Glutathione-protected fluorescent gold nanoclusters for sensitive and selective detection of Cu2+

We report a novel and environmentally friendly fluorescent probe for detecting copper ion (Cu2+) using glutathione (GS)-protected Au nanoclusters (GS-Au NCs). The fluorescence-based sensing behavior by GS-Au NCs toward metal ions was investigated in buffered aqueous media. Among the metal ions studied, Cu2+, Hg2+ and Pb2+ were found to efficiently quench the fluorescence emission of GS-Au NCs. In differentiation of Cu2+ and Hg2+ (or Pb2+), we found that (1) in the presence of Pb2+, the GS-Au NCs solution first appeared turbidity, but with ethylenediaminetetraacetate (EDTA) added to the solution, the fluorescence recovered and the turbidity disappeared; (2) in the presence of Hg2+, EDTA could not recover the quenched fluorescence of GS-Au CNs by Hg2+, which is in contrast with Pb2+ and Cu2+. The Cu2+ detection limit was determined to be approximately 86 nM based on the fluorescence quenching and linear fluorescence response in the Cu2+ concentration range 1.00 × 10−7 to 6.25 × 10−6 mol/L. The high sensitivity of 86 nM Cu2+ and selectivity to Cu2+ among 17 types of metal cations make GS-Au NCs a good candidate for fluorescent sensors for Cu2+.