Electrochemical Immunosensing Strategies Based on Immobilization of Anti-IgC on Mixed Self-Assembly Monolayers Carrying Surface Amide or Carboxyl Groups

Abstract

In the development of electrochemical immunosensing strategies, stability or activity of the immobilized biocomponents and signal amplification of the immunoconjugates are two key factors. In this study, a comparative study of immunoglobulin G antibody (anti‐IgG) immobilization, as a model, was performed on cysteine (Cys), 2‐aminoethane thiol (AET), and 11‐mercaptoundecanoic acid (MUA) monolayers. The change of anti‐IgG layer formation on the three base layers as a function of the anti‐IgG concentration was investigated in parallel via electrochemical impedance spectroscopy, cyclic voltammetry, surface plasmon resonance, and quartz crystal microbalance. Through the parallel measurements, we demonstrate that the Cys‐modified layer is more suitable for the immobilization of the anti‐IgG molecules than the MUA or AET‐modified layer. Based on the CV and EIS analyses, it was determined that the current responses decreased with the increment of anti‐IgG concentration, while the resistance responses increased with the concentration of anti‐IgG increased. Moreover, the current and resistance shifts were more remarkable on the Cys layer than that of the other two layers. In the SPR and QCM measurements, the SPR and QCM response signals were similar in shape but differing in time scales, reflecting differences in detection mechanisms. With regard to the fundamental problem of comparing different measurement principles, the mechanism of the IgG immobilized on the three layers was proposed. Consequently, the surface concentration of anti‐IgG immobilized on the electrode should be optimized to improve the sensitivity of the immunosensors.     

The change in thickness of the solidified liquid layer rather than the immobilized mass determines the frequency response of a quartz crystal microbalance

The "solidified liquid layer" model has been examined using a quartz crystal microbalance(QCM) with a polymeric matrix.The model is shown to give a reasonable explanation for the following experimental observations:(i) The opposite response of the QCM and surface plasmon resonance(SPR) for the activation process;(ii) the marked difference in the responses for IgG/anti-IgG interaction between QCM and SPR.Theoretical analysis and experimental results indicated that QCM is sensitive to the thickness change of the "solidified liquid layer" but not the mass of captured biomolecules(i.e.,the immobilized mass),implying caution must be taken in interpreting QCM results.     

Measurement of hydrolysis kinetics of galactose-substituted fluorescein by β-galactosidase at the toluene–water interface by spinning microtube fluorometry

A new analytical technique, spinning microtube fluorometry (SMF), was developed and applied to the study of interfacial hydrolysis of 5-dodecanoylaminofluorescein di-β-D-galactopyranoside (C₁₂FDG) by β-galactosidase (β-gal) in the toluene–water system. The nonfluorescent lactone form of C₁₂FDG in the toluene phase was converted at the interface to 5-dodecanoylaminofluorescein (C₁₂F), which was fluorescent in the aqueous phase as a dianion at pH 7.3, though some part of C₁₂F was extracted into the toluene phase as its nonfluorescent lactone form. The distribution ratios of C₁₂FDG and C₁₂F at pH 7.3 were determined as 1.4×10² and 1.97, respectively. The interfacial adsorption constants from the toluene phase to the interface at pH 7.3 were 4.8×10⁻⁴ and 1.7×10⁻² dm for C₁₂FDG and C₁₂F, respectively. The kinetic experiments with the SMF method concluded that the rate-determining step of the enzymatic hydrolysis at the interface and in the aqueous phase was the 1:1 reaction of C₁₂FDG and β-gal and that the hydrolysis reaction rate constant at the interface at pH 7.3 was 1.84×10³ M⁻¹s⁻¹, almost equal to that in the aqueous solution, 1.76×10³ M⁻¹s⁻¹. Finally, the SMF method revealed that the contribution of the interfacial reaction to the overall hydrolysis reaction rate of the toluene–water system was as high as 97%.     

Comparison of fluorescence and QCM technologies: Example of explosives detection with a π-conjugated thin film

A π-conjugated compound was synthesized as a sensitive material for explosives detection. The detection of vapors of 2,4-dinitrotoluene was demonstrated with quartz crystal microbalance (QCM) and fluorescence transduction methods. The fluorescence intensity monitoring shows a higher sensitivity and selectivity than the monitoring of the QCM frequency. Both methods appear to be synergic when used simultaneously as the sensor helps to discriminate interferent vapors from nitroaromatics.     

Electrochemical Quartz Crystal Microbalance Study of FeS Particles Attached to Au Surface

Electrochemical quartz crystal microbalance (EQCM) measurements were employed for studying of the redox processes of FeS microparticles immobilized on Au electrode surface in contact with aqueous solutions of NaCl, NaCl‐NaHCO₃, and NaCl‐Na₂S. The objective was to shed light on the complexity of the iron sulfide electrochemistry. For the sake of comparison electrochemical behavior of FeS suspension was also investigated on the paraffin‐impregnated graphite (PIGE) and hanging mercury drop (HMDE) electrodes. In order to understand the complex nature of the redox transformations of FeS, Mohr‐salt was dissolved in NaCl and NaCl‐NaHCO₃ solutions, respectively, and the deposition‐dissolution processes occurring in the course of the reduction of Fe(II) and reoxidation of Fe(0) were also monitored.     

基于石英音叉增强型光谱技术(QEPAS)的实时探测系统研究

利用石英音叉增强型光谱技术(QEPAS)结合基于Lab-VIEW设计的数字 频率锁定技术建立了一套气体实时探测系统, 该方案使用3f信号作为误差反馈信号, 将激光器锁定在待测气体吸收峰的中心位置, 保证了长时间测量的准确度并且提高了探测效率. 实验中采用中心波长位于1.396 μm的DFB半导体激光器作为光源, 选择常压下空气中的水汽作为研究对象, 对系统性能进行了测试, 并对影响影响系统探测灵敏度的主要因素进行了分析. 实验结果表明, 该系统可以将激光器稳定在± 0.001 cm^-1范围内, 对激光器长时间工作时的波长漂移起到了很好的抑制作用, 系统的检测限约为1 ppm, 该方案可以直接应用于工业气监测、痕量污染物实时测量等领域.     

电化学石英晶体微天平及其应用

本文介绍了ＥＱＣＭ的原理及其应用，探讨了ＥＱＣＭ在生物大分子，纳米技术方面的应用，详细介绍了ＥＱＣＭ在气味检测，金属电沉积、药物分析等方面研究的优点和ＥＱＣＭ的发展前景。     

基于胸腺嘧啶-汞离子-胸腺嘧啶结构和纳米金放大传感器检测汞离子

利用Hg2+与DNA中胸腺嘧啶(T)结合的高度特异性和纳米金在石英晶体微天平(QCM)上的信号放大作用,设计了一种简便灵敏的Hg2+检测方法.纳米金采用柠檬酸钠还原法制备,其表面用末端带巯基的寡核苷酸探针进行自组装修饰,并用6-巯基己-1-醇(MCH)部分取代表面探针,以减少杂交空间位阻.结果表明,寡核苷酸链长为9bp、T个数为7的序列具有较高灵敏度;线性范围为5.0～100 nmol/L;检出限为2.0 nmol/L;Ca2+、Mg2+等其它金属离子无明显干扰.用于环境水样中Hg2+的测定, RSD<2.9%;加标回收率为97.3%～101.2%     

Invisible gold in Colombian auriferous soils

Optic microscopy, X-ray diffraction (XRD), Mössbauer spectroscopy (MS), Electron microprobe analysis (EPMA) and secondary ions mass spectroscopy (SIMS) were used to study Colombian auriferous soils. The auriferous samples, collected from El Diamante mine, located in Guachavez-Nariño (Colombia), were prepared by means of polished thin sections and polished sections for EPMA and SIMS. Petrography analysis was made using an optical microscope with a vision camera, registering the presence, in different percentages, of the following phases: pyrite, quartz, arsenopyrite, sphalerite, chalcopyrite and galena. By XRD analysis, the same phases were detected and their respective cell parameters calculated. By MS, the presence of two types of pyrite was detected and the hyperfine parameters are: δ ₁ = 0.280 ± 0.01 mm/s and ΔQ ₁ = 0.642 ± 0.01 mm/s, δ ₂ = 0.379 ± 0.01 mm/s and ΔQ ₂ = 0.613 ± 0.01 mm/s. For two of the samples MS detected also the arsenopyrite and chalcopyrite presence. The mean composition of the detected gold regions, established by EPMA, indicated 73% Au and 27% Ag (electrum type). Multiple regions of approximately 200 × 200 μm of area in each mineral sample were analyzed by SIMS registering the presence of “invisible gold” associated mainly with the pyrite and occasionally with the arsenopyrite.     

酸性和碱性介质中甘氨酸解离吸附和氧化的EQCM研究

用电化学石英晶体微天平(EQCM)研究酸性和碱性介质中甘氨酸在Pt电极上的吸附和氧化过程.结果表明,甘氨酸的解离吸附和氧化行为与溶液的酸碱性密切相关.酸性溶液中甘氨酸吸附较弱,碱性溶液中则产生强吸附物,且当电位低于0V(vs.SCE)时可吸附于Pt电极表面.此外,碱性溶液中甘氨酸还表现出较高的电氧化活性.通过EQCM定量检测上述过程中Pt电极表面的质量变化,测定了不同电位区间(氢区、双电层区和氧区)每传递一个电子所对应的电极表面吸附物种的平均摩尔质量.