Single entity electrochemistry (SEC) has been attracting increasing interests over the past few years because of its extremely high sensitivity.This method offers the penetrating insights into the properties of individual entities that are masked in traditional ensemble measurements.Electrocatalytic amplification,blocking and direct electrochemical reaction of individual entities by detecting the current transients were employed as single entity collides at an electrode.However,it remains a challenge to enhance the current resolution in the SEC field,especially for the complex electrochemical behaviors.In this work,a strategy using a small-sized ultramicroelectrode and nanoelectrode was performed to reduce both background current and collision frequency,which allowed to reach the typical electrochemical signals.A low-noise electrochemical measurement system was used to acquire the data of single silver nanoparticles (AgNPs) collision at 480 nm Pt nanoelectrode and 10 μm ultramicroelectrode.The electrochemical measurement was carried out in 20 mmol·L^-1 phosphate buffer (pH=7.4) at an applied potential of+0.6 V vs.Ag/AgCl wire in the presence of 58 nm AgNPs.The sampling rate was of 100 kHz by using an A/D convertor and the low-pass fitter was set at 5 kHz.Signal-noise ratio was improved by 50% when the diameter of working electrode decreased from 10 μm to 480 nm,resulting in more detailed information available at nanoelectrode during the collision processes of individual AgNPs.Both the employed nanoelectrode as working electrode and low-noise electrochemical measurement platform can significantly enhance the current resolution of SEC.High current resolution signals with picoampere and sub-millisecond sensitivity were observed for electrochemical oxidation of single AgNPs on nanoelectrode.In addition,the experimentally observed collision frequencies at varying size of ultramicroelectrode and nanoelectrode were in reasonable agreement with the theoretically calculated ones by Fick's Diffusion Laws within a typical variation associated with stochastic measurements.The electrochemical result indicate that individual AgNPs collisions are governed mainly by diffusion process.The high accuracy of the proposed current signal makes it possible to understand the electrochemical behavior of individual AgNPs as a function of the dwell time.Our results have demonstrated that the nanoelectrode would be a powerful platform for better delivering a complete picture of electrochemical behavior of individual entities,visualization of the electrons transfer process at single entity level.

Key words: single nanoparticle electrochemistry, nanoelectrode, collision frequency, high current resolution