Studies On The Os～(2+)/Os～(3+) Redox Polymer Thin Film Modifeid Electrodes And Their Applications In Biosensing

Osmium redox polymers with high electron diffusion coefficient play important roles in developing electrochemical sensors. It was reported that when osmium redox polymers were electroreduced, they were exchanged their inner-sphere chlorides with more strongly coordinating pyridine or imidazole groups on the polymer backbones, and were thereby irreversibly crosslinked onto the electrode surface. The resulting films can be extremely hydrophilic and exist as hydrogels whose open structure was permeable to the substrates and the products of the electrode reaction. Compared with the chemical crosslinking, electrodeposition took place faster and provided a better control on the sensor construction in a simple one-step procedure, especially when it was applied to microsensor construction.In this thesis, several amperometric sensors were fabricated by electrodepositing osmium redox polymers or osmium redox polymers and glucose oxidase(GOD) composite onto the electrodes. The electrochemical and electrocatalytic properties of these sensors were studied in detail as follows:(i) An osmium redox polymer, named PVI-PAA-dmeOs, was electrodeposited onto a gold electrode by applying repetitive double-potential step chronoamperometry. The resulting film conducted fast electron transfer and was permeable to the substrates as well as the products of the catalyzed reaction. The frequency variation during the potential step process was recorded using electrochemical quartz crystal microbalance (EQCM), and a reaction mechanism for electrochemical deposition of the osmium redox polymer was proposed. The characteristics of the PVI-PAA-dmeOs film were investigated by EQCM and cyclic voltammetry. It was shown that the hydrated osmium redox polymer film exhibited excellent electrocatalytic activity towards the oxidation of epinephrine. In contrast to that at a bare gold electrode, the oxidation current of epinephrine increased greatly and the oxidation peak potential negatively shifted to about 0.16 V (vs. Ag/AgCl) at the PVI-PAA-dmeOs film modified electrode. Under optimized conditions, amperometric measurements were performed at an applied potential of 0.18 V and a linear relationship with epinephrine concentration was obtained in the range from 5.10 -7 to 1 x 10 -4 mol L-1 with a limit of detection (LOD) of 1.5 x 10 -7 mol L-1 (S/N=3).(ii) A glucose biosensor based on the co-electrodeposition of PVI-PAA-Os, an osmium redox polymer, and glucose oxidase (GOD) on a gold electrode surface, was developed. In order to obtain a satisfactory PVI-PAA-Os/GOD composited film, the conditions of the electrodeposition were optimized. The PVI-PAA-Os/GOD composited film modified electrode exhibited the classical features of a kinetically fast redox couple bound to an electrode surface and the redox potential of the PVI-PAA-Os/GOD film was 0.14 V (vs. SCE). At scan rates up to 200 mV s"1, the peak-to-peak potential separation was less than 25 mV. In the presence of glucose, a typical catalytic oxidation current was observed, which reached a plateau at 0.23 V. Under the optimal experimental conditions, the steady-state electrooxidation current measured at 0.25 V was linear with the glucose concentration in the range of 0.1 - 30 mM, with a limit of detection (LOD) of 0.03 mM (S/N =3). The glucose response was further investigated with respect to the Michaelis-Menten kinetics of the biosensor. The apparent Michaelis constant of 16.55 mM and the maximum current density of 202.64 A cm2 were evaluated. This glucose sensor was successfully applied to the determination of glucose in blood samples.(iii) In this part, a glucose nanosensor based on the co-electrodeposition of PVI-PAA-Os and GOD on a low-noise carbon fiber nanoelectrodes (CFNE), was described for the determination of GOD. The SEM image showed that the PVI-PAA-Os/GOD composited film was uniform. The PVI-PAA-Os/GOD composited film modified CFNE exhibited the classical features of a kinetically fast redox couple bound to the electrode surface. In addition, a strong and stable electrocatalytic c...