Facile synthesis of N-doped graphene quantum dots as a fluorescent sensor for Cr(vi) and folic acid detection.

The development of stable fluorescent sensors for toxic pollutants and drugs is meaningful to the environment and public health. In this work, nitrogen-doped graphene quantum dots (N-GQDs) were facially synthesized by a one-step hydrothermal method using soluble starch and l-arginine as carbon and nitrogen sources in pure water at 190 °C for 4 h. The as-synthesized N-GQDs were well characterized and displayed blue fluorescence emission at 445 nm with excellent pH stability, salt tolerance, thermostability, photobleaching resistance and reproducibility. Moreover, N-GQDs could serve as an "on-off" sensor for selective detection of Cr(vi) and folic acid with low detection limit (0.80 and 2.1 μM), good linear correlation over wide linear range (0-50 μM and 0-200 μM) as well as short response time (<10 s). The practical applications of N-GQDs for Cr(vi) and folic acid detection in actual samples were further investigated and showed acceptable recoveries (92-105%) with relative standard deviations less than 5%. These results indicated that this N-GQDs-based sensor could be a potential alternative for Cr(vi) and folic acid detection in the fields of environmental monitoring and drug analysis.