Synthesis of CuInS₂ Quantum Dots Modified with Alanine for Sensitive and Selective Detection of Pb²⁺ and Cysteine

In this study, a novel fluorescent probe based on CuInS₂ quantum dots modified with alanine (Ala-CuInS₂ QDs) was developed for the detection of lead ions and cysteine (Pb²⁺ and Cys). Ala-CuInS₂ QDs were synthesized through a one-step hydrothermal method exhibiting uniform size, good stability and water solubility. The QDs were then utilized as an “on-off-on” fluorescence sensor to detect Pb²⁺ and Cys in the ranges of 0–20 µM and 0–55 µM respectively, with detection limits of 0.29 µM and 0.66 µM. The mechanism of fluorescence quenching and recovery processes was also explored. Furthermore, Ala-CuInS₂ QDs have been successfully applied to detect Pb²⁺ in tap and river water and detect cysteine in serum.