Porous silicon as the carrier matrix in microstructured enzyme reactors yielding high enzyme activities

Abstract

Miniaturization and silicon integration of micro enzyme reactors for applications in micro total analysis systems (µTASs) require new methods to achieve structures with a large surface area onto which the enzyme can be coupled. This paper describes a method to accomplish a highly efficient silicon microstructured enzyme reactor utilizing porous silicon as the carrier matrix. The enzyme activity of microreactors with a porous layer was recorded and compared with a microreactor without the porous layer. The microreactors were fabricated as flow-through cells comprising 32 channels, 50 µm wide, spaced 50 µm apart and 250 µm deep micromachined in 110 oriented silicon, p type (20-70 cm), by anisotropic wet etching. The overall dimension of the microreactors was 13.1 × 3.15 mm. To make the porous silicon layer, the reactor structures were anodized in a solution of hydrofluoric acid and ethanol. In order to evaluate the surface enlarging effect of different pore morphologies, the anodization was performed at three different current densities, 10, 50 and 100 mA cm −2. Glucose oxidase was immobilized onto the three porous microreactors and a non-porous reference reactor. The enzyme activity of the reactors was monitored following a colorimetric assay. To evaluate the glucose monitoring capabilities, the 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 µl. The result from the studies of glucose turnover rate clearly demonstrates the potential of porous silicon as a surface enlarging matrix for micro enzyme reactors. An increase in enzyme activity by a factor of 100, compared to the non-porous reference, was achieved for the reactor anodized at 50 mA cm −2 .

Vapor-phase silanization of oxidized porous silicon for stabilizing composition and photoluminescence

“…4 The roomtemperature luminescence, which has been observed from PSi usually formed in a concentrated HF based electrolyte by Canham 5 in 1990, has attracted considerable attention because of its potential use in the development of silicon-based optoelectronic devices, 6 such as electroluminescent displays 7 and photodetector. 8 The porous structure and a relatively large surface area have also made the silicon an ideal matrix for immobilization of a variety of biomolecules including enzymes, 9 DNA fragments, 10 and antibodies. 11 The electronic or optical properties of porous silicon can also be used as the transducer of biomolecular interactions, thus qualifying its utility in biosensor applications.…”

New concepts of integrated photonic biosensors based on porous silicon

“…These molecules have two functional groups: one reacting with the material and one reacting with the biomolecules to be immobilized. PSi has already been used as a large surface area matrix for immobilization of different kinds of biomolecules including enzymes (Drott et al, 1997), DNA fragments and antibodies (Betty, 2009). Chemical functionalization of PSi can either involve the native Si-H terminated surfaces or the Si-O bond resulting from PSi oxidation.…”

The Quest for High-Speed and Low-Volume Bioanalysis

“…Examples of this have been demonstrated in highly efficient open-tubular micro-enzyme reactors fabricated in monocrystalline silicon (34). The surface of the reactor channel wall was electrochemically made porous by a network of micro-and nanoscale pores that provide a vastly increased surface area for enzymes ( Figure 2).…”