Layer-by-Layer Construction of Ultrathin Hybrid Films with Proteins and Clay Minerals

Abstract

Mono- and multilayered clay mineral−protein films were constructed with the layer-by-layer deposition technique. The clay mineral saponite and three proteins (protamine, lysozyme, and papain) were tested. Multilayers with up to 15−15 alternating layers of saponite and protein were built up on glass, quartz, and ZnSe. In some cases these supports were primed with the poly(diallyldimethylammonium) cation before clay/protein deposition. The deposition process can be followed by UV and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and by atomic force microscopy (AFM). X-ray diffraction (XRD) patterns confirm the regular ordering of the layers. The “average” protein layer has the thickness of single molecules. The thickness of the “average” saponite layer is proportional to the positive charge density of the protein and varies between 0.6 and 3 elementary saponite sheets. The layers of protamine and lysozyme are stable. However, a small amount of papain is lost upon deposition of the subsequent saponite layer. H−D exchange of proteins in the films is fast and reversible.