Fig. 6

a Diagram of nanoparticle synthesis. The IR775c/PDL is electrostatically bound to the silica coated AuNRs. The particle is composed of the polymer/dye mixture on the outside of the AuNR (green), allowing for ROS to interact with the dye and degrade it (red), while the inert AuNR does not change, thus giving different photoacoustic signals due to ROS interaction. TEM images of b gold nanorods, c silica-coated AuNRs, d PDL layered silica-AuNRs, and e PDL/IR775c layered silica-AuNR were obtained. Scale bar is equal to 100 nm. f The hydrodynamic diameter increased for each step with the final nanoparticle having a diameter of 400 nm. g The \(\zeta\)-potential for each step was collected displaying flipping \(\zeta\)-potential with each layer and a relatively neutral \(\zeta\)-potential for the final particle. h The absorbance spectra displayed changing peak absorbance from 875 nm for AuNR to 910 nm for silica–AuNR and PDL-coated silica–AuNR, and 780 nm for the final nanoparticle. Scale bar is equal to 100 nm. i Imaging stem cells in vivo. The US/OA image of transplanted stem cells on day 0 is visualized at 795 and 920 nm excitation, correlating with the IR775c dye and AuNR peak. The labelled stem cells are circled in blue. The last image is a heatmap using the ratio of 795 nm/920 nm. The stem cells display a high ratio as expected due to them being alive directly after transplantation. j Ratiometric imaging of stem cell viability in vivo. OA images of day 0, 1, 3, 5, 7, and 10 at 795 and 920 nm were obtained, and the ratiometric images were created. The surrounding tissue signal was subtracted to better visualize the change in stem cell viability during the study. Reduction in ratio and signal is visible. Adapted with permission from [61].Copyright \(\copyright\) 2019, American Chemical Society