The synthesis of nitrogen and sulfur co-doped graphene quantum dots for fluorescence detection of cobalt(ii) ions in water

Abstract

A fluorescent sensor based on nitrogen and sulfur co-doped graphene quantum dots (N,S-GQDs) has been developed for the convenient, sensitive, and selective detection of cobalt(II) ions (Co²⁺). Co²⁺ can quench the fluorescence intensity of N,S-GQDs through metal–ligand interaction between the metal ions and the surface functional groups of the fluorescent probe. Furthermore, the addition of Co²⁺ induces the aggregation of N,S-GQDs, resulting in an enhancement of UV-Visible absorption at 430 nm and color change from colorless to yellow-brown within 3 minutes. The fluorescence intensity of N,S-GQDs can be used to sense Co²⁺ under the optimal circumstances with a detection limit of 1.25 μM and a working linear range of 0–40 μM. In addition, the sensor probe was applied successfully to the determination of Co²⁺ in real water samples. Due to its low cytotoxicity, the proposed sensor may potentially be applied in environmental and biological fields.