Efficient sensitization of CdTe QDs towards PTCDA for sensitive photoelectrochemical Hg²⁺ assay

Herein, a sensitive photoelectrochemical (PEC) biosensor was designed for the detection of mercury ions (Hg²⁺) on the basis of the efficient sensitization of cadmium telluride quantum dots (CdTe QDs) towards 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and the significant quenching ability of a thymine-Hg²⁺-thymine (T-Hg²⁺-T) structure. The proposed CdTe QD/PTCDA sensitized structure was successfully constructed via continuous incubation of PTCDA and CdTe QDs on the glassy carbon electrode (GCE) interface, which embraced strong light absorption capacity and high carrier separation efficiency, giving rise to a remarkably improved initial photocurrent response. Notably, the PEC signal generated from the CdTe QD/PTCDA sensitized structure was almost fivefold higher than that of PTCDA owing to the efficient sensitization of CdTe QDs towards PTCDA. Once target Hg²⁺ ions were added, a T-rich S1 strand modified on the surface of 1-hexanethiol (HT)/S1/gold nanoparticles (Au NPs)/CdTe QDs/PTCDA/GCE immediately reacted with Hg²⁺ to produce multiple stable T-Hg²⁺-T structures. Therefore, the initial PEC signal would be considerably quenched by a high steric hindrance effect derived from the T-Hg²⁺-T structures. As a result, a quenched PEC response could achieve the detection of Hg²⁺ in concentrations ranging from 100 fM to 1000 nM. More importantly, the combination of the CdTe QDs/PTCDA sensitization structure and the T-Hg²⁺-T structure paves a promising pathway to developing a novel PEC biosensing platform for Hg²⁺ detection and also provides a favorable strategy for monitoring environmental pollution related to Hg²⁺.