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

Abstract 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.