POROUS SILICON AS THE CARRIER MATRIX IN MICROSTRUCTURED ENZYME REACTORS YIELDING HIGH ENZYME-ACTIVITIES

Miniaturization and silicon integration of micro enzyme reactors for a pplications in micro total analysis systems (mu TASs) require new meth ods to achieve structures with a large surface area onto which the enz yme can be coupled. This paper describes a method to accomplish a high ly efficient silicon microstructured enzyme reactor utilizing porous s ilicon as the carrier matrix. The enzyme activity of microreactors wit h a porous layer was recorded and compared with a microreactor without the porous layer. The microreactors were fabricated as flow-through c ells comprising 32 channels, 50 mu m wide, spaced 50 mu m apart and 25 0 mu m deep micromachined in [110] oriented silicon, p type (20-70 Ome ga cm), by anisotropic wet etching. The overall dimension of the micro reactors was 13.1 x 3.15 mm. To make the porous silicon layer, the rea ctor structures were anodized in a solution of hydrofluoric acid and e thanol. In order to evaluate the surface enlarging effect of different pore morphologies, the anodization was performed at three different c urrent densities, 10, 50 and 100 mA cm(-2). Glucose oxidase was immobi lized onto the three porous microreactors and a non-porous reference r eactor. The enzyme activity of the reactors was monitored following a colorimetric assay. To evaluate the glucose monitoring capabilities, t he reactor anodized at 50 mA cm(-2) was connected to an FIA system for glucose monitoring. The system displayed a linear response of glucose up to 15 mM using an injection volume of 0.5 mu l. The result from th e studies of glucose turn-over rate clearly demonstrates the potential of porous silicon as a surface enlarging matrix for micro enzyme reac tors. An increase in enzyme activity by a factor of 100, compared to t he non-porous reference, was achieved for the reactor anodized at 50 m A cm(-2).