Piezoelectric Quartz Crystal Impedance Technique Research Articles

Analysis for Effect of Dimehypo on Proteolytic Enzyme Activity in the Midgut of the Spider <i>Pardosa pseudoannulata</i> with a Piezoelectric Quartz Crystal Impedance

A piezoelectric quartz crystal impedance technique has been applied for in situ monitoring of the whole process of the proteolytic enzyme-catalyzed hydrolyzation of casein and the effect of pesticide dimehypo (formula: C5H11NNa2O6S4) on the proteolytic enzyme activity in the midgut of the spider Pardosa pseudoannulata, based on its real-time reponses to the density-viscosity change of the tested solution due to the hydrolyzation occurring on the casein molecules. The results indicated that the hydrolyzation was significantly increased in the presence of low-dose dimehypo, where significantly inhibited in the presence of high-dose dimehypo, and a correlation was found precisely between the enzyme activity reflected by the final frequency shift after the hydrolyzation and the concentration of dimehypo, with a significant frequency response observed even at a 2.88 x 10-4 volume ratio of dimehypo to distilled water. The present work may have presented a novel method feasible for study on the mechanism of excitability of spiders under low-dose dimehypo pesticide and quick detection of proteolytic enzyme activity.

Stereoselective histidine sensor based on molecularly imprinted sol-gel films

A piezoelectric sensor coated with a thin molecularly imprinted sol-gel film has been developed for the determination of l-histidine in the liquid phase. Without preprotection, l-histidine was imprinted directly into silica sol-gel films that consisted of a hybrid mixture of functionalized organosilicon precursors (phenyltrimethoxysilane and methyltrimethoxysolane). The viscoelasticity of the film in the air and in buffer solution has been studied by the piezoelectric quartz crystal impedance technique. The binding of l-histidine to the imprinted film in the liquid phase was investigated by the piezoelectric microgravimetry and electrochemical impedance technique. Scatchard analysis showed that the maximum binding site ( Q max) of the l-histidine imprinted sol-gel film is about 23.7 μmol/g. A linear range from 5.0 × 10 −8 to 1.0 × 10 −4 M for a detection of l-histidine has been observed with a detection limit of 2.5 × 10 −8 M for S/N = 3. The proposed imprinted sol-gel sensor exhibits good stability, high specificity, and excellent stereoselectivity.

Investigation of double stranded DNA damage induced by quercetin–copper(II) using piezoelectric quartz crystal impedance technique and potentiometric stripping analysis

DNA damage by quercetin–Cu 2+ was monitored in real time by piezoelectric quartz crystal impedance (PQCI) technique. In the PQCI analysis, the frequency change was caused mainly by the changes in density–viscosity of DNA solution in the damage course. The influences of DNA, Cu 2+, and quercetin concentrations on the motional resistance change (Δ R m) were investigated in detail. The results showed that quercetin exhibited pro-oxidative damage at lower concentrations while anti-oxidative protection at higher concentrations, and Δ R m exhibited a linear relationship in the DNA concentration range from 200 to 1600 μg/ml. Potentiometric stripping analysis (PSA) was also used to observe the electrochemical behavior of damaged DNA. From PSA, a new peak at 0.84 V and a higher peak at 1.06 V were discovered, which suggested that more purines were exposed to the electrode surface during the damage course. In agarose-gel electrophoresis, catalase and biquinoline were found to effectively inhibit DNA damage, therefore, a possible damage mechanism was proposed.

Estimation of kinetics parameters for the adsorption of human serum albumin onto hydroxyapatite-modified silver electrodes by piezoelectric quartz crystal impedance analysis.

The adsorption of human serum albumin onto hydroxyapatite-modified silver electrodes has been in situ investigated by utilizing the piezoelectric quartz crystal impedance technique. The changes of equivalent circuit parameters were used to interpret the adsorption process. A kinetic model of two consecutive steps was derived to describe the process and compared with a first-order kinetic model by using residual analysis. The experimental data of frequency shift fitted to the model and kinetics parameters, k1, k2, psi1, psi2 and qr, were obtained. All fitted results were in reasonable agreement with the corresponding experimental results. Two adsorption constants (7.19 kJ mol(-1) and 22.89 kJ mol(-1)) were calculated according to the Arrhenius formula.

Electrostatic assembly of calf thymus DNA on multi-walled carbon nanotube modified gold electrode and its interaction with chlorpromazine hydrochloride

The electrostatic assembly of calf thymus DNA on multi-walled carbon nanotubes (MWNTs)-modified gold electrode via poly(diallyldimethylammonium chloride) (PDDA), a cationic polyelectrolyte, has been studied. Piezoelectric quartz crystal impedance (PQCI) technique was employed to monitor the assembly of DNA in real time. Electrochemical impedance spectroscopy was also used to characterize the modification process. It has been found that modification of the electrode with MWNTs has significantly enhanced the effective electrode surface area in addition to providing negatively charged groups for the electrostatic assembly of cationic polyelectrolyte. PDDA plays a key role in the attachment of DNA to MWNTs and acts as a bridge to connect DNA with MWNTs, though the direct adsorption of DNA on MWNTs has been observed. Moreover, the interaction between DNA and chlorpromazine hydrochloride was observed with PQCI technique. This shows that DNA assembled on MWNTs still has the ability to interact with drug molecules, which has great importance in the construction of new types of miniature DNA biosensors.

Real-Time Monitoring of Activated Bleomycin-Induced Cleavage of DNA with Piezoelectric Quartz Crystal Impedance Analysis

A novel process analysis method, with a piezoelectric quartz crystal impedance technique based on the mass effect, for real-time monitoring the activated Bleomycin-induced cleavage of DNA process was proposed. The DNA-coated piezoelectric sensor was in contact with Bleomycin solution at the existence of H2O2 and Fe3+. The optimized experimental condition was determined through the experiments about the effect of pH and ionic strength. The experimental results indicated that activity of Bleomycin is maximal when pH = 8.0 and the ionic strength is low. Under the chosen experimental condition, Bleomycin concentration, which was in the range of 40–250 µg mL−1, had an effect on the interaction, while Fe3+ concentration did not. And then the results about other antibiotics, Cefradine, Streptomycin, Benzylpenicillin, Doxycycline, Acetylspiramycin, showed that these antibiotics did not show the same behavior like Bleomycin.

Piezoelectric quartz crystal impedance study of the Pb2+-induced precipitation of bovine serum albumin and its dissolution with EDTA in an aqueous solution.

The piezoelectric quartz crystal impedance technique (QCI) was employed to monitor in situ the Pb2+-induced precipitation of BSA onto a gold electrode and the precipitate dissolution with EDTA in an aqueous solution. The critical precipitation concentration of Pb2+, at which the resonant frequency decreased significantly, was estimated to be 4.78 x 10(-4) mol/L. The saturated adherence of the precipitate on the electrode was observed when the concentration of Pb2+ was greater than 7.53 x 10(-2) mol/L. The frequency response was mainly caused by the mass effect of the precipitate adherence to the electrode, rather than the changes in the physico-chemical properties of the contacting liquid. An excess addition of Na2EDTA after the Pb2+-BSA dissolution led to new precipitation, probably due to the formation of an EDTA precipitate in this medium (pH approximately 3). The pH effect on the response of the resonant frequency was analyzed by using the sum of two exponential functions. A larger frequency response occurred at a pH greater than pI. These findings have been reasonably explained. Also, a decrease in the concentration of the background electrolyte increased the frequency response.

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°C. Equivalent circuit parameters and resonant frequencies as well as the half-peak width of the electroacoustic conductance spectrum δƒG1/2 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.

The detection of bovine serum albumin by using Cu 2+ based on a piezoelectric quartz crystal impedance technique

The bovine serum albumin (BSA) was monitored by piezoelectric quartz crystal impedance (QCI) technique through the precipitation of BSA by Cu 2+. The linear range for determining BSA was from 4×10 −3 g/l to 4×10 −1 g/l, with the detection limit being 1.9×10 −4 g/l. The recovery was 101.4%; the R.S.D was 3.7% ( n=6). The effect of low molecular weight alcohol, pH and common serum contaminate was also discussed.

Real-time monitoring of formaldehyde-induced DNA-lysozyme cross-linking with piezoelectric quartz crystal impedance analysis.

A novel method for monitoring, in real time, the formaldehyde (FA)-induced DNA-protein cross-linking process with the piezoelectric quartz crystal impedance (PQCI) technique is proposed. The method was used to monitor FA-induced DNA-lysozyme cross-link formation. Lysozyme was directly immobilized on the silver electrode surface of a piezoelectric quartz crystal by adsorption. The lysozyme-coated piezoelectric sensor was in contact with FA and DNA solutions. The time courses of the resonant frequency and equivalent circuit parameters of the sensor during the cross-linking were simultaneously obtained and are discussed in detail. On the basis of the feature of the multi-dimensional information provided by the PQCI technique, it was concluded that the observed frequency decrease could be mainly ascribed to the mass increase resulting from the cross-linking. According to the frequency decrease with time, the kinetics of the cross-linking process were quantitatively studied. A piezoelectric response model for the cross-linking was theoretically derived. Fitting the experimental data to the model, the kinetic parameters, such as the binding and dissociation rate constants (k(1) and k(-1)) and the cross-linking equilibrium constant (Ka), were determined. At 37 degrees C, the k(1), k(-1) and Ka values obtained were 7.0 (+/-0.1) x 10(-5) (microg ml(-1))(-1) s(-1), 6.6 (+/-0.1) x 10(-3) s(-1) and 1.06 (+/-0.02) x 10(-2) (microg ml(-1))(-1), respectively.