Fluorescent gold clusters as nanosensors for copper ions in live cells

This paper reports the use of fluorescent gold nanoclusters synthesized using bovine serum albumin (Au–BSA) for the sensing of copper ions in live cells. The fluorescence of the clusters was found to be quenched by Cu²⁺ enabling its detection in cells. The selectivity of the nanosensor was demonstrated in the presence of several cations excluding Hg²⁺. We did not study the effect of Hg²⁺ since it was reported earlier. The present study suggests that Cu²⁺ induced fluorescence quenching is due to its binding to BSA rather than the fluorescence quenching by metal–metal interaction as in the case of Hg²⁺. The Au–BSA showed excellent selectivity to Cu²⁺ at various pH conditions. The ‘turn off’ of fluorescence can be retrieved by a Cu²⁺ chelator glycine. Our results showed that gold clusters can be used as a ‘turn off’ sensor for copper and a ‘turn on’ sensor for glycine. Under the experimental conditions, the probe showed a response for Cu²⁺ over a range of 100 μM to 5 mM with a detection limit of 50 μM. The role of Cu²⁺ in the misfolding and disassembly of Prion Protein (PrP) leading to various maladies is well ascertained. The methodology we reported here seems to be useful in supplementing other techniques in predicting disease conditions involving Cu²⁺.