Tim Gibson - Academia.edu (original) (raw)
Papers by Tim Gibson
PLOS Neglected Tropical Diseases, 2019
Background Visceral leishmaniasis (VL) in Brazil is a neglected, vector-borne, tropical parasitic... more Background Visceral leishmaniasis (VL) in Brazil is a neglected, vector-borne, tropical parasitic disease that is responsible for several thousand human deaths every year. The transmission route involves sand flies becoming infected after feeding on infected reservoir host, mainly dogs, and then transmitting the Leishmania infantum parasites while feeding on humans. A major component of the VL control effort is the identification and euthanasia of infected dogs to remove them as a source of infection. A rapid, non-invasive, point-of-care device able to differentiate between the odours of infected and uninfected dogs may contribute towards the accurate diagnosis of canine VL. Methodology/Principal findings We analysed the headspace volatile chemicals from the hair of two groups of dogs collected in 2017 and 2018 using a bench-top eNose volatile organic chemical analyser. The dogs were categorised as infected or uninfected by PCR analysis of blood samples taken by venepuncture and the number of parasites per ml of blood was calculated for each dog by qPCR analysis. We demonstrated using a robust clustering analysis that the eNose data could be discriminated into infected and uninfected categories with specificity >94% and sensitivity >97%. The eNose device and data analysis were sufficiently sensitive to be able to identify infected dogs even when the Leishmania population in the circulating blood was very low. Conclusions/Significance The study illustrates the potential of the eNose to rapidly and accurately identify dogs infected with Le. infantum. Future improvements to eNose analyser sensor sensitivity, sampling methodology and portability suggest that this approach could significantly improve the
ACS Symposium Series, 1992
One of the most important problems in the development of commercial biosensors is the stabilizati... more One of the most important problems in the development of commercial biosensors is the stabilization of the enzymes used as the biological detection agents in the sensor. Although many different bio sensors have been constructed, few have been developed in commer cially ...
Meta Gene
Abstract The current gold standard for protein biomarker measurement is the ELISA, which shows go... more Abstract The current gold standard for protein biomarker measurement is the ELISA, which shows good sensitivity and specificity but is typically quite slow and requires expensive and complex equipment. For applications such as early cancer diagnosis, this may limit access, whilst for critical conditions such as acute kidney injury (AKI), sepsis, stroke then rapid measurement has the potential to drive the clinical response. Other applications such as immediate confirmation of bacterial Vs viral infection to inform antibiotic prescribing, also require a fast analysis. Biosensors offer the prospect of reagent-less, processing-free measurements at the patient's bedside. We have fabricated electrochemical immunosensors against a wide range of medical analytes; such sensor operate by virtue of an immobilized bioreceptor, typically an antibody or antibody fragment, or more recently a synthetic binding protein (Affimer) onto an electrode surface. Sensor readout after exposure to the biomarker, in blood, urine or other bio-fluid is then by electrochemical impedance measurement. We have also developed lanthanide ion doped nanoparticles, typically 20–40 nm diameter which are surface-functionalized with antibodies or Affimers. Here, readout after biomarker presentation is via alteration of luminescence intensity, either quenching or enhancement. Also since the nanobiosensors are in suspension and the emission profile can be tuned, then real time measurement, e.g. of the AKI biomarker NGAL in urine should be possible. With all of these devices, the surface nanostructure is absolutely key to performance and this will be discussed.
Sensors and Actuators B: Chemical
Research into volatile sensing using arrays of conductive polymer sensors has identified two sign... more Research into volatile sensing using arrays of conductive polymer sensors has identified two significant problems: namely, sensitivity to water vapour and poor sensitivity to hydrocarbons and other hydrophobic molecules. For instance, the humidity responses of conductive polymer sensors are sometimes so high that the small signals produced by important volatiles are lost, leading to a lack of discrimination. In this
Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95
The formation of protein-polyelectrolyte complexes has been directly demonstrated for several enz... more The formation of protein-polyelectrolyte complexes has been directly demonstrated for several enzymes in solution including alcohol oxidase, horseradish pemxidase, lactate oxidase and glucose oxidase using agamse gel electrophoresis. The combination of such complexes with polyhydroxyl compounds has been found to significantly enhance the shelf-life of biosensors when stored in a dehydrated form, examples of lactate and malate biosensors are given. There is evidence from enzyme solution and immobilisation experiments that the protein-polyelectmlyte complexes also have the ability to improve the operational stability of the enzyme activity during catalysis. This ability may be used to produce biosensors having extended working lifetimes for use in analytical devices.
Sensors and Actuators B: Chemical
A novel system for the immobilisation of glucose oxidase onto controlled pore glass (CPG) beads u... more A novel system for the immobilisation of glucose oxidase onto controlled pore glass (CPG) beads using an enzyme-polyelectrolyte complex to increase the thermal and operational stability is discussed. Native glucose oxidase has been shown to be fairly unstable in solution and ...
AIP Conference Proceedings, 2009
AIP Conference Proceedings, 2009
Electronic nose technology has been available commercially for over 12 years but uptake in actual... more Electronic nose technology has been available commercially for over 12 years but uptake in actual industrial applications has yet to be fully realised. We report 2 specific test protocols being used in the textiles industry that allow the direct measurement of anti‐odour and anti‐ ...
Developments in biological standardization, 1996
A method of elevating the storage lifetime of purified proteins has been discovered which appears... more A method of elevating the storage lifetime of purified proteins has been discovered which appears to confer stability to all proteins investigated and may therefore be classed as generic in action. The basic methodology involves the formation of multiple electrostatic complexes between the protein and selected soluble polyelectrolytes to give protein-polyelectrolyte (PP) complexes and then to add solutions of polyalcohols or other compounds containing multiple hydroxyl groups. Dehydration of the resulting solution by vacuum evaporation, freeze drying or forced air convection produces a dry film or powder of stabilised protein. The method has been used mainly in the preparation of active enzymes for analytical tests. It has also been found that the formation of PP complexes also enhances the stability of enzymes in solution and the technique may be applicable to the stabilisation of virus suspensions by polycations. Examples of stabilised enzymes prepared by these methods are given a...
Focus on Biotechnology, 2002
ABSTRACT The stabilisation of enzymes is of great importance in many applications. The two main t... more ABSTRACT The stabilisation of enzymes is of great importance in many applications. The two main types of stability may be defined as: 1) Storage or Shelf Stability and 2) Operational Stability. The first relates to the stability of enzymes when stored as a dehydrated preparation, a solution or immobilised and is particularly concerned with retention of activity over time. The second generally relates to the retention of activity of an enzyme when in use. Both types of enzyme stability will be discussed using case studies from the analytical field (alkaline phosphatase, alcohol oxidase, acetylcholine-esterase and a recombinant luciferase) and enzyme based biosterilisers (peroxidases). The introduction of an electrophoretic technique for predicting protein-polymer interactions will be described. In addition, stabilisation using covalent immobilisation of pre-stabilised enzyme complexes will be presented using glucose oxidase as an example and a brief discussion on the likely factors influencing stability of enzymes is included.
Comprehensive Analytical Chemistry, 2007
Publisher Summary The detection of many pesticides at extremely low levels can be best achieved n... more Publisher Summary The detection of many pesticides at extremely low levels can be best achieved not by direct detection of the pesticide itself but rather by detection of its inhibitory effects on enzyme reactions. The detection of organophosphate and other pesticides based on the inhibition of the enzyme acetylcholinesterase by these compounds has received considerable attention primarily because of high specificity and sensitivity. Other techniques such as use of multiple electrodes, pattern recognition software and flow-injection techniques have enabled the subtraction of matrix effects such as heavy metals from the system as well as the determination of pesticides in systems containing more than one compound. The signal processing algorithms allow automation of the pesticide quantification enabling use of the instrumentation by unskilled personal, thereby removing this sensing platform from specialized laboratories and making it available to the end-users. Thus this application could conceivably be utilized in the field as well as under laboratory conditions. The relative low cost of electrochemical technology compared with many of the other technologies used makes it an attractive alternative, especially if the enzyme electrodes can be inexpensively mass-produced using screen-printing to allow single-shot use.
SPIE Proceedings, 2011
ABSTRACT The WHO declared tuberculosis (TB) a global emergency. An estimated 8-9 million new case... more ABSTRACT The WHO declared tuberculosis (TB) a global emergency. An estimated 8-9 million new cases occur each year with 2-3 million deaths. Currently, TB is diagnosed mostly by chest-X ray and staining of the mycobacteria in sputum with a detection limit of 1x104 bacteria /ml. There is an urgent need for better diagnostic tools for TB especially for developing countries. We have validated the electronic nose from TD Technology for the detection of Mycobacterium tuberculosis by headspace analysis of 284 sputum samples from TB patients. We used linear discriminant function analysis resulting in a sensitivity of 75% a specificity of 67% and an accuracy of 69%. Further research is still required to improve the results by choosing more selective sensors and sampling techniques. We used a fast gas chromatography- mass spectrometry method (GC-MS). The automated procedure is based on the injection of sputum samples which are methylated inside the GC injector using thermally assisted hydrolysis and methylation (THM-GC-MS). Hexacosanoic acid in combination with tuberculostearic acid was found to be specific for the presence of M. tuberculosis. The detection limit was similar to microscopy. We found no false positives, all microscopy and culture positive samples were also found positive with the THM-GC-MS method. The detection of ribosomal RNA from the infecting organism offers great potential since rRNA molecules outnumber chromosomal DNA by a factor 1000. It thus may possible to detect the organism without amplification of the nucleic acids (NA). We used a capture and a tagged detector probe for the direct detection of M. tuberculosis in sputum. So far the detection limit is 1x106 bacteria / ml. Currently we are testing a Lab-On-A-Chip Interferometer detection system.
Sensors and Actuators B: Chemical, 1997
The detection and simultaneous identification of a range of microorganisms by measuring the volat... more The detection and simultaneous identification of a range of microorganisms by measuring the volatile compounds produced from plate cultures has been carried out using an electronic nose and a neural network classifier. Headspace samples were taken from static atmospheres formed from inoculated agar plates after a suitable growth period at 37°C and analysed using a standard 16 sensor array operating in transient flow mode. The response of the sensor array to water and to the control media in the absence of microbial growth was also determined, allowing greater discrimination of microbial volatiles. The response curves produced were processed using standard back propagation neural network techniques to provide identification. The overall classification rate for 12 different bacteria and one pathogenic yeast was 93.4%. Data for a subset of seven bacteria gave 100% classification using the same methods. In a second experiment three similar yeast cultures were compared and correctly classified at a level of 96.3% with no pre-processing to remove the sample signal generated by the media. Principal component analysis on selected data gave clear discrimination between water vapour and the test samples.
Nanotechnology, 2009
The reverse micellar system of dioctyl-sulfosuccinate (AOT)/octane and toluene have been used as ... more The reverse micellar system of dioctyl-sulfosuccinate (AOT)/octane and toluene have been used as a template for polymerization of acrylamide (AA)/bisacrylamide (BAA)-based functionalized polymeric nanoparticles. Such nanoparticles are typically sized between 20 and 90 nm. They can be synthesized with different functional groups according to the monomers added to the polymerization mixture. In our experiments the nanoparticles carried amino and carboxyl groups following incorporation of allylamine (AAm) or methacrylic acid (MAA) monomers, respectively. The available amine or carboxyl groups can then be used for immobilization of enzymes or other biomolecules. These enzymes, subtilisin, laccase and lipase, were immobilized onto polyAA/BAA/MAA nanoparticles covalently after activating the MAA carboxylic groups with Woodward's K reagent. Non-covalent immobilization via electrostatic interaction was also performed.
Journal of Molecular Catalysis B: Enzymatic, 1999
The ability to use model systems to predict the shelf-life of biological products is an extremely... more The ability to use model systems to predict the shelf-life of biological products is an extremely important area for enzyme manufacturers and the diagnostic industry in particular. Biosensor devices where the biological recognition is carried out by enzymes, antibodies or some other relatively unstable material are also subject to deactivation and therefore have a finite lifetime on storage. This shelf stability is obviously of the highest importance to biosensor manufacturers, however the experimental protocols used to predict the shelf-life of these devices are generally well guarded company secrets and little attempt has been made to standardise such methods. This paper presents a generic model system that is able to estimate shelf-stability to a high degree for first order enzyme deactivations and may be used as a rough guide for screening enzyme based systems, including biosensors where the order and mechanism of deactivation is unclear. Dehydrated glucose oxidase in unstabilised and stabilised forms, solution stabilised antibody-enzyme conjugate and glucose oxidase biosensors are presented as experimental examples.
Journal of Electroanalytical Chemistry, 1997
Polymer films were deposited electrochemically on a platinum electrode surface, either by constan... more Polymer films were deposited electrochemically on a platinum electrode surface, either by constant current density electrolysis for polypyrrole or by potential scan for polyphenol and polyaniline. The permeability of these modified electrodes to oxygen, Fe(CN)63-and NADH was measured by constant potential electrolysis. Although it was possible to control to some extent the polypyrrole permeability versus oxygen and Fe(CN)~-by choosing the electropolymerization conditions, the film became almost totally impermeable to larger species such as NADH as soon as its thickness exceeded a few monolayers. A new protocol was proposed, which consisted in adding inert molecules such as polyethylene glycol (PEG) to the electropolymerization solution. These molecules induced change in the polymeric matrix morphology. 70% of the NADH flux obtained at a clean electrode was then recovered with a 5 am-thick polypyrrole modified electrode. The experimental conditions, i.e., the molar mass and the concentration of PEG, were optimized; the maximum polypyrrole permeability of 2.0 × 10-3 cm s-I was recorded with PEG (1000 g mol-J) at I mmol I-i. These conditions also allowed an enzyme such as glucose oxidase to be satisfactorily confined at the electrode surface. Similar results were obtained with polyphenol and polyaniline or when PEG was replaced by dextran molecules.
Journal of Clinical Microbiology, 2010
We investigated the potential of two different electronic noses (EN; code named “Rob” and “Walter... more We investigated the potential of two different electronic noses (EN; code named “Rob” and “Walter”) to differentiate between sputum headspace samples from tuberculosis (TB) patients and non-TB patients. Only samples from Ziehl-Neelsen stain (ZN)- and Mycobacterium tuberculosis culture-positive (TBPOS) sputum samples and ZN- and culture-negative (TBNEG) samples were used for headspace analysis; with EN Rob, we used 284 samples from TB suspects (56 TBPOS and 228 TBNEG samples), and with EN Walter, we used 323 samples from TB suspects (80 TBPOS and 243 TBNEG samples). The best results were obtained using advanced data extraction and linear discriminant function analysis, resulting in a sensitivity of 68%, a specificity of 69%, and an accuracy of 69% for EN Rob; for EN Walter, the results were 75%, 67%, and 69%, respectively. Further research is still required to improve the sensitivity and specificity by choosing more selective sensors and type of sampling technique.
Journal of Biotechnology, 2007
Journal of Biotechnology, 2007
PLOS Neglected Tropical Diseases, 2019
Background Visceral leishmaniasis (VL) in Brazil is a neglected, vector-borne, tropical parasitic... more Background Visceral leishmaniasis (VL) in Brazil is a neglected, vector-borne, tropical parasitic disease that is responsible for several thousand human deaths every year. The transmission route involves sand flies becoming infected after feeding on infected reservoir host, mainly dogs, and then transmitting the Leishmania infantum parasites while feeding on humans. A major component of the VL control effort is the identification and euthanasia of infected dogs to remove them as a source of infection. A rapid, non-invasive, point-of-care device able to differentiate between the odours of infected and uninfected dogs may contribute towards the accurate diagnosis of canine VL. Methodology/Principal findings We analysed the headspace volatile chemicals from the hair of two groups of dogs collected in 2017 and 2018 using a bench-top eNose volatile organic chemical analyser. The dogs were categorised as infected or uninfected by PCR analysis of blood samples taken by venepuncture and the number of parasites per ml of blood was calculated for each dog by qPCR analysis. We demonstrated using a robust clustering analysis that the eNose data could be discriminated into infected and uninfected categories with specificity >94% and sensitivity >97%. The eNose device and data analysis were sufficiently sensitive to be able to identify infected dogs even when the Leishmania population in the circulating blood was very low. Conclusions/Significance The study illustrates the potential of the eNose to rapidly and accurately identify dogs infected with Le. infantum. Future improvements to eNose analyser sensor sensitivity, sampling methodology and portability suggest that this approach could significantly improve the
ACS Symposium Series, 1992
One of the most important problems in the development of commercial biosensors is the stabilizati... more One of the most important problems in the development of commercial biosensors is the stabilization of the enzymes used as the biological detection agents in the sensor. Although many different bio sensors have been constructed, few have been developed in commer cially ...
Meta Gene
Abstract The current gold standard for protein biomarker measurement is the ELISA, which shows go... more Abstract The current gold standard for protein biomarker measurement is the ELISA, which shows good sensitivity and specificity but is typically quite slow and requires expensive and complex equipment. For applications such as early cancer diagnosis, this may limit access, whilst for critical conditions such as acute kidney injury (AKI), sepsis, stroke then rapid measurement has the potential to drive the clinical response. Other applications such as immediate confirmation of bacterial Vs viral infection to inform antibiotic prescribing, also require a fast analysis. Biosensors offer the prospect of reagent-less, processing-free measurements at the patient's bedside. We have fabricated electrochemical immunosensors against a wide range of medical analytes; such sensor operate by virtue of an immobilized bioreceptor, typically an antibody or antibody fragment, or more recently a synthetic binding protein (Affimer) onto an electrode surface. Sensor readout after exposure to the biomarker, in blood, urine or other bio-fluid is then by electrochemical impedance measurement. We have also developed lanthanide ion doped nanoparticles, typically 20–40 nm diameter which are surface-functionalized with antibodies or Affimers. Here, readout after biomarker presentation is via alteration of luminescence intensity, either quenching or enhancement. Also since the nanobiosensors are in suspension and the emission profile can be tuned, then real time measurement, e.g. of the AKI biomarker NGAL in urine should be possible. With all of these devices, the surface nanostructure is absolutely key to performance and this will be discussed.
Sensors and Actuators B: Chemical
Research into volatile sensing using arrays of conductive polymer sensors has identified two sign... more Research into volatile sensing using arrays of conductive polymer sensors has identified two significant problems: namely, sensitivity to water vapour and poor sensitivity to hydrocarbons and other hydrophobic molecules. For instance, the humidity responses of conductive polymer sensors are sometimes so high that the small signals produced by important volatiles are lost, leading to a lack of discrimination. In this
Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95
The formation of protein-polyelectrolyte complexes has been directly demonstrated for several enz... more The formation of protein-polyelectrolyte complexes has been directly demonstrated for several enzymes in solution including alcohol oxidase, horseradish pemxidase, lactate oxidase and glucose oxidase using agamse gel electrophoresis. The combination of such complexes with polyhydroxyl compounds has been found to significantly enhance the shelf-life of biosensors when stored in a dehydrated form, examples of lactate and malate biosensors are given. There is evidence from enzyme solution and immobilisation experiments that the protein-polyelectmlyte complexes also have the ability to improve the operational stability of the enzyme activity during catalysis. This ability may be used to produce biosensors having extended working lifetimes for use in analytical devices.
Sensors and Actuators B: Chemical
A novel system for the immobilisation of glucose oxidase onto controlled pore glass (CPG) beads u... more A novel system for the immobilisation of glucose oxidase onto controlled pore glass (CPG) beads using an enzyme-polyelectrolyte complex to increase the thermal and operational stability is discussed. Native glucose oxidase has been shown to be fairly unstable in solution and ...
AIP Conference Proceedings, 2009
AIP Conference Proceedings, 2009
Electronic nose technology has been available commercially for over 12 years but uptake in actual... more Electronic nose technology has been available commercially for over 12 years but uptake in actual industrial applications has yet to be fully realised. We report 2 specific test protocols being used in the textiles industry that allow the direct measurement of anti‐odour and anti‐ ...
Developments in biological standardization, 1996
A method of elevating the storage lifetime of purified proteins has been discovered which appears... more A method of elevating the storage lifetime of purified proteins has been discovered which appears to confer stability to all proteins investigated and may therefore be classed as generic in action. The basic methodology involves the formation of multiple electrostatic complexes between the protein and selected soluble polyelectrolytes to give protein-polyelectrolyte (PP) complexes and then to add solutions of polyalcohols or other compounds containing multiple hydroxyl groups. Dehydration of the resulting solution by vacuum evaporation, freeze drying or forced air convection produces a dry film or powder of stabilised protein. The method has been used mainly in the preparation of active enzymes for analytical tests. It has also been found that the formation of PP complexes also enhances the stability of enzymes in solution and the technique may be applicable to the stabilisation of virus suspensions by polycations. Examples of stabilised enzymes prepared by these methods are given a...
Focus on Biotechnology, 2002
ABSTRACT The stabilisation of enzymes is of great importance in many applications. The two main t... more ABSTRACT The stabilisation of enzymes is of great importance in many applications. The two main types of stability may be defined as: 1) Storage or Shelf Stability and 2) Operational Stability. The first relates to the stability of enzymes when stored as a dehydrated preparation, a solution or immobilised and is particularly concerned with retention of activity over time. The second generally relates to the retention of activity of an enzyme when in use. Both types of enzyme stability will be discussed using case studies from the analytical field (alkaline phosphatase, alcohol oxidase, acetylcholine-esterase and a recombinant luciferase) and enzyme based biosterilisers (peroxidases). The introduction of an electrophoretic technique for predicting protein-polymer interactions will be described. In addition, stabilisation using covalent immobilisation of pre-stabilised enzyme complexes will be presented using glucose oxidase as an example and a brief discussion on the likely factors influencing stability of enzymes is included.
Comprehensive Analytical Chemistry, 2007
Publisher Summary The detection of many pesticides at extremely low levels can be best achieved n... more Publisher Summary The detection of many pesticides at extremely low levels can be best achieved not by direct detection of the pesticide itself but rather by detection of its inhibitory effects on enzyme reactions. The detection of organophosphate and other pesticides based on the inhibition of the enzyme acetylcholinesterase by these compounds has received considerable attention primarily because of high specificity and sensitivity. Other techniques such as use of multiple electrodes, pattern recognition software and flow-injection techniques have enabled the subtraction of matrix effects such as heavy metals from the system as well as the determination of pesticides in systems containing more than one compound. The signal processing algorithms allow automation of the pesticide quantification enabling use of the instrumentation by unskilled personal, thereby removing this sensing platform from specialized laboratories and making it available to the end-users. Thus this application could conceivably be utilized in the field as well as under laboratory conditions. The relative low cost of electrochemical technology compared with many of the other technologies used makes it an attractive alternative, especially if the enzyme electrodes can be inexpensively mass-produced using screen-printing to allow single-shot use.
SPIE Proceedings, 2011
ABSTRACT The WHO declared tuberculosis (TB) a global emergency. An estimated 8-9 million new case... more ABSTRACT The WHO declared tuberculosis (TB) a global emergency. An estimated 8-9 million new cases occur each year with 2-3 million deaths. Currently, TB is diagnosed mostly by chest-X ray and staining of the mycobacteria in sputum with a detection limit of 1x104 bacteria /ml. There is an urgent need for better diagnostic tools for TB especially for developing countries. We have validated the electronic nose from TD Technology for the detection of Mycobacterium tuberculosis by headspace analysis of 284 sputum samples from TB patients. We used linear discriminant function analysis resulting in a sensitivity of 75% a specificity of 67% and an accuracy of 69%. Further research is still required to improve the results by choosing more selective sensors and sampling techniques. We used a fast gas chromatography- mass spectrometry method (GC-MS). The automated procedure is based on the injection of sputum samples which are methylated inside the GC injector using thermally assisted hydrolysis and methylation (THM-GC-MS). Hexacosanoic acid in combination with tuberculostearic acid was found to be specific for the presence of M. tuberculosis. The detection limit was similar to microscopy. We found no false positives, all microscopy and culture positive samples were also found positive with the THM-GC-MS method. The detection of ribosomal RNA from the infecting organism offers great potential since rRNA molecules outnumber chromosomal DNA by a factor 1000. It thus may possible to detect the organism without amplification of the nucleic acids (NA). We used a capture and a tagged detector probe for the direct detection of M. tuberculosis in sputum. So far the detection limit is 1x106 bacteria / ml. Currently we are testing a Lab-On-A-Chip Interferometer detection system.
Sensors and Actuators B: Chemical, 1997
The detection and simultaneous identification of a range of microorganisms by measuring the volat... more The detection and simultaneous identification of a range of microorganisms by measuring the volatile compounds produced from plate cultures has been carried out using an electronic nose and a neural network classifier. Headspace samples were taken from static atmospheres formed from inoculated agar plates after a suitable growth period at 37°C and analysed using a standard 16 sensor array operating in transient flow mode. The response of the sensor array to water and to the control media in the absence of microbial growth was also determined, allowing greater discrimination of microbial volatiles. The response curves produced were processed using standard back propagation neural network techniques to provide identification. The overall classification rate for 12 different bacteria and one pathogenic yeast was 93.4%. Data for a subset of seven bacteria gave 100% classification using the same methods. In a second experiment three similar yeast cultures were compared and correctly classified at a level of 96.3% with no pre-processing to remove the sample signal generated by the media. Principal component analysis on selected data gave clear discrimination between water vapour and the test samples.
Nanotechnology, 2009
The reverse micellar system of dioctyl-sulfosuccinate (AOT)/octane and toluene have been used as ... more The reverse micellar system of dioctyl-sulfosuccinate (AOT)/octane and toluene have been used as a template for polymerization of acrylamide (AA)/bisacrylamide (BAA)-based functionalized polymeric nanoparticles. Such nanoparticles are typically sized between 20 and 90 nm. They can be synthesized with different functional groups according to the monomers added to the polymerization mixture. In our experiments the nanoparticles carried amino and carboxyl groups following incorporation of allylamine (AAm) or methacrylic acid (MAA) monomers, respectively. The available amine or carboxyl groups can then be used for immobilization of enzymes or other biomolecules. These enzymes, subtilisin, laccase and lipase, were immobilized onto polyAA/BAA/MAA nanoparticles covalently after activating the MAA carboxylic groups with Woodward's K reagent. Non-covalent immobilization via electrostatic interaction was also performed.
Journal of Molecular Catalysis B: Enzymatic, 1999
The ability to use model systems to predict the shelf-life of biological products is an extremely... more The ability to use model systems to predict the shelf-life of biological products is an extremely important area for enzyme manufacturers and the diagnostic industry in particular. Biosensor devices where the biological recognition is carried out by enzymes, antibodies or some other relatively unstable material are also subject to deactivation and therefore have a finite lifetime on storage. This shelf stability is obviously of the highest importance to biosensor manufacturers, however the experimental protocols used to predict the shelf-life of these devices are generally well guarded company secrets and little attempt has been made to standardise such methods. This paper presents a generic model system that is able to estimate shelf-stability to a high degree for first order enzyme deactivations and may be used as a rough guide for screening enzyme based systems, including biosensors where the order and mechanism of deactivation is unclear. Dehydrated glucose oxidase in unstabilised and stabilised forms, solution stabilised antibody-enzyme conjugate and glucose oxidase biosensors are presented as experimental examples.
Journal of Electroanalytical Chemistry, 1997
Polymer films were deposited electrochemically on a platinum electrode surface, either by constan... more Polymer films were deposited electrochemically on a platinum electrode surface, either by constant current density electrolysis for polypyrrole or by potential scan for polyphenol and polyaniline. The permeability of these modified electrodes to oxygen, Fe(CN)63-and NADH was measured by constant potential electrolysis. Although it was possible to control to some extent the polypyrrole permeability versus oxygen and Fe(CN)~-by choosing the electropolymerization conditions, the film became almost totally impermeable to larger species such as NADH as soon as its thickness exceeded a few monolayers. A new protocol was proposed, which consisted in adding inert molecules such as polyethylene glycol (PEG) to the electropolymerization solution. These molecules induced change in the polymeric matrix morphology. 70% of the NADH flux obtained at a clean electrode was then recovered with a 5 am-thick polypyrrole modified electrode. The experimental conditions, i.e., the molar mass and the concentration of PEG, were optimized; the maximum polypyrrole permeability of 2.0 × 10-3 cm s-I was recorded with PEG (1000 g mol-J) at I mmol I-i. These conditions also allowed an enzyme such as glucose oxidase to be satisfactorily confined at the electrode surface. Similar results were obtained with polyphenol and polyaniline or when PEG was replaced by dextran molecules.
Journal of Clinical Microbiology, 2010
We investigated the potential of two different electronic noses (EN; code named “Rob” and “Walter... more We investigated the potential of two different electronic noses (EN; code named “Rob” and “Walter”) to differentiate between sputum headspace samples from tuberculosis (TB) patients and non-TB patients. Only samples from Ziehl-Neelsen stain (ZN)- and Mycobacterium tuberculosis culture-positive (TBPOS) sputum samples and ZN- and culture-negative (TBNEG) samples were used for headspace analysis; with EN Rob, we used 284 samples from TB suspects (56 TBPOS and 228 TBNEG samples), and with EN Walter, we used 323 samples from TB suspects (80 TBPOS and 243 TBNEG samples). The best results were obtained using advanced data extraction and linear discriminant function analysis, resulting in a sensitivity of 68%, a specificity of 69%, and an accuracy of 69% for EN Rob; for EN Walter, the results were 75%, 67%, and 69%, respectively. Further research is still required to improve the sensitivity and specificity by choosing more selective sensors and type of sampling technique.
Journal of Biotechnology, 2007
Journal of Biotechnology, 2007