A novel nonenzymatic biosensor for evaluation of oxidative stress based on nanocomposites of graphene blended with CuI

A high-sensitive nonenzymatic hydrogen peroxide (H₂O₂) biosensor based on cuprous iodide and graphene (CuI/Gr) composites has been explored for the detection of H₂O₂ released by living cells and monitoring the oxidative stress of cells under excellular stimulation. The biosensor properties were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), amperometric i-t curve, and the redox-competition mode of scanning electrochemical microscopy (SECM). Our observations demonstrate that the CuI/Gr nanocomposites modified glassy carbon electrode (GCE) exhibits excellent catalytic activity for H₂O₂ with relatively low detection limit and a wide linear range from 0.5 μM to 3 mM. Moreover, the redox-competition mode of SECM imaging study further illustrates the improved electrochemical catalytic capability for H₂O₂ reduction with CuI/Gr nanocomposites deposited on graphite electrode. Hence, the as-prepared nonenzymatic H₂O₂ biosensor could be used to detect H₂O₂ release from different kinds of living cells under stimulation while eliminating the interference of ascorbic acid.     

ITO上AuPd合金和Au阵列图案的制备及电催化活性的SECM表征

利用电化学湿法印章技术在氧化铟锡(ITO)导电玻璃上制备AuPd合金和Au的双组分阵列图案. 采用具有微浮雕图案的琼脂糖印章存储足够多的溶液,并通过控制电沉积的时间来控制图案厚度. 应用场发射扫描电子显微镜(FE-SEM),X射线能谱分析(EDX)和原子力显微镜(AFM)分别对ITO表面上的AuPd合金和Au的形貌和组分进行表征,并通过循环伏安(CV)技术和扫描电化学显微镜(SECM)研究比较了Au和AuPd合金的催化活性. 利用扫描电化学显微镜(SECM)的针尖产生-基底收集(TG-SC)模式和氧化还原竞争(RC)模式,发现Au电极对二茂铁甲醇氧化物(FcMeOH⁺)电催化还原能力高于AuPd合金电极,而在AuPd合金上催化还原H₂O₂的能力显著高于Au.     

Application of scanning electrochemical microscopy and scanning electron microscopy for the characterization of carbon-spray modified electrodes

Different gold surfaces modified by carbon-spray have been investigated by scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM). A transformation of the SECM image to a distance-location profile is proposed which assists the correlation of both images. The structures found in the transformed SECM images of carbon-spray layers on gold substrates can be explained by the topographic features visible in the SEM pictures. Tempering the carbon spray results in an increased density of electrochemically reactive carbon particles which could be confirmed by cyclic voltammetric investigations. Gold minigrids modified with carbon spray expose some areas of especially large currents which could not be predicted from their SEM images. This effect may result from particles located at the edge of a wire intersection having relatively large active surfaces per particle. They contribute significantly to the total current of the minigrid.     

Oxygen as redox mediator in scanning electrochemical microscopy. Application to the study of localised acid attack of marble

Oxygen from air-saturated aqueous solutions was employed as redox mediator in SECM experiments. Accurate approach curves under negative-feedback conditions were obtained using platinum and gold microelectrodes. Imaging experiments were also carried out, using a 2.5 microns gold microelectrode and oxygen that acted as distance mediator. The topographic images of a glass surface and that of a marble surface prior and after localised acid attack were recorded. High concentrations of hydrogen ions were produced locally, at the microelectrode tip held 3 microns above the marble surface, by applying a large enough positive potential within the oxygen evolution region. Under these conditions, the dissolution of CaCO3 occurred. Pits were produced, and the crater volumes thus obtained were linearly dependent on the electrolysis time.     

SECM基本原理及其在金属腐蚀中的应用

扫描电化学显微镜（SECM）是一种具有较高空间分辨率的化学显微镜,在成像和动力学研究已经广泛应用. 本文简要介绍SECM基本原理,综述2009年以来SECM在腐蚀方面的应用,包括扫描成像和异相转移电子化学活性的研究,并简要介绍了作者课题组在SECM方面的研究工作,展望SECM在腐蚀研究的应用.     

Fabrication and Use of Dual‐function Iridium Oxide Coated Gold SECM Tips. An Application to pH Monitoring above a Copper Electrode Surface during Nitrate Reduction.

The fabrication of a gold microelectrode modified with iridium oxide film (IrO_x) and its use as tip with a dual function in SECM experiments is reported. The defective structure of the coating onto the microelectrode surface was used as strategy to combine the advantages of both amperometric (for current‐distance determination) and potentiometric (for pH sensing) SECM operation modes. Approach curves, using oxygen and hexaammineruthenium(III) as redox mediators, were obtained without significant loss of the performance and reproducibility of the potentiometric pH response. This allowed the precise positioning of the proposed tip above a substrate in SECM experiments and, subsequently, to monitor pH at the substrate surface. The IrO_x modified microelectrode was applied successfully in SECM experiments involving the local proton consumption during the nitrate reduction at a copper cathode surface.     

Imaging the Origins of Coating Degradation and Blistering Caused by Electrolyte Immersion Assisted by SECM

A new method to image the origins of coating degradation and the nucleation and subsequent growth of blisters by using SECM in the feedback mode is proposed. The unique role of chloride ions towards coating performance has been established at a very early stage following immersion of the sample. We believe this to show the earlier stages of blistering in a coated metal system ever recorded. The method allowed for the first time to detect the nucleation and to monitor quantitatively the growth process of an individual blister, because it effectively advanced towards the microelectrode when scanned at constant height over the sample.     

Development of Solid Contact Micropipette Zn-Ion Selective Electrode for Corrosion Studies

Micron-size ion selective micropipettes can be used in scanning electrochemical microscopy (SECM). They can provide excellent spatial resolution. Unfortunately the resistance of these small sensors is high. Their application needs special shielding and slow scanning rates. Usually their lifetime hardly exceeds a few days.

Zinc layer or dispersed zinc particles containing films are often used for providing cathodic protection against corrosion in case of metal surfaces. Therefore, in corrosion studies, measurements of local zinc ion concentration can give important information about the nature of the process. For corrosion studies we needed SECM measuring tips for imaging concentration profiles of Zn²⁺ions involved in surface processes. Based on our earlier experience, solid contact micropipettes for selective measurements of Zn²⁺ion concentration were prepared with a tip size of a few micrometers. The properties of the micropipettes were investigated. They were also used in SECM imaging. In this paper, details of Zn²⁺ion selective microelectrode preparation are described. Data about their properties, lifetime, resistance, and ion activity response are shown. Preliminary findings in SECM imaging of zinc ion concentration profiles are shown. The improvement of the scanning rate achieved by lowering tip resistance is a main advantage in potentiometric SECM.     

Local electron transfer rate measurements on modified and unmodified glassy carbon electrodes

A natural and artificial distribution of electron transfer activity on glassy carbon electrodes can be observed and quantified by the use of scanning electrochemical microscopy (SECM). A large (sevenfold) spread in rate constant is found for randomly sampled sites on polished, untreated glassy carbon surfaces. Direct-mode oxidation with the SECM tip was used to produce small regions of oxidized carbon on a polished surface. A large increase in electron transfer rate for the Fe(II/III) ion is observed on the locally oxidized carbon surface in comparison to the unoxidized region. Rate constant measurements made along a line profiles the transition from unoxidized to oxidized surfaces. SECM images of defect sites show reaction–rate variations. Rate constants measured at several locations of the defective surface allows discrimination between the kinetic and topographic components of the SECM image. Dedicated to the 80th birthday of Keith B. Oldham     

Self-healing characteristic of praseodymium conversion coating on AZNd Mg alloy studied by scanning electrochemical microscopy

Application of rare earth conversion coatings as a surface treatment for magnesium has been the subject of several studies revealing the potential to act as an effective passivating layer. Herein a mechanistic study is presented on the formation of a rare earth conversion layer based on Pr(NO₃)₃ on AZ80X magnesium alloy in simulated biological (buffered) solution. Scanning electrochemical microscopy (SECM) was used to investigate the insulating properties and degradation behaviour of the Pr conversion layer. The self-healing properties of the conversion layer in the presence of Pr^3 + were also studied using SECM. Results revealed the self-healing characteristic of the Pr conversion film in the presence of active, Pr^3 +, species. The Pr conversion layer provided passivation in the short term by producing an electrochemically inert and insulating layer. SECM results in potentiometric mode elucidated the role of near surface pH in the formation of the conversion coating.     

In-situ Study the Corrosion Degradation Mechanism of Tinplate in Salty Water by Scanning Electrochemical Microscopy

In this work, the corrosion degradation of tinplate in contact with salty water is investigated by scanning electrochemical microscopy (SECM) electrochemical impedance spectroscopy (EIS). Experimental results indicate tin maintains at passive state during the exposure; however, pores and defects existed in tin coating leads to an exposure of carbon steel substrate to the electrolyte, in which localized corrosion tends to occur within the pore. A phenomenological model is proposed to interpret corrosion mechanism of tinplate in contact with salty food based on the proposed electrochemical equivalent circuit.     

Fabricating and imaging carbon-fiber immobilized enzyme ultramicroelectrodes with scanning electrochemical microscopy.

The scanning electrochemical microscope (SECM) is used to image the activity of enzymes immobilized on the surfaces of disk-shaped carbon-fiber electrodes. SECM was used to map the concentration of enzymatically produced hydroquinone or hydrogen peroxide at the surface of a 33-microm diameter disk-shaped carbon-fiber electrode modified by an immobilized glucose-oxidase layer. Sub-monolayer coverage of the enzyme at the electrode surface could be detected with micrometer resolution. The SECM was also employed as a surface modification tool to produce microscopic regions of enzyme activity by using a variety of methods. One method is a gold-masking process in which microscopic gold patterns act as mask for producing patterns of chemical modification. The gold masks allow operation in both a positive or negative process for patterning enzyme activity. A second method uses the direct mode of the SECM to produce covalently attached amine groups on the carbon surface. The amine groups are anchors for attachment of glucose oxidase by use of a biotin/avidin process. The effect of non-uniform enzyme activity was investigated by using the SECM tip to temporarily damage an immobilized enzyme surface. SECM imaging can observe the spatial extent and time-course of the enzyme recovery process.     

锈层下碳钢和耐候钢的微区和宏观腐蚀电化学行为

采用扫描电化学显微镜(SECM), 辅以极化曲线和电化学阻抗谱(EIS), 并结合SEM和XRD研究了耐候钢和碳钢在干湿交替环境下的腐蚀行为, 包括微区阳极溶解过程和阴极还原行为、 宏观腐蚀过程和微观结构及组成等. SECM测试结果表明, 锈层下碳钢和耐候钢的腐蚀过程都受阳极控制, 锈层的存在促进氧的还原. 宏观和微区电化学测试结果均表明, 在实验周期内, 初期形成的锈层降低了Fe阳极溶解速率, 从而提高碳钢和耐候钢的耐蚀性能, 后期形成的锈层由于其组成和结构特征的变化, 2种钢的腐蚀速率增加; 同时耐候钢的腐蚀速率较碳钢大, 且氧还原也较碳钢强, 有利于锈层的形成, 从而有利于长期的防护, 但是耐候钢的锈层在短期内并没有很好的保护性. 锈层不够致密, 呈疏松多孔状, 其组成主要有晶态的γ-FeOOH, Fe₃O₄和γ-Fe₂O₃等, 相同的干湿循环条件制备的耐候钢锈层较碳钢厚.     

Constant-distance mode scanning electrochemical microscopy (SECM)--Part I: Adaptation of a non-optical shear-force-based positioning mode for SECM tips

A non-optical shear-force-based detection scheme for accurately controlling the tip-to-sample distance in scanning electrochemical microscopy (SECM) is presented. With this approach, the detection of the shear force is accomplished by mechanically attaching a set of two piezoelectric plates to the scanning probe. One of the plates is used to excite the SECM tip causing it to resonate, and the other acts as a piezoelectric detector of the amplitude of the tip oscillation. Increasing shear forces in close proximity to the sample surface lead to a damping of the vibration amplitude and a phase shift, effects that are registered by connecting the detecting piezoelectric plate to a dual-phase analogue lock-in amplifier. The shear force and hence distance-dependent signal of the lock-in amplifier is used to establish an efficient, computer-controlled closed feedback loop enabling SECM imaging in a constant-distance mode of operation. The details of the SECM setup with an integrated piezoelectric shear-force distance control are described, and approach curves are shown. The performance of the constant-distance mode SECM with a non-optical detection of shear forces is illustrated by imaging simultaneously the topography and conductivity of an array of Pt-band microelectrodes.     

In situ scanning electrochemical microscopy (SECM) detection of metal dissolution during zinc corrosion by means of mercury sphere-cap microelectrode tips

This work presents a scanning electrochemical microscopy (SECM)-based in situ corrosion probing methodology that is capable of monitoring the release of zinc species in corrosion processes. It is based on the use of Hg-coated Pt microelectrodes as SECM tips, which offer a wider negative potential range than bare platinum or other noble-metal tips. This allows for the reduction of zinc ions at the tip to be investigated with low interference from hydrogen evolution and oxygen reduction from aqueous solutions. The processes involved in the corrosion of zinc during its immersion in chloride-containing solutions were successfully monitored by scanning the SECM tip, set at an adequate potential, across the sample either in one direction or in the X-Y plane parallel to its surface. In this way, it was possible to detect the anodic and cathodic sites at which the dissolution of zinc and the reduction of oxygen occurred, respectively. Additionally, cyclic voltammetry (CV) or constant potential measurements were used to monitor the release of zinc species collected at the tip during an SECM scan.     

Scanning electrochemical microscope observation of defects in a hexadecanethiol monolayer on gold with shear force-based tip-substrate positioning

Scanning electrochemical microscopy (SECM) was used for imaging of n-hexadecanethiol-modified Au surfaces. In these studies, small defects were observed in the monolayer when a submicrometer electrode was used as an SECM tip, although a cyclic voltammogram of a Au disk electrode showed that the surface of the Au was completely covered with n-hexadecanethiol. The dependence of the SECM images on the potential of the Au electrode was also examined. A comparison of the current at the Au electrode and the tip current in the SECM images showed that direct electron transfer through the monolayer was dominant, rather than electron transfer at the defects. The size of the defects was estimated from the tip current to be 1-100 nm, under the assumption that the defects were small compared to the SECM probe.     

Biological applications of scanning electrochemical microscopy: chemical imaging of single living cells and beyond

Recent applications of scanning electrochemical microscopy (SECM) to studies of single biological cells are reviewed. This scanning probe microscopic technique allows the imaging of an individual cell on the basis of not only its surface topography but also such cellular activities as photosynthesis, respiration, electron transfer, single vesicular exocytosis and membrane transport. The operational principles of SECM are also introduced in the context of these biological applications. Recent progress in techniques for high-resolution SECM imaging are also reviewed. Future directions, such as single-channel detection by SECM, high-resolution imaging with nanometer-sized probes, and combined SECM techniques for multidimensional imaging are also discussed.     

Direct Nanomachining on Semiconductor Wafer By Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) is one of the most important instrumental methods of modern electrochemistry due to its high spatial and temporal resolution. We introduced SECM into nanomachining by feeding the electrochemical modulations of the tip electrode back to the positioning system, and we demonstrated that SECM is a versatile nanomachining technique on semiconductor wafers using electrochemically induced chemical etching. The removal profile was correlated to the applied tip current when the tip was held stationary and when it was moving slowly (<20 μm s⁻¹), and it followed Faraday's law. Both regular and irregular nanopatterns were translated into a spatially distributed current by the homemade digitally controlled SECM instrument. The desired nanopatterns were “sculpted” directly on a semiconductor wafer by SECM direct-writing mode. The machining accuracy was controlled to the sub-micrometer and even nanometer scales. This advance is expected to play an important role in electrochemical nanomachining for 3D micro/nanostructures in the semiconductor industry.     

Localized Electrografting of Vinylic Monomers on a Conducting Substrate by Means of an Integrated Electrochemical AFM Probe

An electrochemical lithographic tool for locally electrografting a non‐conducting organic coating on a conducting substrate with a submicrometer resolution is provided by atomic force scanning electrochemical microscopy (AFM‐SECM). The picture shows the topographic AFM image of the line pattern drawn with an AFM‐SECM tip on a gold surface by direct reduction of an aryl diazonium salt/acrylic acid electrolyte solution.

     

Filming a live cell by scanning electrochemical microscopy: label-free imaging of the dynamic morphology in real time

ABSTRACT: The morphology of a live cell reflects the organization of the cytoskeleton and the healthy status of the cell. We established a label-free platform for monitoring the changing morphology of live cells in real time based on scanning electrochemical microscopy (SECM). The dynamic morphology of a live human bladder cancer cell (T24) was revealed by time-lapse SECM with dissolved oxygen in the medium solution as the redox mediator. Detailed local movements of cell membrane were presented by time-lapse cross section lines extracted from time-lapse SECM. Vivid dynamic morphology is presented by a movie made of time-lapse SECM images. The morphological change of the T24 cell by non-physiological temperature is in consistence with the morphological feature of early apoptosis. To obtain dynamic cellular morphology with other methods is difficult. The non-invasive nature of SECM combined with high resolution realized filming the movements of live cells.