CuInS2 Quantum Dots as a Selective Turn-Off Fluorescence sensor for Fe3+ ions in Water

Detection of Fe 3+ ions in food, water, and ecosystems is vital to maintaining both the environment and human health. The real-time application of currently developed sensor technologies for this purpose is limited by high cost, lengthy analysis time, poor selectivity and sensitivity, and low accuracy. Herein, we present a “turn-off” fluorescence probe based on Copper Indium Sulfide quantum dots (CuInS 2 QDs) for the selective sensing of Fe 3+ metal ions in aqueous media. A considerable Stokes shift in CuInS 2 QDs reduces spectral overlap and background interference, leading to enhanced accuracy and sensitivity for heavy metal detection. In this case, 3-Mercaptopropionic acid (3-MPA)-capped CuInS 2 QDs are highly selective and sensitive to Fe 3+ ions owing to their interaction in the aqueous media. Moreover, the strong interaction with 3-MPA removes the necessity for an external buffer, unlike many conventional sensors that rely on such media for Fe³⁺ detection. The potential of CuInS 2 QDs for the rapid sensing of Fe 3+ ions is further demonstrated by the limit of detection (LOD) of 3.89 micro molar (µM) with a correlation coefficient R 2 = 0.993 in the concentration range of 0 µM to 60 µM. The developed method was applied to detect Fe 3+ in real water samples. Additionally, the possibility of detecting Fe 3+ ions based on current-voltage (I-V) characteristics of CuInS 2 QD film was also shown. This sensing approach using heavy metal-free QDs offers a greener way to selectively determine Fe 3+ ions in the presence of other ions in aqueous solutions.