Fluorescence/colorimetric dual-signal sensor based on carbon dots and gold nanoparticles for visual quantification  of Cr³⁺

A convenient and sensitive dual-signal visualization method is constructed for detection of trivalent chromium ions (Cr³⁺) based on fluorescent carbon dots (CDs) and glutathione-modified gold nanoparticles (GSH-Au NPs). The fluorescence of CDs can be quenched by GSH-Au NPs due to the inner filter effect. Cr³⁺ induces aggregation of GSH-Au NPs because of the coordination with GSH on the surface of Au NPs, leading to the red shift of surface plasmon resonance absorption of Au NPs that provides a “turn-on” fluorescence and colorimetric assay for Cr³⁺. The fluorescence/colorimetric dual signal detection shows high sensitivity for Cr³⁺ with wide detection linear ranges (0.5–70 μM for fluorescence detection and 2–50 μM for colorimetric detection) and low detection limits (0.31 μM for fluorescence detection and 0.30 μM for colorimetric detection). Besides, the method has high selectivity for Cr³⁺ and can be used for detection of Cr³⁺ in lake water and tap water samples, showing great potential for visual detection of environmental Cr³⁺.