Cytochrome c-Capped Fluorescent Gold Nanoclusters: Imaging of Live Cells and Delivery of Cytochrome c.

Cytochrome c-capped fluorescent gold nanoclusters (Au-NCs) are used for imaging of live lung and breast cells. Delivery of cytochrome c inside the cells is confirmed by covalently attaching a fluorophore (Alexa Fluor 594) to cytochrome c-capped Au-NCs and observing fluorescence from Alexa 594 inside the cell. Mass spectrometry studies suggest that in bulk water, addition of glutathione (GSH) to cytochrome c-capped Au-NCs results in the formation of glutathione-capped Au-NCs and free apo-cytochrome c. Thus glutathione displaces cytochrome c as a capping agent. Using confocal microscopy, the emission spectra and decay of Au-NCs are measured in live cells. From the position of the emission maximum it is shown that the Au-NCs exist as Au8 in bulk water and as Au13 inside the cells. Fluorescence resonance energy transfer from cytochrome c-Au-NC (donor) to Mitotracker Orange (acceptor) indicates that the Au-NCs localise in the mitochondria of live cells.