Biomineralization of gold nanoparticles by lysozyme and cytochrome C and their applications in protein film formation.

Lysozyme (Lys) and cytochrome c (Cyc,c) proteins were used as mild reducing and stabilizing agents to synthesize gold nanoparticles (NPs) at precisely 40 and 80 degrees C. All reactions were monitored simultaneously by UV-visible measurements to determine changes in the nature of the protein during the course of reaction. The synthesis of Au NPs caused the simultaneous denaturation of protein due to the formation of bioconjugate NPs, and the denaturation temperature decreased with the number of NPs. Lys entrapped NPs in a typical gel state, and Cyc,c carried them on well-defined micelles at 80 degrees C or in the form of long fibrils or strands at 40 degrees C. The shape, size, and arrangement of bioconjugate NPs were characterized by atomic force microscopy and transmission electron microscopy measurements. Purified bioconjugate NPs were further used in zein protein film formation. The resulting films were characterized by photophysical and mechanical measurements. The induction of bioconjugate NPs made protein films isotropic and relatively more brittle (with a greater effect for Cyc,c than for Lys conjugate NPs) than in their absence and was considered to be well suited for biomedical applications.