Single Nanoparticle Electrochemistry: Reaction Process Analysis And Cancer Protein Detection

It is well acknowledged that nanoparticles（NPs）electrochemistry mainly focuses on the investigation of the average electrochemical behavior of nanoparticle ensembles supported on a macro electrode.However,the heterogeneity as well as the interaction between nanoparticles makes it very difficult to accurately obtain the intrinsic electrochemical information of a single nanoparticle.Single particle impact electrochemistry,as a rapidly developed electrochemical analysis method in the past decade,is able to analyze and characterize single nanoparticle with a nano-or micro-scale,which is of great scientific significance in revealing physicochemical properties and the corresponding reaction processes at the nano-confined domains.In this thesis,we first reviewed the methods,basic principles and applications of single particle impact electrochemistry in the first chapter,followed by the discussion of two studies based on single particle impact electrochemistry in the later chapters.In the second chapter,by combining experiments and theoretical simulations,the reaction kinetics and mass transport behavior of H₂O₂ electroreduction catalyzed by La Ni O₃nanozyme particles were systematically studied in particle ensembles and single particle manner,respectively.It was found that the selectivity of nanozyme to the catalysis of H₂O₂ can be altered only by the enhanced mass transport efficiency without changing the reaction kinetics between nanozyme particle ensembles and single nanozyme particles.This work provides new insights for improving the efficiency and selectivity of the catalysts,and opens up an avenue for developing efficiently new working modes for the catalysts.In the third chapter,by replacing alpha-fetoprotein（AFP）aptamer preadsorbed on Pt NPs using the strong interaction between AFP protein and AFP aptamer,the recovered hydrazine oxidation current signal can be observed on single Pt NPs in the impact experiments,impact electrochemistrallowing the specific detection of AFP,a typical tumor marker of human primary liver cancer.Since single particle impact electrochemistry has a potential to reduce the detection limit down to a single entity level,liquid biopsy is expected to be achieved with ultra-high sensitivity.The key points of this thesis are summarized below:（1）Cubic La Ni O₃ nanozyme particles with porous structure was successfully synthesized by hydrothermal method.The morphology and crystal structure of the resulting particles were characterized by scanning electron microscope,transmission electron microscope,and X-ray diffraction.The electrochemical process of H₂O₂reduction catalyzed by La Ni O₃ nanocubes（La Ni O₃ NCs）ensembles was studied by cyclic voltammetry,and the corresponding reaction kinetics and mass transport process were deeply explored using theoretical simulation.Meanwhile,the simulation showed that the ratio of the peak current of hydrogen peroxide reduction reaction（HPRR）to that of oxygen reduction reaction（ORR）increased with the increasing H₂O₂ diffusion coefficient.（2）By collecting the current-time curves of H₂O₂ reduction catalyzed by single La Ni O₃ NCs in impact experiments and analyzing the average current generated by single nanoparticle at different potentials,we obtained the voltammetry that is equivalent to H₂O₂ reduction at a single nanozyme particle.At the same time,the voltammetry of H₂O₂ reduction catalyzed by a single La Ni O₃ NC was obtained by theoretical simulation.Combining the experiments and simulations,it was found that the current ratio of HPRR to ORR increased by four times only due to the significantly ehnahcned mass transport of H₂O₂ at a single nanozyme particle,resulting in an altered selectivity of H₂O₂ reduction products catalyzed by La Ni O₃ NCs.（3）Pt NPs were synthesized by a seed growth method and were then characterized by SEM and TEM,showing that Pt NPs were spherical in shape with uniform morphology.During the impact with a carbon ultramicroelectrde（CUME）,single Pt NPs can effectively catalyze the oxidation of N₂H₄,genertinga step-like current signal.After the conjugation of the Pt NPs with AFP aptamer through Pt-N coordination,the AFP aptamer coated on the Pt NPs may significantly inhibit the electron transfer of hydrazine oxidation catalyzed by single Pt NPs.Following the incubation of the Pt NPs-AFP aptamer conjugates with APF protein,the aptamer would desorbed from Pt NPs surface due to the strong specific interaction between AFP and aptamer,leading to the recovery of step-like current signals and in turn realizing the specific detection of AFP.Now,a concentration of 30 ng/m L AFP was tested using the current detection method with a good selectivity.