WO2008040975A1 - Sensors and substances for detecting particles in air - Google Patents

Sensors and substances for detecting particles in air Download PDF

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Publication number
WO2008040975A1
WO2008040975A1 PCT/GB2007/003762 GB2007003762W WO2008040975A1 WO 2008040975 A1 WO2008040975 A1 WO 2008040975A1 GB 2007003762 W GB2007003762 W GB 2007003762W WO 2008040975 A1 WO2008040975 A1 WO 2008040975A1
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WO
WIPO (PCT)
Prior art keywords
sensor
cation
particles
fluid
polyionic
Prior art date
Application number
PCT/GB2007/003762
Other languages
French (fr)
Inventor
Sean Anthony Gillespie
Original Assignee
Smiths Detection-Watford Limited
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 Smiths Detection-Watford Limited filed Critical Smiths Detection-Watford Limited
Publication of WO2008040975A1 publication Critical patent/WO2008040975A1/en

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Classifications

    • 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
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
    • G01N33/543—Immunoassay; Biospecific binding assay; Materials therefor with an insoluble carrier for immobilising immunochemicals
    • G01N33/54393—Improving reaction conditions or stability, e.g. by coating or irradiation of surface, by reduction of non-specific binding, by promotion of specific binding
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
    • G01N1/2211—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling with cyclones

Definitions

  • This invention relates to sensors of the kind having a surface to which particles in a fluid bind for detection.
  • the invention is more particularly but not exclusively concerned with sensors for detecting sub-micron particles and with substances for use with such sensors.
  • Sub-micron biological particles such as bacterial spores and viruses can be detected using a biosensor having one or more regions of exposed antibody material.
  • the antibody material is exposed to a liquid containing the biological particles so that specific particles bind to the antibody.
  • a glass plate has several regions of different antibody materials coated onto it and a beam of light is passed through the plate to illuminate its surface. By viewing the different regions, it is possible to detect if any region has changed its appearance as a result of particles binding to it. Examples of such sensors are described in WO07/007070, WO03/093801 and WO06/090114. When these sensors are used to detect biological particles in air, it is usual practice to concentrate the particles in a liquid, such as by using a cyclone separator of the kind described in US6508864.
  • a sensor of the above- specified kind characterised in that the fluid contains a polyionic cation selected to reduce nonspecific binding to the surface.
  • the cation is selected to bind with negatively-charged atmospheric materials.
  • the cation may selected from a group comprising poly-L-lysine, DEAE-dextran and polyethyleneimine.
  • the surface preferably includes an antibody material.
  • the antibody material may be immobilised to the sensor surface by covalent attachment to a polymer film of carboxymethyldextran.
  • the sensor preferably includes an optical arrangement for illuminating and viewing the surface.
  • apparatus for detecting the presence of a substance in air including an arrangement for extracting particles from air and for supplying extracted particles in a fluid to a sensor having a surface to which particles in the fluid bind for detection, characterised in that the fluid contains a polyionic cation selected to reduce non-specific binding to the surface.
  • the polyionic cation may be present in fluid in the extracting arrangement.
  • the extracting arrangement may include a cyclone separator.
  • a substance for use in a sensor having a sensor surface to which an analyte material can bind characterised in that the substance includes a polyionic cation selected to reduce non-specific binding to the sensor surface.
  • the cation may selected from a group comprising poly-L-lysine, DEAE-dextran and polyethyleneimine.
  • Apparatus including an optical sensor and a substance, according to the present invention, will now be described, by way of example, with reference to the accompanying drawing, which shows the apparatus schematically.
  • the apparatus comprises a cyclone separator 1 by which biological particles are extracted from air, are suspended in a liquid and concentrated for supply to a sensor 2 for detection.
  • the cyclone separator 1 is of a conventional kind, such as described in detail in US6508864. It has an ambient air inlet 10 opening into the interior of a chamber 11 having a porous cylindrical wall 12.
  • the wall 12 forms the inner wall of a sealed annular jacket 13 surrounding the chamber 11 and is connected to a supply 14 of a liquid 15.
  • the liquid 15 fills the jacket 13, permeates the wall 12 and wets its inner surface, that is, the boundary wall surface of the chamber 11. The nature of the liquid 15 will be described later.
  • the chamber 11 opens through an axial air outlet 16.
  • the chamber 11 opens into a lower tapered, conical collection region 17, which connects with a pipe 18 at its lower end.
  • Differential pressure is applied by a fan, blower, or the like (not shown) to draw air into the chamber 11 through the inlet 10 so that it flows in a swirling fashion around the chamber and flows out of the outlet 16. Particles in the air are driven radially outwardly by centrifugal force into contact with the wetted wall 12. The particles are captured by the wetting fluid and flow down with the fluid into the collection region 17 and from there to the pipe 18.
  • the pipe 18 extends to the inlet of a flow cell 20 formed as a part of the sensor 2, and mounted on the upper sensor surface 21 of a glass prism 22.
  • the flow cell 20 defines a flow chamber 23 between the upper surface 21 of the prism 22 and an upper transparent wall 24 of the cell.
  • the upper face 21 of the prism 22 has a thin gold film 25 and supports four discrete stripes 26, each approximately 0.5 x 3mm, of different antibody materials selected to interact with specific biological analyte materials.
  • the antibody materials are immobilised to the sensor surface 21 by covalent attachment to a polymer film of carboxylmethyldextran (CMD), which is subsequently attached to the gold film 25.
  • CMD is preferred because it provides a large number of chemical binding sites for antibody attachment but other binding sites could be used.
  • the sensor 2 also includes a light source 27 mounted to direct a beam of light into one of the other faces 28 of the prism 22 angled such that the light is refracted at the upper surface 21 in the region of the antibody stripes 26. This causes light to be scattered from sub-micron particles bound to the antibody stripes 26 and this scattered light is detected with a far-field photo-detector device 29 responsive to light from each stripe. Alternatively, the antibody regions could be viewed visually via a microscope objective lens or the like. A black optical sink 30 is applied to the third face 31 of the prism 22 to absorb any reflected or non-specific scattered light. The output of the detector 29 is supplied to a processor 32, which provides an indication of the nature of any detected analyte.
  • the fluid 15 supplied to the cyclone separator 1 and which flows with the particles to the sensor 2 includes a conventional buffer solution with water having 0.15M phosphate buffered saline pH7.4 containing 0.01% Tween 80 (PBS/T). Added to this is a polyionic cation, or polycation, such as 0.01% w/v poly-L-lysine, 0.1% w/v DEAE-dextran or polyethyleneimine (PEI).
  • the purpose of the polycation is to reduce non-specific binding (NSB) to the antibody coating 26. It has been observed, without the polycation present, that NSB material primarily binds to the antibody-coated areas 26 of the biosensor surface in preference to other areas.
  • the binding mechanism is an electrostatic interaction between biological material in the sample, which mainly bears a net negative charge, and the antibody coating 26, which bears a net positive or neutral charge.
  • Polycation additives have the property that they bind with negatively-charged material so that there is less unbound negatively-charged material available to bind with the antibody material. Addition of the polycation to the cyclone separator buffer solution 15 has been found significantly to reduce the amount of NSB on the antibody coating 26. It has been found that the addition of the polycation substance reduces background noise, reduces false positive detection, increases signal-to-noise ratio and may also improve the lower limit of detection for a biosensor device. It will be appreciated that the polycation substance need not be added in the cyclone separator 1 but could be added to the analyte material at any stage up to the sensor 2.
  • Polycations can be used to inhibit NSB binding to a very wide range of antibodies. They may also be effective in inhibiting binding to other forms of sensor surfaces, which may not include antibodies, such as microtitre plate assays, protein microassays, other biosensors and western blot tests. Sensors could include various specific recognition entities, for example, specific binding ligands, such as DNA or molecularly imprinted polymers.
  • the action of polycations appears to be particularly effective with materials collected from the atmosphere but may also be effective with other environmental samples. Other forms of environmental sampling and particle capture methods could be used instead of cyclone samplers. For example, filtration, precipitation, impactors, centrifuges or the like could be used.

Abstract

A cyclone separator (1) is connected to supply a buffer solution (15) with captured atmospheric particles to an optical sensor (2) having antibody regions (26) coated on the upper surface (21) of a prism (22). The buffer solution (15) contains a polyionic cation such as poly-L- lysine, DEAE-dextran or polyethyleneimine, which is effective to reduce non-specific binding to the antibody regions (26). A light source (27) illuminates the underside of the prism surface (21). The illuminated antibody regions (26) are viewed from above by a detector (29) or microscope.

Description

SENSORS AND SUBSTANCES FOR DETECTING PARTICLES IN AIR
This invention relates to sensors of the kind having a surface to which particles in a fluid bind for detection.
The invention is more particularly but not exclusively concerned with sensors for detecting sub-micron particles and with substances for use with such sensors.
Sub-micron biological particles such as bacterial spores and viruses can be detected using a biosensor having one or more regions of exposed antibody material. The antibody material is exposed to a liquid containing the biological particles so that specific particles bind to the antibody. This changes the antibody material in a way that can be detected, usually by optical means. Typically, a glass plate has several regions of different antibody materials coated onto it and a beam of light is passed through the plate to illuminate its surface. By viewing the different regions, it is possible to detect if any region has changed its appearance as a result of particles binding to it. Examples of such sensors are described in WO07/007070, WO03/093801 and WO06/090114. When these sensors are used to detect biological particles in air, it is usual practice to concentrate the particles in a liquid, such as by using a cyclone separator of the kind described in US6508864.
One problem with such sensors is that in time the antibody surface becomes coated with non-specific particles, that is, particles other than those biological particles the sensor is intended to detect. This can reduce the signal-to-noise ratio, lead to an increase in false positive identifications and reduce the detection limit.
It is an object of the present invention to provide an alternative sensor and substance for use in a sensor. According to one aspect of the present invention there is provided a sensor of the above- specified kind, characterised in that the fluid contains a polyionic cation selected to reduce nonspecific binding to the surface.
Preferably the cation is selected to bind with negatively-charged atmospheric materials. The cation may selected from a group comprising poly-L-lysine, DEAE-dextran and polyethyleneimine. The surface preferably includes an antibody material. The antibody material may be immobilised to the sensor surface by covalent attachment to a polymer film of carboxymethyldextran. The sensor preferably includes an optical arrangement for illuminating and viewing the surface.
According to another aspect of the present invention there is provided apparatus for detecting the presence of a substance in air including an arrangement for extracting particles from air and for supplying extracted particles in a fluid to a sensor having a surface to which particles in the fluid bind for detection, characterised in that the fluid contains a polyionic cation selected to reduce non-specific binding to the surface.
The polyionic cation may be present in fluid in the extracting arrangement. The extracting arrangement may include a cyclone separator.
According to a further aspect of the present invention there is provided a substance for use in a sensor having a sensor surface to which an analyte material can bind, characterised in that the substance includes a polyionic cation selected to reduce non-specific binding to the sensor surface.
The cation may selected from a group comprising poly-L-lysine, DEAE-dextran and polyethyleneimine. Apparatus including an optical sensor and a substance, according to the present invention, will now be described, by way of example, with reference to the accompanying drawing, which shows the apparatus schematically.
The apparatus comprises a cyclone separator 1 by which biological particles are extracted from air, are suspended in a liquid and concentrated for supply to a sensor 2 for detection.
The cyclone separator 1 is of a conventional kind, such as described in detail in US6508864. It has an ambient air inlet 10 opening into the interior of a chamber 11 having a porous cylindrical wall 12. The wall 12 forms the inner wall of a sealed annular jacket 13 surrounding the chamber 11 and is connected to a supply 14 of a liquid 15. The liquid 15 fills the jacket 13, permeates the wall 12 and wets its inner surface, that is, the boundary wall surface of the chamber 11. The nature of the liquid 15 will be described later. At its upper end, the chamber 11 opens through an axial air outlet 16. At its lower end, the chamber 11 opens into a lower tapered, conical collection region 17, which connects with a pipe 18 at its lower end. Differential pressure is applied by a fan, blower, or the like (not shown) to draw air into the chamber 11 through the inlet 10 so that it flows in a swirling fashion around the chamber and flows out of the outlet 16. Particles in the air are driven radially outwardly by centrifugal force into contact with the wetted wall 12. The particles are captured by the wetting fluid and flow down with the fluid into the collection region 17 and from there to the pipe 18.
The pipe 18 extends to the inlet of a flow cell 20 formed as a part of the sensor 2, and mounted on the upper sensor surface 21 of a glass prism 22. The flow cell 20 defines a flow chamber 23 between the upper surface 21 of the prism 22 and an upper transparent wall 24 of the cell. The upper face 21 of the prism 22 has a thin gold film 25 and supports four discrete stripes 26, each approximately 0.5 x 3mm, of different antibody materials selected to interact with specific biological analyte materials. The antibody materials are immobilised to the sensor surface 21 by covalent attachment to a polymer film of carboxylmethyldextran (CMD), which is subsequently attached to the gold film 25. CMD is preferred because it provides a large number of chemical binding sites for antibody attachment but other binding sites could be used.
The sensor 2 also includes a light source 27 mounted to direct a beam of light into one of the other faces 28 of the prism 22 angled such that the light is refracted at the upper surface 21 in the region of the antibody stripes 26. This causes light to be scattered from sub-micron particles bound to the antibody stripes 26 and this scattered light is detected with a far-field photo-detector device 29 responsive to light from each stripe. Alternatively, the antibody regions could be viewed visually via a microscope objective lens or the like. A black optical sink 30 is applied to the third face 31 of the prism 22 to absorb any reflected or non-specific scattered light. The output of the detector 29 is supplied to a processor 32, which provides an indication of the nature of any detected analyte.
The fluid 15 supplied to the cyclone separator 1 and which flows with the particles to the sensor 2 includes a conventional buffer solution with water having 0.15M phosphate buffered saline pH7.4 containing 0.01% Tween 80 (PBS/T). Added to this is a polyionic cation, or polycation, such as 0.01% w/v poly-L-lysine, 0.1% w/v DEAE-dextran or polyethyleneimine (PEI). The purpose of the polycation is to reduce non-specific binding (NSB) to the antibody coating 26. It has been observed, without the polycation present, that NSB material primarily binds to the antibody-coated areas 26 of the biosensor surface in preference to other areas. It is believed that the binding mechanism is an electrostatic interaction between biological material in the sample, which mainly bears a net negative charge, and the antibody coating 26, which bears a net positive or neutral charge. Polycation additives have the property that they bind with negatively-charged material so that there is less unbound negatively-charged material available to bind with the antibody material. Addition of the polycation to the cyclone separator buffer solution 15 has been found significantly to reduce the amount of NSB on the antibody coating 26. It has been found that the addition of the polycation substance reduces background noise, reduces false positive detection, increases signal-to-noise ratio and may also improve the lower limit of detection for a biosensor device. It will be appreciated that the polycation substance need not be added in the cyclone separator 1 but could be added to the analyte material at any stage up to the sensor 2.
There may be other polycations that have a similar action and could be used.
Polycations can be used to inhibit NSB binding to a very wide range of antibodies. They may also be effective in inhibiting binding to other forms of sensor surfaces, which may not include antibodies, such as microtitre plate assays, protein microassays, other biosensors and western blot tests. Sensors could include various specific recognition entities, for example, specific binding ligands, such as DNA or molecularly imprinted polymers. The action of polycations appears to be particularly effective with materials collected from the atmosphere but may also be effective with other environmental samples. Other forms of environmental sampling and particle capture methods could be used instead of cyclone samplers. For example, filtration, precipitation, impactors, centrifuges or the like could be used.

Claims

1. A sensor (2) having a surface (21, 25, 26) to which particles in a fluid (15) bind for detection, characterised in that the fluid (15) contains a polyionic cation selected to reduce non-specific binding to the surface (21, 25, 26).
2. A sensor (2) according to Claim 1, characterised in that the cation is selected to bind with negatively-charged atmospheric materials.
3. A sensor (2) according to Claim 1 or 2, characterised in that the cation is selected from a group comprising poly-L-lysine, DEAE-dextran and polyethyleneimine.
4. A sensor (2) according to any one of the preceding claims, characterised in that the surface (21, 25, 26) includes an antibody material (26).
5. A sensor (2) according to Claim 4, characterised in that the antibody material (26) is immobilised to the sensor surface (21, 25) by covalent attachment to a polymer film of carboxylmethyldextran.
6. A sensor (2) according to any one of the preceding claims, characterised in that sensor (2) includes an optical arrangement (27, 29, 30) for illuminating and viewing the surface (21, 25, 26).
7. Apparatus for detecting the presence of a substance in air including an arrangement (1) for extracting particles from air and for supplying extracted particles in a fluid (15) to a sensor (2) having a surface (21, 25, 26) to which particles in the fluid (15) bind for detection, characterised in that the fluid (15) contains a polyionic cation selected to reduce non-specific binding to the surface (21, 25, 26).
8. Apparatus according to Claim 7, characterised in that the polyionic cation is present in fluid (15) in the extracting arrangement (1).
9. Apparatus according to Claim 7 or 8, characterised in that the extracting arrangement includes a cyclone separator (1).
10. A substance for use in a sensor (2) having a sensor surface (21, 25, 26) to which an analyte material can bind, characterised in that the substance includes a polyionic cation selected to reduce non-specific binding to the sensor surface (21, 25, 26).
11. A sensor according to Claim 10, characterised in that the cation is selected from a group comprising poly-L-lysine, DEAE-dextran and polyethyleneimine.
PCT/GB2007/003762 2006-10-05 2007-10-04 Sensors and substances for detecting particles in air WO2008040975A1 (en)

Applications Claiming Priority (2)

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GB0619645.5 2006-10-05
GB0619645A GB0619645D0 (en) 2006-10-05 2006-10-05 Sensors and substances

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0230768A1 (en) * 1985-12-20 1987-08-05 Syntex (U.S.A.) Inc. Particle separation method
WO2001094908A2 (en) * 2000-06-07 2001-12-13 Lockheed Martin Naval Electronics And Surveillance Systems System and method to detect the presence of a target organism within an air sample using flow cytometry
WO2001095991A1 (en) * 2000-06-14 2001-12-20 Innovatek, Inc. Mini-cyclone biocollector and concentrator
WO2002027316A2 (en) * 2000-09-25 2002-04-04 Abbott Laboratories Methods and kits for decreasing interferences of assays samples containing plasma or serum in specific binding assays by using a large polycation
US20040048323A1 (en) * 2002-09-11 2004-03-11 Kimberly-Clark Worldwide, Inc. Antibody pair screening methods
WO2004092733A1 (en) * 2003-04-14 2004-10-28 Caliper Life Sciences, Inc. Reduction of migration shift assay interference
WO2005040767A2 (en) * 2003-10-17 2005-05-06 The Government Of The United States Of America As Represented By The Secretary Of The Department Of Health And Human Services, Centers For Disease Control And Prevention Air-sampling device and method of use

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0230768A1 (en) * 1985-12-20 1987-08-05 Syntex (U.S.A.) Inc. Particle separation method
WO2001094908A2 (en) * 2000-06-07 2001-12-13 Lockheed Martin Naval Electronics And Surveillance Systems System and method to detect the presence of a target organism within an air sample using flow cytometry
WO2001095991A1 (en) * 2000-06-14 2001-12-20 Innovatek, Inc. Mini-cyclone biocollector and concentrator
WO2002027316A2 (en) * 2000-09-25 2002-04-04 Abbott Laboratories Methods and kits for decreasing interferences of assays samples containing plasma or serum in specific binding assays by using a large polycation
US20040048323A1 (en) * 2002-09-11 2004-03-11 Kimberly-Clark Worldwide, Inc. Antibody pair screening methods
WO2004092733A1 (en) * 2003-04-14 2004-10-28 Caliper Life Sciences, Inc. Reduction of migration shift assay interference
WO2005040767A2 (en) * 2003-10-17 2005-05-06 The Government Of The United States Of America As Represented By The Secretary Of The Department Of Health And Human Services, Centers For Disease Control And Prevention Air-sampling device and method of use

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Publication number Publication date
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