Carbon quantum dots as a turn-on fluorescent probe for the sensitive detection of Cd²

In this study, fluorescent carbon dots were synthesized for the first time using ammonium citrate and glutamic acid as precursors via a one-pot hydrothermal method. The synthesized carbon dots emit blue fluorescence at 436 nm (excited at 320 nm) and demonstrate excellent photobleaching resistance and fluorescence stability in high salt environments. Within the range of 1-25 μM, the fluorescence of CDs gradually increases with the increasing concentration of Cd²⁺, reaching a limit of detection as low as 13 nM. This phenomenon could be ascribed to the chelation-enhanced fluorescence, a result of Cd²⁺ forming complexes with the abundant surface functional groups such as CN-, -COOH, -OH, -NH₂ in CDs. Furthermore, this turn-on fluorescent probe has been successfully used for the detection of Cd²⁺ in tap water and lake water, providing an efficient and sensitive method for the analysis of environmental metals.