Preliminary Study Of Nucleation And Single Nanoparticle Detection At Liquid-liquid Interface On Micro/nano-pipettes

As a new type of electrochemical analysis platform,the liquid-liquid interface can be used to study electron,ion transfer and coupling reactions.It can also provide a simple approach for biological interface simulation.Therefore,it is often used in various systems such as biology,medicine and chemistry,etc.It is a significant branch of electroanalytical chemistry which is based on the charge transfer across the interface and analyzes the current and voltage signals of the overall liquid-liquid interface system.Compared with the traditional liquid-liquid interface,the micro-liquid-liquid interface has gradually attracted widespread attention due to its advantages of low voltage drop,high mass transfer rate,high detection sensitivity,high stability and simple devices.At the same time,the neat charge arrangement on the liquid-liquid interface makes it an ideal place for nucleation and single nanoparticle detection.However,there are few researches on the collision of single nanoparticles at micro-liquid-liquid interface till now,and only simple interface electrocatalytic reaction collision researches are involved.Based on the liquid-liquid interface supported by micro/nano-pipettes,this thesis systematically explored the nucleation phenomenon that occurs when tetrakis(4-chlorophenyl)borate was used as the organic phase electrolyte,and initially explored the detection of different kinds of single nanoparticles at the liquid-liquid interface with Fourier transform large-amplitude sinusoidal voltammetry,laying the foundation for the establishment of a highly sensitive and selective electrochemical analysis method based on the liquid-liquid interface.This paper mainly finished the following work:(1)The nucleation and collision phenomenon of tetrakis(4-chlorophenyl)borate on the liquid-liquid interface was studied.Tetrakis(4-chlorophenyl)borate was an organic electrolyte that commonly used in liquid-liquid interface system.It was discovered to nucleate at high potential which is outside the potential window.When the interface diameter was narrowed to about 1.4 μm,spike-like response signals which were caused by nucleation collision,appeared in both cyclic voltammetry and constant potential I-t curve.Ion transfer of aqueous electrolytes like HCl,KCl and Li Cl,contributed to the production of insoluble micronuclei such as tris(4-chlorophenyl)boron,potassium tetra(4-chlorophenyl)borate and lithium tetra(4-chlorophenyl)borate.The collision of insoluble micronuclei at interface was the direct cause of spike-like response signals.Further studies showed that the nucleation collision phenomenon will be aggravated with the conditions of smaller interface diameter,higher aqueous electrolyte concentration and applied potential.This work pointed out the potential nucleation problems of common micro-liquid-liquid interface systems,and provided enlightenment for the electroanalysis of micro/nano-liquid-liquid interfaces,especially the electrochemical detection of single particles.(2)The Fourier transform large-amplitude sinusoidal voltammetry was applied to the liquid-liquid interface platform in micro/nano scale,to identify and distinguish single nanoparticles of different types and sizes.This work utilized data processing methods like shorttime Fourier transform to perform time-domain background subtraction of the platinum nanoparticle response current to separate single-period sine volt-ampere curve of the collision process firstly.Then,it subtracted frequency-domain background of the response current to obtain stable and reproducible first harmonic phase angle,and these characteristic information were related closely to the properties of platinum nanoparticles.For platinum nanoparticles with different sizes,there was no obvious monotonic relationship between the first harmonic phase angle of the current response signal and the particle size,but it varied within ±25° with the difference of particle zeta potential.For different kinds of nanoparticles liked Au and Pt,their first harmonic phase angle of collision signal distributed in different areas because of different dielectric constants,which provides a prerequisite for their simultaneous detection.Finally,based on the difference in phase angles of different nanoparticles,the Pt and Au nanoparticles of the same size were successfully detected with highly selective recognition.This work solved the problem of low signal-to-noise ratio within the potential window by applying large amplitude potential,and realized the identification and differentiation of labelfree single nanoparticles with lower technical cost.