Effect of oxidation level of n+-type mesoporous silicon surface on the adsorption and the catalytic activity of Candida rugosa lipase

Abstract

In this work, we present the synthesis and characterization of n +-type porous silicon (PSi) layers. Our final aim is the fabrication of a biosensor that exploits the semiconductive properties of this material. PSi wafers were used as a matrix for enzyme adsorption. These wafers, as a result of their porous nanostructure, had a high surface area (360 m 2/g) and pore size in the range 5–20 nm. The freshly prepared PSi was stabilized through controlled anodic oxidation. Two classes of samples differing for the level of oxidation were prepared. The first class was oxidized up to 2 V (LO-PSi), whereas the second class was oxidized up to 10 V (HO-PSi). Both samples were used for the adsorption of Candida rugosa lipase. A significantly higher loading was ascertained for LO-PSi (140 mg/g) compared to HO-PSi (47 mg/g). The different hydrophobic–hydrophilic balance of the PSi surfaces induced by the different oxidation voltage affects the physical interactions that address the adsorption process of the lipase. The higher loading achieved with the LO-PSi resulted in a higher activity of the immobilized biocatalyst but in a lower catalytic efficiency. The two biocatalysts showed an acceptable stability toward storage (pH 5 buffer solution at 5 °C) within 2 weeks.