Improved performance in silicon enzyme microreactors obtained by homogeneous porous silicon carrier matrix

The catalytic performance of porous silicon (PS) micro enzyme reactors (μIMER) is strongly dependent on the PS matrix morphology for enzyme immobilisation. PS was achieved in the μIMER by anodisation in a HF–ethanol mixture. PS etching of structured silicon surfaces commonly results in an inhomogeneous pore formation. The deep channel microreactors described herein have previously suffered from these phenomena, yielding non-optimised μIMERs. In order to obtain a homogeneous PS layer on the deep microreactor channel walls, different reactor geometries (channel wall thicknesses of 50 and 75 μm) were anodised at 10 and 50 mA cm−2 for anodisation times ranging between 0 and 50 min. The μIMERs were evaluated by immobilising two types of enzymes, glucose oxidase (GOx) and trypsin, and the resulting catalytic turnover was monitored by a colorimetric assay. It was found that reactors with a homogeneous PS matrix displayed improved performance. The trypsin μIMERs were used to digest a protein, β-casein, in an on-line format and the digest was analysed by MALDI-TOF MS. The importance of tailoring the μIMER geometry and the PS-matrix is crucial for the protein digestion. Successful protein identification after only 12 s. digestion was demonstrated for the best reactor, 75 μm channel wall, 25 μm channel width, anodised at 50 mA cm−2 for 10 min.