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.     

Latex piezoelectric immunoassay: detection of agglutination of antibody-bearing latex using a piezoelectric quartz crystal

A method for immunoassay of CRP (C-reactive protein) was developed using a piezoelectric quartz crystal. Previous immunoassays using a piezoelectric crystal have required the formation of a thin film on the crystal, to which an antibody is affixed. The occurrence of antigen-antibody reaction increases the weight attached to the crystal surface, which causes a reduction in the oscillation frequency. In our method, the frequency reduction was observed using antibody-bearing latex without any film. One possible mechanism of the frequency change is that the crystal acts as a sensing apparatus for viscosity or density change in the solution due to aggregation of latex particles. The detection limit was almost the same as that for latex photometric immunoassay (LPIA). The present method has been designated as latex piezoelectric immunoassay (LPEIA).     

The use of a piezoelectric crystal to determine sulphur dioxide in gases

This work describes the detection of sulphur dioxide with a piezoelectric crystal, at a resonance frequency of 9 MHz, covered with an active coating containing trioctylmethylammonium dichromate which irreversibly bonds sulphur dioxide in an oxidation-reduction reaction. The decrease in the vibration frequency of the crystal is directly proportional to the mass of sulphur dioxide bonded. The detector works on the basis of integration of the decrease in the frequency over a given time interval (at least 10 min), resulting in a high measuring sensitivity. The calibration curve is linear for sulphur dioxide concentrations from a few to 500 microg/m(3). Partial exhaustion of the capacity of the active coating, occurring after prolonged use, appears as nonlinearity of the detector concentration response. This nonlinearity can be compensated by a simple mathematical correction that permits the lifetime of the active coating to be lengthened by several orders of magnitude.     

Quartz Crystal Microbalance Biosensor for Saxitoxin Based on Immobilized Sodium Channel Receptors

This work explored the possibility of coupling the toxin receptor-binding principle with the piezoelectric transduction principle. The sensing component of the saxitoxin biosensor involves a piezoelectric quartz crystal that was coated with sodium channel receptors. The sodium channel receptors were isolated from the electroplax organ of Electrophorus electricus. Binding of the sodium channel extracts to the quartz crystal was facilitated by pre-coating the gold electrode with a hydrophobic self-assembled monolayer of dodecanethiol. The instrumentation system consisted of a flow cell that held the quartz crystal, an oscillator circuit, an injection port, and a frequency counter that was connected to a personal computer. The various immobilization and measurement parameters were optimized. Binding of saxitoxin standards with the immobilized sodium channels was monitored through the decrease in the crystal oscillation frequency readings (ΔF) upon the introduction of saxitoxin into the flow cell. A calibration curve for saxitoxin was constructed by plotting the ΔF values vs. saxitoxin concentrations in the range from 0.1 to 2.0 μg/mL. A correlation coefficient of 0.9653 was obtained. The saxitoxin biosensor developed has the potential to be applied to the rapid screening of total paralytic shellfish poisoning toxins.     

Adsorption studies of dodecylamine at the quartz interface using an electrode-separated piezoelectric sensor

The adsorption process of dodecylammonium chloride (DAC) from aqueous solutions onto a quartz crystal interface was investigated in situ using an electrode-separated piezoelectric sensor (ESPS). Increasing amounts of DAC adsorbed onto a quartz crystal surface resulted in linearly decreasing oscillating frequencies of the ESPS. The adsorption density can be monitored by the frequency decrease. The adsorption density obtained by calculation using the Sauerbrey equation in the ESPS method is greater than that in solution depletion method. A calibration coefficient is added into the Sauerbrey equation to correct the influence of surface roughness of the quartz crystal on the adsorption density. The influence of solution properties on the adsorption density measurement was discussed. A dependence of the adsorption density on pH was reported. Received: 17 April 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

Adsorption studies of dodecylamine at the quartz interface using an electrode-separated piezoelectric sensor

The adsorption process of dodecylammonium chloride (DAC) from aqueous solutions onto a quartz crystal interface was investigated in situ using an electrode-separated piezoelectric sensor (ESPS). Increasing amounts of DAC adsorbed onto a quartz crystal surface resulted in linearly decreasing oscillating frequencies of the ESPS. The adsorption density can be monitored by the frequency decrease. The adsorption density obtained by calculation using the Sauerbrey equation in the ESPS method is greater than that in solution depletion method. A calibration coefficient is added into the Sauerbrey equation to correct the influence of surface roughness of the quartz crystal on the adsorption density. The influence of solution properties on the adsorption density measurement was discussed. A dependence of the adsorption density on pH was reported. Received: 17 April 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

一种新的PEG凝聚人血清白蛋白液相压电免疫传感器

以ＰＥＧ为乳剂，建立了一种基于ＰＥＧ凝集的液相压电免疫分析法，并用于人血清白蛋白（Ａｌｂ）的测定。详细考察了ＰＥＧ浓度，抗体稀释度、ＰＥＧ分子量及反应温度等因素对频移的影响，采用终点法和初始速率法测得Ａｌｂ线性范围分别为４７．８３－１０３．１ｍｇ／Ｌ和４０．６２－１０１．２ｍｇ／Ｌ。对７个血清样本的分析，其结果与双缩脲法基本一致。用一简单的方法合晶振再生后可获得重视的结果。     

Determination of procaine hydrochloride by ion-pairing flow injection analysis with piezoelectric detection

A fast and simple method for the determination of procaine hydrochloride by ion-pairing flow injection analysis has been developed. It is based on the formation of an ion-pair with sodium dodecyl phenylsulphonate and piezoelectric detection. The calibration curve was linear between 0.02 and 2.00 mg/mL, with a detection limit of 0.01 mg/mL, a relative standard deviation of 0.3% (10 replicates) and a sampling frequency of 120/h. The proposed method has been satisfactorily applied to the determination of procaine hydrochloride in pharmaceutical preparations.     

压电晶体传感器阵列测定装置及数据采集系统

研究了一种利用微机控制测量和采集压电晶体传感器阵列振荡频率的智能型仪器。介绍了其硬件及数据采集软件的功能，结构等。     

Electrochemically modified piezoelectric crystal biosensor for detection of Staphylococcus aureus

Electropolymerized o-phenylenediamine film is used as a functional coating for the immobilization of anti-S. aureus antibody on the surface of a gold-plated piezoelectric crystal, and this piezoelectric immunosensor is applied to detect S. aureus. The frequency shift (F = F20s - F380s, Hz) between the frequency at the 20th second (after the addition of sample, F20s) and that at 380 seconds later (F380s) was introduced to construct a calibration graph, and shortening of assay time was achieved. The S. aureus concentrations in the range of 105-109 cells/mL can be detected by this system.     

The quantification of sodium in mineral waters using a quartz crystal microbalance

A sensor for sodium based on a piezoelectric quartz crystal is proposed. The quartz crystal was coated with 5% of bis[(12-crown-4)methyl] dodecylmethylmalonate, 33% of PVC and 62% of NPOE to which KTpClPB in a 22% molar proportion to the ionophore was added. Coating amounts producing a frequency decrease around 18 kHz show optimum linear calibration ranges for the analysis of sodium in commercial mineral waters. Besides sensitivity, coating stability and selectivity of the sensor over other cations were adequate for those analyses. The results obtained analysing commercial mineral waters by the proposed method are not significantly different (α=0.05) from the ones obtained by atomic spectrometry.     

Determination of procaine hydrochloride by ion-pairing flow injection analysis with piezoelectric detection

A fast and simple method for the determination of procaine hydrochloride by ion-pairing flow injection analysis has been developed. It is based on the formation of an ion-pair with sodium dodecyl phenylsulphonate and piezoelectric detection. The calibration curve was linear between 0.02 and 2.00 mg/mL, with a detection limit of 0.01 mg/mL, a relative standard deviation of 0.3% (10 replicates) and a sampling frequency of 120/h. The proposed method has been satisfactorily applied to the determination of procaine hydrochloride in pharmaceutical preparations. Received: 19 August 1996 / Revised: 6 November 1996 / Accepted: 12 December 1996     

A Piezoelectric crystal detector for continuous monitoring of water evolved during thermal decomposition reactions

A method for the continuous monitoring of water vapour evolved during thermal decomposition reactions is developed based on the reversible adsorption of water on a bare piezoelectric crystal with nickel electrodes. Gaseous decomposition products formed in the furnace chamber of the thermoanalytical equipment are collected and transported to the detector cell by the carrier gas. A linear relationship exists between the decrease in vibrational frequency of the crystal and the concentration of water in the carrier gas up to 900 mug/l. H(2)O [1200 ppm (v/v)]. The signal curve of the piezoelectric water monitor can be recorded simultaneously along with the TG, DTG and DTA curves and used to identify the decomposition step(s) in which water was formed. CO, CO(2) and low molecular weight hydrocarbons do not interfere. Condensable organic crack products can be removed by a suitable pretrap.     

Determination of bioelectrochemical parameters of red cell using a piezoelectric crystal sensor

Based on the impedance behavior of red cell at high frequency, the frequency response of series piezoelectric crystal sensor in the red cell suspension was derived and verified experimentally. A method of using piezoelectric crystal sensor to determine the conductivity of the interior of the cell was proposed. The experimental results show that the mean conductivity of rabbit red cell cytoplasm was 0.269 S/m and the mean shape factor of red cell was 2.05.     

Comparison of two methods for coating piezoelectric crystals

Quartz piezoelectric crystals were coated with triethanolamine using two procedures: spray and syringe methods. The reproducibility of both coating methods was evaluated comparing the relative standard deviation of batches of four crystals coated by each of the procedures. The relative standard deviation obtained with the spray method is a hyperbolic function of the coating frequency and is, at least, three times lower than the one calculated from results of the syringe method, which is not frequency dependent. An explanation for the poorer reproducibility of the syringe method is given, based on the radial sensitivity theory and the non-uniformity of the coating distribution over the crystal, as evidenced by microscopic photographs.     

The adaptation of coated piezoelectric devices for use in the detection of gases in aqueous solutions

A method for the determination of ammonia and hydrogen sulfide in aqueous solution is presented. This method involves the use of a gas-permeable membrane which isolates the piezoelectric crystal device from the solution yet allows the desired gases to pass. Concentrations up to 0.45 M for NH₃, and 9 · 10^-4 M for H₂S give linear calibration curves of concentration vs. frequency change.     

Rapid diagnosis of M. tuberculosis using a piezoelectric immunosensor.

A piezoelectric immunosensor was developed for detecting Mycobacteria Tuberculosis (M. TB). Protein A was modified onto a silver-coated piezoelectric quartz-crystal sensor. Antibodies could be bond onto the crystal surface in an ordered orientation through protein A. An impendence analyzer was employed to record the admittance-frequency curve. The experimental results showed a successful and less-rigid bonding of protein A and antibodies. Compared with other traditional detection methods of TB, the method suggested in this paper was sensitive, selective and effective. The nonspecific response was limited by using control antibody-rabbit anti-honey bee venom (anti-HBV). A glycine-HCI buffer solution (pH = 2.4) was used to release antibodies from a crystal coated with protein A, and 0.5 mg/mL anti-TB was used to remove TB from a crystal that was bonded by an antibody. Good reusability was exhibited. Spike samples of sputum and saliva from normal people with and without adding M. tuberculosis were diagnosed using the proposed method. Good results were obtained.     

A non-potentiometric sensing method for the determination of pentoxyverine with PQC sensors based on ion-pair complexes.

The construction and general performance characteristics of three piezoelectric quartz crystal sensors responsive to the pentoxyverine are described here. This kind of non-potentiometric sensing method is based on use of ion-pair complexes of the pentoxyverine cation with three counter anions, namely, tungstophosphate, tetraphenylborate and picrolonate. The complexes were embedded in a PVC matrix. Adsorption of the pentoxyverine ion on the complex caused a frequency decrease of the crystal. The frequency decrease was proportional to the amount of adsorbed analyte. The influencing factors were investigated in detail, and then optimized. The proposed sensors exhibit reasonable selectivity and a higher sensitivity than the potentiometric sensors. For a sensor modified with pentoxyverine-phosphotungstate, the calibration graph was linear over concentration of 1.0 x 10(-7) - 5.0 x 10(-5) M with a detection limit of 6 x 10(-8) M at pH 5.4.     

Detection of β-thalassemia by a DNA piezoelectric biosensor coupled with polymerase chain reaction

β-Thalassemia is an inherited disorder mainly caused by mutations in the gene of the β-globin chain of adult haemoglobin (HbA). Clinically, β-thalassemia can be a mild or silent condition, or it can cause severe diseases, leading to transfusion dependence. Studies at the gene level have identified a large number of variations in the β-globin gene in different populations. In the Mediterranean area one of the most common mutation is the C → T substitution in the codon 39 of the gene.A new procedure for detecting codon 39 mutation in the β-globin gene is reported, based on a DNA piezoelectric biosensor. An oligonucletidic probe (25-mer), specific for the region around codon 39, is immobilised on the gold surface of a piezoelectric quartz crystal. The hybridisation between the immobilised probe and the complementary strand in solution is detected recording the variations of the crystal frequency.Experiments with synthetic oligonucleotides were initially performed. Distinguishable frequency shifts were obtained from the interaction between the immobilised probe and the complementary and the mismatch oligonucleotides. A solution containing 50% of both the oligonucleotides has been also tested and distinguished from the others evaluating the resulting signals. Experiments with non-complementary oligonucleotides gave no signal variation. The biosensor was able to distinguish between sequences differing in only one base also using polymerase chain reaction-amplified samples [771 base pairs (bp)] of DNA extracted from human blood of thalassemic and healthy (normal) patients or patients with β-thalassemia traits.The optimised DNA piezoelectric biosensor has been successfully applied to the determination of one of the most frequent mutation characteristic of β-thalassemia in the Mediterranean population.     

A Rapid Method for Determination of Growth of Thiobacillus Ferrooxidans by Series Piezoelectric Quartz Crystal

ABSTRACT

A rapid and simple method for monitoring the growth of Thiobacillus ferrooxidans is put forward by using a series piezoelectric quartz crystal (SPQC). The SPQC was applied to continuously determine the variation of frequency shift during the culture of Thiobacillus ferrooxidans, with a conductive electrode as the probe. The frequency shift as a function of time agrees with a typical 'S - shape' model, a piezoelectric sensor responding well to the growth of Thiobacillus ferrooxidans. The fundamentals for determination of the bacterial growth activity using the SPQC is also described; the frequency shift is only dependent on the electrical conductivity of the solution and the dielectric constant.