An "on-off-on" Fluorescent Sensor Based on Carbon Dots for the Detection of Au (III) and Creatinine

The present study proposes a new approach for detecting trace amounts of creatinine (Cre) through the utilization of a fluorescence sensor system consisting of nitrogen doped carbon dots (NCDs) and gold ions (Au³⁺). Yellow fluorescent carbon dots were prepared using a one-step hydrothermal method with o-phenylenediamine and isopropanol as raw materials. First, gold ions are reduced to gold nanoparticles (Au NPs), which bind to NCDs, resulting in electron transfer and fluorescence quenching of NCDs. After adding creatinine, Cre and Au NPs were preferentially combined to form non-fluorescent complexes, and the NCDs fluorescence was restored. The study achieved a detection limit of 1.06 × 10^-7 M for Au³⁺ and 9.29 × 10^-9 M for creatinine, indicating a high level of sensitivity. The sensing system has also been successfully utilized for detecting Au³⁺ in lake water and Cre in human urine, indicating its promising potential and practical applications in the areas of environmental monitoring and biosensing.