Compact protein (bovine serum albumin/human serum albumin) layer under Langmuir-Blodgett deposition on hydrophilic Si (001) surface

Abstract

Langmuir monolayers of globular proteins (bovine serum albumin, i.e., BSA and human serum albumin, i.e., HSA) are formed on the water surface at pH ≈ 7.0, and compact protein layers are deposited on hydrophilic Si (001) surface using the Langmuir-Blodgett deposition method. Stability of these protein monolayers are studied from the normalized molecular area-time (A/A0-t) curves, which confirms that deposition over a long period of time is possible from both the protein monolayers. Compact bimolecular layered structure of the protein films are deposited on Si surface at higher surface pressure (17 mN/m) of the BSA and HSA monolayers, which is confirmed from the electron density profiles (EDPs) obtained from the analysis of the X-ray reflectivity data. Mostly the thickness of the molecular layers increases as the molecular tilting takes place and new molecules are deposited inside the vacant positions of the layer and as a result the electrons per unit area increases. EDPs obtained from the deposited BSA and HSA films also confirm that the increment in molecular tilting and electrons per unit area is protein specific. EDPs and surface morphology obtained from the atomic force microscopy images of the deposited films confirm that interrupted layer-by-layer or Frank-van der Merwe growth mode is followed in such protein multilayer deposition.