Аннотация:Coherent anti-Stokes Raman scattering (CARS), a nonlinear optical method for rapid visualization of biological objects, represents a progressive tool in biology and medicine to explore cells and tissue structure in living systems and biopsies. In this study, we report efficient non-resonant CARS imaging of silicon nanoparticles (SiNPs) in human cells as a proof of concept. Since both bulk and porous silicon exhibit a high third-order nonlinear susceptibility χ(3), which is responsible for the CARS intensity, it is possible to visualize the SiNPs without specific labels. Porous and solid SiNPs were obtained from layers of porous and non-porous silicon nanowires and mesoporous silicon. Electron microscopy and Raman spectroscopy showed that porous SiNPs consisted of 3 nm silicon nanocrystals (nc-Si) and pores, while solid nanoparticles were 100 nm nc-Si. All types of SiNPs were non-toxic at concentrations up to 500 μg/ml after 24 h of incubation with cells. We demonstrated that although nc-Si possesses a distinguished narrow Raman band of about 520 cm-1, it is possible to detect high CARS signal from SiNPs in the epi-direction even in a non-resonant regime. 3D CARS images showed that all types of studied SiNPs were visualized as bright spots inside the cytoplasm of cells after 3-6 h of incubation due to the contrast provided by the high third-order nonlinear susceptibility of SiNPs, which is 104-105 times higher than that of water and typical biological media. Overall, CARS microscopy can provide localization of SiNPs within biological structures at the cellular level and can be a powerful tool for in vitro monitoring of silicon-based drug delivery systems or use SiNPs as labels to monitor various bioprocesses inside living cells.