Tailoring of Porous Silicon Morphology in Chip Integrated Bioreactors

The influence of the carrier matrix depth and homogeneity was investigated for porous silicon enzyme bioreactors. For the experiments 〈110〉 oriented silicon, p-type (20–70 Ωcm), was used. Porous silicon was generated on planar surfaces and on anisotropically pre-etched high aspect ratio parallel channel reactors. Samples were prepared with three depths, controlled by the anodisation time, and two current densities yielding different morphologies. In a second study, in order to make the porous layer more homogeneous, reactors were fabricated with different channel widths and wall thickness. Glucose oxidase (GOx) was immobilised onto the porous matrix following standard procedures for immobilisation of enzyme to silica. The enzyme activity of the samples was monitored following a colourimetric assay. The results clearly display the influence of the matrix depth for both the planar and the reactor structures. An 170-fold increase in catalytic turn-over, when compared to an identical non-porous reference, was recorded for a reactor with an average porous depth of 10 μm. The importance of a homogeneous porous layer was illustrated, giving an increase in catalytic performance of three times between different structures with the same geometric area prior to anodisation.