Bovine serum albumin adsorption on functionalized porous silicon surfaces

Abstract

Recently, the development of Si-based optical sensors for protein and other biochemicals has become of great interest. Here, we examine the protein and Si-based substrate interaction by studying the BSA interaction with surface derivatized porous Si (pSi). The pSi fabricated through electrochemical anodization of crystalline silicon in hydrofluoric acid showed an average pore diameter of ~ 10 nm. Chemically functionalization of pSi by thermal reaction with undecylenic acid produced an organic monolayer covalently attached to the silicon surfaces. Bovine serum albumin (BSA) was then adsorbed onto the acid-terminated pSi surfaces. The resulting surfaces were characterized using scanning electron microscopy (SEM), ellipsometry and Fourier transform infrared spectroscopy (FTIR). Ellipsometry and SEM both showed that the BSA molecule penetrated more than 1 μm into the porous structure. SEM further revealed the damaged and partially lifted-off porous film from the silicon substrate after a prolonged BSA adsorption. It is caused by the BSA penetrating deep into the porous structure and anchoring itself tightly through strong electrostatic interaction with the acid-covered pSi sidewalls. A change in surface tension during BSA film formation then causes the pSi layer to buckle and lift-off from the underlying Si substrate. FTIR results from the undecylenic acid-modified pSi surfaces after BSA adsorption showed strong characteristic Amide I, II and III vibrational bands. The role of the surface chemistry, wetting properties, substrate porosity and topography will be discussed.