Frequency response of the glucose sensor based on immobilized glucose oxidase membrane

Frequency response of the glucose sensor based on the immobilized glucose oxidase membrane was investigated experimentally by giving the sinusoidal change of glucose concentration to the glucose sensor and observing its output signal. Observed values of gains and phase lags of the frequency response of the glucose sensor followed the frequency response model of the first-order with dead time; The time constant and also the dead time were estimated and found to decrease as the amount of enzyme immobilized in the membrane increased and the thickness of the membrane decreased.

     

Distinguishing Among Gases with a Semiconductor Sensor Depending on the Frequency Modulation of a Cyclic Temperature

A gas‐sensing system based on a dynamic nonlinear response shows enhanced selectivity of the sensor response toward sample vapors. A cyclic temperature composed of fundamental and 1.5‐th harmonics was applied to a SnO₂ semiconductor gas sensor and the resulting conductance of the sensor was evaluated by a polynomial approximation. The dynamic nonlinear responses to the samples were further characterized by the addition of 1.5‐th harmonic perturbation as a frequency modulation. These characteristic sensor responses under frequency modulation were considered theoretically based on a reaction‐diffusion model for the semiconductor surface.     

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.     

A wireless pH sensor using magnetoelasticity for measurement of body fluid acidity.

The determination of body fluid acidity using a wireless magnetoelastic pH-sensitive sensor is described. The sensor was fabricated by casting a layer of pH-sensitive polymer on a magnetoelastic ribbon. In response to an externally applied time-varying magnetic field, the magnetoelastic sensor mechanically vibrates at a characteristic frequency that is inversely dependent upon the mass of the pH polymer film, which varies as the film swells and shrinks in response to pH. As the magnetoelastic sensor is magnetostrictive, the mechanical vibrations of the sensor launch magnetic flux that can be detected remotely using a pickup coil. The sensor can be used for direct measurements of body fluid acidity without a pretreatment of the sample by using a filtration membrane. A reversible and linear response was obtained between pH 5.0 and 8.0 with a measurement resolution of pH 0.1 and a slope of 0.2 kHz pH(-1). Since there are no physical connections between the sensor and the instrument, the sensor can be applied to in vivo and in situ monitoring of the physiological pH and its fluctuations.     

磁弹性无线传感器检测不同液体介质中的金黄色葡萄球菌

研制了磁弹性金黄色葡萄球菌无线传感器,用于检测不同液体介质中的金黄色葡萄球菌。取0.2mL一定浓度菌液加到含2mL无菌液体介质的检测玻璃管中,磁弹性传感器共振频率随细菌的生长而改变。通过改变牛肉膏和蛋白胨的浓度,得出传感器在含有2×105cells/mL金黄色葡萄球菌的培养基CM2-2中共振频率响应最大。结果表明,此传感器可以测定的金黄色葡萄球菌浓度范围在CM2-2中是3×103～2×107cells/mL,在牛奶中是1×104～2×107cells/mL,检出限分别是1×103cells/mL和1×104cells/mL。传感器共振频移大小与金黄色葡萄球菌的浓度呈线性相关关系,相关系数在牛奶中是0.98,在培养基中是0.99。     

Behaviour of series piezoelectric sensor in electrolyte solution : Part II. Applications in titrimetry

The applications of a series piezoelectric sensor for end-point determination in frequencimetric titrations, including neutralization, precipitation, complexation and redox titrations, are reported. The method is based on the fact that a series piezoelectric sensor shows a sensitive and selective frequency response to changes in conductivity of solution and can be applied to sample solutions containing large amounts of unreacted foreign electrolytes.     

新型成膜法的SAW气体传感器聚合物膜的粘弹性分析

An analysis of the response of surface acoustic wave sensors coated with polymer film based on new coating deposition (self-assemble and molecularly imprinted technology) is described and the response formulas are hence deduced. Using the real part of shear modulus, the polymer can be classified into three types: glassy film, glassy-rubbery film and rubbery film. Experimental results show that the attenuation response is in better consistence with the simulation than in Martin's theory, but the velocity response does not accord with the calculation exactly. Maybe it is influenced by the experimental methods and environment. In addition, simulations of gas sorption for polymer films are performed. As for glassy film, the SAW sensor response increases with increasing film thickness, and the relationship between the sensor response and the concentration of gas is pretty linear, while as for glassy-rubbery film and rubbery film, the relationship between the sensor sensitivity and concentration of gas is very complicated. The ultimately calculated results indicate that the relationship between the sensor response and frequency is not always linear due to the viscoelastic properties of the polymer.     

Novel surface acoustic wave-interdigitated array electrode gas sensor for dissolved ammonia

A novel surface acoustic wave-interdigitated array electrode (SAW-IDA) ammonia gas sensor is proposed. A gas-permeable membrane is employed to separate the buffer solution in the inner cell of the gas-sensing probe from the sample solution in the detection cell. The response of the IDA conductive electrodes is based on the impedance change of the buffer solution during ammonia adsorption. Therefore, this gas sensor overcomes the influence of water vapour in the conventional film-coated SAW gas sensor and can be used for the detection of gases in aqueous solutions. The ammonia sensor exhibits a favourable frequency response to 5 × 10⁻⁷−1 × 10⁻³ mol/1 ammonia. The optimal buffer composition and probe parameters have been determined. Dynamic range, response time, selectivity, and temperature drift are discussed. The ammonia sensor was also applied to the determination of serum ammonia. Results were in good agreement with those from the conventional enzymatic-spectro-photometric method.     

A conductance sensor for dissolved sulphur dioxide using a series piezoelectric crystal device

A new piezoelectric crystal impedance sensor for the determination of sulphur dioxide in aqueous solution is presented. It is realized using a series piezoelectric crystal device which is constructed by connecting an AT-cut piezoelectric crystal to a probe in series. The probe is filled with an internal electrolyte solution that is separated from sample solutions by a gas-permeable membrane. The present sensor exhibits a favourable frequency response to 1 x 10(-7)-1 x 10(-3) M sulphur dioxide. The detection limit is 1 x 10(-8) M. The effects of the sensor preparation are considered. Dynamic range, reproducibility, response time and selectivity of the sensor are also discussed. The proposed sensor has been used successfully for lamp sulphur determinations in petroleum samples.     

A quartz crystal resonant sensor (QCRS) study of HSA--drug interactions

Human serum albumin (HSA) was immobilised on the gold surface of a quartz crystal resonance sensor (QCRS) and exposed to warfarin and diazepam. Distinct decreases in frequency of differing magnitudes were observed upon exposure of the protein to each of the compounds suggesting strongly that a ligand interaction was occurring. Moreover, as sequential exposure in any order was observed to yield distinct repeatable frequency decreases for the ligands indicated, screening for site specific binding may be possible. Identically immobilised bovine serum albumin (BSA) gave no response to either compound.     

Superior analytical sensitivity of electromagnetic excitation compared to contact electrode instigation of transverse acoustic waves

Quartz disks incorporated into an electrolyte flow-through configuration have been excited by both direct electrode contact and electromagnetic fields to generate propagating transverse acoustic waves in to the fluid. The conventional thickness-mode device was operated at the first harmonic (9 MHz) whereas the EM excited structure functioned successfully at 453 MHz (nominal 49th harmonic). The nature of signals produced by the two devices and potential contributions to noise are evaluated. A comparison of the response of the higher frequency sensor to the introduction of the protein neutravidin to the system reveals at least a seven times higher signal-to-noise ratio than is the result for the conventional bulk-acoustic wave structure. This increase in sensitivity coupled with the possibilities for tuning the frequency of the electromagnetic device and its potential for non-contact excitation offer significant advantages in terms of analytical sensor technology.     

Novel surface acoustic wave-interdigitated array electrode gas sensor for dissolved ammonia

 A novel surface acoustic wave-interdigitated array electrode (SAW-IDA) ammonia gas sensor is proposed. A gas-permeable membrane is employed to separate the buffer solution in the inner cell of the gas-sensing probe from the sample solution in the detection cell. The response of the IDA conductive electrodes is based on the impedance change of the buffer solution during ammonia adsorption. Therefore, this gas sensor overcomes the influence of water vapour in the conventional film-coated SAW gas sensor and can be used for the detection of gases in aqueous solutions. The ammonia sensor exhibits a favourable frequency response to 5×10^-7–1×10^-3 mol/l ammonia. The optimal buffer composition and probe parameters have been determined. Dynamic range, response time, selectivity, and temperature drift are discussed. The ammonia sensor was also applied to the determination of serum ammonia. Results were in good agreement with those from the conventional enzymatic-spectrophotometric method. Received: 1 December 1995/Revised: 9 April 1996/Accepted: 14 April 1996     

Influence of oscillator phase on oscillation frequency and sensitivity of an electrode-separated piezoelectric sensor

Theoretical consideration was proposed for the influences of the oscillator phase on the response nature of an electrode-separated piezoelectric sensor (ESPS) to liquid properties and verified experimentally. For the oscillators with different phases, the oscillation frequency of the ESPS may increase, maintain nearly constant or decrease with increasing conductivity in low conductivity solutions. The sensitivity of response to density and viscosity increases slightly with increasing oscillator phase. The response to permittivity depends hardly on the oscillator phase. In addition, the dependence of the oscillation frequency of the ESPS on the supply voltage of the oscillator was explained. The ESPS was used to determine atropine sulfate with a detection limit of 1.6×10~7 mol/L.     

Monitoring,and estimation of kinetic data,by piezoelectric impedance analysis,of the binding of the anticancer drug mitoxantrone to surface-immobilized DNA

A new method of monitoring drug binding to DNA, in real-time, by means of the piezoelectric quartz-crystal-impedance (PQCI) technique, is proposed. The method was used to monitor the binding of an anticancer drug, mitoxantrone (MX), to double-stranded calf-thymus DNA covalently immobilized on the thioglycollic acid-modified gold electrode surface of a quartz crystal. Optimum experimental conditions for the immobilization were established. The DNA-anchored piezoelectric sensor was in contact with MX solution. The time courses of the resonant frequency and the equivalent circuit characteristics of the sensor were also obtained during the study of DNA-drug binding. On the basis of the analysis of the multidimensional information provided by the PQCI technique the observed frequency decrease was mainly ascribed to the increase in the mass of the sensor surface resulting from the binding. The kinetics of the binding process were studied quantitatively by monitoring the frequency change with time and a piezoelectric response model for the binding was derived theoretically. The experimental data were fitted to the model and the binding and dissociation rate constants and the binding equilibrium constant were estimated to be 66.0+/-0.1 mol(-1) L s(-1), 1.4+/-0.1x10(-4) s(-1), and 4.71+/-0.07x10(5) mol(-1) L, respectively, at 37 degrees C.     

压电晶体传感器阵列用于混合有机溶剂蒸气中官能团的识别

为模拟生物化学传感体系, 提出了可用于识别有机官能团的传感器阵列, 用作人工气味识别系统。该阵列由八个压电晶体传感器组成, 每个传感器涂以具有广谱响应性能的不同吸附活性材料, 阵列对常见小分子有机溶剂混合蒸气的响应频移数据采用逐步判别分析(SDA)处理, 选出五个供信能力最佳的判别变量, 以此构成的阵列用于小分子有机溶剂混合蒸气中醇羟基、羰基与其它官能团的识别, 并采用主成分分析(PCA)法降维投影, 在二维空间含相同官能团的物质聚为一类; 阵列可用于酒类、软饮料的识别。     

A perfume odour-sensing system using an array of piezoelectric crystal sensors with plasticized PVC coatings

Using PVC polymer as membrane matrix and di-n-octylphenyl phosphate (DOPP) as plasticizer, a piezoelectric crystal sensor (PCS) array with 12 adsorptive materials selected from 68 compounds by cluster analysis has been constructed as a perfume odour-sensing system. The frequency shift data obtained from the sensor array responding to four commercial perfume odours are first autoscaled and then treated by principal component analysis. The experimental results show that the plasticized PVC membrane PCS array provides improved performance of pattern recognition compared with the single adsorptive coating PCS array. The frequency shift response characteristics of these sensors have been investigated experimentally. The proposed sensor array has also been applied to the classification of commercial spirituous liquor, wine and soft drink samples, as well as aliphatic alcohol homologues and isomers.     

A perfume odour-sensing system using an array of piezoelectric crystal sensors with plasticized PVC coatings

Using PVC polymer as membrane matrix and di-n-octylphenyl phosphate (DOPP) as plasticizer, a piezoelectric crystal sensor (PCS) array with 12 adsorptive materials selected from 68 compounds by cluster analysis has been constructed as a perfume odour-sensing system. The frequency shift data obtained from the sensor array responding to four commercial perfume odours are first autoscaled and then treated by principal component analysis. The experimental results show that the plasticized PVC membrane PCS array provides improved performance of pattern recognition compared with the single adsorptive coating PCS array. The frequency shift response characteristics of these sensors have been investigated experimentally. The proposed sensor array has also been applied to the classification of commercial spirituous liquor, wine and soft drink samples, as well as aliphatic alcohol homologues and isomers.     

Oligonucleotide-functionalized gold nanoparticles-enhanced QCM-D sensor for mercury(II) ions with high sensitivity and tunable dynamic range

A quartz crystal microbalance with dissipation monitoring (QCM-D) sensor was developed for highly sensitive and specific detection of mercury(II) ions (Hg(2+)) with a tunable dynamic range, using oligonucleotide-functionalized gold nanoparticles (GNPs) for both frequency and dissipation amplification. The fabrication of the sensor employed a 'sandwich-type' strategy, and formation of T-Hg(2+)-T structures in linker DNA reduced the hybridization of the GNPs-tagged DNA on the gold electrode, which could be used as the molecular switch for Hg(2+) sensing. This QCM-D mercury sensor showed a linear response of 10-200 nM, with detection limits of 4 nM and 7 nM for frequency and dissipation measurements, respectively. Moreover, the dynamic range of the sensor could be tuned by simply altering the concentration of linker DNA without designing new sensors in the cases where detection of Hg(2+) at different levels is required. This sensor afforded excellent selectivity toward Hg(2+) compared with other potential coexisting metal ions. The feasibility of the sensor was demonstrated by analyzing Hg(2+)-spiked tap- and lake-water samples with satisfactory recoveries. The proposed approach extended the application of the QCM-D system in metal ions sensing, and could be adopted for the detection of other analytes when complemented with the use of functional DNA structures.     

Acid Phosphatase Assay with a Wireless Magnetoelastic Biosensor

Abstract

A wireless remote‐query disposable magnetoelastic biosensor is developed for the assay of acid phosphatase (ACP). The sensor was fabricated by applying a layer of pH‐sensitive polymer to a magnetoelastic ribbon and, on top of it, a sensing film containing bovine serum albumin and adenosine‐5′‐monophosphate (5′‐AMP), the substrate of ACP. In response to an externally applied time‐varying magnetic field, the magnetoelastic sensor mechanically vibrates at a characteristic frequency that is inversely dependent on the mass of the attached film. Because the magnetoelastic sensor is magnetostrictive, the mechanical vibrations of the sensor launch magnetic flux that can be detected remotely from the sensor using a pick‐up coil. The ACP‐catalyzed hydrolysis of 5′‐AMP decreases the solution pH, resulting in the polymer shrinking and, consequently, the resonance frequency of the magnetoelastic sensor increasing. The experimental condition was optimized to be 37°C, in 2.5 mM sodium citrate buffer solution (pH 6.5). Using citrate as buffer can enhance the ACP activity, partly offsetting the effect of the buffer capacity on the sensitivity. The kinetic parameter were measured to be: 1.64×10^–3 M (Michaelis constant) and 130 Hz/min (maximum initial rate). This work provides a remote enzymatic assay of ACP. The relative standard deviation in the measurements of six sensors in parallel is 3.4%. The proposed sensor can determine 0.2～1.2 U/ml of ACP.     

In situ growth of nanogold on quartz crystal microbalance and its application in the interaction between heparin and antithrombin III

A novel biosensor for detecting antithrombin III (AT III) was constructed based on in situ growth of nanogold on the gold electrode of quartz crystal microbalance (QCM). The growth process of nanogold was monitored by QCM in real time. Heparin was used as the affinity ligand and immobilized onto the nanogold modified gold electrode. A flow injection analysis-quartz crystal microbalance (FIA-QCM) system was used to investigate the relationship between nanogold growth and the AT III response. Along with the nanogold particle growth within initial 5 min, the amount of heparin immobilized onto the nanogold modified electrode increased quickly. Correspondingly, the frequency response to AT III binding increased rapidly at the same time. After that, both the immobilized amount of heparin and the sensor response to AT III decreased gradually. Compared with the directly immobilized large nanogold particles, the in situ grown particles with the same size occupy more sensor surface, resulting in higher frequency shifts to AT III in the interaction study between heparin and AT III. The obtained constants of AT III binding to immobilized heparin are k(ass)=(1.65+/-0.12)x10(3) L/mols, k diss=(2.63+/-0.18)x10(-2) 1/s and K(A)=(6.27+/-0.42)x10(4) L/mol.