The aim of the project is to develop a method for monitoring CH4, phenolic vapours and toxic vapours in the gas phase in the environment.
To demonstrate the principle of electrochemical gas phase biosensors, polyphenol oxidase (PPO) was selected as a potential biological component for the detection of phenol vapours. PPO can oxidise a number of phenolic compounds to the corresponding catechol intermediate and then to the electroactive quinone product which is subsequently detected at an electrode poised at a suitable cathodic potential. The enzyme is incorporated in the appropriate support medium and tested in the presence of phenol vapours. The electrochemical and biocompatibility properties of a range of support materials such as Nafion polymer films, hydroxyethyl cellulose and tetrabutyl ammonium toluene-4-sulphonate gels (TBATS) have been investigated.
Sensors are exposed to low concentrations of phenol vapours by exposing them to the vapour above aqueous phenol solutions of known concentrations. A calibration curve showing the relationship between concentration of phenol in the aqueous phase and the vapour phase has been prepared and used to establish a range of known phenol vapour concentrations.
A method for measurement of sulphur dioxide is under development based on its dissolution in water (buffer) to form sulphite ions which are enzymatically oxidized by sulphite oxidase. A critical factor for the determination of sulphur dioxide is dissolution of the gas in the biomatrix. The following key properties of a range of hydrogel materials have been investigated: water retention capacity, conductivity and ability to support electrochemistry.
Methane monooxygenase (MMO) from the organism Methylosinus trichosporium OB3b has been evaluated with respect to stability as the biological component for incorporation in a methane sensor. MMO activity was determined using the propene epoxidation assay, with gas chromatography analysis of the products. It was established that the enzyme was extremely unstable, even in intact cells. An alternative approach to methane sensing, the use of chemical mimics of MMO, is currently being investigated.
Thick film fabrication of microelectrodes has been achieved using screen printing techniques. Interdigitated arrays of gold microband electrodes were produced with a line width 100 um and with a separation ratio of 2:1. Using voltammetric techniques, reversible electrochemistry of potassium hexacyanoferrate (II) has been observed at fabricated electrodes. At low scan rates (1 m V/second, current voltage curves approaching non peaked curves were obtained. Non peaked current voltage curves indicate rapid diffusion of redox species to the edges of the electrode. Work is being carried out towards reducing the size of the fabricated electrodes.
In order to achieve the above goal the interaction between a biological component and a specific gas will be monitored electrochemically, using a microelectrode. The biological component will be immobilised onto a solid electrolyte which will coat the microelectrode. The resulting microbiosensor will utilise the advantages of biosensors (specificity and low detection limits) as well as the advantages of microelectrodes (low iR drop, fast responses and miniaturisation).
The project will be divided into three parts: Firstly the fabrication of microelectrodes using thick film technology; secondly the selection of suitable biological components, that interact specifically with CH4, phenolic vapours and toxicity agents, and matching alternative electrolyte media; and thirdly the immobilisation of the biological component on the electrolyte.
Funding SchemeCSC - Cost-sharing contracts
PO6 1SZ Portsmouth
MK43 0AL Cranfield