Ligand displacement-induced fluorescence switch of quantum dots for ultrasensitive detection of cadmium ions

• A simple CdTe QD–Phen sensor is constructed for detecting Cd2+.
• The sensor is operated with a ligand-displacement induced PL switch strategy.
• The detection limit of 0.01 nM for Cd2+ is achieved.
• This sensor features to discriminate Cd2+ versus Zn2+, and succeeds in real water samples.

This paper reports the construction of a simple CdTe quantum dots (QDs)-based sensor with 1,10-phenanthroline (Phen) as ligand, and the demonstration of a novel ligand displacement-induced fluorescence switch strategy for sensitive and selective detection of Cd2+ in aqueous phase. The complexation of Phen at the surface quenches the green photoluminescence (PL) of QDs dominated by a photoinduced hole transfer (PHT) mechanism. In the presence of Cd2+, the Phen ligands are readily detached from the surface of CdTe QDs, forming [Cd(Phen)2(H2O)2]2+ in solution, and as a consequence the PL of CdTe QDs switches on. The detection limit for Cd2+ is defined as ∼0.01 nM, which is far below the maximum Cd2+ residue limit of drinking water allowed by the U.S. Environmental Protection Agency (EPA). Two consecutive linear ranges allow a wide determination of Cd2+ from 0.02 nM to 0.6 μM. Importantly, this CdTe QDs-based sensor features to distinctly discriminate between Cd2+ and Zn2+, and succeeds in real water samples. This extremely simple strategy reported here represents an attempt for the development of fluorescent sensors for ultrasensitive chemo/biodetection.

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