuit that
includes an inductor-capacitor-resistor structure (LCR) coated with
the sensing material 14. The sensing material 14 is applied onto
the sensing region between the electrodes, which form sensor
antenna 18 that constitute the resonant circuit. As will be
described further below, by applying the sensing material 14 onto
the resonant circuit, the impedance response of the circuit will be
altered. The sensor 12 may be a wired sensor or a wireless sensor.
The sensor 12 may also include a memory chip 16 coupled to resonant
antenna 18 that is coupled to a substrate 20. The memory chip 16
may include manufacturing, user, calibration and/or other data
stored thereon. The memory chip 16 is an integrated circuit device
and it includes RF signal modulation circuitry fabricated using a
complementary metal-oxide semiconductor (CMOS) process and a
non-volatile memory. The RF signal modulation circuitry components
include a diode rectifier, a power supply voltage control, a
modulator, a demodulator, a clock generator, and other
components.
[0044] FIG. 3 illustrates an alternative embodiment of the sensor
12, designated by reference numeral 21, wherein a complementary
sensor 23 comprising the sensing material 14 is attached across the
antenna 18 and the integrated circuit (IC) memory chip 16 to alter
the sensor impedance response. In another embodiment (not
illustrated), a complementary sensor may be attached across an
antenna that does not have an IC memory chip and alters sensor
impedance response. Non-limiting examples of complementary sensors
are interdigitated sensors, resistive sensors, and capacitive
sensors. Complementary sensors are described in U.S. patent
application Ser. No. 12/118,950 entitled "Methods and systems for
calibration of RFID sensors," which is incorporated herein by
reference.
[0045] In one embodiment, a 13.56 MHz RFID tag may be employed.
During operation of the sensing system 10, the impedance Z(f) of
the sensor antenna 18 and the digital sensor calibration parameters
stored on the memory chip 16 may be acquired. Referring again to
FIG. 1, measurement of the resonance impedance Z(f) of the antenna
18 and the reading/writing of digital data from the memory chip 16
are performed via mutual inductance coupling between the RFID
sensor antenna 18 and the pickup coil 22 of a reader 24. As
illustrated, the reader 24 may include an RFID sensor impedance
reader 26 and an integrated circuit memory chip reader 28. The
interaction between the RFID sensor 12 and the pickup coil 22 can
be described using a general mutual inductance coupling circuit
model. The model includes an intrinsic impedance Z.sub.C of the
pickup coil 22 and an intrinsic impedance Z.sub.S of the sensor 12.
The mutual inductance coupling B and the intrinsic impedances
Z.sub.C and Z.sub.S are related through the total measured
impedance Z.sub.T across the terminal of the pickup coil 22, as
represented by the following equation:
Z.sub.T=Z.sub.C+(.omega..sup.2B.sup.2/Z.sub.S), (1)
wherein .omega. is the radian carrier frequency and B is the mutual
inductance coupling B coefficient.
[0046] Sensing is performed via monitoring of the changes in the
properties of the sensing material 14 as probed by the
electromagnetic field generated in the antenna 18 (FIG. 2). Upon
reading the RFID sensor 12 with the pickup coil 22, the
electromagnetic field generated in the sensor antenna 18 extends
out from the plane of the sensor 12 and is affected by the
dielectric property of an ambient environment providing the
opportunity for measurements of physical, chemical, and biological
parameters.
[0047] Similarly, sensing is performed via monitoring of the
changes in the properties of the sensing material 14 as probed by
the electromagnetic field generated in the complementary sensor 23
(FIG. 3). Upon reading the RFID sensor 12 with the pickup coil 22,
the electromagnetic field generated in the complementary sensor 23
extends out from the plane of the complementary sensor 23 and is
affected by the dielectric property of an ambient environment
providing the opportunity for measurements of physical, chemical,
and biological parameters.
[0048] FIG. 4 illustrates an example of measured responses of an
exemplary RFID sensor 12, in accordance with embodiments of the
invention, which includes the sensor's full impedance spectra and
several individually measured spectral parameters. To selectively
detect several vapors or fluids using a single RFID sensor, such as
the RFID sensor 12, the real Z.sub.re(f) and imaginary Z.sub.im(f)
parts of the impedance spectra Z(f)=Z.sub.re(f)+jZ.sub.im(f) are
measured from the sensor antenna 18 coated with a sensing material
and at least four spectral parameters are calculated from the
measured Z.sub.re(f) and Z.sub.im(f), as illustrated in the plot 30
of FIG. 4. Seven spectral parameters can be calculated as
illustrated in the plot 30 of FIG. 4. These parameters include the
frequency position F.sub.p and magnitude Z.sub.p of Z.sub.re(f),
the resonant F.sub.1 and anti-resonant F.sub.2 frequencies of
Z.sub.im(f), the impedance magnitudes Z.sub.1 and Z.sub.2 at
F.sub.1 and F.sub.2 frequencies, respectively, and the
zero-reactance frequency F.sub.Z. Additional parameters, such as
quality factor may also be calculated. From the measured
parameters, resistance R, capacitance C, and other parameters of
the sensing film-coated resonant antenna 18 can be also determined.
Multivariate analysis may be used to reduce the dimensionality of
the impedance response, either from the measured real Z.sub.re(f)
and imaginary Z.sub.im(f) parts of the impedance spectra or from
the calculated parameters F.sub.p, Z.sub.p, F.sub.1 and F.sub.2,
and possibly other parameters to a single data point in
multi-dimensional space for selective quantization of different
vapors or fluids, as will be appreciated by those skilled in the
art, and as will be described further below.
[0049] The presence of even relatively low levels of interferences
(0.1-10 fold overloading levels) represents a significant
limitation for individual sensors due to their insufficient
selectivity. This problem can be addressed with an introduction of
a concept of sensor arrays. Unfortunately, in practical situations
(e.g. urban, environmental, and workplace monitoring, breath
analysis, and others), sensor arrays suffer from interference
effects at high (10.sup.2-10.sup.6 fold) overloading levels. These
interference effects reduce the use of both sensors and sensor
arrays. Advantageously, embodiments described herein provide
techniques to overcome these two key scientific limitations of
existing sensors and sensor arrays, such as difficulty or inability
of operating with high overloading from interferences and of
selective measurements of multiple vapors and their mixtures using
a single sensor.
[0050] The well-accepted limitations of impedance spectroscopy in
practical sensors for trace analyte detection include relatively
low sensitivity and prohibitively long acquisition times over the
broad frequency range. Embodiments described herein enhance the
ability to measure changes in properties of the sensing material by
putting the material onto the electrodes of the resonant LCR sensor
circuit. Similarly, the disclosed embodiments enhance the ability
to measure changes in properties of the fluid in proximity to the
electrodes of the resonant LCR sensor circuit. Experimental testing
examined the effects of changing dielectric constant on sensing
electrodes both with and without a resonator. Compared to the
conventional impedance spectroscopy, the bare resonant LCR sensor
provided an at least 100-fold enhancement in the signal-to-noise
(SNR) over the smallest measured range of .DELTA.E with the
corresponding improvement of detection limit of dielectric constant
determinations.
[0051] Performance of the LCR sensor as analyzed using multivariate
analysis tools provides an advantage of improved selectivity over
the processing of individual responses of individual sensors. In
particular, test results indicate the relations between F.sub.p and
Z.sub.p and the relations between calculated sensor resistance R
and calculated sensor capacitance C have much less selectivity
between responses to different vapors or fluids as compared to the
relations between multivariable parameters that show more
variation, as discussed in detail below. Further, the LCR sensors
demonstrate independent contact resistance and contact capacitance
responses that improve the overall selectivity of the multivariable
response of the LCR sensors. This selectivity improvement
originates from the independent contributions of the contact
resistance and contact capacitance responses to the equivalent
circuit response of the sensor.
[0052] Diverse sensing materials may be advantageously utilized on
the sensing region of the LCR resonant sensor because
analyte-induced changes in the sensing material film affect the
impedance of the antenna LCR circuit through the changes in
material resistance and capacitance, contact resistance and
capacitance between the transducer and sensing material, and
resistance and capacitance between the transducer substrate and
sensing material. Such changes provide diversity in response of an
individual RFID sensor and provide the opportunity to replace a
whole array of conventional sensors with a single LCR or RFID
sensor.
[0053] Sensing films for the disclosed LCR and RFID sensors may
include a variety of coordination compounds of a primary alkyl
amine, trialkylphosphine, trialkylphosphine oxide,
alkyldithiocarbamate, alkylxanthate or any combination thereof and
a metal nanoparticle, as long as the environmental changes are
detectable by changes in resonant LCR circuit parameters. The
primary alkyl amine, trialkylphosphine, trialkylphosphine oxide,
alkyldithiocarbamate, alkylxanthate, or combinations thereof may
also be referred to as a ligand or a combination of ligands, which
binds to a central metal atom to form a coordination complex. The
exemplary coordination compound may be represented by the formula:
(X).sub.n-M where X includes an alkylamine group having the formula
(R--NH.sub.2), an alkylphosphine having the formula (R.sub.3--P),
an alkylphosphine oxide having the formula (R.sub.3P.dbd.O), an
alkyldithiocarbamate having the formula (R.sub.2NCS.sub.2), an
alkylxanthate having the formula (ROCS.sub.2), or any combination
thereof and M is the metal nanoparticle. The value of n may be 1,
2, 3, or greater. The alkyl group R may be represented by the
formula: C.sub.yH.sub.2y+1, where y=1 to 18. Metals that may be
used for the metal nanoparticle M include, but are not limited to,
gold, silver, platinum, palladium, alloys thereof, other highly
conductive metal nanoparticles, or combinations thereof. In certain
embodiments, a weak covalent bond exists between the metal
nanoparticle and the ligand. In one embodiment, the coordination
compound is formed between an octylamine-capped C8 ligand and a
gold nanoparticle, as shown in FIG. 5. Other embodiments may
utilize other coordination compounds of a primary alkyl amine,
trialkylphosphine, trialkylphosphine oxide, alkyldithiocarbamate,
or alkylxanthate, and the metal nanoparticle.
[0054] Non-limiting examples of sensing materials include
octylamine-capped C8 ligand and a gold nanoparticle,
octylamine-capped C8 ligand and a silver nanoparticle,
octylamine-capped C8 ligand and a platinum nanoparticle,
octylamine-capped C8 ligand and a palladium nanoparticle,
nonylamine-capped C8 ligand and a gold nanoparticle, and
heptylamine-capped C8 ligand and a gold nanoparticle. The use of
these materials provides the ability to tailor the relative
direction of sensing response upon exposure to vapors of different
natures. The different partition coefficients of vapors into these
or other sensing materials further modulate the diversity and
relative direction of the response.
[0055] "Composites" are materials made from two or more constituent
materials with significantly different physical or chemical
properties, which remain separate and distinct on a macroscopic
level within the finished structure. Non-limiting examples of
composites include carbon black composites with the various
coordination compounds of a primary alkyl amine and a metal
nanoparticle discussed in detail above. "Nanocomposites" are
materials made from two or more constituent materials with
significantly different physical or chemical properties, which
remain separate and distinct on a nanoscale level within the
finished structure. Non-limiting examples of nanocomposites
include: carbon nanotube nanocomposites with exemplary coordination
compounds; semiconducting nanocrystal quantum dot nanocomposites
with exemplary coordination compounds, metal oxide nanowires, and
carbon nanotubes; metal nanoparticles or nanoclusters
functionalized with carbon nanotubes.
[0056] Sensing materials exhibit analyte responses, which can be
described by one or more of three response mechanisms of LCR or
RFID sensors, such as resistance changes, dielectric constant
changes, and swelling changes. A composite sensing material can be
constructed which incorporates the exemplary coordination compounds
with multiple different individual sensing materials, which each
respond to analytes by predominantly different response mechanisms.
Such composite sensing materials produce an enhanced diversity in
the multivariate response. Such composite sensing materials may be
homogeneously or inhomogeneously mixed or locally patterned over
specific portions of the LCR resonator.
[0057] For example, a wide range of metal oxide semiconductor
materials (e.g. ZnO, TiO.sub.2, SrTiO.sub.3, LaFeO.sub.3, etc)
exhibit changes in resistance upon exposure to analyte gases, but
some mixed metal oxides (e.g. CuO--BaTiO.sub.3, ZnO--WO.sub.3)
change their permittivity/capacitance upon exposure to analyte
vapors. By combining these materials either as mixtures, or by
spatially separated deposition onto the same sensor, their separate
contributions to the local environment surrounding the sensor are
used to enhance the diversity of response mechanisms for a single
analyte, thus enhancing selectivity.
[0058] As a further example, the coordination compounds of a
primary alkyl amine and a metal nanoparticle are used as vapor
sensing materials because of their strong changes in resistance due
to localized swelling induced by analyte adsorption into the ligand
shell and the subsequent change in tunneling efficiency between
neighboring conducting nanoparticles and dielectric constant
changes of the environment between these conducting nanoparticles.
In combination with a dielectric polymer (non-limiting examples
include silicones, poly(etherurethane), polyisobutylene siloxane
fluoroalcohol, etc.), conjugated polymer (polyaniline,
polythiophene, poly(vinyl ferrocene),
poly(fluorene)-diphenylpropane), poly(3,4-ethylenedioxythiophene)
polypyrrole, bilypyrrole) or any other material (non-limiting
examples include porphyrins, metalloporphyrins,
metallophthalocyanines, carbon nanotubes, semiconducting
nanocrystals, metal oxide nanowires) that responds to analyte
adsorption with more pronounced changes in capacitance or
resistance, a sensor with a wider range of analyte responses is
developed. Other examples of materials that may be combined with
the exemplary coordination compounds are described in U.S. patent
application Ser. No. 12/942,732 entitled "Highly Selective Chemical
and Biological Sensors," which is incorporated herein by
reference.
[0059] Further, in order to avoid potentially deleterious effects
of disparate materials on each other in a composite sensing
material (e.g. high dielectric constant medium suppressing
conduction in a conductive filler material), the material
components are chosen to locally phase separate due to
hydrophylic/hydrophobic interactions or mutual immiscibility,
allowing the different mechanisms active in each component to be
sensed by the sensor. In another embodiment, a composite sensing
material can be formed as sectors of individual materials deposited
adjacent to each other onto a single sensor. In another embodiment,
a composite sensing material can be formed as layers of individual
materials deposited on top of each other onto a single sensor.
[0060] To further improve selectivity of response, overcoating of
sensing films with auxiliary membrane filter films may be
performed. Non-limiting examples of these filter films include
zeolite, metal-organic framework, and cavitand filters.
[0061] These diverse sensing materials shown as non-limiting
examples are provided on the sensing region of the LCR or RFID
resonant sensor because analyte-induced changes in the sensing
material film affect the impedance of the antenna LCR circuit
through the changes in material resistance and capacitance, contact
resistance and capacitance between the transducer and sensing
material, resistance and capacitance between the transducer
substrate and sensing material. Such changes provide diversity in
response of an individual RFID sensor and provide the opportunity
to replace a whole array of conventional sensors with a single LCR
or RFID sensor, as illustrated further below, with regard to
EXPERIMENTAL DATA.
Experimental Data
[0062] Resonant antenna structures, such as those described above,
were used for demonstration of the disclosed techniques. Various
sensing materials were applied onto the resonant antennas by
conventional draw-coating, drop coating, and spraying processes.
Measurements of the impedance of the RFID sensors were performed
for example with a network analyzer (Model E5062A, Agilent
Technologies, Inc., Santa Clara, Calif.) under computer control
using LabVIEW. The network analyzer was used to scan the
frequencies over the range of interest (i.e., the resonant
frequency range of the LCR circuit) and to collect the impedance
response from the RFID sensors.
[0063] For gas sensing, different concentrations of vapors were
generated using an in-house built computer-controlled
vapor-generation system. Collected impedance data was analyzed
using KaleidaGraph (Synergy Software, Reading, Pa.) and PLS_Toolbox
(Eigenvector Research, Inc., Manson, Wash.) operated with Matlab
(The Mathworks Inc., Natick, Mass.).
Example
Selective Detection of Individual Nine Alcohols with a Single
Sensor
[0064] As illustrated in FIGS. 6 and 7, test results were obtained
to demonstrate the selective detection of individual, closely
related vapors, such as alcohols from their homologous series and
water vapor as an interferent, using a single sensor, such as the
sensor 12 described above. As illustrated in FIG. 6, the sensor was
exposed to the following 10 vapors over a period of time:
TABLE-US-00001 1 water 2 methanol 3 ethanol 4 1-propanol 5
1-butanol 6 1-pentanol 7 1-hexanol 8 1-heptanol 9 1-octanol 10
1-nonanol
The structures of the alcohols 60 are illustrated in FIG. 7.
[0065] The sensing material used to coat the RFID tag was carefully
chosen and provided the ability to selectively detect the listed
vapors. In the present experiment, the chosen sensing material was
octylamine-capped C8 ligand attached to gold nanoparticles, which
was applied as a sensing film onto an RFID sensor chip by drop
casting. Specifically, the nanoparticles of the sensing material
were synthesized as follows. A solution of HAuCl.sub.43H.sub.2O
(112 mg) was dissolved in 25 mL of water. While vigorously stirring
the solution, oleylamine (830 mg) dissolved in 25 mL of toluene was
added and the mixture was stirred until most or all of the Au ions
were transferred into the organic layer. After approximately 30
minutes, NaBH.sub.4 (0.165 g) in 25 mL of water was added drop-wise
and the reaction mixture was stirred for approximately 2 to 3
hours. The reaction mixture was phase separated and the toluene
layer dried over anhydrous MgSO.sub.4. The toluene layer was
reduced to a volume of 5 mL on a rotary evaporator. After addition
of ethanol (100 mL) to the toluene layer, the reaction mixture was
left at approximately -40 degrees Celsius overnight in a freezer
for the nanoparticles to precipitate out. The nanoparticles were
separated from the solution by filtering through filter paper
(Whatman, Piscataway, N.J.) and later redispersed in approximately
10 mL of toluene.
[0066] An interdigital chip served as a complementary sensor that
was attached across an antenna of a passive RFID tag. The chip was
approximately 2 mm by 2 mm and had gold electrodes that were
approximately 10 .mu.m wide and spaced approximately 10 .mu.m from
each other. During the experiment, the RFID sensor was
incrementally exposed to 10 vapors over a period of time. The test
was conducted in steps, where the concentration of each respective
vapor was increased with each step. Measurements were performed
with concentrations of all vapors at 0, 0.089, 0.178, 0.267, and
0.356 P/P.sub.o, where P is the partial pressure and P.sub.o is the
saturated vapor pressure. By monitoring changes in certain
properties and examining various responses over time and at
increasing concentration levels, the data demonstrated the ability
to distinguish the 10 vapors tested in the above-described
experiment.
[0067] For instance, the frequency position F.sub.p, the resonant
F.sub.1 and anti-resonant F.sub.2 frequencies of Z.sub.im(f), the
magnitude Z.sub.p of the real part of the total resistance
Z.sub.re(f), and the impedance magnitudes Z.sub.1 and Z.sub.2 at
F.sub.1 and F.sub.2 frequencies, respectively, are illustrated in
FIG. 6, as response plots 40, 42, 48, and 50, respectively. The
tests for each vapor were conducted and plotted over 4 increments
of increasing concentration, as clearly indicated by the stepped
nature of the response for each vapor. The relative differences in
the direction and the magnitude of these responses constitute a
robust response pattern for these vapors and their different
concentrations using a single sensor. For example, referring to the
plot 40 of the frequency position F.sub.p, the frequency position
F.sub.p for each vapor (1-10) exhibits four steps, correlative to
the increases in concentration of each vapor over time. From
examining this plot alone, certain of the vapors can clearly be
distinguished from one another. By way of example, the frequency
position F.sub.p response for 1-heptanol (8) is very strong, and
notably discernable from each of the other responses. Accordingly,
the exemplary RFID sensor is able to selectively detect 1-heptanol
(8). In contrast, when viewing the frequency position F.sub.p
response of 1-pentanol (6), it appears very similar to the
frequency position F.sub.p of 1-hexanol (7). Based solely on the
frequency position F.sub.p response, the exemplary RFID sensor may
not be suitable for detecting and distinguishing between these two
vapors.
[0068] However, as previously described, a number of other
responses may also be analyzed and may provide further information
that may be manipulated and analyzed in order to provide a way to
distinguish vapors, wherein one particular response may not be
sufficient. Referring to the test data for the magnitude Z.sub.p
response plot 48, the magnitude Z.sub.p of 1-pentanol (6) is
distinguishable from the magnitude Z.sub.p of 1-hexanol (7).
Accordingly, the exemplary RFID sensor may be sufficient for
distinguishing such vapors, when other responses, such as the
magnitude Z.sub.p (as opposed to the frequency position F.sub.p
response alone), are analyzed.
[0069] One convenient way of analyzing various responses of the
sensor is to use principal components analysis (PCA) to produce a
multivariate signature. As will be appreciated, PCA analysis is a
mathematical process, known to those skilled in the art, that is
used to reduce multidimensional data sets to lower dimensions for
analysis. For instance, the various responses for each vapor at a
given concentration may be reduced to a single data point, and from
this, a single response for each vapor, which may be represented as
a vector, may be discerned, as illustrated in FIG. 7. FIG. 7
represents a PCA plot 62 of the various responses of the 10 vapors
described with reference to FIG. 6. As will be appreciated, FACTOR1
represents the response with the most variation, while FACTOR2
represents the response with the next most variation. As shown in
FIG. 7, the ten vapors are clearly distinguishable from one
another. Accordingly, the instant test data provides support for a
sensor capable of discerning between at least ten vapors, here
water (1), methanol (2), ethanol (3), 1-propanol (4), 1-butanol
(5), 1-pentanol (6), 1-hexanol (7), 1-heptanol (8), 1-octanol (9),
and 1-nonanol (10). Individual sensors may not achieve this level
of vapor discrimination, while this discrimination was achieved in
the Example with a single sensor.
[0070] In addition, vapor mixtures may also be discernable from the
PCA plot. For instance, one may be able to extrapolate a vector
plot of a mixture of methanol (2) and 1-octanol (9). Such
additional extrapolated data may also be used to selectively detect
mixtures of selected vapors. Further, by varying the selected
sensing material, even greater numbers of selective vapor detection
has been demonstrated, utilizing a single RFID sensor.
[0071] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *