Biocompatible glutathione-capped gold nanoclusters for dual fluorescent sensing and imaging of copper(II) and temperature in human cells and bacterial cells

Highly red luminescent gold nanoclusters (AuNCs) have been prepared at physiological temperature by using glutathione (GSH) as a stabilizing and capping agent in aqueous media. The resultant AuNCs have been characterized by photoluminescence and X-ray photoelectron spectroscopy, transmission electron microscopy and FTIR. The AuNCs exhibit red fluorescence with a quantum yield of 3.1 %, and fluorescence is strongly quenched by copper(II) ion due to aggregation. This finding is exploited in a fluorometric assay for Cu(II) that has a 2.8 nM detection limit. The method was applied to the determination of Cu(II) ion in (spiked) mineral water and Tai Lake water. In addition, the AuNCs display a strongly temperature-dependent emission that can be used for optical determination of temperature in the 0 to 60 °C range. We finally show that the AuNCs are viable nanomaterials for (a) plain imaging of Hep-2 cells by laser scanning confocal microscopy, and for (b) intracellular imaging of Cu(II) and of temperature in Hep-2 cells and E. coli.