Nitrogen and Sulfur Co-doped Carbon Dots as a Turn-Off Fluorescence Probe for the Detection of Cerium and Iron.

Carbon dots has becoming one of the most promising fluorescence sensors to determine the trace level of heavy metals in environments because of their advantages in optical properties, response time, and convenient operation procedures. Herein, a novel nitrogen and sulfur co-doped carbon dots (NS-CDs) were prepared though microwave assisted approach using DL-malic acid and allyl thiourea for the first time. Due to the existence of nitrogen and sulfur, the as-prepared NS-CDs exhibited bright blue fluorescence at 430 nm upon 330 nm excitation, with a fluorescence quantum yield of 19.8%. The sensitivity study of NS-CDs against metal ions and organic molecules has approved that the fluorescence could be further quenched by Ce and Fe ions, with the same linear detection ranges varying from 10 to 90 µM. The limits of detection (LOD) were determined as low as 0.75 µM and 0.67 µM for Ce and Fe ions, respectively. The possible quenching mechanism is explained by inner filter effect and static quenching mechanism for Ce ions, while the quenching effect caused by Fe ions is attributed to the inner filter effect, static and dynamic quenching mechanisms. Additionally, the developed sensor was used for the detection of Ce and Fe ions in tap water with satisfactory recoveries. Finally, the designed NS-CDs sensor possesses good biocompatibility against MA104 cells, suggesting the sensor can be potentially applied to detect Ce and Fe ions in environment and biological systems.