Facile Preparation of MnO <sub/>2</sub> Quantum Dots with Enhanced Fluorescence via the Micro-environment Engineering with the Assistance of Some Reductive Biomolecules

摘要： MnO2 nanomaterials have been aroused wide attention because of their nano-enzyme activity, redox property, good biocompatibility and therapy-related activities. However, not any report about self-luminescent MnO2 materials are concerned to date, which greatly hampered their further development in various fields. In this paper, luminescent MnO2 quantum dots (MnO2 QDs) has been firstly prepared via a facile one-step ultrasonic method. With the assistant of bovine serum albumin (BSA) or cysteine (Cys), the synthesized MnO2 QDs (BSA-MnO2 QDs or Cys-MnO2 QDs) display strongly enhanced fluorescence (FL). The prepared BSA-MnO2 QDs with the particles size of about 1-2 nm show the maximum excitation and emission peaks at 320 and 410 nm with excellent salt stability, anti-photo bleaching ability and time stability. It is confirmed that BSA play the dual function as the exfoliating agent to promote the exfoliation of bulk MnO2 nanosheets and as the capping agent to provide a friendly micro-environment for MnO2 QDs. Ag ions can destroy the micro-environment of BSA-MnO2 QDs owing to the in-situ formation of Ag nanoparticles (Ag NPs) mediated by the BSA on the surface of the QDs. Then these Ag NPs can quench the FL intensity of the QDs by fluorescence resonance energy transfer. However, the FL strength of BSA-MnO2 QDs is recovered after adding H2O2 and NaHS since they may react with Ag NPs to produce Ag+ and Ag2S, which further confirmed the role of BSA. This work not only opens a facile and universal avenue to synthesize luminescent MnO2 QDs with enhanced FL, but provide a possible sensing platform through tuning the micro-environment of MnO2 QDs. The MnO2 QDs with outstanding performance may show great potential as promising fluorescent probes in the fields of biological imaging, optical sensing, drug delivery and therapy.