Preparation Of Several MnO₂ Based Nanomaterials And Their Applications In Chemical/Biological Sensing

Manganese dioxide?MnO₂?material has been widely used in the fields of optical sensing,supercapacitors,drug transport and release,and photodynamic therapy due to its strong oxidation,easy degradation and good biocompatibility.Based on a comprehensive review of the synthesis,properties and applications of Mn O₂-related nanomaterials,this work further explores the application of MnO₂ nanosheets in biosensors,and first synthesizes two MnO₂ quantum dots?QDs?by one-step ultrasonic method,and explores their application in sensing.The specific contents are as follows:1.A fluorimetric and colorimetric method is described for the determination of glutathione?GSH?and silver?I?.It is based on the use of MnO₂ nanosheets that were prepared by solution mixing and exfoliation.They display oxidase-mimicking activity and can catalyze the oxidation of o-phenylenediamine?OPD?to form yellow 2,3-diaminophenazine?DAP?.GSH can quickly destroy the structure of MnO₂ nanosheets affecting the oxidase-mimicking activity and causing a decrease in fluorescence and absorbance intensity.However,on addition of Ag⁺,a complex is formed with GSH.It prevents the destruction of MnO₂nanosheets so that the enzyme mimicking activity is retained.A dual-method for the determination of GSH and Ag?I?was developed.2.Luminescent MnO₂ QDs has been firstly prepared via a facile one-step ultrasonic method.With the assistant of bovine serum albumin?BSA?,the synthesized MnO₂ QDs?BSA-MnO₂ QDs?display strongly enhanced fluorescence?FL?,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 MnO₂nanosheets 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?FRET?.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 dual role of BSA.This work not only opens a facile and universal strategy to synthesize luminescent MnO₂ QDs with enhanced FL,but provide a possible sensing platform through tuning the micro-environment of MnO₂ QDs.3.MnO₂ quantum dots with strong fluorescent were prepared via a simple one-step ultrasonic method in the presence of cysteine,in which Cys plays dual functions as the exfoliating agent owing to its reducibility and intramolecular hydrogen bond,and as the protective and stabilization agent to provide a friendly micro-environment for Mn O₂ QDs.MnO₂QDs accelerated the self-polymerization of DA to form polydopamine nanoparticles?PDA NPs?,which would approach to the Cys-MnO₂ QDs owing to the Cys can capture PDA NPs through Michael addition/Schiff base reaction.The shortened distance between PDA NPs and MnO₂ QDs resulted the FRET between them and quenched the FL intensity of Cys-MnO₂ QDs.This work develops a sensitive detection strategy for DA via the novel mechanism of chemical reaction induced FRET.