Generation and characterization of surface layers on acoustically levitated drops

Surface layers of natural and technical amphiphiles, e.g., octadecanol, stearic acid and related compounds as well as perfluorinated fatty alcohols (PFA), have been investigated on the surface of acoustically levitated drops. In contrast to Langmuir troughs, traditionally used in the research of surface layers at the air-water interface, acoustic levitation offers the advantages of a minimized and contact-less technique. Although the film pressure cannot be directly adjusted on acoustically levitated drops, it runs through a wide pressure range due to the shrinking surface of an evaporating drop. During this process, different states of the generated surface layer have been identified, in particular the phase transition from the gaseous or liquid-expanded to the liquid-condensed state of surface layers of octadecanol and other related amphiphiles. Characteristic parameters, such as the relative permeation resistance and the area per molecule in a condensed surface layer, have been quantified and were found comparable to results obtained from surface layers generated on Langmuir troughs.     

Physicochemical properties and mixed electronic and ionic conduction of composite ceramics in the system ZrO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

Composites ZrO₂-(Bi₂CuO₄+ 20 wt % Bi₂O₃) (50–80 vol % ZrO₂) are synthesized and their physicochemical properties are studied. It is demonstrated that the composites comprise triple-phase mixtures of ZrO₂ of a monoclinic modification, Bi₂CuO₄, and solid solution Bi_2?x Zr _x O_{3 + x/2} and retain their mechanical strength up to 800°C. Impedance spectroscopy is used to examine their electroconductivity at 700–800°C in the interval of partial oxygen pressures extending from 37 to 2.1 × 10⁴ Pa. Contributions made by electronic and ionic constituents to their overall conductivity are evaluated. The best specimens’ conductivity is ～0.01 S cm^?1, with the electronic and ionic transport numbers nearly equal. The composite consisting of 50 vol % ZrO₂ and 50 vol % (Bi₂CuO₄ + 20 wt % Bi₂CuO₄) is tested in the role of an oxygen-separating membrane. The selective flux of oxygen in the temperature interval 750–800°C amounts to (2.2–6.3) × 10^?8 mol cm^?2 s^?1, testifying that these materials may be used as gas-separating membranes.     

Antiplatelet Activity of Coumarins: In Vitro Assays on COX-1

Atherosclerotic cardiovascular disease is the leading cause of death in developed countries. Therefore, there is an increasing interest in developing new potent and safe antiplatelet agents. Coumarins are a family of polyphenolic compounds with several pharmacological activities, including platelet aggregation inhibition. However, their antiplatelet mechanism of action needs to be further elucidated. The aim of this study is to provide insight into the biochemical mechanisms involved in this activity, as well as to establish a structure–activity relationship for these compounds. With this purpose, the antiplatelet aggregation activities of coumarin, esculetin and esculin were determined in vitro in human whole blood and platelet-rich plasma, to set the potential interference with the arachidonic acid cascade. Here, the platelet COX activity was evaluated from 0.75 mM to 6.5 mM concentration by measuring the levels of metabolites derived from its activity (MDA and TXB₂), together with colorimetric assays performed with the pure recombinant enzyme. Our results evidenced that the coumarin aglycones present the greatest antiplatelet activity at 5 mM and 6.5 mM on aggregometry experiments and inhibiting MDA levels.     

宏观均相多孔电极电化学阻抗谱基础

电化学阻抗谱可用于诊断多孔电极内电荷转移反应,即界面电荷集聚和电荷传导,以及反应物质输运。本文采用复相量方法,在同态假设条件下,重新推演多孔电极阻抗谱模型,厘清传统多孔电极阻抗谱模型中的模糊性表述。(1) 定义多孔电极表征输入参数,包括电极基体电子电导率σ₁ 、电解质离子电导率σ₂、界面电荷传递电导率g_ct、单位面积界面电容C、固相扩散系数D、速度常数k、电极厚度d、特征孔深L_p 和单位体积表面积S_c;(2) 解析阻抗谱特征输出参数,包括场扩散常数K,特征频率ω₀、ω₁、ω₂、ω₃和 ω_max,它们分别相关于界面传导反应、有限场扩散、氧化还原反应、孔内扩散和最小特征孔尺寸,以及分别对应于从传导到扩散和从扩散到饱和的转折频率f_k1 和f_k2;(3) 当参数X和Z同时变化时(X = σ₁和Z = d,S_c,L_p,C,g_ct,D,k),通过阻抗谱特征参数的演变规律,分析了电荷转移反应中X和Ζ参数耦合竞争;(4)为深入分析电荷转移反应中参数X和Z的耦合竞争,引入了分叉频率f_XZ和f_ZX 。f_XZ和f_ZX所处位置可以用于表征参数X和Z影响电荷转移反应的深度和广度。当分叉频率f_XZ和f_ZX不存在时,表明电荷转移反应中参数X和Z在全频率范围内存在耦合竞争。总之,借助于特征频率和分叉频率,本文一方面研究了动力学参数和微观结构参数对多孔电极中电荷转移反应的影响,另一方面分析谱图的变化及其背后的阻抗谱特征演化规律。本文研究结果可为阻抗谱的系统仿真和辨识提供理论基础,可为多孔电极内电荷转移反应的竞争分析提供技术支撑,还可为电化学储能系统的优化设计提供诊断工具。     

玻碳电极界面的阻抗谱数学表达及定量分析

玻碳电极（GCE）是各类电化学传感器常用的基础电极,其界面特征直接影响检测性能。本文详细考察了电极体系的电化学过程,针对GCE传感界面,探讨了一个等效电路中电解质电阻、电荷输运电阻、扩散阻抗、电化学（氧化/还原）反应阻抗、表面吸附阻抗和双电层电容等电学元件的物理意义,并给出了对应的数学模型。通过改变模型中5个参数值,模拟了不同状态下的阻抗谱,分析了电极系统各参数对GCE阻抗谱的贡献规律。最后,采用该数学模型对裸GCE和修饰GCE在铁氰化钾溶液中的阻抗谱进行分析,拟合结果与实验数据吻合度高;基于拟合获得参数,定量对比分析了修饰前后电极表面的特征变化。     

Microelectrode Combinations of Gold and Polypyrrole Enable Highly Stable Two-electrode Electrochemical Impedance Spectroscopy Measurements under Turbulent Flow Conditions

An electrochemical impedance spectroscopy (EIS) sensor design is proposed based on a standard interdigitated electrode layout in which the smaller working electrode consists of gold (Au) whereas the larger combined counter and reference electrode is coated with a porous layer of polypyrrole (PPy) doped with polystyrene sulfonate (PSS) (PPy : PSS). Each electrode material was first characterized by EIS in a standard 3-electrode setup with subsequent spectra fitting by a modified Randles equivalent circuit. The differences in the spectra obtained by the PPy : PSS coated electrodes can be explained by an increased electroactive surface area due to the porous polymer film. The changes in morphology of the film are discussed with respect to the evolution of the elements of the electric equivalent circuit. When applying the Au/PPy : PSS electrode combination to a standard 2-electrode arrangement, the enlarged highly electroactive surface area of the PPy : PSS coating lowers the interfacial impedance in a way that mainly the gold working electrode contributes to the overall system impedance. Therefore, obtaining reproducible EIS signals depends only on the electrode's open-circuit potential (OCP) and on additional adsorption events at the gold electrode/electrolyte interface. We present a protocol for microelectrode coating with PPy : PSS, which enables highly stable 2-electrode EIS experiments without the need of a reference electrode. This combination is believed to be very useful if an integration of sensing electrodes inside Micro Total Analysis Systems is aspired.     

Molecularly Imprinted Electrochemical Sensor for the Detection of Organophosphorus Pesticide Profenofos

The presence of profenofos (PFF) in food has been strictly limited by legislation due to its genotoxic and toxic effects on health. It is therefore very important to establish simple and rapid analytical methods to detect traces of this insecticide. A reusable molecularly imprinted polypyrrole MIP(O-PPy) on a glassy carbon electrode (GCE) has been developed to measure PFF. The PPy was polymerized by cyclic voltammetry (CV) in the presence of template molecules (PFF) in an acidic solution on a GCE. The various experimental parameters such as film thickness, analyte/monomer ratio, and removal/rebinding requirements were examined and optimized. The signal of the redox probe (ferrocyanide/ferrocyanide) was used for the electrochemical detections. All steps of the sensor manufacturing, removal/rebinding of template molecules, and response to different PFF concentrations were tested by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The MIP sensor was able to detect PFF in the linear ranges of 1.0×10⁻⁹ to 1.0×10⁻⁶ M and 1.0×10⁻⁹ to 5.0×10⁻⁶ M, with detection limits, a signal-to-noise ratio (S/N) of three was used to estimate LOD, of about 1 nM using DPV and EIS, respectively. The MIP (PPy) GCE provided excellent PFF recognition performance and was successfully used to quantify PFF in sweet pepper samples, yielding recoveries not greater than 108 %.     

Design and 3D modeling investigation of a microfluidic electrode array for electrical impedance measurement of single yeast cells

High-resolution microscopic imaging may cause intensive image processing and potential impact of light irradiation on yeast replicative lifespan (RLS). Electrical impedance spectroscopy (EIS) could be alternatively used to perform high-throughput and label-free yeast RLS assays. Prior to fabricating EIS-integrated microfluidic devices for yeast RLS determination, systematic modeling and theoretical investigation are crucial for device design and optimization. Here, we report three-dimensional (3D) finite-element modeling and simulations of EIS measurement in a microfluidic single yeast in situ impedance array (SYIIA), which is designed by patterning an electrode matrix underneath a cell-trapping array. SYIIA was instantiated and modeled as a 5 × 5 sensing array comprising 25 units for cell immobilization, culturing, and time-lapse EIS recording. Simulations of yeast growing and budding in a sensing unit demonstrated that EIS signals enable the characterization of cell growth and daughter-cell dissections. In the 5 × 5 sensing array, simulation results indicated that when monitoring a target cell, daughter dissections in its surrounding traps may induce variations of the recorded EIS signals, which could cause mistakes in identifying target daughter-cell dissections. To eliminate the mis-identifications, electrode array pitch was optimized. Therefore, the results could conduct the design and optimization of microfluidic electrode-array-integrated devices for high-throughput and accurate yeast RLS assays.     

[Au25(SR)18]-团簇的相干振动动力学研究

利用飞秒时间分辨光谱,可观测叠加在电子态动力学上的相干振动动力学. 从金团簇的相干振动中,不仅能提取电子与振动的耦合信息,也能得到力学性质和电子结构,进而有望实现微小质量探测等应用. 本文利用飞秒时间分辨的瞬态吸收探测了[Au₂₅(SR)₁₈]^-团簇的相干振动动力学,通过对相干振动的频率、相位、波长分布的详细分析进一步揭示了其来源. 在[Au₂₅(SR)₁₈]^-团簇的飞秒瞬态吸收动力学中可以观测到频率为40 cm^-1和80 cm^-1的两种振动,均来源于团簇中心Au₁₃核的振动. 通过对相干振动的相位分析发现频率为80 cm^-1的振动来自于对电子态之间吸收频率的调制,而频率为40 cm^-1的振动来源于对电子态之间吸收强度的调制. 同时,研究发现[Au₂₅(SR)₁₈]^-团簇相干振动的频率对其表面配体不敏感,该振动是来源于Au₁₃核的本征性质.     

健康视角下幼儿园声环境*

幼儿园作为学前儿童生活和进行认知活动的主要场所,其声环境对学前儿童的健康成长十分重要。本文首先以Web of science核心合集数据库为数据来源,综述幼儿园声环境对学前儿童健康的不利影响以及幼儿园声环境现状。其次讨论不同国家幼儿园声学标准,指出其中不足。研究发现幼儿园声环境对学前儿童的健康影响存在于生理、情绪及行为、认知表现方面。以学前儿童语言声与活动声为主的噪声问题在各国幼儿园十分常见,噪声水平高、声压级波动性强且不可控为幼儿园声环境的显著特征。现有规范不足集中于声学指标的选取与最佳标准限值的确定方面。最后依据现有研究结果,结合我国幼儿园现状提出幼儿园声环境设计指导：幼儿园设计阶段建筑设计与声学设计的结合,使用阶段教育方法与使用人员的合理化均有助于塑造良好的幼儿园声环境,为学前儿童的健康成长提供保障。