Gelatin-coated Silver Nanoparticles And Graphene Oxide Synergizes With Silver Nanoparticles To Enhance Terbium Fluorescence For Dopamine Detection

Dopamine(DA)is one of the important catecholamine neurotransmitters and plays a vital role in various cognitive functions.Many neurodegenerative diseases such as Parkinson’s disease,Huntington’s disease and Alzheimer’s disease are closely related to abnormal DA levels.Monitoring individual DA level fluctuations is very important for early detection of neurodegenerative stress-related diseases.On one hand,the content of DA in biological environments such as blood and urine is very low;on the other hand,many coexisting substances in biological fluids,such as ascorbic acid,uric acid and epinephrine,may interfere with the detection of DA.Therefore,it is very important to develop a highly sensitive and selective detection method for DA.Metal-enhanced fluorescence(MEF)is derived from the near-field interaction of fluorophores and surface plasmon resonance(SPR)of metal nanoparticles.Silver nanoparticles(AgNPs)have a strong surface plasmon resonance effect and are ideal substrate materials for MEF.The distance between the fluorophore and the metal nanoparticle is an important factor that affects the performance of the MEF.By coating the nanoparticle or introducing a spacer agent to control the distance,a large fluorescence enhancement effect can be achieved.Rare earth luminescent ions such as Tb(Ⅲ)and Eu(Ⅲ)have the characteristics of narrow emission band,long fluorescence lifetime(microsecond level),and large Stokes shift.DA has a catechol structure and can coordinate with rare earth luminescent ions such as Tb(Ⅲ).Gelatin carries a variety of chemical groups and has a high affinity for metal surfaces.Gelatin is very suitable to be a coating agent to improve the properties of silver nanoparticles.Graphene oxide(GO)has a rigid plane,good water solubility,and abundant chemical functional groups.The hydroxyl and carboxyl groups on the surface can coordinate with Tb(Ⅲ),This thesis aims to study the fluorescence enhancement effect of gelatin(gel)coated silver nanoparticles(AgNPs@gel)and GO synergistically with AgNPs on Tb(Ⅲ)-DA complexes to improve the detection sensitivity of DA.This thesis is divided into three chapters.The first chapter is an introduction,which summarizes the research progress of DA detection methods,the principle of MEF,the application of MEF based on AgNPs,the research progress of rare earth fluorescence sensitization methods,and briefly introduce the use of GO to detect DA.In chapter two,a composite fluorescent sensing platform was constructed based on the MEF effect of AgNPs@gel on Tb(Ⅲ)luminescence,which realized the highly sensitive and selective detection of DA.We adjusted the mass ratio of silver nanoparticles(AgNPs)to gelatin and screened them based on their fluorescence enhancement effect.The study found that the best fluorescence enhancement effect can be achieved when the mass ratio was 0.08.AgNPs@gel is used as the base material of MEF,and gelatin is used as the bridging substance between Tb(Ⅲ)-DA complex and AgNPs,which regulated the distance between the fluorophore and nanoparticles,promoted the MEF effect,and significantly enhanced Tb(Ⅲ)luminescence.In addition,the coating effect of gelatin effectively improved the aggregation of AgNPs,And gelatin is rich in chemical functional groups such as hydroxyl and carboxyl groups that can coordinate with Tb(Ⅲ)to replace some of the surrounding water molecules,reduce the non-radiative attenuation rate and non-radiative transitions,further promote the fluorescence enhancement effect,and improve DA detection sensitivity.Studies have shown that the composite probe has high selectivity for DA,a variety of amino acids and inorganic salts basically do not interfere with the determination of DA,and has good anti-interference ability.The fluorescence enhancement mechanism of the system was studied by ultraviolet-visible absorption spectroscopy,fluorescence spectroscopy,quantum chemical calculation and light lifetime,the interaction mechanism between AgNPs@gel,Tb(Ⅲ)and DA was explored by Fourier transform infrared spectroscopy,Raman spectroscopy,resonance light scattering spectroscopy and TEM.In chapter three,on the basis of enhanced Tb(Ⅲ)fluorescence from AgNPs,GO was added to further enhance the luminescence through the synergistic effect of GO and AgNPs,so as to realize the sensitive detection of DA.AgNPs was used as the base material of MEF.GO immobilized Tb(Ⅲ)-DA-AgNPs.The hydroxyl and carboxyl groups on the surface of GO participated in the coordination with Tb(Ⅲ),replacing part of the solvent water molecules,reducing the non-radiation attenuation rate,and promoting the energy transfer.In addition,AgNPs were adsorbed on the surface of GO,the LSPR absorption peak of AgNPs broadened,which increased the overlap area of the spectrum with Tb(Ⅲ),which improved the luminous efficiency of the system.Moreover,GO provided a rigid plane,which limited the free movement of molecules,and the MEF effect was realized to greater extent,leading to further enhancement of the fluorescence of the system.This method monitored DA at the concentration of nanomolar level,and had good selectivity and anti-interference ability,the interaction mechanism of Tb(Ⅲ),DA,AgNPs and GO was studied by ultraviolet-visible absorption spectroscopy,fluorescence spectroscopy,TEM and Fourier transform infrared spectroscopy.This system has developed a new method of using GO to enhance fluorescence,which provides a new idea for the construction of fluorescent biosensors.