Figure 5

CARS microscopy of livers isolated from GNP-treated and control mice. The wavelengths of the pump and the Stokes lasers (Pump = 870 nm and Stokes = 1064 nm) were tuned to match a Raman shift (~2100 cm⁻¹), falling in the so-called “silent region” of the vibrational spectra of cells and tissues. As expected, the CARS images of the “control” did not show appreciable contrast under the non-resonant condition whereas the CARS signals were dramatically enhanced and appeared as scattered bright spots on the images taken from the specimens treated with GNPs. The enhancement presumably resulted from strong scattering from the GNPs and the large third-order polarizability of the GNPs. Enhanced bright spots were observed in neither the control group (a) nor the mice injected with 5 nm GNP (b). Livers obtained from 17 nm GNP-treated mice showed intense bright spots (c). Livers obtained from 50 nm GNP-treated mice showed only a moderate number of spots (d)