Use of Electrochemically Machined Porous Silicon to Trap Protein Molecule

Silicon surface chemistry is crucial to allow access to technologically interesting thin films not only for electronic industries but also for biological applications. Silicon wafers were etched electrochemically using ethanolic HF solution under different current densities (143 to 714 mA.cm-2) while etching time was adjusted to obtain a constant charge of 4.5 C.cm-2 to generate pores of different sizes (50 to 1500 nm). Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) studies revealed the properties of porous layer such as pore distribution, diameter, geometric shape of the pores, which depend upon HF concentration, current density during electrochemical etching, temperature etc. Stability of the porous silicon wafer was achieved by thermal oxidation. In this study, attempted were made to determine whether porous silicon can be used to bind protein reversibly. Admittance and visualization of the protein (i.e. Bovine serum albumin) adsorption in pH gated admission experiments were determined by atomic force microscopy. It was observed that the 66 kDa BSA protein (~15 nm diameter) when positively charged (i.e. with citrate buffer, pH 4) would evenly coat the negatively charged surface of an oxidized porous silicon. The bound protein could be eluted under conditions that imparted a net negative charge on bound BSA (i.e., with phosphate buffered saline, pH 7). Thus, the electrochemically machined porous silicon can be used as molecular sieve to trap protein molecule, which could allow the in vitro study of protein-protein interactions.