Latex piezoelectric immunoassay: Effect of interfacial properties

Latex piezoelectric immunoassay is a technique for detecting agglutination of antibody- or antigen-bearing latex by an immunoreaction using a piezoelectric quartz crystal; the agglutination decreases the oscillation frequency of the crystal. This is advantageous in that immobilization of antibody or antigen on the crystal surface is unnecessary. In this report, different kinds of chemical functional groups were immobilized on the electrode surface, allowing us to consider the effect of interfacial structure on the frequency change. Electrode modifications such as self-assembly of alkanethiol and aminoalkoxysilane monolayers, and polyethylenimine-glutaraldehyde coating as well as plasma treatment were examined. The sensitivity of the system was found to imitate the interfacial properties so that modification of the electrode surface could improve the response. Among the methods examined for this electrode surface modification, the polyethylenimine-glutaraldehyde modification had the advantages of high reproducibility, fast operation and simplicity. It was also suggested that the frequency change originated primarily from the immunoreaction at the interface.     

Relative humidity measurement using a coated piezoelectric quartz crystal sensor

Miniature piezoelectric quartz crystals, which are manufactured cheaply by photolithographic and chemical etching techniques, have a high mass sensitivity. AT-cut 10 MHz quartz crystals have been coated with four materials and used to measure the relative humidity in various gases. The coated crystal is used as a resonator in an oscillator circuit, the frequency of which varies as a function of the change in mass. Characteristics that determine the usefulness of the coatings, such as sensitivity, response linearity, response time, selectivity, hysteresis and ageing, were evaluated. The detector has potential for use as a hygrometer, provided that the appropriate coating is chosen for a specific application.     

Improvement of latex piezoelectric immunoassay: Detection of rheumatoid factor

Latex piezoelectric immunoassay is a method for detection of agglutination of antibody- or antigen-bearing latex by immunoreaction using a piezoelectric quartz crystal; the agglutination decreases the oscillation frequency of the crystal. This is advantageous in that coating the surface of the crystal followed by fixation of antibody or antigen is unnecessary. There is, however, a drawback, and to improve this, we designed a micro-cell in which only one side of the crystal is exposed to the solution. A method for regenerating the crystal was also devised. Measurement was carried out using a calibration curve of the frequency change against rheumatoid factor activity. The improvement made it possible to use one crystal repeatedly and reproducibility was satisfactory. The calibration curve became almost independent of the crystal used.     

Silver-selective sensor using an electrode-separated piezoelectric quartz crystal modified with a chitosan derivative.

Silver(I) adsorbed selectively onto a quartz plate modified with N-(2-pyridylmethyl)chitosan in an ammonium chloride buffer solution containing EDTA, and the frequency of the quartz plate increased. It was supposed that the increasing frequency was caused by the desorption of adsorbed water on the chitosan derivative, which was induced from the reaction of silver(I) with the chitosan derivative. The concentration of the buffer, pH, temperature, conductivity and eluent affected the frequency shift resulting from the adsorption of silver(I). The frequency decreased at a conductivity lower than 2.2 mS/cm, and increased with increasing conductivity above this value. The frequency shifts caused by the adsorption of silver(I) were proportional to the concentration over the range 10-80 nM of silver(I), and the correlation coefficient was 0.9969. The detection limit and the relative standard deviation at 50 nM for five times were 6 nM and 3.4%, respectively. The proposed method was simple while showing higher sensitivity and selectivity.     

Oscillating frequency of piezoelectric quartz crystal in solutions

Oscillating frequencies of a piezoelectric crystal were measured in various solutions. One side of the crystal surface was coated with a silicon sealant. This coating was useful for measuring the oscillation of crystals in solutions for a wide range of products of density (?) and viscosity (η) and in electrolyte solutions. For measurement in solutions, the frequency change depended on the circuit used, whereas for measurements in air the circuit did not influence the frequency change. All experimental data showed that the frequency change from pure water, ΔF_w, followed ΔF_w = ? K(√?η ? √?_wη_w) except for electrolyte and polymer solutions, where K is a proportionality constant, η_w the density of pure water and η_w the viscosity of water.     

Adsorption of metal ions from solution onto a piezoelectric quartz crystal

Many metal ions are spontaneously adsorbed onto a piezoelectric quartz crystal and change the oscillation frequency. The pH ranges in which the metal ions adsorbed were just below that of precipitate formation as the ‘hydroxides’; frequency changes caused by adsorption were not observed in these pH ranges where the ‘hydroxides’ formed. Cationic organic reagents, such as crystal violet and methylene blue, were also adsorbed on the piezoelectric quartz crystal but non-ionic and anionic organic compounds were not. These results showed that the crystal was negatively charged on the surface.     

High sensitive piezoelectric quartz crystal liquid density sensor

<正>We report for the first time a cleavage phenomenon in the resonant peak of a piezoelectric quartz crystal(PQC) in liquid phase.In the presence of a strong longitudinal wave effect,an additional resonant peak appears in the conductance-frequency curve.With gradually increasing liquid density,the additional peak moves from low to high frequency region then disappears.The frequency of the additional resonant peak is sensitive to the change in liquid density.The frequency shift of the additional peak is linear with the liquid density in a given range.For a 5 MHz PQC with a reflection distance of 16 mm for longitudinal wave,the sensitivity to liquid density is 2.61×10~6 Hz g~(-1) cm~3.The overlap between the primary resonant peak and the additional resonant peak causes a decrease in the intensity of the former and an increase in the intensity of the latter.In a combined impedance analysis method,the changes in surface mass loading,density and viscosity of the liquid were monitored simultaneously by a PQC sensor.     

Electrodeless piezoelectric quartz crystal and its behaviour in solutions

An electrodeless piezoelectric quartz crystal system was constructed with a quartz crystal plate, electrolyte solutions and platinum plates or rods immersed in the solutions for connecting to an oscillator, instead of the electrodes. The crystal without electrodes oscillates in the solutions. The frequency varies with temperature, specific conductance of the solutions and the mass change of the plate caused by the adsorption of material from the solution in, the same way as a normal piezoelectric quartz crystal with electrodes.     

Monitoring of DNA oxidative damage with piezoelectric quartz crystal method

The piezoelectric quartz crystal (PQC) sensor was used to detect the whole process of DNA damage oxidized by H(2)O(2) system containing Cu(2+) or Zn(2+) based on the density-viscosity change of the detected solution. The PQC impedance method has been applied to further investigate the damage process of DNA oxidized by H(2)O(2) system containing Cu(2+). It was found that the ratio of DeltaR(1) to Deltaf(0) or DeltaL(1) coincided well with that calculated from Martin's equations reflecting the solution density-viscosity effect, suggesting that the continuing change in liquid loading on to the PQC surface caused the significant variation of Deltaf(0), DeltaR(1) and DeltaL(1). It has also been found that the H(2)O(2) system containing Cu(2+) could oxidize DNA more completely than that containing Zn(2+), and a trace Cu(2+) in the system could cause DNA damage. However, no significant breakage in the DNA backbone was observed if the system contained only H(2)O(2). The DNA concentration was linearly related to Deltaf(0s), which is the different between the initial frequency and the frequency after a reaction time of 45 min, in the range of 50-1000 mug ml(-1). The effect of H(2)O(2) or Cu(2+) concentration of was also investigated. The above-mentioned results that the H(2)O(2) system containing Cu(2+) or Zn(2+) could break the DNA backbone were also supported by the agarose gel electrophoresis technique.     

Monitoring of mutagenic process with piezoelectric quartz crystal impedance analysis

A novel method for monitoring of mutagenic process of dimethyl sulfate to Salmonella typhimurium strain (TA100) was proposed by using piezoelectric quartz crystal impedance (PQCI) analysis technique. The time courses of responses piezoelectric impedance parameters for a quartz crystal in a culture system were simultaneously obtained and discussed. It was found that the motional resistance variation (DeltaR(m)) increases and frequency shift (Deltaf) of PQC sensor decreases correspondingly during the mutagenic process of the bacteria. These parameters could reflect the variations of viscosity and density of culture system. By fitting DeltaR(m) versus time curves toward Gompertz bacterial growth model, we obtained and discussed the bacterial growth parameters for both normal growth and mutagenic process. The experiments showed that the proposed method could provide real time and multidimensional impedance information to the monitoring of mutagenic process.     

Electrolytic determination of traces of iodide in solution with a piezoelectric quartz crystal

The frequency of a piezoelectric quartz crystal is decreased when iodide is electrodeposited on the silver electrode of the crystal at—0.05 V vs. Ag/AgCl. From 3 × lO^-7 M to 1 × 10^-5 M iodide can be determined with few interferences, and a procedure for removal of interfering species is given. Iodide is removed from the electrode by electrolysis at —0.4 V after each determination.     

Single-drop method for determination of cyanide in solution with a piezoelectric quartz crystal

The change in frequency of a horizontal quartz crystal in contact with a single drop of solution is measured. When the gold electrode of the crystal is dissolved by reaction with cyanide in alkaline solution, the further change of frequency is linearly related to cyanide concentration in the range 10^-3–10^-4 M at pH 10.4. Only silver(I) and mercury(II) interfere if EDTA is added.     

Selective determination of silver in solution by adsorption on a piezoelectric quartz crystal

Electrodeposition of metal ions on the crystal is eliminated by using a specially constructed transistorized oscillator. When tartrate, citrate, EDTA or their mixtures are present, silver adsorption occurs. The frequency change is proportional to the silver concentration in the range 2 × 10^?7?1 × 10^?5 M after adsorption for 10 min from a 1 mM EDTA/3 mM tartrate solution. No significant interferences are caused by other metal ions. On the basis of cyclic voltammetric studies, it is suggested that silver is adsorbed as a silver (I) complex.     

Lectin-carbohydrate affinity measured using a quartz crystal microbalance

The association of two molecules is described by two parameters, association equilibrium and association rate constants, which are characteristic for a given type of interaction. Usually, they are determined for interacting molecules dissolved in solution. However, for many applications one type of molecules is immobilized on a substrate, which may influence the binding kinetics. The studied complex of concanavalin A and carboxypeptidase Y belongs to the lectin-carbohydrate type of interaction involving the recognition of oligosaccharide moieties. The concanavalin A was immobilized on a gold electrode of quartz crystal, while carboxypeptidase Y was added to a buffer (Tris-buffered saline). The constants describing the association of the investigated molecules were determined on the basis of measurements performed using a quartz crystal microbalance in liquid. The obtained values were (0.59+/-0.01)x10(6) M(-1) for the association equilibrium constant and (5.6+/-0.1)x10(4) M(-1)s(-1) for the association rate constant. The saturation binding experiment gave another value of the association constant, (2.7+/-0.02)x10(6) M(-1). The comparison of obtained values with previously published ones verifies that the molecule orientation and binding site accessibility for specific ligands could influence the association equilibrium constant value. The presented measurements demonstrate the ability of a quartz crystal microbalance to detect and to evaluate the association process occurring between molecules.     

A quartz crystal piezoelectric device for monitoring organic gaseous pollutants

The behavioural pattern of a coated piezoelectric crystal detector for the monitoring or traces of atmospheric gases partitioning into the coating on the crystal is predicted. The effects of variable experimental parameters such as detector cell volume, gas flow rate, analyte concentration, distribution and size of detector coating are described and the intrinsic properties of the coating material are discussed. The behaviour of model systems set up arbitrarily for traces of chloroform and toluene is in agreement with expectations.     

Enantioselective piezoelectric quartz crystal sensor for d-methamphetamine based on a molecularly imprinted polymer

A piezoelectric quartz crystal (PQC) sensor based on a molecularly imprinted polymer (MIP) has been developed for enantioselective and quantitative analysis of d-(+)-methamphetamine (d(+)-MA). The sensor was produced by bulk polymerization and the resulting MIP was then coated on the gold electrode of an AT-cut quartz crystal. Conditions such as volume of polymer coating, curing time, type of PQC, baseline solvent, pH, and buffer type were found to affect the sensor response and were therefore optimized. The PQC-MIP gave a stable response to different concentrations of d(+)-MA standard solutions (response time = 10 to 100 s) with good repeatability (RSD = 0.03 to 3.09%; n = 3), good reproducibility (RSD = 3.55%; n = 5), and good reversibility (RSD = 0.36%; n = 3). The linear range of the sensor covered five orders of magnitude of analyte concentration, ranging from 10⁻⁵ to 10⁻¹ μg mL⁻¹, and the limit of detection was calculated as 11.9 pg d(+)-MA mL⁻¹ . The sensor had a highly enantioselective response to d(+)-MA compared with its response to l(−)-MA, racemic MA, and phentermine. The developed sensor was validated by applying it to human urine samples from drug-free individuals spiked with standard d(+)-MA and from a confirmed MA user. Use of the standard addition method (SAM) and samples spiked with d(+)-MA at levels ranging from 1 × 10⁻³ to 1 × 10⁻² μg mL⁻¹ showed recovery was good (95.3 to 110.9%).     

Piezoelectric transmission spectroelectrochemistry with a normal piezoelectric quartz crystal as an optically-transparent electrode

Piezoelectric transmission spectroelectrochemistry (PTSEC), i.e., the combination of electrochemistry and spectroelectrochemistry (SEC) with electrochemical quartz crystal microbalance (EQCM) technique is reported by using a normal piezoelectric quartz crystal (PQC) as an optically-transparent electrode (OTE). A theoretical relationship between the PQC response and the spectroelectrochemical response is derived and used to estimate the apparent molar absorptivity of the absorbing species deposited on the OTE on the PQC surface. The complex of copper with aspartic acid is used to test this new PQC-SEC technique. Results show that the combination of three such diverse techniques provides a very useful methodology for studying electrode processes and electrode surface characteristics in situ.     

Kinetic determination of organic vapor mixtures with single piezoelectric quartz crystal sensor using artificial neural networks

A single piezoelectric quartz crystal coated with one kind of crown ether was applied to the simultaneous determination of binary acid and amine vapor mixtures. From the adsorption and desorption curves of analytes, which were somewhat different in shape, frequency shifts from ten time windows were taken as inputs for artificial neural networks (ANN). Prediction results were satisfactory for ANN in both sample sets. The average relative errors, for formic acid and acrylic acid were 5%, for n-butylamine and aniline, they were 3% with ANN respectively. The effects of number of neurons in the hidden layer of ANN on the performance of the network are also discussed.     

Electrolytic determination of nanomolar concentrations of silver in solution with a piezoelectric quartz crystal

Silver in solution is determined in situ by the frequency change of a piezoelectric quartz crystal on electrodeposition on the electrode of the crystal. The electrolyte solution flows through a cell containing the platinum-plated electrode (cathode) of the quartz crystal, a coiled platinum-wire anode and a silver—silver(I) chloride reference electrode, and is electrolyzed at —0.2 V vs. $\text{Ag}\text{AgCl}$. The frequency change is proportional to the silver concentration in the range 10^-5–5 × 10^-7 M after electrodeposition for 5 min, and in the range 10^-8–10^-9 M by recycling 20 ml of the solution over the electrodes for 3 h.