Enhanced enzyme activity in silicon integrated enzyme reactors utilizing porous silicon as the coupling matrix

The performance of porous silicon as a coupling matrix for silicon integrated enzyme reactors has been investigated. A porous silicon layer in a wafer is expected to yield an increased catalytic activity when coupling an enzyme to the wafer due to the surface enlargement of the porous structure. The porous silicon layer is obtained by anodizing a 1 cm x 1 cm silicon die in a hydrofluoric acid/ethanol mixture at a constant current density of 10, 50 or 100 mA cm(-2) for 50 min. Glucose oxidase is immobilized on the porous matrix of three dice and the enzyme activity of the silicon samples is monitored using a colorimetric assay. As a reference sample a polished die is also submitted to the enzyme immobilization. The three porous dice display higher glucose turn-over rates than the unetched reference die. Samples etched at lower current densities show increased turn-over rates. The maximum rise in turn-over rate is more than 30 times for the 10 mA cm(-2) sample compared with the reference die. Porous silicon has the potential of being incorporated in a micro total analysis system (mu TAS) to give highly efficient enzyme reactors.