A dual-emission carbon dots/gold nanoclusters fluorescent probe for ratiometric and colorimetric detection of Pb2+ and Hg2+

A novel fluorescent probe, carbon dots/gold nanoclusters (CDs/AuNCs), was prepared for ratiometric and colorimetric detection of Pb²⁺ and Hg²⁺ simultaneously. The as-prepared probe exhibited two distinct emission peaks at 445 nm and 610 nm. During the detection process, Pb²⁺ could quench blue fluorescence due to the formation of the CDs-Pb²⁺ complex and does not affect orange fluorescence. Conversely, Hg²⁺ could quench the orange fluorescence greatly due to the Hg²⁺-Au⁺ metallophilic interaction and keep blue fluorescence unaffected. Accordingly, ratiometric fluorescence sensing approaches of Pb²⁺ and Hg²⁺ are achieved and dramatic color changes from pink to orange/blue can be observed under UV illumination upon the addition of Pb²⁺/Hg²⁺. Furthermore, good linear relationships between the fluorescence intensity ratio (I₆₁₀/I₄₄₅) and Pb²⁺/Hg²⁺ concentration were demonstrated in ranges of 0-130 nM for Pb²⁺ and 0 to 280 nM for Hg²⁺, with detection limits of 6.5 nM for Pb²⁺ and 3.7 nM for Hg²⁺, respectively. The probe showed excellent selectivity and the mutual interference problem of coexistence of Pb²⁺ and Hg²⁺ could be effectively solved by introducing masking agents. In addition, the application of CDs/AuNCs proved successful in detecting Pb²⁺ and Hg²⁺ in actual water samples, yielding satisfactory recovery rates. These results indicated that the probe provides a new approach for visualizing and semi-quantitatively detecting Pb²⁺ and Hg²⁺, making it highly promising for monitoring environmental water samples.