Gold Nanoparticles are subject of intense research as biomaterials for their combination of size-dependent properties, small size, flexible surface chemistry and plasmonic properties. One particular area of research in which they are promising, is the PhotoThermal Therapy (PTT). PTT relies on the ability of gold nanoparticles to efficiently absorb light at specific wavelengths thanks to their plasmonic resonance, and convert it to heat. This opened the possibility to generate large amounts of heat in very localized volumes and to use this localized heat to fight tumors without the systemic side effect of anti cancer drugs.

To be able to efficiently perform this photothermal therapy, the AuNP nanotherapeutics have to meet several criteria: absorb light that is transparent to tissues, concentrate at the tumor mass and recognize tumor cells. Other very important requirements are: to be water-dispersible, chemically stable, photothermally efficient, and biocompatible. 

The most common method for the synthesis of particles (the reduction with citrate salts) provide large amounts of gold particles, that are weakly functionalized on the surface and have poor stability in the physiological environment that is rich in salts and proteins. To overcome this drawback, capping agents are conjugated with the surface of the gold particles. One of the most commonly studied is CTAB, that unfortunately have a very poor biocompatibility. In this contribution I will present our most recent study in the utilization of keratin proteins for the functionalization of the gold nanoparticles. Keratin proteins are fibrous structural proteins that can be found in many animal tissues: hairs, feathers, claws, where their function is to provide mechanical strength. We used keratin proteins extracted from wool to functionalize the surface of gold particles, providing a biomimetic and biocompatible coating that preserve the efficient conversion of light into heat and provides an excellent stability of the particles in the physiological environment. We studied the optical properties of these functionalized nanoparticles in vitro and we tested their efficacy on glioma cell line (U87-MG).