Fig. 4

a Vis-NIR spectrum of GNRs before and after silica coating. b TEM pictures of GNRs coated 35 nm silica shells. c Cross section images of spleen (blue ROI) and GNR-Si35-labeled cells (red ROI). Both regions have strong  OA intensity. However, only the  OA spectrum of labelled cells fits the absorbance spectrum of GNRs, which allows distinguishing the GNR-labelled cells from any other region with a high endogenous  OA signal. MSOT imaging of the cell clusters 3 days after injection of \(2\times 10^4\) and \(1\times 10^5\) (d) and \(2\times 10^5\) GNR-Si35-labeled cells. Scale bars are 5 mm. e The left column shows a single wavelength maximum intensity projection in the xy plane of the regions of interest. The great anatomical resolution of MSOT is observed here, allowing visualization of small vessels (e.g., renal artery and renal vein). The middle column shows the same regions after multispectral processing, enabling high sensitivity detection of GNR-Si35-labeled cells. Volume views of the regions of interest are shown in the right column. Scale bars are 5 mm. Colour scale range is 0 to \(1.1\times 10^5\) MSOT au. Reproduced with permission from (https://pubs.acs.org/doi/10.1021/acsnano.6b03246) [38].Copyright ©2016, American Chemical Society. All rights reserved. Further permission related to the material excerpted should be directed to the ACS