Gold nanorods as new metasurfaces for biomedical applications (COMUNICATION)

Because of their peculiar optical and electronic characteristics, gold nanorods (GNRs) have been widely studied for applications in plasmon-enhanced spectroscopy, photonics, therapeutics, chemical sensing and bioimaging. We address the effect of small thiols on the thermal and photostability of gold nanorods. As-synthesized colloids were treated with mixtures of thiolated polyethylene glycol and methylbenzenethiol. We found that small thiols dramatically enhance the thermal stability of gold nanorods. For instance, after 1 h at 90 °C samples with pure PEG lost more than 70% of optical absorbance at their initial peak position, while particles coated with a thicker layer of methylbenzenethiol remained nearly unchanged. We ascribe this effect to a modulation of the activation barrier for surface diffusion of gold atoms. Our findings will help researchers design novel tags that overcome the limitations related to thermal and photoinstabilities in a broad variety of applicative contexts. Thanks to roughness, a major photoacoustic conversion is achieved because of the larger surface. However, this feature is at the expense of the photostability, and because of the high mobility of gold atoms when heated, they tend to move back forming a straight surface. We disclose the use of hybrid materials featuring Au/Ag core/shell nanorods in porous chitosan/polyvinyl alcohol scaffolds for applications in tissue engineering and wound healing. The combination of Au and Ag in a single construct provides synergistic opportunities for optical activation of functions as near infrared laser tissue bonding, and remote interrogation to return parameters of prognostic relevance in wound healing monitoring. In particular, the bimetallic component ensures optical tunability, enhanced shelf life and photothermal stability, serves as a reservoir of germicidal silver cations, and changes in near-infrared and visible color according to the environmental level of oxidative stress.