The synthesis of novel polythiophene and investigation of their physio-chemical and biosensor properties
Poly(3-alkylthiophene)s (P3ATs) are considered to be an important class of electro chromic materials because of their reasonably high solubility, convenient processability and environmental stability. The adhesion of electrochromic polymers coated on a conducting substrate is a significant factor affecting the durable colour-changing life of electro chromic devices, Traditional electrochromic coatings on indium-tin oxide (ITO) glass electrodes have poor lifetimes due to the incompatibility between polymers and inorganic substrates. However, providing a bonding network between organic electrochromics and ITO glass is an efficient method to increase the adhesion and also extend the service life, and this research used Suzuki-Miyaura coupling ofN¬(3-methoxysilylpropyl)pyrrole (3TPP) onto poly(3-hexylthiophene) (P3HT) as a precursor of the sol-gel reaction. The Si-O-Metal network produced between the siloxane groups and the metal oxide after the sol-gel reaction served to enhance the adhesion of the poly(3-hexyIthiophene) onto ITO glass. With this stronger bonding, the colour-changing service life was found to be extended considerably by the observation of repeated colour-changing tests over a period of time. In addition, the electro-optic and electrochemical properties of copolymers with various substituted molar ratios of 3TPP on P3HT were investigated by cyclic voltammetry and UV -visible spectroscopy. The 1t 1t* transition energy ofP3HT was augmented by increasing the degree of bromo-substitution and diminished again after substituting with 3TPP. Hysteresis in the electro chromic switching was more noticeable with increased bromo-substitution on the P3HT, but it decreased when 3TPP was attached to the thiophene rings. The concentration of urea in serum samples is used to monitor diabetes and also to indicate the onset of kidney failure and liver malfunction, A potentiometric biosensor was found to be a convenient detector to quantify the urea concentration, because of the clear rest potential variation when urea hydrolysed by urease (Urs) resulted in a p[OHl change in the analyte. Other workers have investigated the immobilisation of enzymes on polypyrroles due to their high biocompatibility. However, ope of the drawbacks can be the uneven surface of polypyrrole film, which may cause the detection to be insensitive. In this project, the copolymer poly«3-hexyIthiophene)-co-(3- thiopheneacetic acid)) (P(3HT-co-3TAA)) was synthesised via iron (III) chloride polymerisation, and characterised by IH-NMR and FT-IR spectrometry, Urease was immobilised on the smooth surface of this copolymer via a carbodiimide coupling reaction provided by N-(3-dimethylaminopropyl)-N' -ethyl-carbodiimidehydrochloride (EDC) and N-hydroxysuccinimide (NHS). The electrochemical behaviour of Urs/P(3HT-co-3TAA)/ITO glass electrode was investigated by cyclic voltammetry. The enzyme activity of Urs/P(3HT-co-3TAA)/ITO glass electrode was confirmed by spectrophotometric assay. Potentiometric response studies also indicated this electrode could detect the concentration of urea in aqueous solution at a level of approximately 5 millimoles (mM).