High sensitive and selective multivariate detection of Hg2+ and Ag+ in real food samples via Ca, N-co-doped carbon dots based dual-mode platform

Heavy metals adversely affect the environment, ecosystems, and human health. The effective detection and treatment of heavy metals has become a major global concern. Herein, calcium and nitrogen co-doped carbon dots (E-CDs) were developed using cheap kitchen waste eggshells as precursors, and utilized as dual-mode fluorimetric/colorimetric sensor for the multivariate detection of Hg²⁺ and Ag⁺. The E-CDs exhibited yellow emission at 420 nm excited at 567 nm, with a quantum yield of 15.49% and lifetime of 12.92 μs. The multivariate detection of Hg²⁺ and Ag⁺ can be achieved selectively by distinguishing via dual-mode respectively. The limit of detection (LOD) for Hg²⁺ reached 11.28 nM, while the Ag⁺ can be determined by fluorimetric/colorimetric dual-mode with LODs of 128.23 nM and 1.02 μM, respectively. Remarkably, the E-CDs integrated with a smartphone-based paper sensor supported by RGB analysis achieved the detection of Hg²⁺ and Ag⁺ with LODs of 56.2 nM and 90.96 nM, respectively. Notably, the recoveries in real samples attained 96.3–105.7% with excellent environmental tolerance. Furthermore, a logic gate circuit was developed to support the potential practical intelligent application. This work highlighted a cost-effective, multi-functional sensing strategy with significant potential for monitoring heavy metal contaminants in environmental and food safety applications.