Biocompatible AgS quantum dots for highly sensitive detection of copper ions

A simple aqueous approach for synthesizing biocompatible red and near-infrared (NIR) emitting Ag 2 S quantum dots (QDs) at low temperature without a required oxygen-free process has been developed. The fluorescence of the obtained red emitting Ag 2 S QDs could be selectively quenched by Cu 2+ . Based on this, a novel Ag 2 S QD based fluorescent sensor for highly selective and sensitive detection of Cu 2+ was developed. This method showed a low limit of detection (LOD) of 27.6 nM for Cu 2+ sensing in a wide linear range concentration of 25 nM-10 μM. The quenching mechanism was discussed by the time-resolved photoluminescence, absorption spectra, TEM and energy-dispersive X-ray (EDX) results. Cation exchange of Ag 2 S QDs between Cu( ii ) and Ag( i ), and dynamic quenching due to excited state electron transfer from Ag 2 S QDs to Cu 2+ were considered to be the quenching mechanism. Furthermore, to understand the interaction between Ag 2 S QDs and Cu 2+ , the thermodynamic process was investigated by means of isothermal titration calorimetry (ITC). The values of Δ H , Δ S and Δ G were calculated from the ITC results to be −79.43 kJ mol −1 , −142.18 J K −1 mol −1 and −37.06 kJ mol −1 , respectively. The Ag 2 S QD based Cu 2+ detection had advantages of nontoxicity, fast response, high sensitivity and selectivity, wide linear range and easy preparation. An Ag 2 S QD fluorescent sensor for highly selective and sensitive Cu 2+ detection was developed and the quenching mechanism was investigated.