The Formation and Characterisation of a Polypyrrole Based Sensor for the Detection of Urea

This thesis originates with the development and characterisation of polypyrrole (PPy), formed in the presence of a large protein, bovine serum albumin (BSA). The BSA was incorporated into the polymer film during electropolymerisation from an aqueous solution of pyrrole monomer, BSA and NaCl as a supporting electrolyte. The presence of the BSA within the polymer film was confirmed using cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy (SEM) coupled with electron dispersive X-Ray analysis (EDX). Optimum conditions for the growth of the polypyrrole-bovine serum albumin film (PPy-BSA) were obtained by varying the concentration of the monomer and BSA, the applied potential and the polymerisation charge. Highly adherent polymers were formed at 0.70 V vs. SCE in a 0.10 mol dm-3 NaCl supporting electrolyte with high concentrations of pyrrole (0.5 mol dm-3) and low concentrations of BSA (< 200 μL). The presence of the BSA within the polymer film greatly reduced the electroactivity of the film. The urease enzyme was also immobilised in the polypyrrole film. The modified polypyrrole film was formed at 0.70 V vs. SCE from an aqueous solution of pyrrole and urease (4000 mg dm-3) in the presence of 0.10 mol dm-3 NaCl as a supporting electrolyte. The presence of urease within the polypyrrole-urease (PPy-Urs-Cl) film was confirmed using SEM and EDX and the PPy-Urs-Cl was then investigated as a sensing material for urea. The PPy-Urs-Cl film exhibited a reasonable sensitivity towards urea of 5.41 μC μM-1 in the 1.0 x 10-5 to 1.0 x 10-3 mol dm-3 urea concentration range. Sulphonated-β-cyclodextrin (SCD) was then incorporated into the polymer to give a PPy-Urs-SCD film. This PPy-Urs-SCD polymer film was investigated as a sensing material for urea in a phosphate buffer solution. It was found that the SCD dopant greatly enhanced the detection of urea, with detection of urea in the 1.0 x 10-10 mol dm-3 region and a sensitivity of 46.09 μC μM-1. A wide variety of interfering compounds was examined to establish their effect, if any, on the detection of urea using the modified PPy-Urs-SCD. The interference from the common biological interfering compound, ascorbic acid, was effectively blocked and no interference was observed in the presence of common salts, such as ammonium chloride. Interference was observed in the presence of uric acid, hydroxyurea, thiourea and creatinine. The urease enzyme and the SCD are large, giving rise to porous PPy-Urs-SCD films and this allows access of the interfering compounds to the electrode surface. However, this interference was reduced by depositing a layer of the more compact PPy-Urs-Cl followed by the PPy-Urs-SCD film. A detailed investigation into the host-guest complexation properties of SCD with urea, and the interfering compounds, was performed using cyclic voltammetry. Clear evidence for complexation between SCD as the host molecule and urea as the guest molecule was obtained, which accounts for the high sensitivity in the detection of urea. No inclusion complex was formed between urea and the α-SCD or between SCD and the interfering compounds