A carbon dot-based ratiometric fluorescent probe for the fluorescence “on–off–on” detection of Fe3+ and amitrole herbicides

Abstract

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 form 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 ranges 0–50 μM and 0–30 μM. The detection limits of Fe³⁺ and AMT are as low as 24 nM and 0.18 μM, respectively. In addition, fluorescence color changes are converted into RGB values using a smartphone sensing device, and the concentration of Fe³⁺ and AMT is determined via 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.