A visualized ratiometric fluorescence sensing system for copper ions based on gold nanoclusters/perovskite quantum dot@SiO2 nanocomposites

Excessive copper ions (Cu2+) cause serious environmental pollution and even endanger the health of organisms. Fluorescence chemosensing materials are widely used in the detection of metal ions due to their simple operation and high sensitivity. In this study, SiO2-encapsulated single perovskite quantum dot (PQD@SiO2) core-shell nanostructures which show strong, stable, and green fluorescence are synthesized and composited with gold nanoclusters (AuNCs) which show Cu2+-sensitive and red light-emitting fluorescence to obtain a visualized ratiometric fluorescence sensor (AuNCs/PQD@SiO2) for the detection of Cu2+. In the visualized detection of Cu2+, the green fluorescence emitted from the ion-insensitive PQD@SiO2 component is used as a reference signal and the red fluorescence emitted by ion-sensitive AuNC component is adopted as a sensing signal. In the presence of Cu2+, the red fluorescence is quenched whereas the green fluorescence remains stable, which results in a visualized fluorescence color change from orange-red to yellow and finally to green with increasing Cu2+ concentration. The significant change in the fluorescence color of AuNCs/PQD@SiO2 in response to Cu2+ enables a rapid, sensitive, and visualized detection of Cu2+. Further accurate and sensitive ratiometric fluorescence analysis of Cu2+ can be accomplished by measuring the ratio of fluorescence intensities at 643 and 520 nm (I643/I520) at a certain Cu2+ level. The developed AuNCs/PQD@SiO2-based sensor has been validated by its satisfactory application in the detection of Cu2+ in human serum and environmental water samples.