Synthesis Of Novel Fluorescent Polydopamine Nanoparticles Based On Michael Addition Reaction And Its Application In Analysis

Polydopamine?PDA?nanoparticles are prepared by self-polymerization of dopamine under alkaline conditions.They have been widely used in surface modification,metal deposition,and drug delivery due to the unique physical and chemical properties or good biocompatibility.Bes ides,PDA is also an endogenous fluorescent nanoparticle.However,there are few applications about the fluorescent properties of PDA.The reason for this result is the low fluorescence quantum yield of PDA.Therefore,enhanced the fluorescence quantum yield of PDA and synthesized PDA with higher fluorescence intensity have important value in expanding its application.Based on the above purpose,we have conducted reseach on the synthesis,properties and the applications of PDA.In this paper,the aim is to screen out small biomolecules used to modify PDA,obtain PDA derivatives with higher fluorescent quantum yield and explore the mechanism.The morphological structure,stability and optical properties of PDA derivatives were investigated by various characterization methods.Then,they were been applied to fluorescent analysis.The main researc h contents are as follows:Part 1:Preparation of bright fluorescent polydopamine-glutathione nanoparticles and their application for sensing of glucose in human serum.A novel water-soluble fluorescent polydopamine derivative,is prepared by the Michael addition reaction between thiol and dopamine?DA?.The effects of different thiol compounds:N-acetylcysteine?N-Cys?,cysteine?Cys?,and glutathione?GSH?on the fluorescence intensity of nanoparticles were also discussed.GSH,which improved the fluorescence of nanoparticles most,was used as reagent to prepared polydopamine-glutathione nanoparticles?PDA-G?-S-?NPs?.The mechanisms of GSH and H₂O₂ in enhanced fluorescence intensity of nanoparticles have been analyzed.Compared with directly polymerized of dopamine,the asprepared PDA-G?-S-?NPs have stronger fluorescence emission.Besides,any hazardous organic solvents does not involve duing the synthesis and the processes are simple.Additionally,the roles of GSH and hydrogen peroxide?H₂O₂?in enhancing the fluorescence intensity are discussed in detail.The thiother in PDA-G?-S-?NPs is easily oxidized by hydrogen peroxide to sulfoxide and sulfone groups,accompanied by a decrease in fluorescence intensity.Therefore,the PDA-G?-S-?NPs can be applied to construct a fluorescent sensor for the detection of H₂O₂.Due to the glucose can be transferred into gluconic acid and H₂O₂in the presence of glucose oxidase,the PDA-G?-S-?NPs system was further applied to sensing glucose.Part 2:Fluorescent polydopamine-glutathione nanoparticles as an analysis platform to detect iron ions and pyrophosphate in environmental analysis.Unique water-soluble endogenous fluorescent polydopamine-glutathione nanoparticles?PDA-GNPs?with high fluorescence quantum yield were firstly prepared referring the above-mentioned method in part 1 and the obtained PDA-GNPs were used to build a probe for Fe³⁺and PPi analysis continuously.The fluorescence intensity of PDA-GNPs decreased sharply with the introduction of Fe³⁺based on electro transfer mechanism.Interestingly,the fluorescence can restore after the adding of PPi in the system of PDA-GNPs/Fe³⁺.Based on the above phenomena,a probe for quantification of Fe³⁺and PPi was set up.In addition,the probe can be used to determine Fe³⁺in practical water samples because of its nanomolar magnitude detection limit and negligible influences of other interferences.Part 3:A sensitive fluorescent sensor for melamine in food based on FRET effect.Utilizing polydopamine-glutathione nanoparticles?PDA-GNPs?as a reducing agent,Ag nanoparticles?AgNPs?were synthesized quickly by one step method.The PDA-GNPs and the generated AgNPs acted as energy donor and energy acceptor,respectively.Accordingly,the fluorescence of PDA-GNPs was quenched based on fluorescence resonance energy transfer?FRET?.In the presence of melamine,the preferential combination of Ag?I?and melamine to form Ag?I?-melamine complex prevents Ag?I?from forming AgNPs,together with fluorescence enhancement compared to the absence of melamine.Under the optimal conditions including the concentration of AgNO₃,reaction time,reaction temperature and pH medium,the fluorescence enhancement efficiency has a linear response to the concentration of melamine from 0.1 to 40?M with a detection limit of 23 nM for melamine.The proposed method is simple,time-saving and low-cost,which was further applied to detect melamine in real milk products with satisfactory results.