There is considerable interest in using nanoparticles as labels or to deliver drugs and other bioactive compounds to cells in vitro and in vivo. Fluorescent imaging, commonly used to study internalization and subcellular localization of nanoparticles, does not allow unequivocal distinction between cell surface-bound and internalized particles, as there is no methodology to turn particles™. We have developed a simple technique to rapidly remove silver nanoparticles outside living cells, leaving only the internalized pool for imaging or quantification. The silver nanoparticle (AgNP) etching is based on the sensitivity of Ag to a hexacyanoferrate-thiosulphate redox-based destain solution. In demonstration of the technique we present a class of multicoloured plasmonic nanoprobes comprising dye-labelled AgNPs that are exceptionally bright and photostable, carry peptides as model targeting ligands, can be etched rapidly and with minimal toxicity in mice, and that show tumour uptake in vivo.
Bibliographical noteFunding Information:
This work was supported by US DoD awards W81XWH-10-1-0199 and W81XWH-09-0698; R01 CA152327, R01 CA167174, and CA 030199 (Cancer Center Support grant) from the NCI; and by the Defense Advanced Research Projects Agency (DARPA) under Cooperative Agreement HR0011-13-2-0017. The findings and views expressed are those of the authors and do not reflect the official policy or position of the Department of Defense or the US Government. Approved for Public Release, Distribution Unlimited. G.B.B. was supported by the Cancer Center of Santa Barbara and by an NIH training grant (T32 CA121949), and A-M.A.W., and T.T. by the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Starting Grant Agreement No. 291910. The authors thank L. Agemy, R. Chen and M. Moskovits for helpful discussions, A. K-Clark for assistance and technical support with ICP-MS, F. Zhang for guidance in Ag synthesis, F. Vitti for helpful discussions on silver amplification, J. Wang for flow cytometry assistance, the NRI-MCDB Microscopy Facility at UCSB, and Histology and Cellular Imaging cores at the Sanford-Burnham Medical Research Institute.