CdTe Quantum Dots (QDs) Based Kinetic Discrimination of Fe²⁺ and Fe³⁺, and CdTe QDs-Fenton Hybrid System for Sensitive Photoluminescent Detection of Fe²⁺

A method based on the quenching kinetics for the fluorescence of glutathione capped CdTe quantum dots (GSH-CdTe QDs) was developed for discriminating Fe 2+ and Fe 3+, and a GSH-CdTe QDs-Fenton hybrid system was constructed for sensitive and selective determination of trace Fe 2+ . Although both Fe 2+ and Fe 3+ could quench the fluorescence of GSH-CdTe QDs, the quenching kinetics was quite different for Fe 2+ and Fe 3+ . The fluorescence of the GSH-CdTe QDs (30 nM) was quenched by about 18% in 1 min after the addition of Fe 3+ (10 μM), and remained unchanged with further increase of reaction time. In contrast, the fluorescence intensity of the GSH-CdTe QDs decreased by about 65% in the first 5 min after the addition of Fe 2+ (10 μM), then slowly decreased by 15% in the next 25 minutes. Other transition metal ions like Cu 2+, Ni 2+ and Co 2+, Zn 2+, and Mn 2+ also gave very different quenching kinetics of the GSH-CdTe QDs from Fe 2+ . No significant effect of the capping agents (GSH, thioglycolic acid, and mercaptopropionic acid) for the QDs on the pattern of the time course of the fluorescence of the QDs for Fe 2+ or Fe 3+ was observed. To achieve selective determination of Fe 2+ in the presence of Fe 3+, trace H 2 O 2 was introduced to establish a QDs-Fenton hybrid system. The Fenton reaction between Fe 2+ and H 2 O 2 resulted in hydroxyl radicals which can effectively quench the fluorescence of the QDs through electron transfer from the conduction band of the QDs to the single occupied molecular orbit of hydroxyl radicals. The high redox potential of hydroxyl radicals (2.8 V) permits more effective quenching of the fluorescence of the QDs than Fe 2+ . The detection limit of the developed method was 5 nM for Fe 2+ . The recovery of Fe 2+ spiked in water samples ranged from 96% to 105%.