Self-Catalyzed Surface Reaction-Induced Fluorescence Resonance Energy Transfer on Cysteine-Stabilized MnO₂ Quantum...

A simple one-step ultrasonic method was developed for the synthesis of luminescent MnO₂ quantum dots (MnO₂ QDs) in the presence of cysteine, in which cysteine acted as the exfoliating agent and stabilization ligand. The cysteine-stabilized MnO₂ QDs (Cys-MnO₂ QDs) possess a fluorescence quantum yield of 4.7%, and the fluorescence intensity of Cys-MnO₂ QDs is sensitive to dopamine (DA). The mechanism by which the Cys-MnO₂ QDs catalyzed the self-polymerization of DA to form polydopamine nanoparticles (PDA NPs) and caused the fluorescence resonance energy transfer (FRET) between MnO₂ QDs and PDA NPs was revealed. The sensing platform displayed a wide detection range (0.1-200 μM) with a low detection limit of 28 nM for the detection of DA. Moreover, the Michael addition/Schiff base reaction between the PDA NPs and cysteine on MnO₂ QDs was demonstrated to facilitate the excellent selectivity toward DA detection in the presence of various interferences. This work not only develops a robust method for the preparation of highly luminescent MnO₂ QDs but also provides a universal strategy on the basis of surface chemical reaction-induced FRET for the detection of DA with high sensitivity and selectivity, which is promising in the application of clinical diagnosis, drug delivery, and fluorescence-guided cancer therapy.