Dye-doped organosilicate nanoparticles as cell-preserving labels for photoacoustic signal generation

Nanoparticle-assisted ultrasound generation by pulsed laser or photoacoustic (PA) techniques has been employed in the study of several tissues both in vivo and in vitro. Among the many applications of this technology, the detection of few cells in vitro is of particular interest. However, the toxicity induced by laser irradiation used for PA signal generation, whether in the absence or the presence of PA enhancers, within single isolated cells has not yet been investigated in detail. Herein, we report our studies of the cellular health of two different nanoparticle-labeled cell lines one hour after being subjected to a single laser pulse in vitro. We selected for this study an Hs936 skin epithelial melanoma cell line, which can be naturally detected photoacoustically, as well as a T47D human mammary breast gland epithelial cell line which has proven difficult to detect photoacoustically due to the absence of natural melanin. We have evaluated the amplitude of the PA signal derived from these two cell types, unlabeled and labeled with nanoparticles of two types (gold nanoparticles, AuNPs, or rhodamine 6G-doped organosilicate nanoparticles, R6G-NPOs), and assessed their health one hour subsequent to laser treatment. The current work corroborates previous findings that, for unlabeled cells, Hs936 produces a detectable PA signal whereas the T47D line does not. Cells labeled with AuNPs or R6G-NPOs produced a detectable PA signal of similar amplitude for the two cell lines. A significant number of Hs936 cells (both unlabeled cells and those labeled with AuNPs) exhibited cell nuclei alterations, as revealed by DAPI staining conducted an hour after photo treatment. Remarkably, the T47D cells suffered damage only when labeled with AuNPs. A significant finding, the R6G-NPOs proved capable of non-destructive PA signal generation in both cell types. Our findings advocate a transformational path forward for the use of dye-doped silicate nanoparticles in cell-compatible PA studies permitting the handling and culturing of cells subsequent to their photoacoustic analysis.