Electrochemical nanogravimetric study on the ruthenium(III) trichloride–polyaniline nanocomposite

Ruthenium(III) trichloride microcrystals were soaked in aniline and aniline/acetonitrile mixtures. In all cases, polyaniline (PANI) was formed as a result of the intercalation of aniline into the layered structure of RuCl₃ crystal and the reaction between aniline and the host material. The appearance of polyaniline was proven by infrared spectroscopy. The as-formed (PANI) _x ^z+(RuCl₃) _y ^z− nanocomposites were attached to gold surfaces and studied by cyclic electrochemical nanogravimetry. The sorption of aniline and its effect on the nanocomposites immobilized on gold were also studied in supporting electrolytes. The redox behaviour of the composite shows the electrochemical transformations of both polyaniline and RuCl₃. The redox waves of PANI are similar to those observed for very thin PANI films. It attests that the response is originated from monolayer-like PANI film situated between RuCl₃ layers. The transport of the charge-compensating ions reflects the variation of the oxidation states of both PANI and RuCl₃. The nanocomposites behave as self-doped layers in the potential region when both constituents are charged, i.e. PANI is partially oxidized while RuCl₃ is partially reduced, since the electroneutrality is assured by mutual charge compensation. When PANI is reduced, cations enter the layer to counterbalance the negative charge resulting from the reduction of Ru(III) to Ru(II). It was also found that the intercalation of water molecules is—albeit still substantial—smaller than that of pure RuCl₃ microcrystals, which is related to the presence of PANI between the RuCl₃ layers. Dedicated to Prof. Mikhail A. Vorotyntsev on the occasion of his 60th birthday     

Formation and redox behaviour of polycarbazole prepared by electropolymerization of solid carbazole crystals immobilized on an electrode surface

Carbazole solid crystals have been mechanically attached to platinum or gold electrodes by two different methods and investigated by cyclic electrochemical quartz crystal microbalance measurements in the presence of aqueous acidic media. It was demonstrated that oxidative dimerization and polymerization can also be accomplished under such conditions. During electropolymerization, anions and water molecules enter the surface layer; however, these species leave the film after the reduction of the polymer formed. The mass changes observed in the course of the redox transformations of polycarbazole film can be explained by potential- and time-dependent sorption/desorption of H⁺ and ClO₄ ⁻ ions. The electroactivity of the polymer diminishes in more dilute acid media; however, it is recovered again in concentrated HClO₄ solutions. In more dilute acid solution the extent of the water sorption (film swelling) increases.     

Electrochemically induced transformations of ruthenium(III) trichloride microcrystals in salt solutions

Ruthenium (III) trichlorid solid crystals have been mechanically attached to gold surfaces and studied by cyclic electrochemical quartz crystal microbalance measurements in the presence of aqueous solutions of different concentrations containing M⁺Cl⁻, where M⁺=H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺. The RuCl₃ and the complexes formed during the electrochemical transformations show two or more reduction and reoxidation pairs of waves, depending on the experimental conditions (concentration, scan rate, and potential range). The voltammetric peaks are shifted into the direction of higher potentials with increasing electrolyte concentrations except at very high concentrations when the peaks belong to the first reduction/reoxidation processes move oppositely. The mass change was reversible, during reduction mass increase, while during oxidation mass decrease occurred at medium electrolyte concentrations in two, more or less distinct steps. At high or low concentrations the mass excursions are more complex involving different mass increase/decrease regions as a function of potential which vary with the potential range of the measurements. The peak potentials and the electrochemical activity strongly depend on the nature of the cations and pH. It is related to the formation of complexes in different compositions. The mass change decreases with increasing electrolyte concentrations attesting the important role of the water activity and the transport of solvent molecules. It was concluded that in dilute solutions during the first reduction step M⁺ ions enter the surface layer. The strongly hydrated Li⁺ ions transfer water molecules into the microcrystals, while simultaneously with the incorporation of K⁺, Rb⁺, and Cs⁺ ions H₂O molecules leave the surface layer. The opposite transport of ions and solvent molecules occur during oxidation. In the course of further reduction the incorporation of all ions studied except that of Cs⁺ ions is accompanied with water sorption. The number of sorbed water molecules is proportional to the hydration number of these ions. A reaction scheme is proposed in which M⁺ _m-3[Ru^IIICl _m (H₂O) _n ]^3-m · xH₂O (m≥3) and [Ru^IIICl _m (H₂O) _n ]^3-m (Cl⁻)_3-m · xH₂O (m≤3) type complexes are reduced to the respective – or depending on the electrolyte concentration higher or lower – Ru(II)chloro complexes resulting in mixed valence compounds (phases). Taking into account the layered structure of RuCl₃ the electrochemical reduction can be explained as an intercalation reaction in that mixed valence intercalation phases with a general formula M _x ⁺(H₂O) _y [RuCl₃] ^x− are formed from RuCl₃·x H₂O. The reduction/reoxidation waves are related to the redox transformations of Ru(III) to Ru(II) sites, while the composition of the polynuclear complexes and the structure of microcrystals change. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13.−16., 2005.     

Electrochemical quartz crystal microbalance study of ion transport accompanying charging-discharging of poly(pyrrole) films

Electrochemical quartz crystal microbalance studies on poly(pyrrole) electrodes revealed a complex nature of the potential-dependent sorption of ionic substances. It is found that the relative contribution of anions and cations to the overall charge transport process depends upon several factors, such as the oxidation state of the polymer, the composition of the supporting electrolyte as well as on the film thickness. The phenomena observed are discussed in terms of morphological transformations arising as a result of interactions between the polymer and the mobile substances. Received: 21 August 1998 / Accepted: 21 October 1998     

电化学石英晶体微天平研究六氰亚铁铜膜修饰电极及其离子效应

利用电化学石英晶体微天平（EQCM）手段，结合循环伏安法．计时电流法对六氰亚铁铜（CuHCF)膜修饰电极及其在不同水溶液中的离子交换机制进行了研究。结果表明；通过循环伏安法，在Pt电极上可以牢固地形成CuHCF膜．在氧化还原过程中，不仅是阳离子，阴离子也参与了在CuHCF膜中的传输。     

Electrochemical quartz crystal microbalance analysis of the cathodic process in a lithium-ion battery

The surface processes at carbon and platinum electrodes have been studied using the electrochemical quartz crystal microbalance technique in organic electrolyte solutions for lithium ion batteries. The changes in resonance frequency were analyzed as a function of the electrode potential, indicating that the process depended not only on the electrode material but also on the cathode potential. In the solution containing LiBF₄ as the electrolyte, the main product at the platinum surface was Li₂CO₃ and LiF, whereas formation of lithium alkylcarbonates was the primary process at the platinum and carbon electrodes in LiPF₆ solution.     

Electrochemical determination of melamine using oligonucleotides modified gold electrodes

A novel and simple electrochemical method for determination of melamine is developed based on oligonucleotides film modified gold electrodes. The electrochemical probe of ferricyanide was used to investigate the interactions between oligonucleotides and melamine. Results of cyclic voltammetries, differential pulse stripping voltammetries, electrochemical impedance spectrometry and atomic force microscope, proved that melamine might interact with oligonucleotides mainly through electrostatic and hydrogen-bonding interactions. The interactions between oligonucleotides and melamine lead to the increase in the peak currents of ferricyanide, which could be used for electrochemical sensing of melamine. The redox peak currents of ferricyanide were linear with the concentration of melamine in the range from 3.9 × 10⁻⁸ to 3.3 × 10⁻⁶ M with a linear coefficiency of 0.990. The detection limit was 9.6 × 10⁻⁹ M. The proposed electrochemical biosensor is rapid, convenient and low-cost for effective sensing of melamine. Particularly, the proposed method was applied successfully to the determination of melamine in milk products, and the recovery was 95%.     

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH₄⁺, Li⁺, Na⁺ and K⁺), anions (SO₄²⁻ and NO₃⁻) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry.     

Adsorption of fission products on stainless steel and zirconium

Contamination of the structural materials of nuclear reactors is a crucial question in view of radiation protection, especially, if due to some leakage, uranium and its fission products appear in the cooling water. Since it is rather difficult to obtain in situ experimental data on the actual amount of adsorbed radioactive species, the surface contamination may be quantified by measuring bulk activity concentrations of the cooling water and by calculating the amount of adsorbed material on the surfaces by using a partition coefficient. To do this, the knowledge of an appropriate adsorption isotherm is needed. Thus, our paper presents results, based on electrochemical measurements, about the extent and effect of the adsorption of certain fission products—caesium and iodide—in their ionic forms on the surface of some alloys used in the nuclear industry. Our findings allow the conclusion that the adsorption of these ions can be described by a Langmuir-type isotherm, where the saturation values correspond to surface monolayers.     

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.     

鸟嘌呤、鸟苷、鸟苷酸的电化学石英晶体微天平研究

利用电化学石英晶体微天平(EQCM)研究了鸟嘌呤、鸟苷和鸟苷酸在金电极上的电化学行为.结果表明,三种生物活性分子均能在1.1V电位被氧化,对应于它们所含的共同基团嘌呤环中CN键的氧化,根据氧化反应电量和质量的变化,求得电子转移数为4.氧化电流的大小次序为鸟苷酸>鸟苷>鸟嘌呤,这可能与三者在电极上的吸附量不同有关.     

Charge Transport Processes of Immobilized Heteropolyanions at Self-assembled Monolayer Modified Gold Electrode by Electrochemical Quartz Crystal Microbalance Measurement

The in situ electrochemical quartz crystal microbalance(EQCM) technique was used to investigate the ion transport of immobilized heteropolyanions at a self-assembled monolayer(SAM) modified gold electrode during electrochemical redox process.A mixed transfer method was presented to analyse the abnormal change of resonant frequency based on the simultaneous insertion/extraction of different ions.The results indicate that the migration of HSO4-anions was indispensable in the redox process of the heteropolyani...     

自组装膜上细胞色素c的电化学石英晶体微天平实时表征和定量检测

采用电化学石英晶体微天平(EQCM)实时表征和定量检测细胞色素c(Cytc).在压电石英晶振表面上自组装巯基十一酸(MUA)单层膜,以盐酸1-乙基-3-(3-二甲基氨基丙基)碳二亚胺(EDC)和N-羟基琥珀酰亚胺(NHS)活化羧基,将Cytc共价固化到电极表面.EQCM实时监测了MUA的自组装和Cytc的固化过程,测定了二者在电极表面的覆盖度和Cytc的固化量.结果表明,Cytc在0.03～3.00μmol/L浓度范围内呈线性变化,检测限可达到1.19×10^-9mol/L.     

电化学石英晶体微天平应用研究和背景扣除

基于用循环伏安法研究非理想可逆体系时,电极本身的氧化峰电量与还原峰电量存在一比值。据此建立了一种用于电化学石英晶体微天平应用研究的背景扣除新方法。用这种方法研究了腺嘌呤、腺苷、腺苷一磷酸在金电极上的电化学氧化行为。结果表明:3种活性分子均能在1.2V左右氧化,对应的氧化电流大小顺序为:腺嘌呤>腺苷>腺苷一磷酸,氧化过程的电子转移数为6。     

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。     

电化学石英晶体微天平研究界面电场对DNA杂交的影响

采用电化学石英晶体微天平, 现场监测不同界面电场下完全匹配的靶标DNA和不完全匹配的靶标DNA分别与寡聚核苷酸探针分子杂交的过程. 结果表明, 电极表面荷正电时DNA表观杂交效率比电极表面荷负电时高, 但假阳性比较显著; 而电极表面荷负电时能有效地抑制错配杂交. 探讨了引入界面电场后探针分子取向和微观作用力对DNA杂交的影响.     

Electrochemical quartz crystal microbalance study of copper ad-atoms on gold and platinum electrodes Part I. Adsorption of anions in sulfuric acid

The deposition and dissolution processes of copper ad-atoms on a gold or a platinum electrode in sulfuric acid electrolyte solution were investigated by using the electrochemical quartz crystal microbalance. It was found that the weight loss in the removal of the Cu-adlayer from the Au substrate was considerably larger than that expected from Faraday's law whereas the deviation for the Pt substrate was very small. The adsorption of bisulfate or sulfate anions both on Cu ad-atoms and on the electrode substrates was discussed quantitatively. It was demonstrated that higher coverage with Cu ad-atoms and lower adsorbability with bisulfate or sulfate anions were obtained on the Pt electrode than on the Au, and these effects could be ascribed to the difference in electronegativity between Pt and Au substrates.     

Electrochemical piezoelectric quartz crystal impedance study on the interaction between concanavalin A and glycogen at Au electrodes

The carbohydrate research has emerged as a "new frontier" in chemical/biological field. The binding of lectin with carbohydrate is one of the important courses of life activities. The report studies concanavalin A (Con A)-glycogen interaction on gold electrode surfaces by electrochemical piezoelectric quartz crystal impedance (EPQCI) method. The piezoelectric quartz crystal (PQC) parameters, resonant frequency shift (Deltaf(0)) and the motional resistance change (DeltaR(1)), and the electrochemical impedance (EI) parameters, electrolyte resistance change (DeltaR(s)) and the double layer capacitance change (DeltaC(s)), were measured and discussed simultaneously. Two methods were adopted for measuring the Con A-glycogen association. Based on EPQCI measurement during Con A reaction with glycogen adsorbed on Au electrode, association constant K(a) and the amount of the binding sites s calculated are 1.48 x 10(6) M(-1) and 4.09, respectively. Based on single PQC measurement of glycogen reaction with Con A assembled on Au electrode, K(a) was estimated to be 1.26 x 10(6) M(-1).     

The study of electrochemical palladium behavior using the quartz crystal microbalance

The electrochemical quartz crystal microbalance (EQCMB) method has been used to evaluate the processes which occur in/on the palladium electrode in basic solutions. Hydrogen electrosorption in palladium is accompanied by an additional frequency shift that can be attributed to the stresses generated inside the Pd metal. A non-linear dependence between the mass change and the charge consumed during hydrogen oxidation in the Pd electrode has been found for hydrogen absorbed in the α- and β-phases. This effect precludes the objective estimation of the amount of hydrogen absorbed inside the Pd electrode. The EQCMB method has been used, however, for studying the surface electrode processes on the Pd electrode, i.e. specific anion adsorption, surface oxidation and dissolution. Also, the structure of the palladium oxide formed on the Pd surface during electrochemical oxidation is discussed in this paper and the effect of the anodic limiting potential on the oxide structure is reported. Received: 10 August 1999 / Accepted: 24 September 1999     

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.