Application Of Nanoelectrodes And Solid-State Nanopores In Single-Entity Electrochemistry

Single-entity electrochemistry（SEE）describes a recent trend in state-of-the-art electrochemistry applied to the study of individual“things.”The“thing”measured could be anything（a cell,a molecule,a reaction）that represents a unit of interest.Advances in single entity electrochemistry over the past several decades have been rapid,and are largely driven by the development of new theoretical and experimental tools.Among all of these tools,nanoelectrodes and nanopores are two promising tools at present.Based on this,the paper aims to explore the application of nanoelectrodes and solid nanopores in single-entity electrochemical field.The main work is as follow:1)In this work,functionalized magnetic core-shell Fe₃O₄-Au nanoparticles,which acted as a molecular carrier,were introduced into nanopore electrochemical system for micro RNA sensing in complicated samples with high sensitivity,selectivity,and signal-to-noise ratio（SNR）.This strategy is based on the specific affinity between neutral peptide nucleic acids（PNA）-modified Fe₃O₄-Au nanoparticles and negative miRNA,and the formation of negative Fe₃O₄-Au-PNA-miRNA complex,which can pass through the nanopore by applied a positive potential and eliminate neutral Fe₃O₄-Au-PNA complex.To detect miRNA in complicated samples,a magnet has been used to separate Fe₃O₄-Au-PNA-miRNA complex with good selectivity.This facile and effective method will open up a new approach in the nanopore sensing field.2)Stochastic single-nanoparticle collision amperometry is used to measure the dynamic collision behavior of the electro-oxidation of single Ag nanoparticles at Au nanoelectrode.Results show that the Ag nanoparticles partially oxide by an oxidation event consists of a series of 1 to～10 discrete“sub-events”over a～20 ms interval from the Au nanoelectrode into the bulk solution.Nanodisk electrode and nanopore electrode show a different quantity of sub-events,and oxygen or ions like chlorine could also affect the events numbers.These behaviors could clarify the hidden but intrinsic feature of single nanoparticles help understand its potential for diverse applications.3)Herein we demonstrate a single entity electrochemical method to help us investigate the enhancing hydrogen evolution reaction（HER）activity at a single Mo S₂ QDs level by using silver ultramicroelectrodes（UMEs）.At Ag UMEs,the i-t response for Mo S₂ QDs collision consists of repeated current“spikes”that return to the background level as hydrogen formation and covering QDs surface.In contrast,a stepwise“staircase”i-t response is observed for Mo S₂ QDs colliding on carbon UMEs（C UMEs）.Results also show that the current density of single Mo S₂ QDs collision on Ag UMEs is much higher than on C UMEs,revealing the unique property of metal-Mo S₂ interface on HER performance,which has been demonstrated by thermodynamic analysis and density functional theory（DFT）calculations.It has been found that the interactions between Mo S₂ QDs and substrate UMEs lead to significant changes in the hydrogen adsorption energies(ΔE_ads)and Gibbs free energy（ΔG_H）,resulting in the difference in HER activity.4)In this work,we develop an electrochemical amplification strategy to monitor the electrocatalytic behavior of single G-quadruplex/hemin（GQH）for the reaction between hydrogen peroxide and hydroquinone（HQ）through the collision upon a gold nanoelectrode.The intrinsic peroxidase activities of a single GQH were investigated by stochastic collision electrochemical measurements,giving further insights to understand biocatalytic processes.Based on the unique catalytic activity of GQH,we have also designed a hybridization chain reaction（HCR）strategy to detect miRNA-15with good selectivity and sensitivity.This work provided a meaningful strategy to investigate the electrochemical amplification and the broad application for nucleic acid-sensing at single molecules/particles level.