Improvements of silicon integrated GOx micro enzyme reactors by the use of porous silicon as a surface enlarging matrix

Micro flow-through cells were fabricated in silicon and were designed to work as micro enzyme reactors (columns) for glucose monitoring. The reactor design comprised a parallel channel structure with 32 channels, 50 μm wide. A reactor with vertical channels yields a much larger surface area than a corresponding v-groove channel structure. Therefore, (110) silicon was used to allow the fabrication of channels with vertical walls (channel depth was 250 μm). Glucose oxidase (GOx) can be immobilized to the silicon surface and earlier measurements have shown that the increase in enzyme activity corresponded to the surface area increase of such a channel structure. A new approach to surface enlargement was investigated. Planar silicon surfaces were anodised in an HF/ethanol etchant, yielding a spongious nanoporous silicon surface. Dice with three different porosities were fabricated and GOx was coupled to the porous dice. The increase in enzyme activity due to surface enlargement of the nanoporous structure was 33 times compared to a planar surface. The two surface enlarging strategies (vertical channel reactors and porous silicon) were subsequently combined, giving a parallel vertical channel structure covered by a porous silicon layer. This reactor structure displayed an enzyme activity increase of 100 times when compared to a non-porous channel structure