Influence of self-assembled monolayer surface chemistry on Candida antarctica lipase B adsorption and specific activity

Immobilization of Candida antarctica B lipase was examined on gold surfaces modified with either methyl- or hydroxyl-terminated selfassembled alkylthiol monolayers (SAMs), representing hydrophobic and hydrophilic surfaces, respectively. Lipase adsorption was monitored gravimetrically using a quartz crystal microbalance. Lipase activity was determined colorimetrically by following p-nitrophenol propionate hydrolysis. Adsorbed lipase topography was examined by atomic force microscopy. The extent of lipase adsorption was nearly identical on either surface (approximately 240 ng cm−2), but its specific activity was sixfold higher on the methyl-terminated SAM, showing no activity loss upon immobilization. A uniform, 5.5 nm high, highly packed monolayer of CALB formed on the methyl-terminated SAM, while the adsorbed protein was disordered on the hydroxyl-terminated SAM. Hydrophobic surfaces thus may specifically orient the lipase in a highly active state.