Nitrogen and Sulfur co-doped Carbon dots as an "on-off-on" Fluorescent Sensor for the Detection of Hg and Ampicillin.

Herein, a fluorescent "on-off-on" nanosensor based on N,S-CDs was developed for highly precise and sensitive recognition of Hg and ampicillin (AMP). Nitrogen and sulfur co-doped carbon dots with blue fluorescence were synthesized by one-pot hydrothermal method using ammonium citrate and DL-methionine as precursors. N,S-CDs exhibited a surface abundant in -OH, -COOH, and -NH groups, aiding in creating non-fluorescent ground state complexes when combined with Hg, leading to the suppression of N,S-CDs' fluorescence. Subsequent to additional AMP application, the mixed system's fluorescence was restored. Based on this N,S-CDs sensing system, the thresholds for detection for AMP and Hg were discovered to be 0.121 µM and 0.493 µM, respectively. Furthermore, this methodology proved effective in identifying AMP in real samples of tap and lake water, yielding satisfactory results. Consequently, in the area of bioanalysis in intricate environmental sample work, the sensing system showed tremendous promise.