Study On New Electrochemical Methods Of Stochastic Collision Of Single Nanoparticles On Ultramicroelectrode

This paper studied the collision between single nanoparticles(NPs) and ultramicroelectrode(UME) by adopting forced convection and fourier transformed sinusoidal voltammetry(FT-SV), and proposed a new method for characterizing the NPs from multidimensional scaling. We employed all kinds of electron microscopy and optical method to study the properties of NPs traditionally. By contrast, the electrochemical method is low-cost and easier to operate, and it’s also fast and efficient. What’s more, in terms of revealing the electrochemical properties of NPs, the electrochemical method is the most immediate way. Therefore, the single nanoparticle collision electrochemical method proposed by Bard has been gained great attention as soon as possible. Because the effective collision time is extremely short between NPs and UME, amperometry was commonly used to detect the collision response signal in the reports which have been published at present. Although the principle and operation of such methods are simple and their sensitivity are relatively high, the critical shortcoming was that when analyzing the response signal, we can only obtained the limited information of concentration of NPs and particle size statistical distribution, and so on, which is far from enough to recognize the characterization of single nanoparticles.For the problem of significant lower collision frequency compared with that of predicted by theory, this phenomenon has been reported by many literatures and encountered by us in the process of actual experiments. Study carried out by us suggests that the collision frequency will increase dramatically if forced convection(stir or flow injection) is applied during detection. But when using the method of stir to introduce forced convection, we can’t control the convection intensity accurately. In order to better study the relationship between convection intensity and collision frequency, we carried out the collision experiments on the condition of flow injection seriously. We counted the number of collisions for a period of 100 s for the experiments carried out with each flow velocity under the same condition of concentration of NPs and got the relation curve between flow rate and the number of collisions. What’s more, we further put forward the possible interaction mechanism between NPs and UME. In order to validate the proposed mechanism that is widely applied, multiple system were used to carry out relevant experiments and similar experimental results were obtained.When adopting amperometry to conduct the experiments, the low potential resolution led to the gaining of limited information that related to the properties of NPs. In this paper, we combined FT-SV, which was researched deeply in our group, with NPs collision experiments. A high frequency and large amplitude sinusoidal potential was continuously applied to the UME, and then the current response was monitored and eliminated the interference of background signal by adopting dynamic way. The collision signal was converted to the frequency domain to achieve the purpose for characterizing single nanoparticles from multidimensional scaling. Study showed that any collision event can be indicated by a sudden change in the phase angle, signals corresponding to each individual NP can be easily isolated and analyzed in both the time domain and the frequency domain. The time domain analysis can provide both temporal and potential resolution, and it enables us to focus on any detail. The frequency domain analysis is even more powerful because it is more immune to noise, and it enables us to grasp the overall information. The combination of time and frequency domain analysis makes the method a very powerful tool in single NP characterization. The FT-SV method was employed to investigate the complex emulsion droplet system, and many new insights with respect to the physical and chemical behavior of the emulsion droplets were therefore revealed. The proposed method is very general and is not limited to signal NP characterization. It has the potential to be employed in many other applications, where the interested signal is small in amplitude, short in duration and appears to be discrete.