The Preparation Of Fluorescent Organic Nanoparticles Based On Polydopamine And Their Applications In Fluorescence And Electrochemiluminescence Detection

Fluorescent organic nanoparticles(FONs)have been widely used in the fields of biotechnology,chemical sensing,biosensing,medicine,photocatalysis,etc as their photophysical,chemical and electrochemical properties may change with their composition,size or shape,which are different from single molecules.In particular,FONs have the advantages of abundant elements,low toxicity,good biocompatibility,potential biodegradability and diverse structural properties compared with other inorganic fluorescent nanoparticles.Since dopamine(DA)and its analogs are easily oxidized to initiate self-polymerization in alkaline solution,these molecules have been commonly utilized for the preparation of FONs.Moreover,FONs with different fluorescence properties can be prepared by changing the related reaction conditions(such as buffer solution,oxidant,reaction time,etc.).In this thesis,different FONs were prepared by the electrochemical oxidation of 3,4-dihydroxyphenylalanine(DOPA)monomer or the hydroxyl radical degradation of polydopamine and used to construct the fluorescence and electrochemiluminescence(ECL)sensors for metal ion and biomolecule determination,respectively.This thesis consists of the following three parts:(1)FONs of polylevodopamine(polyDOPA-FONs)were prepared by electrochemical methods,which were utilized to construct fluorescent sensors for detecting Fe3+,Cu2+ and Hg2+,respectively.3,4-dihydroxyphenylalanine(DOPA),an analogue of dopamine(DA),has been used to prepare FONs through the electrochemical oxidation method.The as-prepared polyDOPA-FONs have good optical properties,polyDOPA-FONs contain diverse functional groups at the surfaces,such as-COOH,-NH2,-OH,etc.,which can serve as the binding sites of different metal ions.Then,the fluorescence sensing properties for metal ions of polyDOPA-FONs was systematically explored.The same kind of polyDOPA-FONs were used to establish fluorescence sensors for the detection of Fe3+,Cu2+and Hg2+in different buffer solution systems and the parameters affecting the performance of the sensor were explored.The results showed that a turn-off sensor based on the polyDOPA-FONs was further established for the detections of Fe3+,Cu2+and Hg2+ in the linear ranges of 0.10?13.00,0.10?3.50 and 0.10?11.00 ?M with the corresponding detection limits of 7.00×10-8,3.00×10-8 and 6.00×10-8 M,respectively.This sensor could also be applied to analyze the three metal ions in water samples.Finally,the possibility for the fabrication of an "ON-OFF" sensor and the recycling of the polyDOPA-FONs was confirmed by reversibly switching the fluorescence in Fe3+/pyrophosphate ion(PPi),Cu2+/cysteine(Cys)and Hg2+/ascorbic acid(AA)couples.(2)In order to further realize the detection of lower concentration of Hg2+,we constructed an ECL sensor for detection of Hg2+by taking the advantages of ECL sensing and the significant quenching effect of Hg2+on ECL of FONs of polylevodopamine(polyDA-FONs).Firstly,DA was utilized as a monomer and polymerized by dissolved oxygen in an alkaline solution.Secondly,the reaction solution was further heated and aged in a reactor,where large black polydopamine nanoparticles were perpared.Thirdly,polyDA-FONs were prepared by the degradation of large black polydopamine nanoparticles in alkaline solution containing H2O2.Finally,strong ECL was produced on the glassy carbon electrode(GCE)when polyDA-FONs were used as the ECL emitter and K2S2O8 was used as the coreactant(compared to bare GCE).Moreover,an ECL sensor for detecting Hg2+ was constructed based on the significant quenching effect of Hg2+on the ECL of polyDA-FONs,and the parameters affecting the performance of the sensor were explored.The results showed that the linear range of the sensor is 0.030?10.00 ?M,and the detection limit is 1.51×10-10 M(lower than the detection limit in Chapter 2).In addition,the sensor has good selectivity and reproducibility,and can be applied to the detection of Hg2+ in the wastewater of aquaculture plants.(3)This chapter extended the application of polyDA-FONs to the detection of glutathione(GSH)based on the excellent ECL performance of polyDA-FONs/S2O82-system.GSH widely exists as the antioxidant and free radical scavenger in human body and can react with the free radical oxidant SO4·-produced by reduction of S2O82-.Therefore,GSH can impede the ECL production of the polyDA-FONs,and ECL signal decreased linearly with the increase of GSH concentration.It is feasible to apply polyDA-FONs/S2O82-system to detect GSH.The parameters that affect the performance of the ECL sensor are optimized The results showed that under the optimal conditions,the ECL sensor had a good linear relationship in the concentration of 0.10?70.00 ?M,and a low detection limit(9.77×10-10 M)for the detection of GSH,meanwhile,showed good selectivity and reproducibility.It was also used for the detection of GSH in human serum samples.