纳米电极上单个银纳米颗粒氧化电流分辨能力的研究

Study on the Resolution of Single Silver Nanoparticles Electrochemical Behavior at Nanoelectrode

在单体电化学的研究中,提高信号分辨能力是一项挑战.缩小电极尺寸有利于对体系噪音电流的控制,有望提高电流的分辨能力.本研究制备了直径为480 nm的铂纳米圆盘电极,选用银纳米颗粒碰撞电极产生银电化学氧化行为作为模型,考察了纳米电极相对于微米电极在单体电化学信号分辨能力上的优化作用.研究表明,不同尺寸电极上观察到的银纳米颗粒的碰撞频率符合扩散控制的碰撞规律.说明单个电流信号对应于单个纳米颗粒的电化学氧化过程.同时,当电极尺寸缩小至纳米尺度后,噪音电流下降50%左右,提高了对银纳米颗粒碰撞电极过程中氧化电流的分辨能力.研究结果表明使用纳米电极能进一步提高对单体电化学中微小电流的检测能力.

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 prn ultramicroelectrode. The electrochemical measurement was carried out in 20 mmoloL-1 phosphate buffer （pH= 7.4） at an applied potential of ＋0.6 V vs. Ag/AgC1 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 diam- eter of working electrode decreased from 10/am 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 sig- nals with picoampere and sub-millisecond sensitivity were observed for electrochemical oxidation of single AgNPs on nano- electrode. In addition, the experimentally observed collision frequencies at varying size of ultramieroelectrode and nanoelec- trode 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 electro- chemical behavior of individual AgNPs as a fimction 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, visu- alization of the electrons transfer process at single entity level.