U.S. patent application number 15/250407 was filed with the patent office on 2016-12-22 for methods for manufacturing sensors for sensing airborne contaminant of tobacco smoke.
This patent application is currently assigned to The Trustees of Dartmouth College. The applicant listed for this patent is The Trustees of Dartmouth College. Invention is credited to Joseph J. BelBruno, Susanne E. Tanski.
Application Number | 20160370310 15/250407 |
Document ID | / |
Family ID | 49758936 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160370310 |
Kind Code |
A1 |
BelBruno; Joseph J. ; et
al. |
December 22, 2016 |
METHODS FOR MANUFACTURING SENSORS FOR SENSING AIRBORNE CONTAMINANT
OF TOBACCO SMOKE
Abstract
A method for manufacturing a sensor for sensing an airborne
contaminant of tobacco smoke includes forming interdigitated
electrodes on a substrate and depositing, on the substrate above
the two interdigitated electrodes a conductive polyaniline bulk
film having resistance sensitive to binding of the airborne
contaminant of tobacco smoke thereto, such that resistance of the
conductive polyaniline bulk film is measurable using the
interdigitated electrodes.
Inventors: |
BelBruno; Joseph J.;
(Hanover, NH) ; Tanski; Susanne E.; (Grantham,
NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Trustees of Dartmouth College |
Hanover |
NH |
US |
|
|
Assignee: |
The Trustees of Dartmouth
College
|
Family ID: |
49758936 |
Appl. No.: |
15/250407 |
Filed: |
August 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13495258 |
Jun 13, 2012 |
9429536 |
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15250407 |
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PCT/US2011/051169 |
Sep 12, 2011 |
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13495258 |
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61466101 |
Mar 22, 2011 |
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61381512 |
Sep 10, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 33/0073 20130101;
G01N 27/126 20130101; H05K 3/10 20130101 |
International
Class: |
G01N 27/12 20060101
G01N027/12; H05K 3/10 20060101 H05K003/10 |
Claims
1. A method for manufacturing a sensor for sensing an airborne
contaminant of tobacco smoke, comprising: forming interdigitated
electrodes on a substrate; dissolving bulk polyaniline and the
airborne contaminant of tobacco smoke in a protonating agent to
form a partially protonated and conductive polyaniline solution;
depositing the partially protonated and conductive polyaniline
solution on the substrate above the interdigitated electrodes to
form a conductive polyaniline bulk film that is partially
protonated; and doping the conductive polyaniline bulk film with a
secondary dopant to fully protonate the conductive polyaniline bulk
film, so as to form the sensor.
2. The method of claim 1, the step of dissolving comprising
dissolving the bulk polyaniline and the airborne contaminant in a
protonating agent that is at least 98% pure.
3. The method of claim 2, the step of dissolving comprising
dissolving the bulk polyaniline and the airborne contaminant in
formic acid.
4. The method of claim 1, the step of doping comprising doping the
conductive polyaniline bulk film with HCl.
5. The method of claim 1, the step of doping comprising dip-coating
the conductive polyaniline bulk film in the secondary dopant.
6. The method of claim 1, the step of depositing comprising
spin-coating the partially protonated and conductive polyaniline
bulk solution onto the substrate.
7. The method of claim 6, the step of spin-coating comprising
forming the conductive polyaniline bulk film with a thickness of
approximately 100 nanometers.
8. The method of claim 1, the step of forming interdigitated
electrodes comprising forming two interdigitated electrodes
separated apart by approximately 20 microns.
9. The method of claim 8, the step of depositing comprising forming
the conductive polyaniline bulk film with a thickness of
approximately 100 nanometers.
10. The method of claim 1, the airborne contaminant being
nicotine.
11. A method for manufacturing a sensor for sensing an airborne
contaminant of tobacco smoke, comprising: forming two
interdigitated electrodes on a substrate, the two interdigitated
electrodes being separated apart by approximately 20 microns; on
the substrate above the two interdigitated electrodes, depositing a
conductive polyaniline bulk film having resistance sensitive to
binding of the airborne contaminant of tobacco smoke thereto, such
that resistance of the conductive polyaniline bulk film is
measurable using the two interdigitated electrodes.
12. The method of claim 11, the step of depositing comprising
producing the conductive polyaniline bulk film with thickness of
approximately 100 nanometers.
13. The method of claim 12, the step of depositing comprising
spin-coating a conductive polyaniline solution onto the substrate
above the two interdigitated electrodes.
14. The method of claim 11, the step of depositing comprising
forming each of the two interdigitated electrodes with finger width
of approximately 40 microns.
15. The method of claim 14, the step of depositing comprising
producing the conductive polyaniline bulk film with thickness of
approximately 100 nanometers.
16. The method of claim 15, the step of forming comprising forming
each of the two interdigitated electrodes with thickness of
approximately 120 nanometers.
17. The method of claim 11, the step of depositing comprising
depositing a fully protonated conductive polyaniline bulk film on
the substrate.
18. The method of claim 11, in the step of depositing, the
conductive polyaniline bulk film being molecularly imprinted with
the airborne contaminant.
19. The method of claim 11, the airborne contaminant being
nicotine.
20. The method of claim 11, further comprising measuring background
resistance between the two interdigitated electrodes when the
device is not exposed to the airborne contaminant.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation of U.S. patent
application Ser. No. 13/495,258, filed Jun. 13, 2012, which is a
continuation-in-part application of PCT/US2011/051169, filed Sep.
12, 2011, which claims the benefit of priority from U.S.
Provisional Application Ser. No. 61/466,101 filed Mar. 22, 2011 and
from U.S. Provisional Application Ser. No. 61/381,512 filed Sep.
10, 2010. Each of the aforementioned references is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] Molecular imprinting is a technique that allows for the
production of molecule specific receptors that are analogous to
biological receptor binding sites without the cost or environmental
sensitivity of the natural systems (Shea (1994) Trends Polym. Sci.
2:166; Wulff (1995) Angew. Chem. Int. Ed. 34:1812; Mosbach &
Ramstrom (1996) Biotechnology 14:163; BelBruno (2009) Micro and
Nanosystems 1:163). Molecularly imprinted polymers (MIPs) may be
based on either covalent or non-covalent binding between the host
polymer and the target or template molecule. Various MIP-based
devices have been suggested for use in the detection of
surface-binding molecules, inorganic compounds, organic compounds,
polymers, biological molecules, nanoparticles, viruses, and
biological arrays (WO 2008/063204 and US 2009/0115605).
[0003] Nicotine is a characteristic component of tobacco smoke and
cotinine is a major metabolite of nicotine that is detected in the
urine of smokers. Other reports of nicotine MIPs have appeared in
the literature. For example, nicotine-targeted MIPs based on the
synthesis of the polymer from methacrylic acid monomers have been
reported (Sambe, et al. (2006) J. Chromatog. A 1134:88; Thoelen et
al. (2008) Biosensors and Bioelectronics 23:913-918). However,
poly(methylacrylic acid) exhibits solvent incompatibility with
nicotine, thereby making the production of thin films
challenging.
SUMMARY OF THE INVENTION
[0004] The present invention is a device for monitoring exposure to
airborne contaminants. In one embodiment, the device is composed of
at least two poly(4-vinylphenol) or nylon films, each molecular
imprinted with an airborne contaminant; a sensor for detecting
binding between the airborne contaminant and the film, and a radio
frequency interrogator unit to read the sensor and transmit an
interrogation signal. In other embodiments, the sensor is a
capacitive or conductive sensor, e.g. composed of polyaniline or
polycarbozole. In particular embodiments, the poly(4-vinylphenol)
or nylon film is produced by phase inversion-spin coating. In
another embodiment, the device is composed of a polyaniline
conductive sensor, molecular imprinted with an airborne
contaminant, and a radio frequency interrogator unit. In certain
embodiments, the airborne contaminant is selected from the group of
CO, nicotine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and
formaldehyde. Methods for monitoring exposure to airborne
contaminants using a device of the invention is also provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a schematic drawing of an RFID circuit of the
instant device.
[0006] FIG. 2A-2C is a schematic drawing showing sensor placement
over the circuit.
[0007] FIG. 3A shows the response of the sensor to vapor phase
nicotine from liquid nicotine held at a series of different
temperatures; diamond=22.degree. C., square=55.degree. C.,
triangle=80.degree. C.
[0008] FIG. 3B shows a plot of signal as a function of nicotine
vapor pressure.
[0009] FIG. 4 shows the response of the sensor in terms of relative
resistance to exposure of vapor phase nicotine generated from a
single cigarette in the Teague system. Note also, that the sensor
detects nicotine adsorbed on the walls in the chamber from previous
experiments, so called third hand smoke.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The present invention is a MIP-based personal sensor that
can be readily interrogated using radio frequency identification
(RFID) technology for use in simultaneously monitoring airborne
contaminants, such as those from second-hand tobacco smoke. The
personal monitoring device is similar to the small badges used to
monitor radiation doses and can be monitored locally such that
immediate feedback on exposure is provided. The specific airborne
molecules detectable with the instant device include, but are not
limited to, CO, nicotine,
4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and
formaldehyde. Quantification of one or a combination of these
components of second-hand smoke can indicate that second-hand smoke
is present.
[0011] In some embodiments, the device is composed of at least two
poly(4-vinylphenol) (PVP) and/or nylon films, each molecular
imprinted with an airborne contaminant; a sensor; and a radio
frequency identification component. As is conventional in the art,
molecular imprinting is a process by which guest or host molecules
(functional monomers or polymers) are allowed to self-assemble
around a molecular template, thereby forming a recognition element,
which has binding sites corresponding to functional groups in the
template molecule. The recognition elements form a binding cavity
which is cross-linked into a matrix. The template molecule is
removed, leaving behind a molecularly-imprinted polymer (MIP)
complementary in shape and functionality to the template molecule,
which will rebind chemical targets identical to the original
molecular template. In this invention, the host molecule is PVP or
nylon composite, which non-covalently binds the template molecules,
has solvent compatibility with the template molecules and is
capable of forming a binding cavity around airborne contaminants.
For use in this invention, the nylon can be any nylon
conventionally used in preparing molecular imprinted films and
includes, but is not limited to, nylon 6 and nylon 6/6.
[0012] Thin films of the invention can be produced by any
conventional method. However, the ability to control the thickness
and formulate the films in an environment typical of printed
circuit production is an important feature of film production for
the instant sensors. Thus, in particular embodiments, the instant
films are produced by phase inversion-spin coating onto a suitable
substrate. The wet phase inversion procedure (Wang, et al. (1997)
Langmuir 13:5396; Shibata, et al. (1999) J. Appl. Poly. Sci.
75:1546; Trotta, et al. (2002) J. Membr. Sci. 201:77) for
preparation of MIPs involves a polymerized starting material that
is dissolved with the template in a theta solvent. A template-host
network is allowed to form in solution and precipitated by
immersion in a non-solvent. Originally developed to produce MIP
membranes, this procedure has been adapted to the production of
thin, 300 nm to 5 .mu.m, films via spin coating (Crabb, et al.
(2002) J. Appl. Polym. Sci. 86:3611; Richter, et al. (2006) J.
Appl. Polym. Sci. 101:2919; Campbell, et al. (2009) Surface and
Interface Analysis 41:347) and hydrogen bond interactions between
the template and host polymer.
[0013] By way of illustration, thin films containing PVP can be
produced by mixing PVP (e.g., 10%-15% by weight) in conventional
casting solution with the template molecule (e.g., about 5%-10% by
weight) in a suitable solvent. For example, nicotine is readily
dissolved in methanol, whereas dimethylformamide (DMF) is a
suitable solvent for formaldehyde and NNK. The solution is allowed
to mix at room temperature, e.g., from six to 24 hours, to form the
hydrogen-bonded network in solution. Subsequently, thin films are
cast onto a substrate using a spin coater at 5000-7000 rpms for
about 30 seconds. The thin film is allowed to dry and the template
molecule is removed by washing with water. In accordance with this
invention, a separate molecular imprinted film is produced for each
template molecule so that detection in the assembled device occurs
independently for each airborne contaminant. In this respect,
certain embodiments of the device feature at least two films each
independently molecular imprinted with CO, nicotine,
4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) or
formaldehyde.
[0014] The substrate of the molecular imprinted film can be a rigid
or flexible material, which may be conducting, semiconducting or
dielectric. The substrate can be a monolithic structure, or a
multilayer or other composite structure having constituents of
different properties and compositions. Suitable substrate materials
include quartz, glass, alumina, mica, silicon, III-V semiconductor
compounds, and other suitable materials. Optionally, additional
electronic elements may be integrated into the substrate for
various purposes, such as thermistors, integrated circuit elements
or other elements.
[0015] To detect an interaction (i.e., binding) between a molecular
imprinted film and a template molecule (i.e., airborne
contaminant), the device further includes one or more sensors. Any
suitable electrical property may provide the basis for sensor
sensitivity, for example, electrical resistance, electrical
conductance, current, voltage, capacitance, transistor on current,
transistor off current, and/or transistor threshold voltage. In the
alternative, or in addition, sensitivity may be based on a
measurements including a combination of properties, relationships
between different properties, or the variation of one or more
properties over time. In some embodiments of this invention, the
sensor is a capacitive sensor, a conductive sensor or a combination
thereof. Depending on the type of sensor, the sensor can be a
separate element of the device or integrated with the molecular
imprinted film.
[0016] Capacitive sensors are well-known in the art and any
suitable sensor can be employed. For example, the capacitive sensor
can have a sandwich-type electrode configuration, wherein the
molecular imprinted film is placed between two capacitor elements
or electrodes. The electrode material can be chosen from any
suitable conductor or semiconductor e.g., gold, platinum, silver,
and the like. By way of illustration, the instant device can use a
set of interdigitated electrodes with the molecular imprinted film
coated onto the electrode assembly. Specifically, a sandwich-type
capacitive sensor can be produced by depositing chromium on a
glass, silicon or mica substrate by thermal evaporation. The
chromium is patterned by photolithography and treated,
subsequently, by wet etching. An insulating SiO.sub.2 layer with a
thickness between 40 nm and 200 nm is deposited onto the bottom
electrode surface using an electron-gun thermal deposition
technique. Subsequently, the molecular imprinted polymer layer is
spun coated on the substrate surface. In the final step, a Cr film
with a thickness of 70 nm is deposited on the molecular imprinted
polymer film surface by thermal evaporation, followed with
patterning by photolithography and wet etching.
[0017] As indicated, this device can alternatively incorporate one
or more conductive sensors. In this embodiment, a conductive
polymer can be used such that the template molecule becomes the
doping agent. Accordingly, in the presence and absence of the
template molecule, the conductivity of the polymer will be
different. Conductive polymers of use in this embodiment of the
invention are so-called it electron-conjugated conductive polymers.
For example, polyaniline or a derivative thereof, polypyrrole or a
derivative thereof, polythiophene or a derivative thereof, or a
copolymer of two or more kinds of these materials are suitable
conductive polymers. By way of illustration, polyaniline films were
prepared for the detection of formaldehyde (see Example 3) and
nicotine (see Example 4). Accordingly, in particular embodiments,
airborne contaminants are detected using a conductive polymer such
as polyaniline or polycarbozole.
[0018] To remotely communicate the output of the sensors, the
device further includes a radio frequency interrogator unit. Such
interrogator units typically include an antenna, and transmit an
interrogation signal or command via the antenna. The instant device
can operate over a wide range of carrier frequencies. For example,
the device can operate with carriers of 915-5800 MHZ, wherein the
frequency selectivity is based on selection of the antenna.
Moreover, in so far as the device employs one or more MIP films to
simultaneously detect multiple airborne contaminants, the device
further includes multiplexing RFID circuitry. The sensors of the
instant device have a range of values and the interrogator unit
must be capable of reading two or more separate sensors (FIG. 1).
As such, in certain embodiments, the instant device also has a
multiplexing amplifier circuit that includes on-board memory to
store values. This includes assembling on-board memory and
addressing hardware and certifying the operational status before
calibration of the final device to assure that the assembled sensor
functions within the same parameters as the individual components.
An example of an RFID circuit of the instant device is shown in
FIG. 2A-2C.
[0019] Interrogator units also generally include dedicated
transmitting and optionally receiving circuitry. Active
transmitters are known in the art. See, for example, U.S. Pat. No.
5,568,512, which also discloses how the transmit frequency for the
transmitter is recovered from a message received via radio
frequency from the interrogator. Moreover, many examples of
wireless communications circuits are known in the art, and any
suitable low-power circuit may be employed. The invention is
intended to be practiced with any radio communications circuit with
low power requirements, for example, a circuit appropriate for
extended operation in a remote battery-powered device without need
for recharging.
[0020] The device of the invention can transmit radio frequency
signals to a receiver and/or host computer in communication with
the interrogator. An exemplary receiver includes a conventional
Schottky diode detector. When a host computer is employed, the host
computer can act as a master in a master-slave relationship with
the interrogator. The host computer can include an applications
program for controlling the interrogator and interpreting
responses, and a library of radio frequency identification device
applications or functions. Most of the functions communicate with
the interrogator.
[0021] Although sensor systems described herein are particularly
suitable for efficient operation by conventional power sources used
in portable/remote electronics (e.g., battery, solar cell,
miniature fuel cell), the instant device can also use alternative
energy resources, such as a thermocouple, radio-frequency energy,
electrochemical interactions, supercapacitors, energy scavenging
mechanisms, or the like, or combinations thereof.
[0022] In so far as the device can detect airborne contaminants
such as CO, nicotine,
4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and/or formaldehyde,
the device of this invention is of particular use in monitoring
exposure to second-hand tobacco smoke. Upon exposure of the device
to an air sample, the molecular imprinted films bind airborne
contaminants in the air sample, sensors of the device sense said
binding, and radio frequency signals are transmitted to alert the
user of exposure to the airborne contaminants.
[0023] While conventional technologies can measure nicotine and
particulate matter in indoor environments, the current technology
involves large air sampling devices and hinders the process of
immediate feedback, since complex procedures are required, in an
analytical laboratory, to quantify the samples. Moreover, the
sampling technique collects all airborne material and the
analytical instruments are required to sort out the adsorbed
material. The device is unique in that it is small (personnel badge
sized), easy to read, simple (no laboratory analysis is needed),
the MIP films are targeted to specific contaminants and a number of
contaminants can be simultaneously detected. As a wall-mountable or
wearable, personal badge-type, second-hand smoke detector, the
instant device finds application in, e.g., medical centers to
monitor the environment of pediatric (and other) patients, and to
measure tobacco smoke contamination in supposedly smoke-free
environments such as hotel rooms and rental cars. Since the
specific sensor in the monitor may be readily changed to monitor a
different air-borne contaminant, the instant device can be adapted
to detect an array of different molecules or hazardous vapors.
[0024] The invention is described in greater detail by the
following non-limiting examples.
Example 1
Production of PVP MIP Films
[0025] The aromatic nature and hydrogen bonding potential make
Poly(4-vinylphenol) (PVP) an ideal host matrix for MIPs. The PVP
films were produced by spin coating; a simple deposition technique
that is sensitive to the composition and viscosity of the solution
and the rotating speed of the plate (Bronside, et al. (1987) J.
Imaging Technol. 13:122).
[0026] Solutions composed of 10 mL of methanol (Acros Organics; ACS
Reagent Grade 99.8%) with 10 wt % of PVP powder obtained from
Polysciences, Inc. (MW=22,000; T.sub.g 150.degree. C.) and 5 wt %
of nicotine or cotinine were nitrogen purged, covered, and stirred
at room temperature for 24 hours. Control films (NIPs) were
similarly produced, but without the nicotine or cotinine Films were
spin cast from these solutions onto 22 mm square glass microscope
cover slips. Typically, the slides were prewashed with
spectroscopic grade isopropanol and acetone prior to polymer
deposition. The coating solution was dropped onto a stationary
substrate and the spin coater was operated at 4000 rpm for 30
seconds with negligible ramp up time. The rotation spreads the
solution evenly over the surface and also causes the solvent to
evaporate leaving a thin film of material on the substrate. The
concentration of PVP in the casting solution is the dominant
variable for the film thickness, which increases rapidly with
increasing concentration (solution viscosity). Cast films are quite
stable and may be stored or used for an indefinite time.
[0027] The template molecule was removed from the film by immersion
in deionized water for five hours. Nicotine (or cotinine) removal
was confirmed by FTIR measurements. Template reinsertion (or
reinsertion of the complementary template molecule) was
accomplished by immersion of the template extracted (or control)
film in a 5 wt % solution of the molecule in deionized water for
2.5 hours. This reinsertion, as with the template removal
procedure, is an equilibrium-controlled process and reinsertion
occurs to approximately 50% of the initial concentration (via
qualitative FTIR measurements). Additional immersion time was not
found to increase the relative amount of template molecule
reinserted into the film. FTIR spectra were recorded over a narrow
region of interest, .about.3400 cm.sup.-1 for the OH stretch of
PVP, which is missing when hydrogen bonded to nicotine or cotinine
or .about.1700 cm.sup.-1 in the carbonyl region of cotinine, to
confirm the interaction of the template with the polymer in the
film. The surface topography of the films is characterized by
average roughness measurements, R.sub.a, using scanning force
microscopy (SFM). It is defined as the average deviation of the
profile from a mean line or the average distance from the profile
to the mean line over the length of the assessment. The surface
roughness, R.sub.a, is given by the sum of the absolute values of
all the areas above and below the mean line divided by the sampling
length.
[0028] All nanoindentation experiments were performed using the
electrostatic transducer of the Hysitron triboscope in the UBI 1
(Hysitron User Handbook: Feedback Control Manual. 10025 Valley View
Road, Minneapolis, Minn.; Hysitron, Inc.). The transducer is a
three-plate capacitor, the mid-plate of which carries the indenter
fixed to a thin stylus. Application of a DC voltage generates an
electrostatic force driving the indenter into the sample surface,
while the capacitance change as a measure of penetration depth is
recorded. The data consist of a force-displacement curve. For soft
samples such as polymers, the stiffness of the internal springs
holding the indenter must be subtracted from the applied load in
order to obtain the sample stiffness. Hardness, H, is calculated as
the applied load, F, divided by the area, A.sub.c, of the indenter
tip at the contact depth, v.sub.hc; the area is depth-dependent
(Olivier & Pharr (1992) J. Mater. Res. 7:1562). The modulus is
derived from the slope of the force-displacement curve upon
unloading when the sample elastically recovers. The tip elastic
properties can effectively be ignored for polymeric materials.
Investigations are performed with a blunted 90.degree. diamond cube
corner tip. The calibration of the tip to determine the depth
dependent area function A.sub.c(hc) was obtained with the standard
curve-fitting method using fused quartz with its known reduced
modulus as the reference material. Additionally, calibration with a
sharp silicon grating was performed (Richter, et al. (2006) High
Pressure Res. 26:99). A commercial grid with ultra sharp conical
silicon tips was used. The small apex angle of the grid tips (below
20.degree.) together with their large height (700 nm) offers the
opportunity for exact examination of the shape of the diamond
indentation tip apex. By means of the AFM software using the
so-called bearing function, the shape of the diamond indenter can
be reconstructed and the area function A.sub.c can be obtained. The
advantage of this technique over the curve-fitting method is the
direct observation of the tip shape, which also allows the
estimation of the blunt tip radius, which was 600 nm in our
experiments.
[0029] Thermal drift and creep behavior of the piezoelectric
scanner must be minimized. At the nanoscale, drift is measured and
compensated in the resulting data. This compensation factor is part
of the standard UBI software and a correction measurement is
performed before each indent. Typical drift rates range up to 0.5
nm/s. The penetration depth of the indent should not exceed 30% of
the polymer film thickness to avoid substrate effects. Most
experiments were performed with smaller penetration depths, however
depth-dependent measurements sometimes show an increase in hardness
and reduced modulus with increasing penetration indicating the
influence of the glass substrate.
[0030] Depth-dependent mechanical properties are obtained through
indentation tests where repeated loading and unloading are
performed at the same location on the sample surface (Richter, et
al. (2006) Colloids and Surfaces, A 284/285:401; Fischer-Cripps
(2002) Nanoindentation, Springer, New York; Olivier & Pharr
(1992) supra; Wolf & Richter (2003) New J. Phys. 5:15.1; Maier,
et al. (2002) Mater. Character. 48:329; Ward & Hadley (1993) An
Introduction to the Mechanical Properties of Solid Polymers, John
Wiley & Sons, Chichester; Nowicki, et al. (2003) Polymer
44:6599; Du, et al. (2000) Polymer 42:5901; Drechsler, et al.
(1998) Appl. Phys. A 66:825; Tsui, et al. (2000) Macromolecules
33:4198; VanLandingham, et al. (2001) in: Tsukruk & Spencer
(Eds.) Macromolecular Symposia, Wiley-VCH Verlag, Weinheim, pp.
15-43). Eight cycles of multi-indentation were performed to
calculate the depth-dependent hardness and the indentation modulus.
In general, multi-cycling means, after loading to a maximum load,
F.sub.n, the sample is partially unloaded to a minimum load,
F.sub.min=0.1 F.sub.max to 0.25 F.sub.max, required to prevent the
tip from losing contact with the sample and sliding to a new
lateral position. The sample is then reloaded to the same or an
increased maximum load (F.sub.max+.DELTA.F) and the cycle is
repeated. After the onset of plastic deformation, the loading curve
is an overlap of both plastic and elastic deformations.
Multi-cycling delivers a set of data that includes the entire
material response, from the first indenter-sample contact to the
maximum penetration.
[0031] Computational Details.
[0032] All optimizations were performed with NWChem, a
Computational Chemistry Package for Parallel Computers, v5.1, with
no symmetry or geometric constraints. The correlation and exchange
effects were calculated using the Perdew-Burke-Ernzerhof (PBE)
exchange-correlation functional (Adamo & Barone (1998) J. Chem.
Phys. 110:6158) with the 6-31G* basis set (Hariharan & Pople
(1973) Theoret. Chimica Acta 28:213) both for all atoms. Several
relative orientations of the PVP molecule(s) relative to nicotine
or cotinine were optimized to ensure that the total energy of the
complex was not dependent upon this factor. All calculations were
run in parallel on a Linux cluster composed of 94 Quad-Core
(2.times.) AMD Opteron nodes (752 cpus), and 6 Quad-Core (2.times.)
Intel nodes (48 cpus). In aggregate, the Linux cluster had 3
terabytes of memory and more than 35 terabytes of disk space.
Geometric structures were visualized using the AVOGADRO molecular
editor program.
Example 2
Nanohardness Analysis of Nicotine- and Cotinine-Imprinted
Poly(4-vinylphenol) Films
[0033] Control PVP and MIP Film General Features.
[0034] The structure of the MIP and NIP films was dependent on the
viscosity of the solution. This was mainly controlled by the
temperature and spin casting conditions such as speed and
deposition time, in addition to the PVP concentration in the
solution. The pure PVP films deposited from the casting solution
containing 10% polymer had a characteristically smooth morphology.
In the present analysis, the pure PVP film had a surface roughness,
R.sub.a, of 11.5 nm, over a 130 .mu.m.times.130 .mu.m sample. No
significant morphological features were found in the control PVP
films; the films were flat. The `as produced` MIP films containing,
for example nicotine template molecules, showed a different surface
morphology in comparison to the control films. Surface stripes,
representing different heights, were the main surface feature. The
surface roughness of this type of sample was measured to be 69.2
nm, over the same 130 .mu.m.times.130 .mu.m sampling size. Removal
of the nicotine from the MIP resulted in a loss of the stripe
morphology and the observation of a number of pores in the surface.
The pores were apparently formed during the solidification process
of the polymer films and were caused by the presence of the
template molecules and the porogen solvent during the film growth
process (Campbell, et al. (2009) supra). The assumption was that
the pores were present in the `as produced` samples, but lay
beneath the stripe morphology. The template molecules were smaller
than the size of the pores observed in the films. The additional
volume of the measured pores resulted in part from: the geometrical
form of the template molecule, the arrangement of that molecule
within the polymer host, and the evaporation of the solvent through
the polymer film. The surface roughness R.sub.a, of the
nicotine-removed MIP was 44.1 nm, over the 130 .mu.m.times.130
.mu.m sample. Reinsertion of nicotine into this MIP restored the
strip morphology somewhat, but had minimal effect on the roughness
of the surface (R.sub.a=33.1 for the 130 .mu.m square sample). The
different film morphology in the SFM images was characteristic for
the presence of the template molecules.
[0035] Nanomechanical Properties.
[0036] The contact pressure (hardness) can vary even for
homogeneous matter such as the control sample, since the
deformation starts with purely elastic deformation, and after
yielding, the plastic contributions increase after a saturation
value of H is obtained for very large indents. This means the
hardness decreases with increasing indentation depth. Within the
indentation size effect model (Wolf & Richter (2003) supra) the
hardness will be higher in a small indentation area where fewer
defects are encountered. With increasing indentation size (depth),
more defects such as dislocations, are generated by the contact
pressure. For very thin polymer films, the indentation modulus is
not constant due to the increased substrate influence with
increasing depth. The elastic behavior of pure PVP films occurs by
deformation of the polymer molecules and movement of the chains
after the adhesion energy has been overcome.
[0037] The multi-cycling load-depth curves for MIP films with
template molecules in the casting solution for the spin coating
process showed significant differences in comparison to pure PVP
films. From the load-depth curves, it was clear that the `as
produced` nicotine-loaded MIP films had indentation depths of
approximately 175 nm with a maximum applied force of 300 .mu.N;
removal of the nictoine increased the penetration depth to nearly
200 nm Unexpectedly, reinsertion of nicotine reduced the
penetration depth to a value 35 nm less than the original imprinted
film. Clearly, the presence of the template molecule in the MIP led
to a stiffer film and analogous results were recorded for cotinine
imprinted films. The assignment of the basis of the change in
nanomechanical properties to the template was reinforced by the
fact that the MIP with the template removed was less stiff than a
pure PVP film for the same applied force.
[0038] The nanomechanical behavior of the polymer films indicated
that hardness decreased slightly with increasing depth, whereas the
indentation modulus increased slightly with increasing depth. The
hardness of the control PVP film had the value of 0.38 GPa with an
indentation modulus of 11.7 GPa. MIP films with cotinine were
stiffer with a hardness value of 0.59 GPa and an indentation
modulus of 14.7 GPa. Nicotine imprinted films were slightly stiffer
than the control film with a hardness value of 0.43 GPa and a
modulus of 11.6 GPa. Extraction of the template molecules meant
that the molecular cavities were still in the polymer matrix, but
the space was empty. Thus, the network character and therefore the
mechanical properties changed. For example, the hardness for MIP
films with nicotine extracted yielded smaller values of 0.31 GPa
for the hardness. Reloading of either template resulted in an
increase of the hardness to values greater than those of the
original `as produced` MIP films. The percentage increase in
hardness was greater for the reinsertion of nicotine into a
nicotine-targeted MIP than for cotinine into a cotinine-targeted
MIP. Loading, extraction and reloading of nicotine or cotinine in
the MIP films were clearly measurable with the nanoindentation
method.
[0039] These results indicate a strongly hydrogen-bonded network
between the polymer chains via the template molecules. In the ideal
case, the molecular cavities with nicotine template molecules were
formed by two hydrogen bonds that cross-linked between two PVP
molecules; cotinine had three such potential hydrogen bonding
sites. However, the imprinting process could be incomplete with
fewer hydrogen bonds established. Template molecules can bond to
the polymer molecule at several points along the chain with
efficiencies dependent on the number and distribution of template
molecules in the MIP film. From the nanomechanical investigations
it was contemplated that hydrogen bonds of the template molecules
between the PVP chains resulted in a cross-linking between the
chains, separated the PVP molecules, (preventing an easy movement
of the chains, and could reduce the adhesion energy between pure
PVP molecules. This could result in either, mechanically stiffer or
softer MIP networks. Two different molecular mechanisms were
proposed for the polymer response during an applied external
contact pressure. In pure PVP, the indentation tip could cause a
deformation of the PVP molecules and a sliding motion between the
chains. The molecular cavities and micro-pores change the
mechanical properties in two directions compared to pure polymer
films. Filled cavities (template-loaded MIP) showed an increase in
hardness in comparison to pure PVP films. This meant a stiffer
molecular network was established. In MIP films, the chains are
fixed by hydrogen bonds and the sliding motion is inhibited in
general. The filled molecular cavities prevent strong elastic
deformation. Empty cavities after extraction of the template,
result in a large decrease in the hardness. This could be caused by
the fact that the empty MIP network can be easily squeezed
together, resulting in a lower hardness in comparison to the pure
polymer network. In MIP films, the PVP chains are fixed by the
hydrogen bonds and the formed molecular cavities, but the
deformation around the empty cavities is flexible (breathing
cavities). Therefore, no gliding motion of the chains occurs. This
means, the main effect for the change of the mechanical properties
in different stages of MIP films originates from the formed
molecular cavities. If they are filled with the template molecule
the material is harder; if the cavities are empty, the compression
of the cavities leads to a much softer material. The elastic
compression of the empty cavities and pores acts in the same
direction as the mechanism of deformation and gliding of the PVP
chains.
[0040] Computational Study of Hydrogen Bonding.
[0041] Reports in the literature indicate the usefulness of
computational chemistry in selecting a polymer host for MIP
development with a particular target molecule (Breton, et al.
(2007) Biosens. Bioelectron. 22:1948). However, it was contemplated
that computational studies would be of use in providing information
to understand experimental MIP results. The optimized structures of
nicotine and cotinine were first obtained for reference. These
molecules differ only by the addition of a carboxyl group on the
pyrrolidine ring of cotinine. The geometry of the planar pyridine
ring, including bond lengths, in the two molecules is identical.
The presence of the oxygen atom in cotinine results in bond
shortening in the pyrrolidine ring, as well as a further distortion
from planarity relative to the nicotine pyrrolidine ring. The
pyrrolidine nitrogen becomes more sp2-like rather than the
pyramidal angle observed in the nicotine molecule. As a final
reference point, the 4-vinylphenol dimer structure was optimized
and was found to have a hydrogen bond length of 1.876 .ANG. and a
hydrogen bond energy of 0.34 eV. The geometric parameters of the
4-vinylphenol molecule were unchanged in the dimer.
[0042] Nicotine has two potential hydrogen binding sites and
cotinine has three such sites. In both clusters, the 4-vinylphenol
geometry was identical to that of the unbonded molecule and the
pyridine rings bond lengths were unaffected by the hydrogen bond.
The hydrogen bond from 4VP to the pyridine nitrogen in nicotine had
a length of 1.822 .ANG., while that to the pyrrolidine nitrogen was
1.788 .ANG.. The C--N bond lengths in this ring both increased. The
total hydrogen bonding energy was 0.84 eV. In cotinine, only two
hydrogen bonds formed. The bond to the pyridine nitrogen had a
length of 1.820 .ANG. and that to the carboxyl-oxygen was 1.784
.ANG. with a total hydrogen bonding energy of 1.00 eV. Attempts to
add a third hydrogen bond at the pyrrolidine nitrogen site failed,
as the additional PVP molecule was repulsed from the ring. The C--N
bond lengths in the pyrrolidine ring both decreased upon hydrogen
bonding. Finally, it was noted that attempts to obtain a .pi.-.pi.
complex between cotinine and 4VP indicated that the ring
interactions were repulsive. Clearly, the DFT calculations
indicated that cotinine would complex to the PVP host matrix with a
greater binding energy than would the nicotine template and the
experimental results reflected the results of those
calculations.
Example 3
Preparation of Polyaniline-Nylon Films
[0043] Polyaniline has the general structure:
##STR00001##
Polyaniline was selected for the film given its conductivity
(Scheme 1).
##STR00002##
[0044] Using phase inversion, formaldehyde cavities were created in
a polyaniline (PANI)-Nylon 6 composite film. Films were produced by
dissolving 0.2 g of PANI, 0.2 g of Nylon 6 and 200 .mu.l of
formaldehyde in formic acid. The formic acid dissolved the
composite and formaldehyde to form a rigid polymer-formaldehyde
network. After sufficient mixing, the imprinted polymer solution
was uniformly spin-coated onto a glass substrate to form a thin
film. After making the formaldehyde imprinted films, the
formaldehyde molecules were extracted from the film aerially,
leaving behind formaldehyde-specific receptor sites that were
capable of molecular recognition and binding of formaldehyde
molecules with remarkable specificity.
[0045] Infrared spectra analysis conclusively indicated that
formaldehyde molecules could bind to the PANI-Nylon 6 composite
through strong hydrogen bonding due to the presence of an elongated
carbonyl group at 1722 cm.sup.-1. This peak was present in the
imprinted polymer composite and noticeably absent in the control.
This analysis indicated that PANI-Nylon 6 was successfully
imprinted with formaldehyde. Moreover, the intensity of the peak
indicated the efficacy of the imprinting process.
[0046] Changes in electrical resistance of imprinted polymer and
control polymer following controlled exposure to formaldehyde vapor
were determined using lithographically patterned interdigitated
electrodes. The results of this analysis indicated that because the
imprinted polymer had formaldehyde-specific cavities, it was able
to selectively adsorb the formaldehyde molecules, which caused a
dramatic increase in resistance of the film. In contrast, the
control film with no cavities exhibited a relatively insignificant
increase in electrical resistance in response to the formaldehyde
vapor.
Example 4
Preparation of Polyaniline Films in Sensors for Detecting
Nicotine
[0047] Materials and Methods.
[0048] Polyaniline was purchased from Polysciences, Inc. as the
undoped emeraldine base form with a molecular weight of 15,000 and
a conductivity of 10.sup.-10 S/cm. Formic acid, >98%, was
purchased from EMD Chemicals and used to dissolve the polyaniline
prior to spin casting. Secondary doping increased the sensitivity
of the films and HCl, purchased from Fisher Scientific (ACS
Certified), was used in a 1.0 M aqueous solution. For laboratory
studies, nicotine purchased from Alfa-Aesor, 99%, was used. All
reagents were used as received without any further treatment. The
standard cigarettes used in the smoking chamber were 3RF4 reference
cigarettes, containing .about.0.8 mg of nicotine.
[0049] The polymer films for detecting nicotine were spin-cast
polyaniline. Polyaniline in its conductive form is insoluble.
However, the emeraldine base may be dissolved in several solvents,
including the 98% formic acid used herein. The spin casting
solution was produced from formic acid as a 1% (by weight) polymer
solution. Because the pK.sub.a of formic acid is 3.77, polyaniline
in this solution was 50% protonated; the amine and imine nitrogen
atoms had different pK.sub.a values. To complete the protonation
process and increase the sensitivity of the film, secondary
protonation in 1.0 M HCl was employed. Protonated solutions are
green, while solutions of the base are deep blue. Morphology and
roughness were investigated by atomic force microscopy using a
Pacific Nanotechnology Nano-1 microscope in close contact mode.
[0050] The conductive sensors were constructed on oxidized silicon
substrates using chromium metal with a nickel overlayer for the
electrode and the protonated polyaniline film as the active element
above the electrode. The electrode was patterned into an
interdigitated grid with 40 .mu.m fingers and 20 .mu.m spacing.
[0051] Prime grade silicon wafers with a 5000 .ANG. thermally
deposited oxide layer were used for the substrate. These films were
patterned by photolithography and subsequently wet-etched to
produce the final electrodes with a total area of 376 mm.sup.2,
following vapor deposition of 200 .ANG. of chromium and a 1000
.ANG. overlayer of nickel. Liftoff was accomplished using acetone,
with final rinses of water.
[0052] Subsequently, the polyaniline polymer layer was spun on the
sample. An aliquot of 0.5 ml of solution was dropped onto the
substrate (oxidized silicon), and allowed to spread for 20 seconds.
The spin-coater was then brought up to 4000 rpm for 30 seconds.
This resulted in deposition of films with a typical thickness of
approximately 100 nm. In the final step, secondary doping with 1.0
M HCl was accomplished by dip-coating for 30 seconds. After this
treatment, background (washed) resistance values were measured, and
the sensor was ready for use in binding studies.
[0053] Smoking machine experiments were carried out in a Teague
Enterprises package (Teague Enterprises, Davis, Calif.), composed
of a TE-10 smoking system and a mouse exposure system. The smoking
device was microprocessor controlled and produced both mainstream
and sidestream (separately or simultaneously) smoke from filtered
research cigarettes produced with controlled nicotine content. Up
to ten cigarettes could be smoked simultaneously following the
Federal Trade Commission procedure and expended cigarettes could be
automatically extinguished and ejected. Smoke was captured and
transferred to a mixing chamber for exposure experiments;
sidestream or mainstream smoke was mixed with air and then passed
into the exposure chamber. However, for the experiments described
here, the system including sample lighting and extinguishing was
operated in manual mode. A filter was available for venting and
purging the system. The exposure chamber was calibrated for total
suspended particles (TSP), carbon monoxide and nicotine
concentration determined for selected mixing valve and fan
settings. All measurements using the Teague Enterprises system were
made with the polymer sensors in the exposure box, using calibrated
operational parameters.
[0054] The laboratory sample system was composed of a small nylon
box, containing spring-mounted electrodes and a small (.about.3
cm.sup.3) well filled via a syringe through a septum. The sensor
assembly was placed on the electrodes above the well and a nylon
cap was attached using a torque wrench to ensure reproducible
pressure of the sensor against the spring-mounted electrodes.
Nicotine (1 mL) was injected into the well and the response of the
sensor was recorded. To follow the recovery of the sensor after
exposure to nicotine, dry nitrogen was passed through the well to
evaporate the nicotine. In both experimental chambers, the change
in the resistance of the sensor was measured using a multimeter
connected to a laboratory computer.
[0055] The resistance, R, of the polymer sensor was measured using
a Keithley Model 2100 61/2 Digit Multimeter. During the
measurement, constant current of 1 mA was applied and the voltage
through the film was recorded, providing a resistance value via
Ohm's law. Total dissipated power within the sensor was less than 2
W. Four point measurements were found unnecessary and all of the
reported data were obtained using two contacts. Data were taken at
a rate of 1 Hz over as long as 9 hours, but typically over
considerably shorter times. The resistance increased from its low
background value prior to exposure, typically 600 .quadrature.,
through to a plateau, associated with the level of nicotine in the
sample chamber. Data are reported as normalized resistance,
referenced to the initial, out of chamber background value.
[0056] Films were exposed to analyte concentrations that ensure a
challenge to the adsorption process. The results provided an
indication that the shift in the resistance value and the rate of
change in the resistance, were proportional to the quantity and
identity of the analyte adsorbed.
[0057] Results and Discussion.
[0058] The morphology of the film surface was investigated by
atomic force microscopy (AFM) of films produced on both silicon
oxide and glass under the coating conditions described above. The
undoped film was rougher than the doped material and more irregular
with surface defects. The doped film was somewhat smoother and the
minimal occurrence of surface defects provided an ideal material
for adsorption of the target molecule from the vapor phase.
[0059] The physical property associated with the target molecule
presence in the film was the increase in the resistance. Sensor
functionality depended upon detecting differences in this property
as a function of the adsorption of the target nicotine onto the
sensor chip. Numerous films were tested using both pure nicotine in
the small lab-built chamber and nicotine emitted from cigarette
consumption as measured in the Teague smoking system. Data
presented here are typical of these observations.
[0060] Testing of the sensor in the laboratory chamber indicated
that injection of nicotine into the sample well evoked an immediate
rise in the measured resistance. Nicotine vapor pressure was quite
small at room temperature, so a series of experiments, injecting
nicotine at different initial temperatures (providing different
vapor pressures and, hence, vapor phase concentrations of nicotine
in air) and recording the resistance was completed. The
relationship of nicotine vapor pressure to sample temperature is
well established and was used in this analysis (Young & Nelson
(1928) Ind. Eng. Chem. 20:1381-1382). The results of this study are
shown in FIG. 3A for three different noiminal temperatures. For
example, consider the film response to the injection of nicotine at
a nominal 80.degree. C. The rise of the signal as the sample was
injected and the beginning of a plateau of the signal (and slight
decrease) as the sample cooled was clearly demonstrated. FIG. 3B
shows a plot of the signal (15 seconds post injection) as a
function of the nicotine vapor pressure at the nominal
temperatures. A linear fit to the data with a correlation
coefficient of 0.99 is shown. The nicotine began to cool almost
immediately, therefore, deviation of the fit from an exact
correlation with temperature was to be expected. The absence of
constant temperature capability in this device precluded its use as
a calibration system. However, the trend of increasing resistance
with increasing temperature was clear and demonstrated the
responsiveness of the film to pure nicotine. The nicotine
concentrations in this device were estimated to be of the order of
a few ppm.
[0061] FIG. 4 shows the time evolution of the sensor film signal
for smoking a single cigarette in the Teague system. The system
calibration at the inflow/outflow settings of the exposure chamber
provides that the dynamic nicotine concentration in this situation
from the cigarette consumption alone was 0.5 ppb. The actual
concentration was, of course, higher since there was clearly
background nicotine adsorbed onto the chamber surface. In general,
the resistance increased as the cigarette was consumed, increasing
by 50% over the signal assigned to the chamber background. It was
interesting to note that the background reading of the sensor, the
resistance at the zero time point, immediately increased by 20% as
the film was placed into the exposure chamber, indicating a
background level of nicotine before engaging the smoking apparatus.
Prior to this experiment, the smoking chamber had been in constant
use for 8 hours and deliberately not cleaned in the 2 hours prior
to its application in the current experiment. The sensor was
capable of measuring nicotine that was outgassing from the plastic
chamber walls, an event labeled as "third hand smoke" when this
event occurs in inhabited rooms and automobiles (Sleiman, et al.
(2010) PNAS 107:6576-6581). During the smoking process, sidestream
smoke was fed into the exposure chamber and, as long as the smoking
was continued, the resistance increase indicated adsorption of
nicotine in to the film. The signal stopped increasing as the
cigarette was extinguished and decreased as air blown into the
exposure chamber from the smoking system contained no additional
nicotine component. After approximately six minutes, the chamber
was purged with 100% fresh (room) air and the sensor resistance
dropped accordingly to a level approximately 20% above the chamber
background.
[0062] A set of sequential exposures in the Teague system, using
varied number of simultaneously smoked cigarettes followed by a
brief fresh air blowout was conducted. Cigarettes were smoked over
a period of eight minutes during which the sidestream smoke filled
air from the smoking device was mixed with an equal volume of fresh
air and fed into the exposure chamber. Following the extinguishing
of the consumed cigarette, fresh air was blown into the exposure
chamber for a period of six minutes. The fresh air phase was shown
to allow at least some of the nicotine to be removed from the
sensor and restore the resistance measurement to a smaller value.
These two different regimes were clearly discernible. The fresh air
phase of the repetitive experiment was not sufficient to bring the
sensor back to the original baseline. That is, the process of
removing the nicotine from the film was slower than the time used
in the study and subsequent exposures included increased residual
levels of nicotine from the walls of the chamber in addition to
nicotine that remained on the sensor film from the previous
cigarette consumption. However, the final exposure cycle, with a
longer smoke-free period, indicated that a return approximately to
the original baseline was possible. Indeed, a resistance
measurement made several hours after completing the experiments
resulted in a value nearly equal to the initial resistance. The
slopes of the rising signals were also related to the number of
cigarettes simultaneously consumed and, hence, the concentration of
nicotine in the chamber. The system provided a dynamic
concentration of 0.75 ppb and 1.11 ppb, for sidestream smoke
generated solely by two and three cigarettes, respectively. But as
described earlier, this underestimated the true nicotine
concentration. It was noted that the first, single cigarette
consumed increased the signal by .about.60% and second, consecutive
single cigarette furthered the increase by 32%. The next sample
involved two cigarettes and resulted in a 40% signal increase with
a final sample of three cigarettes and a 42% increase in
resistance. The "blow out" phase returned the signal to
approximately the resistance measured after the first
experiment.
[0063] To test the response and recovery in a heavy smoking
situation, several successive runs were conducted in which 10
cigarettes (nominally providing 3.16 ppb of nicotine) were
simultaneously smoked. The sensor background resistance was
measured in ambient room air prior to insertion in the exposure
chamber, providing a clear visualization of the ability to detect
nicotine from the chamber walls. The first cigarette burn resulted
in a steep increase in resistance. After a six minutes delay
(following cigarette extinguishment), a new burn was begun,
followed by two additional ten cigarette exposures. The absence of
significant recovery time post-exposure decreased the absolute
increase in signal (although the third and fourth exposures
provided similar increases) with measured changes in resistance of
110%, 25%, 15% and 9%. The fresh air purge at the end of the
experiment did lower the signal substantially. Most importantly,
this particular study indicated that the film is sensitive to its
environment, even if the ambient atmosphere has a relatively heavy
concentration of smoking generated nicotine.
[0064] This analysis demonstrated that a simple chemiresistor based
on a polyaniline film and interdigitated electrode can monitor
nicotine to provide a real time indication of exposure to second
hand cigarette smoke. The polyaniline film was shown to be
sensitive to the number of cigarettes consumed, demonstrated
reasonable recovery between exposures and was functional in the
presence of simulated heavy smoking. The detection of nicotine
outgassing or "third hand smoke" was also demonstrated to be
feasible using the polymer film assembly.
* * * * *