Novel Polythiophenes for Biosensor Applications

The development of an enzyme biosensor employing a novel functionalised polythiophene matrix is presented. The research upon conducting polymer platforms for biological immobilisation is extensive but by no means exhaustive and therefore
this investigation contributes to the field of glucose detection with covalently immobilised glucose oxidase upon novel copolymers of N-succinimido thiophene-3- acetate/3-methylthiophene (STA-MT), trans-3-(3-thienyl) acetic acid/3- methylthiophene (TTA-MT) and N-succinimido trans-3-(3-thienyl) acetate/3-
methylthiophene STTA-MT.

Polymer characterisation was performed using electrochemical techniques, primarily cyclic voltammetry. The examination of various substituted conducting polymers from the polythiophene family was performed where 3-methylthiophene was selected for copolymerisation due to its low oxidation potential and redox behaviour. Copolymerisation of the novel monomers provided reversible and stable films and succeeded in generating a range of copolymer ratios characterised by cyclic
voltammetry with the available binding sites calculated using SEM-EDX. Film morphology and dopant intercalation were investigated, providing supporting evidence for the successful copolymerisation of novel monomers with 3-
methylthiophene.

Optimisation of the biosensor format was investigated through analysis of film thickness, copolymer ratio and enzyme immobilisation time. A film thickness generated with 50 mC provided a stable film with good response to glucose over a
wide range of immobilisation times and was employed for all other biosensor investigations. A 10% functional monomer content provided enhanced current signals upon glucose addition which supported the findings of Kuwahara et al where a 10% thiophene-3-acetic acid content within a thiophene-3-acetic acid/3-methylthiophene
copolymer demonstrated enhanced biosensor behaviour. All studies were compared against the thiophene-3-acetic acid and 3-methylthiophene system generated under the optimised conditions of the novel copolymer films.

The evaluation of the immobilised glucose oxidase as an amperometric biosensor within a mediated system employing p-benzoquinone was performed generating fast response times within 4 seconds, good stability and excellent current response to
glucose between 1.4 and 1.9 mA/cm2 after the addition of 15 mM of glucose. All three novel biosensor systems exhibit good analytical performance demonstrating excellent repeatability typically over 90%, reproducibility of over 80% and shelf-life stability of 85-96% over a seven day analysis and between 50-78% after 1 month.