Pore morphology influence on catalytic turn-over for enzyme activated porous silicon matrices

Abstract

The enzyme glucose oxidase (GOx) was coupled to porous silicon of different morphologies and the catalytic turn-over of glucose was recorded for the samples. The recorded catalytic turn-over of the samples clearly indicated the influence of morphology, with respect to dopant concentration and current density, of the porous silicon carrier matrix. The highest rise in catalytic turn-over (350 times), when compared to a non-porous surface, was recorded for a sample with an n-type epilayer on an n+-type substrate anodised at 100 mA/cm2. A storage and operational stability measurement was performed on the sample showing the highest catalytic efficiency. After 5 months of refrigerated storage a 2% loss of activity was noted, and after 4 days of constant glucose load (0.5 mM) a 56% loss of activity was recorded. A BET (Brunauer, Emmet, and Teller) nitrogen adsorption analysis was performed on one of the substrate types, p+-type (0.001–0.025 Ω cm). In spite of the fine porous morphology with a high surface area the recorded enzyme activities were moderate. The pore morphology achieved on this substrate most likely comprised too small pores in a too dense porous matrix giving poor diffusion conditions to give efficient access for the enzyme during the coupling procedure and for the reactant transport during operation to fully utilise the surface enlargement of the porous layer.