Research And Application Of Single-particle Interface Reaction Based On Single Molecule Fluorescence Technology

The interfacial reaction of nanoparticles plays an important role in many fields of the chemical industry.The improvement of industrial production efficiency needs to realize the rapid reaction by adjusting the reaction conditions and the interface properties of nanoparticles.Therefore,it is necessary to discuss the mechanism of kinetics and thermodynamics of the interfacial reaction process.In the traditional research methods,the conclusions obtained in the experiment are the average results of many nanoparticles,which often ignore the heterogeneity information.This information often contains more accurate conclusions about the relationship between structure and activity as well as the relationship between reaction condition and activity.With the development of physicochemical characterization technology,various optical microscopes were widely used in the study of the single-particle interface reaction process because of their high temporal and spatial resolution.In this paper,we used single-molecule fluorescence microscope to study the adsorption/desorption process and catalytic reaction process at the single-particle level.The specific contents are as follows:(1)In order to study the adsorption/desorption process,we designed a detection system with carbon quantum dots(CDs)as fluorescence probes and adsorbed material and graphene oxide(GO)as adsorption material.The in-situ monitoring of the adsorption/desorption process was realized by collecting the fluorescence intensity time trajectory.This work reveals the kinetic model of the adsorption/desorption process at the single-cycle level and the activity and distribution of adsorption active sites on the GO surface.In addition,we also studied the effect of the change of microenvironment on the adsorption/desorption process by adding sodium pyrophosphate(PPi).The experimental results show that due to the electronic interaction between PPi and CDs,PPi can not only accelerate the desorption process by increasing the desorption pathway,but also promote the adsorption process thermodynamically.This fouding provides an idea for the regulation of adsorption and desorption process in the process of catalytic reaction.(2)The catalytic oxidation process on the surface of Ag nanoparticles and Au@AuAg nanoparticles was studied by monitoring the fluorescence products by single-molecule fluorescence microscope.Due to the high time resolution of this technology,the reaction process on the surface of two catalysts can be divided into three steps:reactant adsorption,reaction activation,and product desorption.And the reaction kinetic model was also constructed.Combined with the structural characterization,theoretical calculation,and single-molecule experimental results,we further studied the source of the synergistic effect between Au and Ag and its influence on the three reaction steps.These conclusions deepen the understanding of the synergistic effect and have guiding significance for the structural design of highly active bimetallic catalysts.(3)We found that the higher electron cloud density at the active site of the catalyst will significantly improve its reaction activity.Based on this conclusion,we further regulated the surface composition of bimetallic nanoparticles to change the degree of electron transfer between Au and Ag.Through structural optimization,the electron cloud density of the Ag sites was further increased to obtain a higher activity peroxidase-like catalyst.Applying this high-performance catalyst in the sensing system of hydrogen peroxide(H2O2)and cysteine(Cys),we realized the detection of H2O2 in a wide linear range and the quantitative detection of Cys at ultra-low concentration.