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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Self Assembly for Surface Functionalisation to improve biocompatibilities in Ti-based implants and Enzyme immobilisation of Biofuel cells.

Author: GU, Qiong

Year: 2010

Supervisor(s): Xiao Guo

A systematic investigation was carried out to optimize the self-assembly of an APTES-modified film on an oxidized titanium surface in order to improve its biocompatibility as an implant material and molecular selectivity, e.g. for CO2 capture. A clean TiOx layer was formed on titanium after the treatment in a Piranha solution of H2SO4 : H2O2 = 3:1. The IR spectra confirmed that the formation of the APTES-modified film (called APS film) on the surface by the presence of the Si-O-Ti and Si-O-Si covalent bonds. The ordering of the self-assembled film did not show strong temperature dependence from 30 to 70°C, although a thicker film was noted at a higher temperature. Anhydrous toluene as the solvent is essential to the formation of a well-ordered and thin film, compared with hydrous toluene. The well-assembled film was formed on the oxidised titanium surface in the anhydrous toluene solution of ~0.2 v% APTES at 30°C for 16 hours.

In the application of biofuel cells, the laccase from Trametes versicolor was immobilized on titanium and graphite with the APS film by the covalent bond, respectively. Compared with the native laccase, optimum pH of the immobilized laccase decreased to 3 because of the increase of turnover number (Kcat). Further comparison of Michaelis-Menten constant (Km) of the immobilized laccase with the native one clearly shows that the increase of Km value is mainly due to the change of configuration of the active site, further leading to the lower affinity of immobilized laccase towards the substrate. The laccase on graphite shows higher optimum temperature and twice lower the Km value, compared with the laccase on titanium, which results from the surface morphology of graphite after oxidation.