Amperometric biosensors based on conducting nanotubes
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[S.l. : s.n.]
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This thesis describes a multidisciplinary study towards the development of a glucose biosensor that in the future can be used for in vivo implantations. The research focuses on three major topics, viz. the construction of the glucose sensor, the development of a biocompatible coating and a study of the factors influencing the in vivo behaviour of implanted biosensors. The first part of this thesis describes the construction of an amperometric glucose sensor based on the enzyme glucose oxidase, which is immobilized inside the pores of a track-etch membrane. In these pores polypyrrole or poly(3,4-ethylenedioxythiophene) (PEDOT) has been chemically deposited to yield hollow conducting tubules. It is shown that glucose oxidase can be immobilized inside these conducting microtubules while retaining its catalytic activity. The immobilization is based on electrostatic interactions between the positively charged polypyrrole and the negatively charged biomacromolecule, and on the complementary dimensions of the corrugated interior of the pores and those of glucose oxidase. Glucose is detected amperometrically by applying a potential to the membrane and upon oxidation of this analyte by the enzyme a current is observed. In this way a sensor configuration is obtained that can be used to continuously measure glucose over a long period of time. For this sensor a mechanism of direct electron transfer between the active site of glucose oxidase and the conducting polymer is proposed. The second topic described in this thesis concerns the synthesis and in vitro testing of two types of biocompatible coatings. Hybrid silica based sol-gel materials are shown to be excellent in vitro and in vivo biocompatible coatings. A second series of coatings is based on polystyrenes bearing pendant tetraethylene glycol and phosphorylcholine groups. Cell culture assays have shown that these copolymers are biocompatible as well and that the composition of the polymers has an effect on their cell proliferation properties. The factors influencing in vivo glucose measurements in general are investigated in the last part of this thesis
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