WO2006087568A1 - Chemical sensing apparatus - Google Patents

Chemical sensing apparatus Download PDF

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Publication number
WO2006087568A1
WO2006087568A1 PCT/GB2006/000565 GB2006000565W WO2006087568A1 WO 2006087568 A1 WO2006087568 A1 WO 2006087568A1 GB 2006000565 W GB2006000565 W GB 2006000565W WO 2006087568 A1 WO2006087568 A1 WO 2006087568A1
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WO
WIPO (PCT)
Prior art keywords
membrane
layer
analyte
medium
electrical
Prior art date
Application number
PCT/GB2006/000565
Other languages
French (fr)
Inventor
Seamus Patrick John Higson
Frank Davis
Original Assignee
Cranfield University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cranfield University filed Critical Cranfield University
Publication of WO2006087568A1 publication Critical patent/WO2006087568A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—Specially adapted to detect a particular component
    • G01N33/0054—Specially adapted to detect a particular component for ammonia
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Definitions

  • This invention relates to chemical sensing apparatus, and particularly to a rapid assay or sensor for volatile compounds in the atmosphere or aqueous solution.
  • US 2004/0014235 relates to the use of colour- changing polymers as chemical sensors, e.g. for monitoring packaged foodstuffs.
  • WO 00/20852 concerns conductive organic sensors, e.g. using polyaniline. The sensor interacts with the surrounding atmosphere, and its electrical properties are monitored.
  • the invention provides chemical sensing apparatus comprising
  • a sensor assembly which comprises (i) a sensing layer of polymeric material whose electrical and/or optical properties are subject to variation when it interacts with an analyte material, and (ii) a membrane covering the layer, the arrangement being such that, in use, analyte material must pass through the membrane to interact with the layer;
  • (B) means for monitoring electrical and/or optical properties of the sensing layer comprising one or more of (a) electrical contacts for coupling the layer to a detector for monitoring an electrochemical property such as electrical resistance or electrical impedance, and (b) optical components comprising an electromagnetic radiation source for directing radiation at the layer, and a detector arranged to detect radiation which has interacted with the layer or is emitted by the layer (eg via fluorescence) following irradiation by the incident radiation source.
  • the mention provides a method of detecting an analyte comprising providing apparatus of the above type, exposing the membrane to a medium potentially containing the analyte; and using the monitoring means to detect variation in an electrical and/or optical property of the sensing layer.
  • the membrane may be hydrophilic or hydrophobic.
  • a hydrophilic membrane may assist in capturing some, generally polar, analytes, e.g. from the gaseous phase, and enabling them to pass through to the sensing layer. For this purpose it may help to keep it moist. It may comprise a hydrogel such as polyHEMA, or a polymer with ionic groups such as a perfluorosulfonic acid polymer (e.g. a Nafion [trademark] membrane).
  • a hydrophobic layer can be a selective barrier, e.g. allowing volatile components such as ammonia to pass through while keeping out polar but non-volatile species such as hydroxide ions . It may comprise PTFE (e.g. Goretex [trademark]
  • the membrane is generally permeable, e.g. it may be porous, in which case it may provide selectivity by size exclusion .
  • Fig. 1 is a schematic view of an apparatus embodying the invention which employs an electrical measuring technique.
  • Fig 2 is a schematic view of an apparatus embodying the invention which employs an optical measuring technique .
  • a disposable electrode assembly consisting of a suitable polymer (in the first example, conducting polyaniline) deposited using any of a variety of techniques (including chemical deposition, stencilling or screen printing of an aqueous dispersion) onto one side of a porous hydrophobic substrate such as PTFE, HDPE or polypropylene. This is placed with the uncoated side in contact with the required sample, be it the atmosphere or an aqueous solution.
  • Electrochemical measurements can be carried out using a dedicated laboratory instrument, a hand-held measuring device or an automated sample collection and measurement device. Electrochemical measurements that can be made include DC resistivity or AC impedance.
  • Figure 1 schematically displays an apparatus in which the sensor assembly 10 is a porous PTFE film 12 having a polyaniline layer 14 on one surface. A spaced pair of contact electrodes 16 are coupled by leads 18 to a meter 20 for monitoring the resistance/conductance between them. As shown in Fig 1, the apparatus is for monitoring the atmosphere or other gas content with the uncovered face of the PTFE film 12.
  • ammonia e.g. ammonia
  • it will diffuse across the porous support and into the polyaniline coating. Detection of ammonia can be made electrochemically, as the polymer becomes less conducting.
  • Fig 2 shows an "optrode" sensor assembly 110 having a polyaniline layer 114 which has been deposited on one face of a transparent, non-permeable substrate 130, suitably a plastics material such as Melinex.
  • a transparent, non-permeable substrate 130 suitably a plastics material such as Melinex.
  • the other face of the polyaniline layer 114 is covered with a porous PTFE film 112.
  • Optical components for monitoring the polyaniline layer 114 include an electromagnetic radiation source 132 (e.g. a lamp and collimator) arranged to direct radiation 134 through the substrate 130 to the layer 114, and a detector 136 arranged to receive radiation resulting from the interaction of the incident radiation 134 and the layer 114. It may include an analyzer. For example, it may compare the relative intensities of blue and green light to monitor the status of the polyaniline. It may provide an electrical output to a computing and/or display and/or memory unit 140.
  • electromagnetic radiation source 132 e.g. a lamp and collimator
  • detector 136 arranged to receive radiation resulting from the interaction of the incident radiation 134 and the layer 114.
  • It may include an analyzer. For example, it may compare the relative intensities of blue and green light to monitor the status of the polyaniline. It may provide an electrical output to a computing and/or display and/or memory unit 140.
  • the sensor assembly is shown as forming part of a sample vessel having a side wall 142 and holding a liquid 144 potentially containing an analyte which can pass through the PTFE film 112, and affect the optical properties of the polyaniline.
  • Volatile species such as ammonia in solution generate a partial pressure, i.e. of ammonia vapour, which diffuses across the porous support and into the polyaniline coating. Note that in this case there is no actual contact between the polyaniline and the solution, thereby eliminating non-volatile interferents such as hydroxide.
  • a basic species such as ammonia causes green to blue colour transition in the polyaniline. Concentrations of ammonia in solution of less then lOppm can be detected by monitoring the colour change.
  • the polyaniline is initially in its protonated, green form. A deprotonating analyte tends to turn it blue. It is also possible to provide an analogous disposable electrode or optrode assembly consisting of a suitable polymer (such as polyaniline) in its neutral, non-conductive form. This leads to the construction of a similar sensor which behaves in similar fashion except it would react to acidic impurities in the air (or other gas to be monitored) or in solution, such as HCl, NOx or SOx.
  • a suitable polymer such as polyaniline
  • This sensor format lends itself to mass fabrication due to the simplicity and inexpensiveness of the materials and methods used.
  • membranes of other materials such as Nafion (trademark) and hydrogels (e.g. polyHEMA) can be used.
  • a membrane film is to be applied over an existing component as in (a) , it is possible to apply a previously produced membrane.
  • a polymerisable composition for example a hydrogel membrane can be produced by applying a liquid composition containing a monomer, and effecting polymerisation (e.g. thermal polymerisation, with the aid of a chemical initiator in the liquid composition, or photopolymerisation, possibly with the aid of a photoinitiator .
  • the liquid composition may contain a porogen.

Abstract

Chemical sensing apparatus employs a sensor assembly with (i) a sensing layer of polymeric material whose electrical and/or optical properties are subject to variation when it interacts with an analyte material, and (ii) a membrane covering the layer. Analyte material must pass through the membrane to interact with the layer. Electrical and/or optical properties of the sensing layer are monitored, e.g. electrical resistance or interaction with radiation. For example a polyaniline film can change in colour and resistance on interaction with a redox or pH-altering analyte.

Description

CHEMICAL SENSING APPARATUS
TECHNICAL FIELD
This invention relates to chemical sensing apparatus, and particularly to a rapid assay or sensor for volatile compounds in the atmosphere or aqueous solution.
Background Art
US 2004/0014235 relates to the use of colour- changing polymers as chemical sensors, e.g. for monitoring packaged foodstuffs. WO 00/20852 concerns conductive organic sensors, e.g. using polyaniline. The sensor interacts with the surrounding atmosphere, and its electrical properties are monitored.
Disclosure of Invention
In one aspect the invention provides chemical sensing apparatus comprising
(A) a sensor assembly which comprises (i) a sensing layer of polymeric material whose electrical and/or optical properties are subject to variation when it interacts with an analyte material, and (ii) a membrane covering the layer, the arrangement being such that, in use, analyte material must pass through the membrane to interact with the layer; and
(B) means for monitoring electrical and/or optical properties of the sensing layer comprising one or more of (a) electrical contacts for coupling the layer to a detector for monitoring an electrochemical property such as electrical resistance or electrical impedance, and (b) optical components comprising an electromagnetic radiation source for directing radiation at the layer, and a detector arranged to detect radiation which has interacted with the layer or is emitted by the layer (eg via fluorescence) following irradiation by the incident radiation source.
In another aspect the mention provides a method of detecting an analyte comprising providing apparatus of the above type, exposing the membrane to a medium potentially containing the analyte; and using the monitoring means to detect variation in an electrical and/or optical property of the sensing layer.
We have determined that levels of ammonia of less than lOppm and more than lOOOppm can be easily detected in solution. Many conducting polymers are known to rapidly interact with vapours, leading to a marked change in conductivity. Polyaniline is especially suitable since it exists in a protonated conductive form and a neutral non-conductive form. We have used this as a basis for a sensor, where the conductivity of a film is measured and used to provide a quick quantification of the levels of volatile present.
The membrane may be hydrophilic or hydrophobic.
A hydrophilic membrane may assist in capturing some, generally polar, analytes, e.g. from the gaseous phase, and enabling them to pass through to the sensing layer. For this purpose it may help to keep it moist. It may comprise a hydrogel such as polyHEMA, or a polymer with ionic groups such as a perfluorosulfonic acid polymer (e.g. a Nafion [trademark] membrane).
A hydrophobic layer can be a selective barrier, e.g. allowing volatile components such as ammonia to pass through while keeping out polar but non-volatile species such as hydroxide ions . It may comprise PTFE (e.g. Goretex [trademark]
The membrane is generally permeable, e.g. it may be porous, in which case it may provide selectivity by size exclusion .
Brief Description of Drawings
Fig. 1 is a schematic view of an apparatus embodying the invention which employs an electrical measuring technique.
Fig 2 is a schematic view of an apparatus embodying the invention which employs an optical measuring technique .
Modes for Carrying Out the Invention
In one type of embodiment of the present invention, there is provided a disposable electrode assembly consisting of a suitable polymer (in the first example, conducting polyaniline) deposited using any of a variety of techniques (including chemical deposition, stencilling or screen printing of an aqueous dispersion) onto one side of a porous hydrophobic substrate such as PTFE, HDPE or polypropylene. This is placed with the uncoated side in contact with the required sample, be it the atmosphere or an aqueous solution. Electrochemical measurements can be carried out using a dedicated laboratory instrument, a hand-held measuring device or an automated sample collection and measurement device. Electrochemical measurements that can be made include DC resistivity or AC impedance.
Figure 1 schematically displays an apparatus in which the sensor assembly 10 is a porous PTFE film 12 having a polyaniline layer 14 on one surface. A spaced pair of contact electrodes 16 are coupled by leads 18 to a meter 20 for monitoring the resistance/conductance between them. As shown in Fig 1, the apparatus is for monitoring the atmosphere or other gas content with the uncovered face of the PTFE film 12.
If there is a suitable species, e.g. ammonia, present in the gas, it will diffuse across the porous support and into the polyaniline coating. Detection of ammonia can be made electrochemically, as the polymer becomes less conducting.
Other volatile amines, such as those released by spoiling meat or fish would also have similar effects providing a high enough vapour pressure is generated.
Fig 2 shows an "optrode" sensor assembly 110 having a polyaniline layer 114 which has been deposited on one face of a transparent, non-permeable substrate 130, suitably a plastics material such as Melinex. The other face of the polyaniline layer 114 is covered with a porous PTFE film 112.
Optical components for monitoring the polyaniline layer 114 include an electromagnetic radiation source 132 (e.g. a lamp and collimator) arranged to direct radiation 134 through the substrate 130 to the layer 114, and a detector 136 arranged to receive radiation resulting from the interaction of the incident radiation 134 and the layer 114. It may include an analyzer. For example, it may compare the relative intensities of blue and green light to monitor the status of the polyaniline. It may provide an electrical output to a computing and/or display and/or memory unit 140.
In Fig 2, the sensor assembly is shown as forming part of a sample vessel having a side wall 142 and holding a liquid 144 potentially containing an analyte which can pass through the PTFE film 112, and affect the optical properties of the polyaniline.
Volatile species such as ammonia in solution generate a partial pressure, i.e. of ammonia vapour, which diffuses across the porous support and into the polyaniline coating. Note that in this case there is no actual contact between the polyaniline and the solution, thereby eliminating non-volatile interferents such as hydroxide.
A basic species such as ammonia causes green to blue colour transition in the polyaniline. Concentrations of ammonia in solution of less then lOppm can be detected by monitoring the colour change.
In the above examples, the polyaniline is initially in its protonated, green form. A deprotonating analyte tends to turn it blue. It is also possible to provide an analogous disposable electrode or optrode assembly consisting of a suitable polymer (such as polyaniline) in its neutral, non-conductive form. This leads to the construction of a similar sensor which behaves in similar fashion except it would react to acidic impurities in the air (or other gas to be monitored) or in solution, such as HCl, NOx or SOx.
This sensor format lends itself to mass fabrication due to the simplicity and inexpensiveness of the materials and methods used.
Examples
(a) A sheet of commercial Melinex plastic was rolled up into a tube and then placed into a solution of IM aniline hydrochloride in 0.1M HCl. An equal volume of 0.3 M ammonium persulphate was added and the solution rapidly turned green. After 20 minutes the plastic was removed and rinsed with 0.1 M HCl, a green film of emeraldine form (protonated) polyaniline had been grafted to the plastic. A film of porous PTFE (Goretex ™) was placed over the polyaniline.
(b) The initial part of example (a) was repeated using a sheet of porous PTFE instead of Melinex. Contact electrodes were applied to the green film at opposite edges of the sheet using a conductive ink. (c) A piece of the green-coated plastic as initially produced in (a) or (b) was dipped in 1% ammonia solution for a few seconds, removed and dried, converting it to the blue (deprotonated) form. This could then be given a PTFE membrane layer as in (a) or contact electrodes as in (b) .
(d) As alternatives to PTFE, membranes of other materials such as Nafion (trademark) and hydrogels (e.g. polyHEMA) can be used. When a membrane film is to be applied over an existing component as in (a) , it is possible to apply a previously produced membrane. Alternatively in appropriate cases it can be generated in situ, by applying a polymerisable composition. For example a hydrogel membrane can be produced by applying a liquid composition containing a monomer, and effecting polymerisation (e.g. thermal polymerisation, with the aid of a chemical initiator in the liquid composition, or photopolymerisation, possibly with the aid of a photoinitiator . The liquid composition may contain a porogen.

Claims

Claims
1) Chemical sensing apparatus comprising
(A) a sensor assembly which comprises (i) a sensing layer of polymeric material whose electrical and/or optical properties are subject to variation when it interacts with an analyte material, and (ii) a membrane covering the layer, the arrangement being such that, in use, analyte material must pass through the membrane to interact with the layer; and
(B) means for monitoring electrical and/or optical properties of the sensing layer comprising one or more of (a) electrical contacts for coupling the layer to a detector for monitoring an electrochemical property, and (b) optical components comprising an electromagnetic radiation source for directing input radiation at the layer, and a detector arranged to detect radiation resulting from interaction of the input radiation with the layer.
2) Apparatus according to claim 1 wherein the membrane is hydrophobic.
3) Apparatus according to claim 1 wherein the membrane is hydrophilic.
4) Apparatus according to any preceding claim wherein the polymeric material comprises a conjugated polymer.
5) Apparatus according to any preceding claim wherein the polymeric material comprises a polymer which is susceptible to protonation and/or deprotonation and/or a redox reaction, with consequent alteration of its electrical and/or optical properties.
7) Apparatus according to any preceding claim wherein the polymeric material comprises a polymer selected from polyanilines, polythiophenes, polypyrroles, polyacetylenes, polyphenylenes and polyphenylene vinylidines .
8) Apparatus according to claim 7 wherein the polymer is polyaniline .
9) Apparatus' according to any of the preceding claims wherein said monitoring means comprise said electrical contacts and a detector coupled thereto.
10) Apparatus according to claim 9 wherein said monitoring means is adapted to monitor the electrical resistance or conductivity of the layer.
11) Apparatus according to any of claims 1-8 wherein said monitoring means comprise optical components for measuring the absorbance or fluorescence of the sensing layer .
12) A method of detecting an analyte comprising providing apparatus according to any preceding claim, exposing the membrane to a medium potentially containing the analyte; and using the monitoring means to detect variation in an electrochemical or optical property of the sensing layer. 13) A method according to claim 12 wherein the medium is gaseous .
14) A method according to claim 13 wherein the analyte is water-soluble and the membrane is hydrophilic.
15) A method according to claim 14 wherein the membrane is moist.
16) A method according to claim 15 wherein the membrane comprises a hydrogel .
17) A method according to claim 12 wherein the medium is liquid .
18) A method according to claim 17 wherein the medium is an aqueous medium.
19) A method according to claim 18 wherein the analyte is dissolved in the medium.
20) A method according to claim 18 wherein the analyte is dispersed in the medium.
21) A method according to any of claims 17-20 wherein the membrane is hydrophilic.
22) A method according to claim 19-20 wherein the medium is aqueous and the membrane is hydrophobic.
23) A method according to any of claims 17-22 wherein the medium contains one or more potential interferents and the membrane restrains them from reaching the sensing layer.
PCT/GB2006/000565 2005-02-19 2006-02-20 Chemical sensing apparatus WO2006087568A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB0503460.8A GB0503460D0 (en) 2005-02-19 2005-02-19 Gas or vapour sensor
GB0503460.8 2005-02-19

Publications (1)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2467338A (en) * 2009-01-30 2010-08-04 Sharp Kk Electrical analyte sensor with optical output
US9018060B2 (en) 2010-06-15 2015-04-28 3M Innovative Properties Company Variable capacitance sensors and methods of making the same

Citations (4)

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US5658451A (en) * 1995-02-01 1997-08-19 Avl Medical Instruments Ag Method for calibration of a pH measuring element
AT407199B (en) * 1992-09-16 2001-01-25 Gerald Dipl Ing Dr Urban pH sensor
US6546268B1 (en) * 1999-06-02 2003-04-08 Ball Semiconductor, Inc. Glucose sensor

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5208301A (en) * 1988-05-13 1993-05-04 Ohio State University Research Foundation Sulfonated polyaniline compositions, ammonium salts thereof, process for their preparation and uses thereof
AT407199B (en) * 1992-09-16 2001-01-25 Gerald Dipl Ing Dr Urban pH sensor
US5658451A (en) * 1995-02-01 1997-08-19 Avl Medical Instruments Ag Method for calibration of a pH measuring element
US6546268B1 (en) * 1999-06-02 2003-04-08 Ball Semiconductor, Inc. Glucose sensor

Non-Patent Citations (3)

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Title
CUI G ET AL: "POTENTIOMETRIC PCO2 SENSOR USING POLYANILINE-COATED PH-SENSITIVE ELECTRODES", ANALYST, LONDON, GB, vol. 123, no. 9, 1998, pages 1855 - 1859, XP009020263 *
JIN Z ET AL: "An improved optical pH sensor based on polyaniline", SENSORS AND ACTUATORS B, ELSEVIER SEQUOIA S.A., LAUSANNE, CH, vol. 71, no. 1-2, 15 November 2000 (2000-11-15), pages 118 - 122, XP004221453, ISSN: 0925-4005 *
TSAI Y-T ET AL: "Tuning the optical sensing of pH by poly(diphenylamine)", SENSORS AND ACTUATORS B, ELSEVIER SEQUOIA S.A., LAUSANNE, CH, vol. 96, no. 3, 1 December 2003 (2003-12-01), pages 646 - 657, XP004475591, ISSN: 0925-4005 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2467338A (en) * 2009-01-30 2010-08-04 Sharp Kk Electrical analyte sensor with optical output
US9018060B2 (en) 2010-06-15 2015-04-28 3M Innovative Properties Company Variable capacitance sensors and methods of making the same

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