Surface pressure and pH dependent structure and optical emission behaviors of protein (BSA) thin films

Abstract

Langmuir monolayers of Bovine serum albumin (BSA) are formed at the air-water interface nearly at (pH ≈ 5.0) and below (pH ≈ 4.0) the isoelectric point (pI ≈ 4.8) of BSA. The thin films are deposited on Si (001) substrates for different physiochemical conditions using Langmuir–Blodgett method. Photoluminescence spectroscopy is used to study the optical emission behavior of deposited BSA thin films. In-plane morphology and out-of-plane structure are obtained from the atomic force microscopy and X-ray reflectivity respectively from the deposited protein thin films. Below the isoelectric point of BSA, i.e., when BSA possesses some net surface charge, it exhibits reversible structural and optical emission behaviors. But at isoelectric point, i.e., when net surface charge on BSA is nearly zero the reversibility behaviour ceases.