Facile preparation of Langmuir–Blodgett films of water-soluble proteins and hybrid protein–clay films

Water-soluble protein monolayers have been prepared by spreading protein (lysozyme (Lys) and bovine serum albumin (BSA)) aqueous solutions over water and diluted clay (saponite) dispersions in a Langmuir–Blodgett (LB) trough. LB films of protein and hybrid protein–clay were prepared by vertical upstroke deposition at a desired surface pressure. Surface pressure–time (π–t) curves and surface pressure–area isotherms (π–A) indicate that the equilibrium time between the injection and compression plays an important role in forming a protein monolayer. Atomic force microscopy (AFM) suggests that heterogeneous films, consisting of regions of protein clusters and regions of saponite layers covered with protein clusters, are obtained. Both lysozyme and BSA accumulate particularly well at the edges of the saponite layers. The main difference is that the positively charged lysozyme is much more efficient in attracting negatively charged saponite layers at the air–water interface. The amount of lysozyme immobilized (nS) is 0.2–0.4 ng mm−2 for the water–lysozyme film and 0.5–0.6 ng mm−2 for the saponite–lysozyme film, as determined using UV-Vis spectroscopy. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the presence of clay and proteins in the hybrid LB films. No significant change in the position of amide I or II bands was observed, suggesting little or no conformational changes upon immobilization of the proteins.