应用扫描电化学显微镜研究水/1,2-二氯乙烷界面上离子诱导的电子转移反应

应用扫描电化学显微镜和微电极技术研究了水/1,2二氯乙烷界面上的反向电子转移反应.分别以K₄Fe(CN)₆和7,7,8,8四氰代二甲基苯醌(TCNQ)作为水相和有机相的电活性物质,通过选择合理的共同离子(TPAs⁺与TBA⁺)来控制界面电位差,实现了这一在热力学上通常不可能实现的反向电子转移反应.利用扫描电化学显微镜给出的正负反馈信息,研究了界面电位差驱动的液/液界面上的电子转移反应,并进一步得到了在不同的共同离子浓度比时,此异相界面反应速率常数k_f为1.3×10^-31.8×10^-2cm/s(共同离子为TBA⁺)和2.5×10^-32.8×10^-2cm/s(共同离子为TPAs⁺).验证了此反应速率常数k_f是由界面电位差所决定的.在此实验条件下,此反应速率常数kf与界面电位差的关系遵守Butler-Volmer公式.     

Development of a Temperature-pulse Enhanced Electrochemical Glucose Biosensor and Characterization of its Stability via Scanning Electrochemical Microscopy

Glucose oxidase (GOx) is an enzyme frequently used in glucose biosensors. As increased temperatures can enhance the performance of electrochemical sensors, we investigated the impact of temperature pulses on GOx that was drop-coated on flattened Pt microwires. The wires were heated by an alternating current. The sensitivity towards glucose and the temperature stability of GOx was investigated by amperometry. An up to 22-fold increase of sensitivity was observed. Spatially resolved enzyme activity changes were investigated via scanning electrochemical microscopy. The application of short (<100 ms) heat pulses was associated with less thermal inactivation of the immobilized GOx than long-term heating.     

Sphere‐Cap Mercury Microelectrodes for Scanning Electrochemical Microscopy Above an Insulating Substrate

Sphere‐cap mercury microelectrodes, fabricated onto platinum microdisks 1 and 10 μm radius, were employed as tips in scanning electrochemical microscopy (SECM). Experimental current vs distance curves were acquired above an insulating substrate with a series of sphere caps whose aspect ratio h/a (h is the height of mercury deposit, a is the disk basal radius) varied between 0.28 and 2.14. It was found that the hindered diffusion effect of the insulating surface was the less pronounced the higher was the h/a parameter of the sphere cap. Comparison of experimental and theoretical approach curves displayed a fairly good agreement for subhemisphere caps (h<a), and a less satisfactory agreement for hemispherical (h=a) and superhemispherical (h>a) caps. Preliminary coupled anodic stripping voltammetry and SECM measurements were also performed for the investigation on local chemical equilibria involving heavy metals at sediment/water interfaces.     

ITO基底上ZnO薄膜的制备以及刻蚀图形的扫描电化学显微镜表征

在氧化铟锡(ITO)导电玻璃的衬底上,利用直接电沉积方法制备了ZnO纳米线或ZnO薄膜.然后利用存储有HCI刻蚀剂的琼脂糖微图案印章对其进行了化学刻蚀以形成不同的图形.利用扫描电子显微镜(SEM)、X射线衍射(XRD)和扫描电化学显微镜(SECM)分别对ITO衬底上的ZnO薄膜的结构、形貌和电化学性质进行表征.     

Detection and Quantification of Sulfonamide Antibiotic Residues in Milk Using Scanning Electrochemical Microscopy

The use of scanning electrochemical microscopy (SECM) for the qualitative and quantitative determination of sulfapyridine (SPY) in milk is described. A direct competitive immunoassay was performed involving an antibiotic horseradish peroxidase (HRP)‐labeled analog and using selective capture antibodies immobilized on the surface of Protein G‐modified glassy carbon plates. SECM detection was accomplished by means of the sample generator/tip collector (GC) mode involving the reduction of benzoquinone (BQ) generated upon the HRP‐catalyzed oxidation of hydroquinone (HQ) at the modified substrate surface in the presence of H₂O₂. The detection limit for SPY in milk samples was as low as 0.13 ng mL^?1.     

扫描电化学显微镜用于研究生物膜微环境的电子传递

生物电化学系统(BESs)的核心是生物膜在电极/溶液界面的电子传递反应,研究生物膜微区环境中的电子传递有助于阐明微生物的胞外电子传递(EET)机制,从而有针对性地提高BESs中的电子转移效率。微生物的EET机制包括直接电子传递和间接电子传递,由于生物膜组成复杂,含有多种分泌物、胞外聚合物等,常规电化学方法只能从生物膜宏观层面研究EET机制,无法有效区分这两种电子传递途径的贡献。本文采用电化学循环伏安方法研究了电子穿梭体二茂铁甲醇(FcMeOH)与希瓦氏菌(Shewanella)相互作用的界面过程;基于扫描电化学显微技术构建了穿透模式,通过微电极介导FcMeOH与Shewanella反应,收集仅来自间接电子传递途径产生的电流,同时测定了Shewanella在电极/溶液界面的氧化还原性质和空间分布。本论文将电化学扫描探针显微技术应用于EET的研究,从物理化学角度揭示微生物在代谢过程中与外界的电子传输机制。     

Study on Electrocatalytic Activity of Platinum for Hydrogen Oxidation in Acidic Solution by Scanning Electrochemical Microscopy

The electrocatalytic activity of platinum for hydrogen oxidation in 0.01 M H₂SO₄ + 0.1 MNa₂SO₄ solution has been investigated by scanning electrochemical microscopy (SECM) technique. The cyclic voltammogram (CV), approach curve, area scan imaging and chronoamperometric methods have been used. The results indicate that the imaging capability of the SECM feedback mode can be used more efficiently to visually identify materials' electrocatalytic activity, compared with the approach curve method for identification of the conductive or insulating nature of a surface. The SECM imaging method has demonstrated the effects of Pt substrate potential on the electrocatalytic oxidation of hydrogen under a constant tip potential. It is found that the more positive the Pt substrate potential, the lower the electrocatalytic activity of the Pt. Furthermore, the chronoamperometric results support the variation of the electrocatalytic activity with the Pt substrate potential as well.     

Scanning Electrochemical Microscopy for Electrochemical Detection of Single‐base Mismatches by Tagging Ferrocenecarboxylic Acid as a Redox Probe to DNA

Scanning electrochemical microscopy (SECM) was employed for sensitive detection of single base mismatches (SBMs) in a sandwiched dsDNA. Ferrocenecarboxylic acid (Fc), covalently conjugated to the dsDNA, was oxidized to Fc⁺ via the DNA‐mediated charge transfer from the underlying gold substrate, and reduced back to Fc by SECM tip generated ferrocyanide. The electrocatalytic oxidation of SECM tip‐generated ferrocyanide was sensitive to presence, as well as the type of SBMs. Apparent standard rate constants (k⁰_app) values for different SBMs, both near the electrode surface and far from it, were evaluated by SECM. The method can detect SBMs independent of their position in dsDNA.     

应用扫描电化学显微镜研究极化液/液界面上的电子转移反应

将含有氧化还原电对的水溶液滴涂在铂盘电极表面, 然后将该电极插入到1,2-二氯乙烷溶液中, 形成稳定的油/水界面. 液滴中的K3Fe(CN)6和K4Fe(CN)6氧化还原电对既可以作为水相中的参比电对参与控制液/液界面上的电势差, 同时又可以作为水相的电子授受体参与界面上的电子转移反应. 结合扫描电化学显微镜电化学系统的特点, 利用其双恒电位仪分别控制界面电势差和现场扫描的优点, 通过扫描电化学显微镜的渐进曲线得到了不同界面电势差控制的电子转移反应速率常数. 实验结果表明, 应用此方法获得的液/液界面可以被外加电位极化, 在一定的电势差范围内, 反应速率常数与界面电势差的关系遵守Butler-Volmer公式.     

Scanning Electrochemical Microscopy (SECM) Based Detection of Oligonucleotide Hybridization and Simultaneous Determination of the Surface Concentration of Immobilized Oligonucleotides on Gold

The direct mode of scanning electrochemical microscopy (SECM) was used for the local deposition of oligonucleotide (ODN) patterns on thin gold films and the generation‐collection (GC) mode was applied for the determining the amount of surface‐accessible oligonucleotides. The local deposition was achieved through the micrometer‐sized formation of a conducting polymer bearing 15^mer single‐stranded oligonucleotide strands. After the interaction of the oligonucleotide with its biotin‐labeled complimentary strand, streptavidin was bound. The molecular assembly was completed by linking biotin‐labeled β‐galactosidase from Escherichia coli to the streptavidin. The activity of the linked β‐galactosidase was mapped with SECM in the GC mode by monitoring the oxidation of p‐aminophenol (PAP) formed in the enzyme‐catalyzed hydrolysis of p‐aminophenyl‐β‐D ‐galactopyranoside. The feedback effect due to recycling of the reaction product at the gold surface was analyzed. It was shown experimentally that this effect becomes insignificant at ultramicroelectrode (UME)‐substrate distances larger than 3 UME radii. The flux of formed PAP allowed the determination the surface density of accessible oligonucleotide strands in the functionalized polymer. It was shown that that thicker pyrrole/ODN–Pyrrole polymer films do not lead to a significantly increased accessible ODN surface concentration.     

应用扫描电化学显微镜研究电子在室温离子液体与1,2-二氯乙烷混合溶液/水相界面上的转移反应

应用扫描电化学显微镜研究了室温离子液体(Omim·Tf2N)与1,2-二氯乙烷(DCE)混合溶液/水界面上的电子转移反应. 在保持共同离子(Tf2N-)的浓度比恒定及异相电子转移反应由界面电势差所决定的条件下, 研究了离子液体和DCE混合溶液中二茂铁(Fc)与水相中亚铁氰化钾[K4Fe(CN)6]之间异相电子转移反应. 探讨了混合溶液中离子液体的体积分数(xRTIL)的变化对混合溶液/水界面上电子转移反应的影响. 结果表明, 随着xRTIL的减小(从1减小到0.1), Fc在混合溶液中的扩散系数单调递增(从2.730×10-7 cm2·s-1增加到9.131×10-6 cm2·s-1); 而异相电子转移反应速率常数(k)则先逐渐减小(从8.0 mol-1·cm·s-1减小到0.32 mol-1·cm·s-1), 之后又略有增大(从0.32 mol-1·cm·s-1增大到0.48 mol-1·cm·s-1). 对这种现象可能的原因进行了较详细探讨.     

纳米尺度扫描电化学显微镜的探针制备及在电催化氧和氢反应研究中的应用

扫描电化学显微镜是一种在检测样品表面物理形貌的同时能提供丰富的电化学信息的扫描探针技术,由于超微电极的引入,它可以高时空分辨率地探究各类样品的物理形貌和电化学性能之间的构效关系. 随着现代纳米科技的不断发展,扫描探针的尺寸也逐渐从亚微米发展到纳米级别. 与此同时,高效优选各类氧反应和氢反应电催化材料,明晰其电化学反应过程和性能是二十一世纪绿色新能源转换存储系统（如可再生燃料电池、金属空气电池等）的重要研究方向. 本文首先概括了可应用于扫描电化学显微镜的纳米级扫描探针的制备及发展,之后着重介绍了近四年纳米尺度扫描电化学显微镜在电催化氧反应和氢反应研究中的一些最新研究进展. 最后以点窥面,对未来纳米尺度扫描电化学显微镜的未来发展趋势作了展望.     

Scanning Electrochemical Cell Microscopy Investigation of Single ZIF‐Derived Nanocomposite Particles as Electrocatalysts for Oxygen Evolution in Alkaline Media

“Single entity” measurements are central for an improved understanding of the function of nanoparticle‐based electrocatalysts without interference arising from mass transfer limitations and local changes of educt concentration or the pH value. We report a scanning electrochemical cell microscopy (SECCM) investigation of zeolitic imidazolate framework (ZIF‐67)‐derived Co?N‐doped C composite particles with respect to the oxygen evolution reaction (OER). Surmounting the surface wetting issues as well as the potential drift through the use of a non‐interfering Os complex as free‐diffusing internal redox potential standard, SECCM could be successfully applied in alkaline media. SECCM mapping reveals activity differences relative to the number of particles in the wetted area of the droplet landing zone. The turnover frequency (TOF) is 0.25 to 1.5 s^?1 at potentials between 1.7 and 1.8 V vs. RHE, respectively, based on the number of Co atoms in each particle. Consistent values at locations with varying number of particles demonstrates OER performance devoid of macroscopic film effects.     

A Comparative Study of Functionalized High‐Purity Carbon Nanotubes towards the V(IV)/V(V) Redox Reaction Using Cyclic Voltammetry and Scanning Electrochemical Microscopy

Functionalized high purity carbon nanotubes (CNTs) with various amounts of oxygen containing surface groups were investigated towards the relevant redox reactions of the all‐vanadium redox flow battery. The quinone/hydroquinone redox peaks between 0.0 and 0.7 V vs. Ag|AgCl|KCl_sat. were used to quantifying the degree of functionalization and correlated to XPS results. Cyclic voltammetry in vanadyl sulfate‐containing 3 M H₂SO₄ as a common supporting electrolyte showed no influence of the amount of surface groups on the V(IV)/V(V) redox system. In contrast, the reactions occurring at the negative electrode (V(II)/V(III) and V(III)/V(IV)) are strongly affected by oxygen surface groups. However, under modified experimental conditions, SECM experiments detecting the consumption of VO²⁺ molecules by CNT thin films in pH=2 solution show improved onset potentials with increased surface oxygen content up to ∼ 3 at%. Further increase in surface oxygen up to 8 at% led to minor improvement. These dissimilar results under different experimental conditions are rationalized by suggesting that oxygen functional groups do not form the active site for the V(IV)/V(V) reaction but wetting of the catalyst layer is of high importance.     

A Practical Approach for the In Vitro Safety and Efficacy Assessment of an Anti-Ageing Cosmetic Cream Enriched with Functional Compounds

(1) Background: Cosmeceuticals are topical products applied to human skin to prevent skin ageing and maintain a healthy skin appearance. Their effectiveness is closely linked to the compounds present in a final formulation. In this article, we propose a panel of in vitro tests to support the efficacy assessment of an anti-ageing cream enriched with functional compounds. (2) Methods: biocompatibility and the irritant effect were evaluated on reconstructed human epidermis (RHE) and corneal epithelium (HCE) 3D models. After a preliminary MTT assay, normal human dermal fibroblasts (NHDF) and keratinocytes (HaCaT) were used to evaluate the extracellular matrix (ECM) protein synthesis, and interleukin-6 (IL-6) and metalloproteinase-1 (MMP-1) production. (3) Results: data collected showed good biocompatibility and demonstrated the absence of the irritant effect in both 3D models. Therefore, we demonstrated a statistical increase in collagen and elastin productions in NHDF cells. In HaCaT cells, we highlighted an anti-inflammatory effect through a reduction in IL-6 levels in inflammatory stimulated conditions. Moreover, the reduction of MMP-1 production after UV-B radiation was demonstrated, showing significant photo-protection. (4) Conclusion: a multiple in vitro assays approach is proposed for the valid and practical assessment of the anti-ageing protection, anti-inflammatory and biocompatible claims that can be assigned to a cosmetic product containing functional compounds.     

Assessing the Inhibitory Potential of Kinase Inhibitors In Vitro: Major Pitfalls and Suggestions for Improving Comparability of Data Using CK1 Inhibitors as an Example

Phosphorylation events catalyzed by protein kinases represent one of the most prevalent as well as important regulatory posttranslational modifications, and dysregulation of protein kinases is associated with the pathogenesis of different diseases. Therefore, interest in developing potent small molecule kinase inhibitors has increased enormously within the last two decades. A critical step in the development of new inhibitors is cell-free in vitro testing with the intention to determine comparable parameters like the commonly used IC₅₀ value. However, values described in the literature are often biased as experimental setups used for determination of kinase activity lack comparability due to different readout parameters, insufficient normalization or the sheer number of experimental approaches. Here, we would like to hold a brief for highly sensitive, radioactive-based in vitro kinase assays especially suitable for kinases exhibiting autophosphorylation activity. Therefore, we demonstrate a systematic workflow for complementing and validating results from high-throughput screening as well as increasing the comparability of enzyme-specific inhibitor parameters for radiometric as well as non-radiometric assays. Using members of the CK1 family of serine/threonine-specific protein kinases and established CK1-specific inhibitors as examples, we clearly demonstrate the power of our proposed workflow, which has the potential to support the generation of more comparable data for biological characterization of kinase inhibitors.