Lili Bao

Determination of microorganisms with a quartz crystal microbalance sensor

A technique using a quartz crystal microbalance sensor coated with a thin culture medium film was developed and successfully applied to determine the number of Staphylococcus epidermidis (S. epidermidis) in the range of 1 × 102 −4.1 × 107 cells ml−1, based on a good linear relationship between the turning point time and the number of S. epidermidis. The technique is fast and accurate for detection of microorganisms due to the thin culture film and the sharp turning point of the response. The experimental conditions were discussed in detail.

A new study of the enzymatic hydrolysis of carboxymethyl cellulose with a bulk acoustic wave sensor

A new bulk acoustic wave (BAW) cellulase sensing technique, which is based on the enzymatic hydrolysis process of sodium carboxymethylcellulose (CMC) by cellulase, was established. The frequency shift curves of BAW sensor indicated that the viscosity of the tested solutions decreased during the hydrolysis process. The hydrolysis rate of CMC by cellulase was calculated from the frequency shift curves. The hydrolysis rate of CMC under different pH conditions at 30 degrees C showed that cellulase had high hydrolysis ability approximately at pH 5.0. Kinetic parameters (the Michaelis constant K(m) and the maximum rate V(max)) of the process were estimated by using a linear method of Lineweaver-Burk plot. K(m) is 1.95+/-0.25 mg ml(-1) and V(max) is -(4.25+/-0.58) x 10(-3) g(1/2) cm(-3/2) cP(1/2) min(-1). Also the activation energy (E(a)) of the enzymatic hydrolysis, with a value of 51.99+/-1.26 kJ mol(-1), was estimated in this work.

A Bulk Acoustic Wave Viscosity Sensor for Determination of Lysozyme Based on Lysis of Micrococcus Lysodeikeicus

Abstract A method for determination of lysozyme with a Bulk Acoustic Wave (BAW) viscosity sensor is presented. It is based on the bacteriolytic action of lysozyme on Micrococcus lysodeikeicus (M. lysodeikeicus) and the response of the sensor to the viscosity and density change of this process. There was a good correlation between the frequency shift and the concentration of lysozyme in the range 10–100 μg/ml. The content of lysozyme in human saliva was determined by this method and the results obtained were in good agreement with those from the conventional turbidimetric method. This method has an advantage over the conventional turbidimetric method in that the amount of sample needed is smaller, the procedure is simpler and the concentration range of the bacterium suspension which can be used in the detection was extended.

Rapid detection of Escherichia coliform with a bulk acoustic wave sensor based on the gelation of Tachypleus amebocyte lysate

A new sensing method (BAW-TAL technique), which combined the bulk acoustic wave (BAW) technique with the gelation reaction of Tachypleus amebocyte lysate (TAL), was used for viscosity and density measurement and applied to the detection of Escherichia coliform (E. coli). This method depended on the fact that the viscosity and density of the mixture increased, and as a result, the resonance frequency decreased correspondingly after TAL was mixed with the heated E. coli solution that contained endotoxin. Results showed that the frequency shift was linearly related to the logarithm of E. coli concentration in the range of 2.7x10(4)-2.7x10(8) cells/ml. The correlation coefficient was 0.996. This BAW-TAL method was compared with the standard pour plate counts (PPC) method. The proposed method was much more rapid and simpler for detection of E. coli than the traditional methods.

A new piezoelectric response model for population growth of bacteria.

A piezoelectric response model on the population growth of microorganism is proposed. This model is based on a novel population growth model, which has a more obvious ecological meaning and the fact that the series piezoelectric quartz crystal (SPQC) sensor responses to conductivity changes of the medium during the growth of the microorganism. From the response model four parameters can be obtained including the maximum specific growth rate mu(m), saturated population size N(m), and two constants C and K(1). The influence of the parameters on the response curve is discussed in which the influences of mu(m) and N(m) are more obvious. With the proposed model the quantitative determination of bacteria may be more accurate than the frequency detection time (FDT) method. Then the growth of Escherichia coliform (E. coli) monitored with a SPQC sensor is compared with the simulated growth curve obtained by the proposed model and a good agreement is obtained.

A thin liquid film thickness shear mode bulk acoustic wave sensor for determination of Proteus mirabilis

A thickness shear mode bulk acoustic wave sensor coated with a thin liquid culture medium film was developed and applied to determine the concentration of Proteus mirabilis (P. mirabilis). Experiments demonstrated that there was a good linear relationship between the turning point time and the logarithm of the P. mirabilis concentration in the range 2.0 x 10(2)-2.0 x 10(6) cells ml(-1). The detection was fast and accurate because of the sharp turning point of the response due to the thin culture film on the sensor surface. Other problems concerning the experiments are discussed in detail.

A rapid method for determination of Proteus vulgaris with a piezoelectric quartz crystal sensor coated with a thin liquid film

Abstract A rapid method for microorganism detection using a piezoelectric quartz crystal sensor (PQC) coated with a thin liquid culture medium film was developed and applied to detect the cell number of Proteus vulgaris . This method employed the viscosity and density response of PQC and utilized the coagulation of gelatine medium solution in which the microorganisms had grown to determine the microorganism indirectly. Three time points (TT 1 , DT, TT 2 ) were obtained from the coagulation curve and were found to be in good linear relationship with the logarithm of the initial number of P. vulgaris in the range 1·3 × 10 2 −1·3 × 10 5 cells/ml. The detection was rapid and accurate because the coagulation of the thin liquid culture medium film was quick and the time points in the response curve were sharp and so were easy to determine accurately. The detection time was less than 4 h and only a micro sample was needed. A 5 h preincubation was needed before detection. Some experimental conditions are discussed in detail.

A Novel Method for Mutagenicity Test of Carcinogen by using a Series Piezoelectric Quartz Crystal Bactrial Growth Sensor

ABSTRACT A new method for mutagenicity testing of carcinogens is proposed in this paper. Mutagenic activity is examined through monitoring of the growth situation of Salmonella typhimurium TA98 strain with a series piezoelectric quartz crystal (SPQC) sensor. This method needs no immobilization and preincubation of microorganism, and is simple and rapid. It can be applied to detect mutagen directly. When it was used to study the mutagenicity of dimethyl sulfate, the test time was 4 h at 37°C. There was a good linear relationship between frequency shift and the dose of mutagen in the range 2.5-20 μg/mL and the regression equation was ∠F = 53.82 + 3.81C. Some experimental conditions are also discussed in detail.

A Novel Immobilized Enzyme Flow-Injection System for Urea with a Bulk Acoustic Wave Impedance Sensor as Detector

Abstract The urea-urease system was chosen as a model system to explore the suitability for the use of a bulk acoustic wave impedance sensor (BAWIS) as a detector in an immobilized enzyme FIA system. In the proposed FIA sysem, the urea in samples was hydrolyzed into ammonium and bicarbonate under the catalysis of the immobilized urease. The ammonium formed was converted into ammonia in an alkaline stream, and the ammonia diffused across a gas-permeable membrane into a recipient solution of dilute hydrochloric acid. The conductance change caused by the trapped ammonia was followed by a BAWIS detector. The system was applied to the analysis of urea in blood and urine samples. It exhibited a linear frequency response up to 10 mM urea with a detection limit of 10 μM. The through-put was 50 h-1, and the relative standard deviation of the peak heights (n=6) ranged between 0.63-1.97%. The effects of several factors, including those affecting the enzymatic reaction, detector performance, and gas-diffusion process...

Study on a modified algorithm—iterative Kalman filter and its application in enzymic kinetics

A modified algorithm, the iterative Kalman filter, for the analysis of enzymic kinetic data was investigated and successfully applied to the determination of urea in human blood by a urease catalytic reaction. This reaction was monitored with a novel sensor, the surface acoustic wave enzyme sensor system recently proposed by our laboratory. The results were compared with those provided by a calibration graph and classical colorimetry methods. In contrast to these conventional methods, the iterative extended-Kalman filter is shown to be an excellent data analysis method for enzyme kinetic analysis. The urease kinetic parameters were also estimated according to the iterative Kalman filtering results.