An electrochemical quartz crystal impedance study on the rising of an aqueous solution meniscus for a partially immersed gold electrode during the electrochemical reduction of oxygen.

An electrochemical quartz crystal impedance system (EQCIS) was used to study the resonance behavior of an AT-cut 9-MHz piezoelectric quartz crystal (PQC) with its Au electrode partially immersed in KCl, Na2SO4 and NaClO4 aqueous solutions, respectively. An in situ determination of the immersed area and the height of the electrode was achieved by simultaneous measurements of the PQC electroacoustic admittance and the electrochemical impedance. The rising of the solution meniscus for a gold electrode partially immersed in aqueous solutions was found at oxygen reduction potentials and evaluated versus the electrolyte, electrolyte concentration, solution pH and oxygen concentration. The solution meniscus rising was explained based on a lowering of the contact-angle hysteresis and a continued collection of the water product at the solid-gas-solution interface during oxygen reduction.     

In Situ Monitoring of Generation and Precipitation of Ferric Hydroxide Sol with a Piezoelectric Quartz Crystal Impedance Analyzer

The piezoelectric quartz crystal (PQC) impedance technique was applied to monitor in situ generation and precipitation of the ferric hydroxide sol in aqueous solutions at 90 degrees C. Equivalent circuit parameters and resonant frequencies as well as the half-peak width of the electroacoustic conductance spectrum deltaf(G1/2) for the PQC resonance were obtained and analyzed. Three stages, sol generation and simultaneous adsorption, adsorption equilibrium, and precipitation of ferric hydroxide sol could be identified in the process of adding the ferric nitrate solution into the hot water. A scheme of two consecutive reactions occurring at the electrode/solution interface was used to analyze the adsorption kinetics of ferric hydroxide sol onto the Au electrode. In addition, the electrolyte-induced precipitation of the colloid was monitored and discussed. Temperature effect on the PQC resonance behavior in liquid was also investigated. Since the PQC impedance technique provides multidimensional piezoelectric information in situ, it is highly recommended for studying the process of sol-gel generation and precipitation. Copyright 2001 Academic Press.     

Simultaneous EQCM and diffuse reflectance UV-visible spectroelectrochemical measurements: poly(aniline-co-o-anthranilic acid) growth and property characterization

Piezoelectric diffuse reflectance spectroelectrochemistry (PDRSEC), a new technique of diffuse reflectance spectroelectrochemistry (DRSEC) in combination with electrochemical quartz crystal microbalance (EQCM), was developed to study the electrochemical copolymerization of aniline and o-anthranilic acid in 1.0 mol l(-1) HClO4 and the properties of these copolymers. The DRSEC using an integral sphere was proven to possess a higher optical sensitivity at the unpolished piezoelectric quartz crystal electrodes used than the mirror reflectance spectroelectrochemistry mode. The copolymers grown from the copolymerization bath of different molar fractions of o-anthranilic acid (F1, relative to the total amount of the two monomers) showed intermediate properties between those of the homopolymers, which varied gradually with F1. The swelling/dissolution behavior of the copolymers vs solution pH was traced via the EQCM frequency and resistance signals, and its large dependence on F1 was found and discussed. In a HAc-NaAc buffer solution at pH 5.6, the amount of adsorbed lysozyme was found to be positively correlated with F1, via an EQCM impedance investigation, demonstrating the feasibility of using poly(aniline-co-o-anthranilic acid) as a load-adjustable immobilization matrix for cationic proteins. The novel PDRSEC method proposed is highly recommended for surface electrochemistry studies at relatively rough electrodes.     

溶菌酶在裸金电极和疏基乙酸或正十二疏烷基醇修饰电极上的吸附

电化学石英晶体阻抗系统;疏基乙酸;溶菌酶在裸金电极和疏基乙酸或正十二疏烷基醇修饰电极上的吸附     

Simultaneous quartz crystal microbalance-electrochemical impedance spectroscopy study on the adsorption of anti-human immunoglobulin G and its immunoreaction at nanomaterial-modified Au electrode surfaces.

The quartz crystal microbalance method (QCM), in combination with electrochemical impedance spectroscopy (EIS), has been utilized to monitor in situ anti-human IgG adsorption on several Au-based surfaces, bare Au, nanogold/4-aminothiophenol (4AT)/Au, and multi-walled carbon nanotubes (MWCNT)/Au, and succeeding human IgG reactions. Also, the immobilization protocol of anti-human IgG via its glutaraldehyde (GA) cross-linking with self-assembled 4AT on an Au electrode and the subsequent surface immunoreaction were examined. The resonant frequency (f(0)) and the motional resistance (R(1)) of the piezoelectric quartz crystal (PQC) as well as electrochemical impedance parameters were measured and discussed. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the ferricyanide/ferrocyanide couple were examined before and after electrode modification, the antibody adsorption and antibody-antigen reactions. We found that the amount for antibody adsorption was the greatest on the colloid Au modified surface, and that at MWCNT ranked the second, while specific bioactivity was almost identical on the four kinds of surfaces. Two parameters simultaneously obtained at the colloid Au modified surface, Deltaf(0) and DeltaC(s) (interfacial capacitance), have been used to estimate the association constant of the immunoreaction.     

Electrodeposited sol-gel-imprinted sensing film for cytidine recognition on Au-electrode surface

A novel thin molecularly imprinted sol-gel film with specific recognition for cytidine was electrodeposited on the surface of piezoelectric quartz crystal (PQC) Au-electrode. In this method, a sufficiently negative potential was applied to the electrode surface to generate hydroxyl ions, which play the role of the catalyst for the hydrolysis and condensation of 3-(aminopropyl)trimethoxysilane (APTMS). The process of the preparation of the imprinted sol-gel film was investigated in detail by using the piezoelectric quartz crystal impedance (PQCI) technique and cyclic voltammetry. The thickness of the imprinted film was controlled easily by adjusting the applied potential and the deposited time. The binding capacity and the selectivity of the electrodeposited imprinted sol-gel film were also studied in detail by using PQCI, electrochemically impedance technique and capacitance technique. The electrodeposited imprinted sol-gel film exhibited high selectivity toward cytidine in comparison to interfering substances. The dissociation constant (K_d) in the nanomolar range indicated a strong imprinted interaction existing between the electrodeposited sol-gel-imprinted film and the template cytidine.     

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).     

A comparative study on the viscoelasticity and morphology of polyaniline films galvanostatically grown on bare and 4-aminothiophenol-modified gold electrodes using an electrochemical quartz crystal impedance system and SEM.

The equivalent-circuit parameters of the 9-MHz piezoelectric quartz crystal (PQC) resonance were measured in situ during the galvanostatic polymerization of aniline on 4-aminothiophenol(4-ATP)-modified and bare Au electrodes for ca. 2000 s, respectively. Two polymerization media, 0.100 mol L-1 aniline in 1.0 mol L-1 H2SO4 and in 2.0 mol L-1 HClO4 aqueous solutions, and two values of the current density, 12 and 36 microA cm-2, were used. At identical levels of the resonant frequency shifts in the solutions, obviously greater increases in the motional resistance (R1) were found after aniline polymerization on bare Au electrodes, though the absolute values of delta f0/delta R1 were all large; also, the resonant frequency shifts in air (delta f0g) were considerably smaller for PANI films grown on bare Au electrodes. It is thus concluded that, under identical polymerization conditions, (1) the PANI film grown on a bare gold electrode is rougher, less compact, and can entrap solution more notably; (2) the deposition efficiency of PANI is higher on a 4-ATP-modified Au electrode, owing to a significantly greater observed "dry" frequency shift, and thus a greater "net" mass value of the polyaniline backbone. SEM observations have confirmed that PANI films on 4-ATP-modified Au electrodes were smoother and more compact than those grown on bare Au ones under identical polymerization conditions. In addition, a technique of simultaneous measurements of the electroacoustic admittance of the PQC resonance and the electrochemical impedance was used to monitor the adsorption of 4-ATP onto a PQC gold electrode.     

Frequency response to liquid density of a piezoelectric quartz crystal sensor with longitudinal wave

Elimination of longitudinal wave effect is an important aspect in the detection cell design, although such consideration is ignored in most of references. Three detection cells were designed to investigate the influence of longitudinal wave effect on the frequency response of a piezoelectric quartz crystal (PQC) to liquid density. In the cell with horizontally mounted quartz crystal, the air/liquid interface acts the reflection surface for the longitudinal wave. The variation in liquid height by regent addition or solvent evaporation can result in fluctuation in the oscillating frequency of the PQC. The influence of the longitudinal wave is more obvious in a test liquid of lower density. In the cell with perpendicularly mounted quartz crystal, the longitudinal wave is mainly reflected back by the inner wall body. The fine structure of plotting of frequency shift (Δf) versus (ρη)^1/2 shows a wave shape, which is different from the well-known linear relationship between of Δf and (ρη)^1/2, where ρ and η are the density and viscosity of the liquid, respectively. And wave-shaped frequency-temperature curves were observed. The longitudinal wave was a kind of potential error source in the PQC measurements. The longitudinal wave effect can be efficiently eliminated by using a rough reflection surface. After eliminating the influence of reflected longitudinal wave, the stability of the sensor PQC was much improved.     

Study of fibrinogen adsorption on hydroxyapatite and TiO2 surfaces by electrochemical piezoelectric quartz crystal impedance and FTIR-ATR spectroscopy

The electrochemical piezoelectric quartz crystal impedance (EQCI), a combined technique of piezoelectric quartz crystal impedance (PQCI), electrochemical impedance (EI), and Fourier transform infrared spectroscopy-attenuated total internal reflectance spectroscopy (FTIR-ATR) were used to in situ study the adsorption process of fibrinogen onto the surface of biomaterials—TiO₂ and hydroxyapatite (Ca₅(PO₄)₃OH, HAP). The equivalent circuit parameters, the resonance frequencies and the half peak width of the conductance spectrum of the two biomaterial-modified piezoelectric quartz crystal (PQC) resonances as well as the FTIR-ATR spectra of fibrinogen during fibrinogen adsorption on TiO₂ and HAP particles modified electrode surface were obtained. The adsorption kinetics and mechanism of fibrinogen were investigated and discussed as well. The results suggested that two consecutive steps occurred during the adsorption of fibrinogen onto TiO₂ and hydroxyapatite (HAP) surface. The fibrinogen molecules were firstly adsorbed onto the surface, and then the rearrangement of adsorbed fibrinogen or multi-layered adsorption occurred. The FTIR-ATR spectroscopy investigations showed that the secondary structure of fibrinogen molecules was altered during the adsorption and the adsorption kinetics of fibrinogen related with the variety of biomaterials. These experimental results suggest a way for enriching biological analytical science and developing new applications of analytical techniques, such as PQCI, EI, and FTIR-ATR.     

间苯二酚杯[4]芳烃为涂层的压电石英传感器测定液相多巴胺

研究了以间苯二酚杯[4]芳烃为敏感涂层的石英压电晶体（PQC）传感器,在中 性磷酸盐缓冲液体系中对神经传递质多巴胺和抗坏血酸的响应,发现间苯二酚杯 [4]芳烃对多能上能下胺有很好的响应选择性,这归因于间苯二酚杯[4]芳烃与多巴 胺分子结构相匹配,形成主客体超分子体系。以间苯二酚杯[4]芳烃为涂层的POC传 感器对液相中多巴胺具有响应快、重现性好、灵敏度高的特点,线性响应范围为3. 5-500 μg/g。     

A Study on a Partially Immersed Gold Electrode Using an Electrochemical Quartz Crystal Impedance System

Simultaneous and fast measurement of the piezoelectric quartz crystal (PQC) impedanceduring electrochemical pertUrbations, i.e., the electrochemical quartz crystal impedancesystem (EQCIS) called by us, characterizes the PQC resonance better by providingmultidimensional in sl'tu piezoelectric information than the conventional electrochemicalquartz crystal microbalance (EQCM)'-'. The PQC impedance has been analyzed basedon the Butterworth-Van Dyke (BVD) equivalent electrical circuit com…     

Scanning electrochemical microscopy in combination with piezoelectric quartz crystal impedance analysis for studying the growth and electrochemistry as well as microetching of poly(o-phenylenediamine) thin films

The combination of scanning electrochemical microscopy (SECM) with piezoelectric quartz crystal impedance (PQCI) analysis was proposed as a novel multiparameter method for investigating the cyclic voltammetric growth of poly(o-phenylenediamine) (PoPD) thin films at Au electrodes in aqueous solutions of various pH values and the potentiostatic microetching (localized degradation) of these films in 0.10 mol/L aqueous H2SO4 for comparative examinations on polymer porosity and stability. Two potential-sweep ranges, -0.4 to 0.9 (I) and 0 to 0.9 (II) V versus SCE, and four solutions, acidic (A, 0.20 mol/L H2SO4 + 0.10 mol/L Na2SO4; B, 0.10 mol/L H2SO4 + 0.20 mol/L Na2SO4), neutral (C, 0.10 mol/L PBS + 0.20 mol/L Na2SO4, pH 7.2), and alkaline (D, 0.20 mol/L NaOH + 0.20 mol/L Na2SO4) aqueous solutions, were selected for PoPD growth. The pH increase for the polymerization solution increased the molar percentage of polyaniline-like chains in PoPD, as quantified from the current peaks at approximately 0.6 V versus a saturated calomel electrode (SCE) for the oxidation of -NH2 groups in as-prepared PoPD (grown from solutions C and D) during their redox switching in 0.10 mol/L aqueous H2SO4 for the first time. The unusual PQCI responses observed at negative potentials (potential range I) in the first several potential cycles during the cyclic voltammetric growth of PoPD in acidic and neutral solutions have been reasonably explained as being due to the precipitation/dissolution of the poorly soluble phenazinehydrine charge-transfer complexes developed during redox switching of oligomers for the first time, which brought about much less compact PoPD films and their higher degradability than those grown in the same solution but over potential range II. SECM, scanning electron microscopy (SEM), and piezoelectric quartz crystal (PQC) frequency were used to estimate the sizes of etched microscale spots. In addition, the x-, y-, or z-axis movement of a Pt microelectrode of 25-mum diameter near the PQC electrode was found to influence negligibly the PQCI responses in 1.0 mol/L aqueous Na2SO4 containing K4Fe(CN)6 up to 0.10 mol/L, and a new protocol of dynamically electrodepositing silver microwires via the chemical-lens method was proposed for examining the local mass-sensitivity distribution on the PQC surface.     

Methodology for Determination of the Key Parameters of Conjugated Polymer Electrodeposition,Based on a Combination of Spectroelectrochemistry and Electrochemical Quartz Crystal Microbalance

Russian Journal of Electrochemistry - Methodology based on a combination of experimental data obtained by in situ methods of spectroelectrochemistry and electrochemical quartz crystal microbalance...     

Impedance and frequency characteristics of electrode-separated piezoelectric quartz crystals in liquids

The electrical equivalent circuit parameters of an electrode-separated piezoelectric quartz crystal (PQC), where the gaps between the electrodes and the crystal plate were filled with various liquids, were evaluated from admittance measurements and were compared with those of a normal PQC with Au electrodes adhering to the crystal plate. The resistance parameter in the equivalent circuit of the electrode-separated PQC was more sensitive to the specific conductivity, density and viscosity of liquids than was that of the normal PQC. This parameter, unlike that of the normal PQC, was also affecteded by the permittivity of the liquid. The effect of the liquid properties on the other parameters in the equivalent circuit and the series resonant frequency are also discussed.     

Piezoelectric quartz crystal biosensors

Biosensing methods utilize the intrinsic selectivity of a biorecognition process to create relatively simple, low cost, analytical alternatives for a variety of research investigations. Here, biosensor applications of the piezoelectric quartz crystal (PQC) are reviewed. The discussion is divided into sections focusing on the development of PQC based analytical techniques, applications in solution phase sensing pertaining to PQC biosensors, and the current state of knowledge in PQC biosensing applications. Immobilization procedures, dip and dry assay techniques, and solution phase sensing methods are considered in detail.     

A piezoelectric method for monitoring formaldehyde induced crosslink formation between poly-lysine and poly-deoxyguanosine

To date, no experimental technique has been used to monitor DNA-protein crosslink formation in real-time. Real-time data is important for understanding the underlying chemical mechanisms associated with this reaction process. Here, the novel adaptation of existing piezoelectric quartz crystal (PQC) or quartz crystal microbalance (QCM) technology was used to monitor, in real-time, the formation of a crosslink bond induced by formaldehyde between lysine and guanine. Previous results showed complexes of lysine and guanine constitute a major portion of the DNA-protein crosslinks formed. Thus, poly-lysine(5) and poly-deoxyguanosine(11) were used as a model system to develop this detection method. Poly-lysine(5) was immobilized on QCM electrode surfaces by covalent attachment through polyethylenimine (PEI). Immobilization was confirmed by the decrease in dry QCM frequency; data consistency suggested uniform coatings were produced. The QCM sensor was configured within a thermostatic environmental chamber. The system was calibrated and baseline responses to variations in the analyte solution matrix were identified. QCMs with immobilized poly-lysine(5) were placed in contact with formaldehyde and poly-deoxyguanosine(11), and crosslink formation was monitored in real-time. Crosslink formation was verified through evaluation of controls. Control assays indicated some of the frequency signal was as aresult of non-specific association. Further assays were conducted after saturation of non-specific binding. This real-time data represents a significant advancement in the state of knowledge of the crosslinking process and provides the experimental foundation for further QCM crosslink investigations.     

Monitoring iodine adsorption onto zeolitic-imidazolate framework-8 film using a separated-electrode piezoelectric sensor

In this work, a separated-electrode piezoelectric sensor (SEPS), constructed by a naked quartz crystal mounted between two electrodes, is reported for applications in a corrosive gaseous phase. The response of SEPS was measured by an impedance analysis method. It was shown that SEPS has an excellent frequency stability because its quality factor is in the order of 10⁵. The SEPS can be operated even with the electrode gap in air larger than 1 cm. Compared with a conventional quartz crystal microbalance, the resonant frequency of the SEPS is independent of the mass change in the electrode. The SEPS was applied to monitor the adsorption of iodine on quartz surface and zeolitic-imidazolate framework-8 (ZIF-8) film as well as in the transfer of iodine between two ZIF-8 films. The SEPS offers the advantages of easy preparation, corrosion-resistant and convenience in combination with mass and optical measurements.     

In situ monitoring of the rising of aqueous solution meniscus for a partially immersed silver electrode during electrochemical reduction of oxygen

Rising phenomena of aqueous solution meniscus were found for the silver electrode of a 5 MHz piezoelectric quartz crystal (PQC) partially immersed in Na₂SO₄, NaClO₄, HClO₄ and NaF aqueous solutions at oxygen reduction potentials, respectively. A detailed study revealed that a decrease in contact‐angle hysteresis (or a contact‐angle decrease) and a continued collection of the water product at the solid‐gas‐solution interface during oxygen reduction, rather than the electrocapillary effect and an agitation effect induced by the oscillation of PQC, are responsible for the meniscus‐rising phenomena. In addition, in situ determination of the immersed height of a partially immersed Ag electrode was studied on the basis of simultaneous measurements of the electroacoustic admittance and electrochemical impedance.     

Construction and analytical application of ion-selective piezoelectric sensor for atropine sulfate

The method describes the use of a piezoelectric quartz crystal (PQC) as a substitute for ion-selective electrodes. The approach is feasible when the membrane materials are electrically non-conductive and membrane potential measurements are consequently not possible. An ion-selective piezoelectric sensor sensitive to atropine sulfate was constructed by coating a PVC membrane containing activant on one the side of a PQC. On the basis of selective adsorption of atropine ions across the modified film and the sensitive mass response of PQC, the method exhibits a sensitive, rapid response and is easy to operate without pretreatment of the sample. The logarithm of the frequency shift gave a linear relationship with the logarithm of atropine sulfate concentration in the 1.0 x 10(-8)-1.0 x 10(-3) M range with a detection limit of 5.0 x 10(-9) M at pH 7.0. Recoveries were from 98.7-102.2%. Two activants, atropine tetraphenylborate and atropine dipicrylaminate, were synthesized and investigated. Influencing factors were also examined and optimized. The results for real samples obtained by the proposed method agreed with those obtained by conventional methods.