Novel switchable sensor for phosphate based on the distance-dependant fluorescence coupling of cysteine-capped cadmium sulfidequantum dots and silver nanoparticles

Abstract

A novel switchable sensor was developed for the determination of phosphate based on Ce³⁺ induced aggregation and phosphate triggered disaggregation of cysteine (Cys)-capped CdS quantum dots (QDs) and silver nanoparticles (AgNPs). The rare earth metal Ce³⁺ could aggregate a mixture of QDs and AgNPs, which induced electron or energy transfer between CdS QDs and AgNPs and serious fluorescence quenching. However, phosphate dissociated the formed aggregation of CdS QDs and AgNPs, restoring the enhanced fluorescence of Cys-capped CdS triggered by AgNPs. Although, CdS QDs alone could also be used to detect phosphate through the aggregation–disaggregation mechanism adjusted by Ce³⁺ and phosphate. It was found that the distance-dependent interaction between AgNPs and CdS QDs driven by Ce³⁺ and phosphate could lead to enhanced quenching or enhancement of the fluorescence of Cys-capped CdS to form a more sensitive detection system for phosphate. The developed method was applied in the detection of phosphate in real water samples with acceptable and satisfactory results.