Improved imaging and preservation of lysosome dynamics using silver nanoparticle-enhanced fluorescence

Abstract

The dynamics of living cells can be studied by live-cell fluorescence microscopy. However, this requires the use of excessive light energy to obtain good signal-to-noise ratio, which can then photobleach fluorochromes, and more worrisomely, lead to photo-toxicity. Upon light excitation, noble metal nanoparticles such as silver nanoparticles (AgNP) generate plasmons, which can then amplify excitation in direct proximity of the nanoparticles surface and couple to the oscillating dipole of nearby radiating fluorophores, modifying their rate of emission and thus, enhancing their fluorescence. Here, we show that AgNP fed to cells to accumulate within lysosomes enhanced the fluorescence of lysosome-targeted Alexa488-conjugated dextran, BODIPY-cholesterol, and DQ-BSA. Moreover, AgNP increased the fluorescence of GFP fused to the cytosolic tail of LAMP1, showing that metal enhanced fluorescence can occur across the lysosomal membrane. The inclusion of AgNPs in lysosomes did not disturb lysosomal properties such as lysosomal pH, degradative capacity, autophagy and autophagic flux, and membrane integrity, though AgNP seemed to increase basal lysosome tubulation. Importantly, by using AgNP, we could track lysosome motility with reduced laser power without damaging and altering lysosome dynamics. Overall, AgNP-enhanced fluorescence may be a useful tool to study the dynamics of the endo-lysosomal pathway while minimizing photo-toxicity. eTOCSilver nanoparticles enhance fluorescence via surface plasmons. Here, we show that loading lysosomes with silver nanoparticles enhances the fluorescence of fluorochrome- and GFP-based molecular probes for lysosomes. This affords reduced excitation and exposure, diminishing photobleaching and phototoxicity, and preserving lysosome dynamics.