Tim Gibson | University of Leeds (original) (raw)

Papers by Tim Gibson

Research paper thumbnail of The preparation of size-controlled functionalized polymeric nanoparticles in micelles

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.

Research paper thumbnail of Application of polymeric nanoparticles for biocatalysis

Journal of Biotechnology, 2007

Nanoparticles offer major advantages for biocatalysis and biosensing applications. They present a... more Nanoparticles offer major advantages for biocatalysis and biosensing applications. They present a large surface area for immobilisation of a wide range of enzymes which can be accomplished in a gentle and efficient manner; enzyme attachment can either be within the particle matrix (biosilicate nanoparticles) on the particle surface (polymeric nanoparticles).

Research paper thumbnail of The nanoscale design of surfaces for building biosensors

Journal of Biotechnology, 2007

Research paper thumbnail of Synthesis and activity of nanosilicates and nanosilicate-entrapped enzymes using biomimetic polymers

Journal of Biotechnology, 2007

Research paper thumbnail of Novel one-pot synthesis and characterization of bioactive thiol-silicate nanoparticles for biocatalytic and biosensor applications

Nanotechnology, 2009

A novel one-pot neutral synthesis using bioinspired polymers to fabricate thiol-nanoparticles is ... more A novel one-pot neutral synthesis using bioinspired polymers to fabricate thiol-nanoparticles is presented. The thiol-particles may be directly tethered to metal surfaces such as gold, allowing the production of self-assembled nanostructured biocatalytic or biosensor surfaces. This one-pot method has also been used to entrap enzymes within the thiol-nanoparticles; it is apparent that once enzyme entrapment is carried out a bimodal distribution of particles is formed, with particles of one mode being very similar in size to thiol-nanoparticles without enzyme entrapped, and particles of the other mode being much larger in size. To this end, efforts have been made to separate the two modes of particles for the sample containing enzyme and it has been observed that the larger mode thiol-nanoparticles do indeed contain significant amounts of enzyme in comparison to the smaller mode ones. As the enzyme-containing thiol-nanoparticles can now be isolated, this means that there are many future possibilities for the use of thiol-particles containing enzyme, as they may be used in a wide range of processes and devices which require catalytic functionalized surfaces, such as biosensors and biocatalytic reactors.

Research paper thumbnail of Chapter 15 Ultrasensitive determination of pesticides via cholinesterase-based sensors for environmental analysis

Comprehensive Analytical Chemistry, 2007

The detection of many pesticides at extremely low levels can be best achieved not by direct detec... more 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.

Research paper thumbnail of Novel one-pot synthesis and characterization of bioactive thiol-silicate nanoparticles for biocatalytic and biosensor applications

Nanotechnology, 2009

A novel one-pot neutral synthesis using bioinspired polymers to fabricate thiol-nanoparticles is ... more A novel one-pot neutral synthesis using bioinspired polymers to fabricate thiol-nanoparticles is presented. The thiol-particles may be directly tethered to metal surfaces such as gold, allowing the production of self-assembled nanostructured biocatalytic or biosensor surfaces. This one-pot method has also been used to entrap enzymes within the thiol-nanoparticles; it is apparent that once enzyme entrapment is carried out a bimodal distribution of particles is formed, with particles of one mode being very similar in size to thiol-nanoparticles without enzyme entrapped, and particles of the other mode being much larger in size. To this end, efforts have been made to separate the two modes of particles for the sample containing enzyme and it has been observed that the larger mode thiol-nanoparticles do indeed contain significant amounts of enzyme in comparison to the smaller mode ones. As the enzyme-containing thiol-nanoparticles can now be isolated, this means that there are many future possibilities for the use of thiol-particles containing enzyme, as they may be used in a wide range of processes and devices which require catalytic functionalized surfaces, such as biosensors and biocatalytic reactors.

Research paper thumbnail of Labeless AC impedimetric antibody-based sensors with pg ml −1 sensitivities for point-of-care biomedical applications

Biosensors & Bioelectronics, 2009

This paper describes the development and characterisation of labeless immunosensors for (a) the c... more This paper describes the development and characterisation of labeless immunosensors for (a) the cardiac drug digoxin and (b) bovine serum albumin (BSA). Commercial screen-printed carbon electrodes were used as the basis for the sensors. Two methods were used to immobilise antibodies at the electrode surface. Aniline was electropolymerised onto these electrodes to form a thin planar film of conductive polyaniline; the polyaniline film was then utilised as a substrate to immobilise biotinylated anti-digoxin using a classical avidin-biotin affinity approach. As an alternative approach, poly(1,2-diaminobenzene) was electrodeposited onto the carbon electrodes and this modified surface was then sonochemically ablated to form an array of micropores. A second electropolymerisation step was then used to co-deposit conductive polyaniline along with antibodies for BSA within these pores to produce a microarray of polyaniline protrusions with diameters of several m, containing entrapped anti-BSA.

Research paper thumbnail of Immobilization of Peroxidase Glycoprotein on Gold Electrodes Modified with Mixed Epoxy-Boronic Acid Monolayers

Journal of The American Chemical Society, 2002

The development of bioelectronic enzyme applications requires the immobilization of active protei... more The development of bioelectronic enzyme applications requires the immobilization of active proteins onto solid or colloidal substrates such as gold. Coverage of the gold surface with alkanethiol selfassembled monolayers (SAMs) reduces nonspecific adsorption of proteins and also allows the incorporation onto the surface of ligands with affinity for complementary binding sites on native proteins. We present in this work a strategy for the covalent immobilization of glycosylated proteins previously adsorbed through weak, reversible interactions, on tailored SAMs. Boronic acids, which form cyclic esters with saccharides, are incorporated into SAMs to weakly adsorb the glycoprotein onto the electrode surface through their carbohydrate moiety. To prevent protein release from the electrode surface, we combine the affinity motif of boronates with the reactivity of epoxy groups to covalently link the protein to heterofunctional boronateepoxy SAMs. The principle underlying our strategy is the increased immobilization rate achieved by the weak interaction-induced proximity effect between slow reacting oxyrane groups in the SAM and nucleophilic residues from adsorbed proteins, which allows the formation of very stable covalent bonds. This approach is exemplified by the use of phenylboronates-oxyrane mixed monolayers as a reactive support and redoxenzyme horseradish peroxidase as glycoprotein for the preparation of peroxidase electrodes. Quartz crystal microbalance, atomic force microscopy, and electrochemical measurements are used to characterize these enzymatic electrodes. These epoxy-boronate functional monolayers are versatile, stable interfaces, ready to incorporate glycoproteins by incubation under mild conditions.

Research paper thumbnail of Permeability enhancement of electropolymerized thin organic films

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. © 1997 Elsevier Science S.A.

Research paper thumbnail of The preparation of size-controlled functionalized polymeric nanoparticles in micelles

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.

Research paper thumbnail of Application of polymeric nanoparticles for biocatalysis

Journal of Biotechnology, 2007

Nanoparticles offer major advantages for biocatalysis and biosensing applications. They present a... more Nanoparticles offer major advantages for biocatalysis and biosensing applications. They present a large surface area for immobilisation of a wide range of enzymes which can be accomplished in a gentle and efficient manner; enzyme attachment can either be within the particle matrix (biosilicate nanoparticles) on the particle surface (polymeric nanoparticles).

Research paper thumbnail of The nanoscale design of surfaces for building biosensors

Journal of Biotechnology, 2007

Research paper thumbnail of Synthesis and activity of nanosilicates and nanosilicate-entrapped enzymes using biomimetic polymers

Journal of Biotechnology, 2007

Research paper thumbnail of Novel one-pot synthesis and characterization of bioactive thiol-silicate nanoparticles for biocatalytic and biosensor applications

Nanotechnology, 2009

A novel one-pot neutral synthesis using bioinspired polymers to fabricate thiol-nanoparticles is ... more A novel one-pot neutral synthesis using bioinspired polymers to fabricate thiol-nanoparticles is presented. The thiol-particles may be directly tethered to metal surfaces such as gold, allowing the production of self-assembled nanostructured biocatalytic or biosensor surfaces. This one-pot method has also been used to entrap enzymes within the thiol-nanoparticles; it is apparent that once enzyme entrapment is carried out a bimodal distribution of particles is formed, with particles of one mode being very similar in size to thiol-nanoparticles without enzyme entrapped, and particles of the other mode being much larger in size. To this end, efforts have been made to separate the two modes of particles for the sample containing enzyme and it has been observed that the larger mode thiol-nanoparticles do indeed contain significant amounts of enzyme in comparison to the smaller mode ones. As the enzyme-containing thiol-nanoparticles can now be isolated, this means that there are many future possibilities for the use of thiol-particles containing enzyme, as they may be used in a wide range of processes and devices which require catalytic functionalized surfaces, such as biosensors and biocatalytic reactors.

Research paper thumbnail of Chapter 15 Ultrasensitive determination of pesticides via cholinesterase-based sensors for environmental analysis

Comprehensive Analytical Chemistry, 2007

The detection of many pesticides at extremely low levels can be best achieved not by direct detec... more 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.

Research paper thumbnail of Novel one-pot synthesis and characterization of bioactive thiol-silicate nanoparticles for biocatalytic and biosensor applications

Nanotechnology, 2009

A novel one-pot neutral synthesis using bioinspired polymers to fabricate thiol-nanoparticles is ... more A novel one-pot neutral synthesis using bioinspired polymers to fabricate thiol-nanoparticles is presented. The thiol-particles may be directly tethered to metal surfaces such as gold, allowing the production of self-assembled nanostructured biocatalytic or biosensor surfaces. This one-pot method has also been used to entrap enzymes within the thiol-nanoparticles; it is apparent that once enzyme entrapment is carried out a bimodal distribution of particles is formed, with particles of one mode being very similar in size to thiol-nanoparticles without enzyme entrapped, and particles of the other mode being much larger in size. To this end, efforts have been made to separate the two modes of particles for the sample containing enzyme and it has been observed that the larger mode thiol-nanoparticles do indeed contain significant amounts of enzyme in comparison to the smaller mode ones. As the enzyme-containing thiol-nanoparticles can now be isolated, this means that there are many future possibilities for the use of thiol-particles containing enzyme, as they may be used in a wide range of processes and devices which require catalytic functionalized surfaces, such as biosensors and biocatalytic reactors.

Research paper thumbnail of Labeless AC impedimetric antibody-based sensors with pg ml −1 sensitivities for point-of-care biomedical applications

Biosensors & Bioelectronics, 2009

This paper describes the development and characterisation of labeless immunosensors for (a) the c... more This paper describes the development and characterisation of labeless immunosensors for (a) the cardiac drug digoxin and (b) bovine serum albumin (BSA). Commercial screen-printed carbon electrodes were used as the basis for the sensors. Two methods were used to immobilise antibodies at the electrode surface. Aniline was electropolymerised onto these electrodes to form a thin planar film of conductive polyaniline; the polyaniline film was then utilised as a substrate to immobilise biotinylated anti-digoxin using a classical avidin-biotin affinity approach. As an alternative approach, poly(1,2-diaminobenzene) was electrodeposited onto the carbon electrodes and this modified surface was then sonochemically ablated to form an array of micropores. A second electropolymerisation step was then used to co-deposit conductive polyaniline along with antibodies for BSA within these pores to produce a microarray of polyaniline protrusions with diameters of several m, containing entrapped anti-BSA.

Research paper thumbnail of Immobilization of Peroxidase Glycoprotein on Gold Electrodes Modified with Mixed Epoxy-Boronic Acid Monolayers

Journal of The American Chemical Society, 2002

The development of bioelectronic enzyme applications requires the immobilization of active protei... more The development of bioelectronic enzyme applications requires the immobilization of active proteins onto solid or colloidal substrates such as gold. Coverage of the gold surface with alkanethiol selfassembled monolayers (SAMs) reduces nonspecific adsorption of proteins and also allows the incorporation onto the surface of ligands with affinity for complementary binding sites on native proteins. We present in this work a strategy for the covalent immobilization of glycosylated proteins previously adsorbed through weak, reversible interactions, on tailored SAMs. Boronic acids, which form cyclic esters with saccharides, are incorporated into SAMs to weakly adsorb the glycoprotein onto the electrode surface through their carbohydrate moiety. To prevent protein release from the electrode surface, we combine the affinity motif of boronates with the reactivity of epoxy groups to covalently link the protein to heterofunctional boronateepoxy SAMs. The principle underlying our strategy is the increased immobilization rate achieved by the weak interaction-induced proximity effect between slow reacting oxyrane groups in the SAM and nucleophilic residues from adsorbed proteins, which allows the formation of very stable covalent bonds. This approach is exemplified by the use of phenylboronates-oxyrane mixed monolayers as a reactive support and redoxenzyme horseradish peroxidase as glycoprotein for the preparation of peroxidase electrodes. Quartz crystal microbalance, atomic force microscopy, and electrochemical measurements are used to characterize these enzymatic electrodes. These epoxy-boronate functional monolayers are versatile, stable interfaces, ready to incorporate glycoproteins by incubation under mild conditions.

Research paper thumbnail of Permeability enhancement of electropolymerized thin organic films

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. © 1997 Elsevier Science S.A.