Proteins in nature are employed for an extremely broad variety of functions: structural components, enzymes, motions, factories in the cells, carriers. This wide variety of behavior arises from the variety of functionalities of the amino acids building the different proteins. Historically humans have used some of these proteins as materials: keratins and fibroin have been used for millennia as source of textile. In recent years, proteins became very attractive as functional biomaterials, in particular as a biopolymers for biomedical applications: fibroins and keratins, extracted from different sources, were used to create scaffolds and drug delivery platforms. Even more recently silk fibroin was studied as a platform to interface technologies like optics and electronic with the biological environment. In this contribution, we will focus on the use of keratins extracted from wool for the development of functional nanocomposites.
Keratins are a family of proteins found in nature as the main structural component of many different tissues: feathers, cornea, and hair just to name the more represented ones. The key feature of keratin that we look to explore is the presence of all the most important organic functionalities: carboxyl groups, amino groups, alcohols, aldehydes, thiols. In our experiments, keratin was extracted from wool fibers. Films of keratin were obtained by simple casting and were used as a tool to characterize the functional properties of keratin-based nanocomposites.
The free thiols group generated during the extraction process were exploited for the reduction of gold salts and, upon formation of a film, for the in-situ synthesis of gold nanoparticles embedded and bound to the protein matrix.
Inorganic nanocrystals were successfully bound to the keratin matrix by a simple ligand exchange process from an organic dispersion of nanocrystals. Furthermore films of keratin an quantum dots with high QD filling factor and strong fluorescence were obtained, showing that keratin can be a promising material for optical applications as well.