Surface Amide–Mediated Synthesis of Bright Blue Fluorescent Carbon Dots for High-Sensitivity Detection of Hg²⁺ Ions

Mercury ions (Hg²⁺) seriously harm the central nervous system of humans, leading to brain damage and even heart failure and death. Therefore, effective detection of Hg²⁺ in water quality has become an urgent research field. It is very important to develop economically efficient fluorescent sensors to achieve rapid and sensitive detection of Hg²⁺. Therefore, the high fluorescence quantum yield fluorescent carbon dots (CDs) with amide group were prepared. The process of preparing CDs was regulated by multiple key factors (carbon source, proportion, time), and the CDs with the best fluorescence performance were selected. It was comprehensively characterized, including fluorescence performance, surface structure, phase, and morphological characteristics. The amide group endows CDs with the ability to act as both donors and acceptors for hydrogen bonding, forming complexes with metal ions, thus making them suitable for the detection of Hg²⁺. It is worth noting that CDs can quickly detect Hg²⁺ within 1 min, and there is a good linear relationship within the ranges of 0.001–200 μM and 200–500 μM. The detection limit of UC-CDs is 8.2 nM. This study provides a fluorescent sensor with fast reaction, excellent sensitivity, and selectivity for the efficient detection of Hg²⁺ in water.