Spectroscopic Study Of Serum Protein Quenching Mechanism And Construction Of Iron Ion Sensor

Fluorescent sensors have been widely used in the fields of environmental water detection,biological detection and biological imaging.The fluorescent sensor can detect the substance by the change of fluorescence intensity caused though the interaction between the fluorescent receptor and substance.Therefore,Fluorescencebased sensors have been extensive applications in environmental monitoring and biomedical since they offer significant advantages of high rapidity,sensitivity,selectivity and simplicity.Quantum dots have been used for long-standing detection of metal ions,but almost all of the traditional quantum dots are made of heavy metals.Compared with the expensive synthetic route of semiconductor quantum dots,CQDs can not only be synthesized on a large scale and cheaply,but also have excellent properties such as water solubility,acceptable biocompatibility,negligible cytotoxicity and chemical inertness.Moreover,CQDs have functional groups such as hydroxyl,carboxyl,carbonyl,and epoxy groups,which make them have good water solubility,and they also have the potential to functionalize organic,biological or polymer.Therefore,CQDs can be considered as a substitute for traditional semiconductor quantum dots,which overcome the problems of expensive synthesis,toxicity and environmental pollution.Based on this,the fluorescence quenching method is used to study the interaction between graphene oxide and bovine serum albumin.Next,fluorescence quenching method is used to construct fluorescent nanoscale sensor for detecting iron ions and applied to water detection.(1)The interaction between BSA and GO was studied by fluorescence spectroscopy,and the fluorescence quenching data between BSA and GO was calculated using the Stern-Volmer equation.At three different temperatures of 298K,306K,and 313K,the quenching constants Ksv were calculated to be 3.025×104 L/mol,1.864×104 L/mol,1.462×104 L/mol,respectively.The quenching constant of BSA and GO decreases with increasing temperature,and the value of the quenching rate constant kq is much larger than the maximum collision rate constant,indicating that there is static quenching between BSA and GO.The corrected Stern-Volmer equation was used to explain the quenching process of BSA to GO,which confirmed the fluorescence quenching mechanism of BSA and GO was mainly determined by static quenching,combined with dynamic quenching.The values of the binding constant KA and the binding site n are calculated by the hyperbolic equation.The value of KA decreases with increasing temperature,further indicating that the quenching process between BS A and GO is mainly a static quenching.And then,the subsequent observation of the UV absorption curve verified the possibility of static quenching between BS A and GO.Thermodynamic studies showed the interaction between BSA and GO was a van der Waals interaction or hydrogen bonding,and the quenching process was exothermic and spontaneous,which was due to the enthalpy change(?H),the entropy change(?S),and the Gibbs value free energy(?G)are all negative.Finally,synchronous fluorescence experiments showed that the presence of GO changed the conformation of BSA.When ??=60nm,the position of the maximum absorption peak of BSA shifted,confirming that GO interacts with tryptophan,causing its microenvironment to change.(2)CQDs/ZnO/CdS nanoparticles were prepared by a simple deposition method and used as a highly sensitive and fast Fe(?)ion fluorescence sensor.XRD and SEM characterization,as well as detection of ultraviolet absorption spectrum and steady-state fluorescence spectrum,verified that the preparation of CQDs/ZnO/CdS nanoparticles was successful.In subsequent ion detection experiments,it was found that the nanoparticles exhibited excellent recognition performance for iron ions,and further interference experiments with other metal ions were performed to verify the specificity of CQDs/ZnO/CdS nanoparticles for detection of Fe(?)ions.Then,according to the changes in the fluorescence intensity of iron ions and nanoparticles with different concentrations,a fitting curve was drawn with the concentration of iron ions,and the detection limit was calculated to be 1.72×10-7M,the detection range was 1-50 ?M.Using this fluorescence sensor,the detection of iron ions in the actual water is realized by the addition method.The quenching constant between composite nanoparticles and Fe(?)ions was calculated by the Stern-Volmer equation.It was concluded that the quenching process should be static quenching by decreasing the quenching constant with increasing temperature.The fluorescence lifetime test also verified that the quenching process was static quenching.According to the thermodynamic analysis,the entropy and enthalpy between the nanoparticles and Fe(?)ions are both positive,and the free energy is negative,indicating that the interaction may be a strong hydrophobic force and the quenching process is endothermic and spontaneous.