Exact charge transfer control in quantum dots/molecule system-induced large emission contrast for ultrasensitive and anti-interfering detection

The design of unique fluorescent probes is of paramount importance for boosting the signal-to-noise ratio (SNR) and improving the sensitivity toward target analytes. Herein, we report a hydrogen-bond-driven self-assembled sensing system (CdSe/ZnS QDs@FNAC) composed of quantum dots capped with 3-mercaptopropionic acid (CdSe/ZnS QDs@MPA) and a naphthol-based molecular probe (FNAC) that enables the precise modulation of photoinduced electron transfer (PET) and twisted intramolecular charge transfer (TICT) processes. The surface carboxyl groups on CdSe/ZnS QDs@MPA facilitate FNAC anchoring through hydrogen bonding, ensure water solubility, and generate a localized acidic microenvironment to enhance the oxidative reactivity of potassium permanganate (KMnO₄). Upon exposure to KMnO₄, the PET process of CdSe/ZnS QDs@FNAC was disrupted, triggering oxidative etching-induced fluorescence quenching of the CdSe/ZnS QDs and suppressing the TICT process of the released FNAC probe, resulting in a distinct green fluorescence turn-on response. The ratiometric fluorescence system with a dual-signal response mode enabled the detection of KMnO₄ with rapid response (1 s), high sensitivity (4.80 nM), and excellent SNR, while interference from other oxidants was negligible. The practicality of CdSe/ZnS QDs@FNAC was further verified by integrating a CdSe/ZnS QDs@FNAC-embedded hydrogel-based sensing chip into a portable detector, which enabled the on-site identification of ng-level KMnO₄ particles with high selectivity.