Carbon dot-based ratiometric fluorescent probe for the fluorescent 'on-off-on' detection of Fe3+ and Amitrole herbicides

In this study, a carbon dot-based ratiometric fluorescence (RF) probe was used as a fluorescent "on-off-on" sensor to detect Fe3+ and the pesticide amitrole (AMT). The RF probe consists of orange carbon dots (O-CDs) and blue carbon dots (B-CDs). B-CDs forms a ground-state complex with Fe3+ which leads to fluorescence quenching, while the addition of AMT restores fluorescence. Based on this "on-off-on" process, a quantitative detection of Fe3+ and AMT is achieved, showing good linearity in the range 0-50 μM and 0-30 μM. The low detection limit of Fe3+ and AMT are as low as 24 nM and 0.18 μM, respectively. In addition, fluorescent color changes are converted into RGB values by a smartphone sensing device., and the concentration of Fe3+ and AMT is determined by colorimetric analysis. The method was further applied to real samples such as lake water, tap water and urine with satisfactory results. Additionally, a portable sensor with a semi-hydrophobic film was fabricated for on-site AMT detection, showcasing practical applicability. This work provides a cost-effective, rapid, and dual-mode strategy for environmental and biological monitoring of Fe³⁺ and AMT.