Silver nanowires as infrared-active materials for surface-enhanced Raman scattering.

Surface-enhanced Raman scattering (SERS) is increasing in significance as a bioanalytical tool. Novel nanostructured metal substrates are required to improve performances and versatility of SERS spectroscopy. In particular, as biological tissues are relatively transparent in the infrared wavelength range, SERS-active materials suitable for infrared laser excitation are needed. Nanowires appear interesting in this respect as they show a very broad localized surface plasmon resonance band, ranging from near UV to near infrared wavelengths. The SERS activity of silver nanowires has been tested at three wavelengths and a fair enhancement at 1064 and 514 nm has been observed, whereas a very weak enhancement was present when exciting close to the nanowire extinction maximum. These experimentally measured optical properties have been contrasted with finite element method simulations. Furthermore, laser-induced optoacoustic spectroscopy measurements have shown that the extinction at 1064 nm is completely due to scattering. This result has an important implication that no heating occurs when silver nanowires are utilized as SERS-active substrates, thereby preventing possible thermal damage.

Gold nanoparticles uptake and cytotoxicity assessed on rat liver precision-cut slices.

A major obstacle in the field of nanotoxicology is the development of an in vitro model that accurately predicts an in vivo response. To address this concern, rat liver precision-cut slices were used to assess the impact of 5-nm gold nanoparticles (GNPs) coated with polyvinylpyrrolidone (PVP) on the mammalian liver, following exposure to different concentrations and for a duration of up to 24 h. The presence of GNPs inside endocytotic vesicles of hepatocytes was appreciable within 30 min of their addition. After 2 h, GNPs were clearly visualized inside endosome-like vesicles within the slice, not only in hepatocytes but also in endothelial and Kupffer cells located within the first two cellular layers. This uptake did not translate into modifications of either phase I or phase II of 7-ethoxycoumarin metabolism or alter activities of cytochrome P450 toward marker substrates. Furthermore, although the GNPs were rapidly internalized, no overt signs of cytotoxicity, assessed through lactate dehydrogenase release, reduction of methylthiazolyldiphenyl tetrazolium bromide, and glutathione levels, were observed. In conclusion, the use of rat liver slices successfully enhanced nanomaterial screening and determined that PVP-coated 5-nm GNPs were biocompatible with rat liver cells.