Dezhong Liu

Clinical analysis of urea in human blood by coupling a surface acoustic wave sensor with urease extracted from pumpkin seeds

Abstract A surface acoustic wave (SAW) urease sensor system was developed in which a SAW resonator oscillating at 61 MHz and a pair of parallel electrodes were utilized by coupling with urease extracted from pumpkin seeds. The Michaelis constant and the maximum reaction rate of urease were estimated as 2.08 × 10 −3 mol/1 and 8.85 kHz/min, respectively, at pH 7.5 and 25.0 ° C. The analytical characteristics of the urease sensor system, including influences of pH, temperature on frequency response, calibration curves, reproducibility, selectivity over enzymatic interferences were determined. The recovery of the sensor system ranged from 96 to 105% and the experimental detection limit of urea was 0.50 μg/ml (i.e., 8.3 × 10−6 M, S N = 3 ). The SAW urease sensor system possesses the characteristics of good reproducibility and specificity. It has been successfully applied to the analysis of urea in human blood samples. The assay results are consistent with the results tested by conventional colorimetry and also support clinical diagnosis.

Determination of urea in urine using a conductivity cell with surface acoustic wave resonator-based measurement circuit

A conductivity cell employing a 61 MHz surface acoustic wave resonator-based measurement circuit was applied to the detection of the urea/urease reaction. The kinetic enzymatic parameters of the urease were estimated from the frequency shifts. The effects of pH, temperature and inhibitor on the response of the enzyme conductivity measurement system were investigated. The system was applied to rapid determination of urea in small urine samples. The lowest detection limit of urea was 30 ng/ml.

Circuit network analysis method applied to surface acoustic wave impedance system in liquids

Abstract The circuit network theory was applied to analyse a surface acoustic wave (SAW) impedance system constructed from a 61-MHz SAW resonator and a pair of conductive electrodes in series. Two oscillation equations were derived and used to explain the effects of solution capacitance and cell constant on the frequency characteristics. The effects of the solution density and the viscosity on the frequency response of the SAW impedance system were also investigated. The SAW impedance system can be applied to conductivity measurements in solution with a high concentration background of foreign electrolytes.

A new urea sensor based on combining the surface acoustic wave device with urease extracted from green soya bean and its application--determination of urea in human urine.

The urea sensor was prepared by combining a surface acoustic wave (SAW) device, in which a SAW resonator operating at 61 MHz and a pair of parallel electrodes were used in series, with urease extracted from green soya bean. The Michaelis constant and maximum reaction rate of the urease were estimated as 2.14 mM and 27.18 kHz min-1, respectively, at pH 7.0 and 25.0 degrees C. Influences of pH, temperature and effectors on the response properties of the SAW urea sensor were investigated. Recovery of the sensor ranged from 95 to 105% and the detection limit of urea was 1.0 micrograms ml-1 (1.7 x 10(-5) M). The proposed sensor has been successfully applied to the rapid determination of urea in human urine samples. The results are consistent with the reported values and also support the clinical diagnosis.

Behaviour of surface acoustic wave interdigitated array electrode sensor in non-aqueous solution and determination of blood plasma recalcification time

A novel SAW-IDA sensor system was constructed for the first time by connecting the IDA electrodes in series with a SAW resonator. The frequency characteristics of the SAW-IDA sensor in non-aqueous solution were investigated. The effects of the parallel capacitance and cell constant were studied, and were calculated with the circuit network theory. These calculations provide guiding rules for design of the SAW-IDA sensor system. The SAW-IDA sensor was applied to determination of recalcification time and activated partial thromboplastin time of blood plasma. The sensor offers a new and effective way of studying clinical and laboratory haemostasis.

Enzymatic analysis of arginine with the SAW/conductance sensor system

Abstract A specific and simple method for the determination of arginine was developed by using a new type sensor, a surface acoustic wave (SAW)/conductance sensor system. The assay was based on two coupling reactions involving arginase (E.C. 3.5.3.1) and urease (E.C. 3.5.1.5) with measurement of frequency shift that resulted from the changes of conducting ions produced in the reactions. Arginase was extracted from fresh bovine liver and required no further separation step. The optimum pH (8.5) and reaction medium (Tris-HCl-EDTA, pH 8.5) were determined. We also investigated the influences of reaction medium, pH, temperature, and amount of urease or arginase on the frequency response of the SAW/conductance sensor system. The results were linear up to 4.0 × 10 −4 m of arginine, and the detection limit was 2.0 × 10 −6 m . When the SAW/conductance sensor system was applied to arginine analysis, the results obtained compared well with those of the pharmaceutical method.

Determination of trace level of mercury(II) based on the inhibition of urease using SAW/impedance enzyme transducer

Abstract A novel and sensitive method for the enzymatic determination of trace amount of mercury ion based on its inhibitory action on urease is proposed. Mercury(II) inhibits the urease-catalysed urea hydrolysis by binding with sulphydryl groups of urease. The inhibited enzymatic reaction is monitored in-situ with a SAW/impedance enzyme transducer which is composed of a SAW resonator oscillating at 61 MHz and a pair of parallel electrodes. The inhibition mechanism of Hg(II) on urease is discussed. The kinetic parameters and inhibition parameters are estimated. The frequency response of the transducer is proportional to mercury concentration over the range of 50-350 ng/mL. The detection limit is 20 ng/mL. The relative standard deviation was 2.9% for six measurements of 150 ng/mL Hg(II). The effect of potential major interferences was investigated. The method was successfully applied to the determination of Hg(II) in waste water and the results obtained by proposed methods compared well with those obtained...

Rapid detection of L-glutamic acid using a series-electrode piezoelectric quartz crystal sensor

Abstract Two methods are described for the determination of l -glutamic acid using a series-electrode piezoelectric quartz crystal sensor. The effect of formaldehyde solution on the frequency shift is discussed. For the calibration curve method, in formaldehyde medium, the detection limit is 3.8 · 10 −5 M, the recovery is 100.4%, the relative standard deviation is 3.32% ( n = 5) and the frequency shift is linear up to 8 · 10 −4 M; in aqueous medium, the above values are 2.0 · 10 −5 M, 99.1%, 3.01% ( n = 6) and 1.1 · 10 −3 M, respectively. The frequencimetric titration method is also described and the lowest titratable concentration of l- glutamic acid is 7.0 · 10 −5 M. The detecting results for tablet samples show good agreement with the values determined by the pharmaceutical method.

A novel glutamine biosensor system based on a conductance-surface acoustic wave frequency response

Abstract A new type of glutamine biosensor system based on a conductance-surface acoustic wave (SAW) frequency response, in which a SAW resonator oscillating at 61 MHz and a biosensor involving kidney cortex tissue or Escherichia coliform and a pair of parallel electrodes were used, was developed for the determination of glutamine. Glutaminase from porcine kidney or Escherichia coliform was used as a biocatalyst of the hydrolysis reaction of glutamine. There was an excellent linear relationship between the frequency shift response and the glutamine concentration in the range of 6.8 · 10 −4 m to 6.8 · 10 −3 m . The SAW frequency responses obtained from the proposed biosensor system were compared with the conductance response. Some other factors such as pH and selectivity are also discussed.

Determination of dipyridamole by modified extraction-gravimetry with a surface acoustic wave resonator sensor

A simple and sensitive extraction-gravimetric method for the determination of dipyridamole is presented. The method is based on the extraction of free dipyridamole with chloroform, after neutralization with a basic agent, followed by measurement of the frequency shift response of the specially designed surface acoustic wave resonator sensor after evaporation of the extractant from the surface of the resonator. The frequency shift response was proportional to the amount of dipyridamole in the range 0.065-1.12 micrograms. Experimental parameters and the effect of interfering substances on the assay of dipyridamole were also examined in this study. The method was applied to the determination of dipyridamole in tablets.