Ratiometric fluorometric detection of Cu2+ through a hybrid nanoprobe composed of N-doped CQDs and l-cysteine-capped CdSe/ZnS QDs

The present work fabricated a novel dual-emission responsive ratiometric fluorescent hybrid nanoprobe using a mixture of blue fluorescence-emitting N-Doped Carbon Quantum Dots (N-CQDs) and red fluorescence-emitting l-cysteine-capped CdSe/ZnS Quantum Dots (Lcys-CdSe/ZnS QDs). The addition of Cu2+ resulted in the strong and specific fluorescence quenching in Lcys-CdSe/ZnS QDs while N-CQDs retained their fluorescence intensity. Further exploration of the nanoprobe showed that the detection limit was 3.78 × 10−9 M and the linear range was below 3.2 × 10−6 M. The nanoprobe possessed excellent anti-interference in the Cu2+ determination and its application was successful in natural water samples. Experimental results suggested that the superficial left cysteine (Lcys) combines with Cu2+ causing static quenching. Results of density functional theory (DFT) computation explained that Cu2+ has the greatest possibility to combine with surficial Lcys and furthermore illustrated the role of the combination in static quenching. The work showed one of origin of the selectivity of the nanoprobe and a potentially guidance to design high selective ratiometric fluorescent nanoprobes.