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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 2.7×104–2.7×108 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 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.

An ion chromatographic (IC) method with doublecell bulk acoustic wave (DCBAW) detection is described for determination of ammonia and low-molecular- mass aliphatic amines in food. A 9 MHz AT-cut quartz crystal is used as the resonator. This detection technique provides high sensitivity, good reproducibility, and wide work region. Its sensitivity is independent of background conductivity of the mobile phase in the range 10-2700 μS. Detection limits (peak = 3 δ) for NH4+, CH3NH3+ (CH3)2NH2+and (CH3)3NH+ were 0.02, 0.05, 0.13, and 0.6 μg/mL, respectively. Relative standard deviations for NH4+, CH3NH3+, (CH3)2NH2+, and (CH3)3NH+ were 0.7,1.0, 0.8, and 1.2%, respectively. For IC analysis, the analytical column is a Shim-pack IC-C1 column and the mobile phase is 2.0 mmol/L nitric acid solution at a flow rate of 1.5 mL/min. Detection with DCBAW was compared with series bulk acoustic wave and conventional conductivity. The method was applied to analyses of egg, fish, and cured meat

A series piezoelectric quartz crystal (SPQC) sensor was utilized to determine the number of bacteria based on the coagulation of milk in which Staphylococcus aureus (S. aureus) had grown. Compared with the method based on a PQC coated with a thin film, earlier it had the advantage that no dilution of the medium was needed and cease of the oscillation can be avoided throughout the experiment. Moreover, it was rapid, the turning-point time (TT) for quantitative detection which was the time at which the frequency begins to return after a drop in response curve was easy to determine and there was a good relation between TT and logarithm of the initial concentration of S. aureus in the range of 2.4×102–2.4×105 cells ml−1.

A bulk acoustic wave (BAW) impedance sensor has been applied to rapid determination of in vitro concentrations of cefotaxime sodium. The method based on the growth frequency curve of Proteus Morganii, inhibited by cefotaxime sodium, is continuously monitored by using a BAW impedance sensor. The growth kinetic parameter, e.g. asymptote or maximum frequency shift (AF, Hz), estimated by fitting a modified Gompertz model to the growth frequency curve, is proportional to the logarithm of antibiotic concentration. The proposed method exhibits a favourable response to 0.25 – 20.0 μg mL−1 cefotaxime sodium with a detection limit of 0.03 μg mL−1, and the recoveries range from 97.3 to 107.5% (n=9). The results are in good agreement with those obtained by the conventional disk diffusion test (DDT) method. The effects of temperature and pH on the determination are discussed and in vitro susceptibility to cefotaxime of the genus Proteus has been investigated in detail. On leave from Department of Mathematics,...

A bulk acoustic wave (BAW)-impedance sensor has been successfully applied to determine the number of Proteus mirabilis (P. mirabilis) in the range of 2.77 × 102 ± 9.53 × 106 cells ml−1, based on a linear relationship between the frequency detection time (FDT) and the logarithm of the P. mirabilis concentration in this paper. The antimicrobial properties of various teas on growth of P. mirabilis have also been studied. The method is simple and rapid. Factors that might affect the determination such as pH value and temperature are discussed in detail. A comparison between the proposed method and the traditional pour plate count (PPC) method has also been investigated.

A new type of bulk acoustic wave sensing device based on a conductivity-bulk acoustic wave frequency response is applied in ion chromatography to determine nitrate and other inorganic ions in vegetables. The present method has the advantages in its rapidity, simplicity, sensitivity and accuracy. Detection limits (peak=3[sgrave]) are obtained for NO3 −, Cl−, NO2 −, H2PO4 − and SO4 2− at concentrations of 1, 0.6, 1, 7 and 3 ng (on column), respectively. Neither derivatization nor a clean-up step is necessary besides filtration. For the IC analysis, the analytical column is a Shim-pack IC AI column, and the eluent is 2.0 mM phthalic acid solution with pH 4.0. A comparison of IC-SBAW with conventional IC is made. The method allows the simultaneous determination of nitrate and other inorganic ion levels in vegetables.

A flow injection analysis (FIA) method was developed for the rapid determination of sulfite in wines and fruit juices. The method is based on an on-line membrane separation of the SO2 released from a stream of 0.5 M H2SO4 into a stream of 0.01 M H2O2–0.15 mM H2SO4. The conductance increase due to the oxidation of SO2 to H2SO4 is monitored by a bulk acoustic wave impedance sensor and the signal is proportional to the concentration of sulfite present in the original sample. At a throughput of 78 samples h–1, the method exhibited a linear frequency response up to 1.0 mM sulfite with a detection limit of 5.0 µM, and the relative standard deviation of the peak height (n = 6) ranged from 0.57 to 1.23%. Results obtained by the proposed method agreed well with those obtained by conventional iodimetry. The effects of several factors, including those affecting the detector performance and gas transfer process, on the performance of the proposed FIA system were also examined.

A feasible chromatographic method for the determination of iodide using ion chromatography (IC) with series bulk acoustic wave (SBAW) detection has been developed. The advantages of the good selectivity of ion chromatography and the highly sensitive response of SBAW have been combined to improve detection limit, linearity, and reproducibility. The detection limit has been estimated to be 5 ng/ml. For the IC analysis a 12.5-μm polymethacrylate resin column incorporating a quaternary base was used, with the mobile phase being 5.0 m M phthalic acid. The method has been applied to the determination of iodide in some dairy products and table salt.

The diffusion of solvents from a coating layer and their evaporation at the surface of the coating film during the curing process of the coating are investigated by bulk acoustic wave (BAW) admittance analysis and can be expressed as change in the relative diffusion rate (J). The porosity and permeability of the coating film are related to the curing degree (η). The changes in J and the values of J s (the relative diffusion rate at the surface dry time, t s , Δt p (the time difference between the surface dry time t s and the turning point time t p when the diffusion behaviour changes), and η can provide much useful information on selecting solvents and optimizing coating ingredients in the preparation of coatings. The effects of the coating film thickness, solvent content of the coating liquid, and the volatility of the solvent on the diffusion of solvent from the film are also discussed.

A convenient and sensitive method based on the inhibition of the lipase-catalyzed hydrolysis by binding hydroxyl groups of lipase with organophosphorus pesticide is described for the enzymatic determination of organophosphorus pesticides. Employing the method proposed, the frequency response is proportional to organophosphorus pesticide concentration over the range of 250 ng/ml∼1.25 μg/ml. the detection limit is 58 ng/ml. The effects of temperature, pH value, incubation time and solvent are also investigated.

The possibility of continuously on-line measuring the growth of Salmonella typhimurium on solid medium was studied. The medium used is SS agar which is not only suitable for isolation and identification of Gram-negative intestinal bacilli but also fit for monitoring bacteria with a thickness shear mode (TSM) acoustic resonator in series. It was found that the method is simple, realtime, and rapid. The concentration of the bacteria detected by this method was in the range of 10 2 –3.6 × 10 6 cells ml −1 .

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 × 102–2.0 × 106 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 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 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.

The possibility of using a long path length spectroelectrochemical cell to determine the rate constant and diffusion coefficient for a catalytic reaction was explored. An optimization technique combined with a semi-expanding space grid digital simulation was utilized for fitting response curves obtained with the cell to estimate the parameters. The method possesses excellent capability of accurate and precise parameter estimation using synthetic response curves under potential step disturbance, with 0.003 absorbance unit normally distributed noise, for one-electron transfer coupled to a homogeneous catalytic process. Then the technique was used to determine the rate constant of ascorbic acid oxidized by ferricyanide and the diffusion coefficient of ferrocyanide for the system of ferrocyanide-ascorbic acid in glycine-nitric acid solution, which are 6.81 M −1 s −1 and 6.68 10 −6 cm 2 s − are not sensitive to experimental conditions.

This paper proposed a direct electrodeposition approach to synthesis of graphene–chitosan (GR–CS) composite onto glassy carbon electrode (GCE) under controlled potential. This direct electrodeposition approach for the construction of GR-based hybrid was environmentally friendly, which would not involve the chemical reduction of graphene oxide (GO) and therefore result in no further contamination. The whole procedure was simply and cost only several minutes. Moreover, Combining the advantages of GR (large surface-to-volume ratio and high conductivity) and CS (good biocompatibility and adsorption), the GR–CS composite could be highly efficient to capture OPs and used as solid phase extraction (SPE). The GR–CS/GCE was used to detect organophosphate pesticides (OPs), using methyl parathion (MP) as a model analyte. The significantly redox response of MP on the GR–CS/GCE was proved. The linear range was wide from 4.0 ng mL−1 to 400 ng mL−1, and a low detection limit of 0.8 ng mL−1 for MP was achieved. Moreover, the proposed sensor exhibited high reproducibility, long-time storage stability and satisfactory anti-interference ability. The proposed GR–CS/GCE opens new opportunity for green, fast, simple, and sensitive analysis of OP compounds.

A piezoelectric quartz crystal with one separated electrode that could be immersed in liquid was applied to the simultaneous determination of atropine sulphate and sodium chloride in atropine sulphate eye drops. The average relative errors were 4.0% for atropine sulphate and 2.7% for sodium chloride.

A new detector of water based on the piezoelectric crystal with separated electrode (PCSE) is proposed. The frequency response of the PCSE to the dielectric constant of nonelectrolyte solution is derived. The detector was applied to determine the microcontent of water in organic solvents. The detection limits are 0.022, 0.013 and 0.010 g/L in acetone, tetrahydrofuran, and dioxane, respectively. For the water content in ethanol, linear and nonlinear regression methods are employed, and the average relative errors of prediction are 1.67% and 2.77%, respectively

A nonlinear regression model of reversible ion transfer across the interface between aqueous and organic phases is derived theoretically with consideration of background current and resistance. We used the Marquardt nonlinear regression method to fit the response curves for reversible ion transfer of tetramethyl ammonium and vitamin B1 across the water—organic phase interface and simultaneously estimated values of their aqueous diffusion coefficients, charge-transfer resistances, half-wave potentials and the background current. The analysis of the residuals indicates that the model reflects the true behavior of the test systems. The results obtained show that the technique is not sensitive to the experimental conditions.

Theory of chronoabsorptometry of a single reversible electrode reaction after a potential-step perturbation using a long-pathlength spectroelectrochemical cell is presented. Assuming that the oxidized species is the only absorber at the monitored wavelength, three cases, thin-layer diffusion for Red⇄OX+ ne and semiinfinite diffusion for Ox+ ne⇄Red and Red⇄Ox+ ne, are examined by computation of the analytical solutions or digital simulation. All the theoretical results are verified by experiments

This paper presents the theory of derivative linear sweep and derivative cyclic voltabsorptometry (DLSVA and DCVA) of the long-path-length spectroelectrochemical (SEC) cell for the single reversible electrode reaction. Assuming that only the oxidized species (Ox) absorbs at the measurement wavelength initially, the first- and second-derivative optical responses for two cases, i.e. thin layer diffusion for Ox + ne − ⇄ Red (reduced species) or Red ⇄ Ox + ne − and semi-infinite diffusion for Ox + ne − ⇄ Red or Red ⇄ Ox + ne −, have been discussed via digital simulation, etc. All types of theoretical behaviour have been compared with that of the optically-transparent electrode (OTE). The results show that DLSVA and DCVA of the long-path-length SEC cell are more sensitive (by several decades or more) than those of the OTE. The theoretical results are verified experimentally by the well-characterized reversible electrochemical system Fe(CN) 6 3− /Fe(CN) 4 3− in 0.5 M HNO 3 + 0.5 M glycine buffer.

A robust procedure, called sine function M-estimator (SFME), used in multivariate analysis, is described and utilized in multicomponent simultaneous analysis and measurement wavelength selection for a pharmaceutical system with two analytes (ephedrine hydrochloride and furaciline) by a direct calibration method. The regression results indicated that, when the noise distribution is not normal, SFME can obtain far better estimated concentration parameters than the commonly used least squares method. For the system tested, SFME yielded a four- to seven-fold improvement in prediction capability over the least squares method, together with good results in wavelength selection. The computational problems associated with SFME are discussed.

The magnetic field effect on the electrochemical behavior of hemoglobin at the silver electrode was investigated by cyclic voltammetry. When a 0.4 T magnetic field was applied to the cell containing 1×10−6 M hemoglobin (pH 5.0), both anodic and cathodic peak currents increased observably at 10 mV/s due to the MHD convection. In addition, the influence of scan rate, adding promotor, increasing homoglobin concentration and removing oxygen on the peak currents under the magnetic field were investigated and analyzed with the classical MHD phenomena.

A qualitative method for the identification of 5 main glycosidic flavor precursors in tobacco was developed by using ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI MS/MS) and gas chromatography-mass spectrometry (GC-MS). The glycosidic flavor precursors in tobacco were extracted with methanol, cleaned up with an XAD-2 column. The aglycones were later released by enzyme-mediated hydrolysis under the condition of pH 5. The 5 volatile aglycone moieties were identified by GC-MS standard spectra library. The precursor ions of glycosides were determined by using electrospray ionization mass spectrometry in negative ion mode, then the 5 glycosidic flavor precursors were identified by using product ion scan (MS2) finally, using UPLC-ESI MS/MS, separation and identification of 5 glycosidic flavor precursors were accomplished on an RP-C,8 column in the multiple reaction monitoring (MRM) mode by using methanol and acetic acid-ammonium acetate aqueous solution as eluent. This work lays a foundation for the analysis of glycosidic flavor precursors without the standards by using liquid chromatography-mass spectrometry.

A colloidal gold-modified carbon ionic liquid electrode was constructed by mixing colloidal gold-modified graphite powder with a solid room temperature ionic liquid n-octyl-pyridinium hexafluorophosphate (OPPF6). Glucose oxidase (GOD) was entrapped in this composite matrix and maintained its bioactivity well and displayed excellent stability. The effect conditions of pH, applied potential and GOD loading were examined. Especially, the glucose oxidase entrapped in this carbon ionic liquid electrode fully retained its activity upon stressing in strongly acidic conditions (pH 2.0) for over one hour. The proposed biosensor responds to glucose linearly over concentration range of 5.0 × 10−6 to 1.2 × 10−3 and 2.6 × 10−3 to 1.3 × 10−2 M, and the detection limit is 3.5 × 10−6 M. The response time of the biosensor is fast (within 10 s), and the life time is over two months. The effects of electroactive interferents, such as ascorbic acid, uric acid, can be significantly reduced by a Nafion film casting on the surface of resulting biosensor.

A non-linear model connecting the frequency response of the piezoelectric quartz crystal detector in acid-base titration with the added quantity of titrants has been derived in detail. It has been verified theoretically and used for the regression analysis of response curves of acid-base titrations for four acid solutions with different dissociation constants to estimate the original acid concentrations of the solutions to be titrated, dissociation constants of the acid, the equivalent ionic conductivities and the other two crystal response parameters, viz., the response sensitivity for conductivity and the basic frequency when the conductance contribution of the reacting substances equals zero. the experiments and computations indicate that the technique possesses good estimation precision and accuracy.

Based on the linear relationship between the conductivity of an aqueous solution and the piezoelectric quartz sensor frequency, it was derived that under certain experimental conditions the frequency shift should show a linear dependence on concentration for common acids and aspirin. This verified experimentally. A calibration model for the simultaneous determintaion of aspirin (ASA) and salicylic acid (SA) was established. The usefulness of the technique was evaluated by the analysis of mixtures of known composition using a P-matrix calibration method. The average relative errors were 0.81% for ASA and 1.63% for SA.

The direct electron transfer and electrocatalysis of hemoglobin (Hb) entrapped in the MCM-41 modified carbon ionic liquid electrode (CILE) were investigated by using cyclic voltammetry in 0.10 M pH 7.0 phosphate buffer solution (PBS). Due to its uniform pore structure, high surface areas and good biocompatibility, the mesoporous silica sieve MCM-41 provided a suitable matrix for immobilization of biomolecule. The MCM-41 modified CILE showed significant promotion to the direct electron transfer of Hb, which exhibited a pair of well defined and quasi-reversible peaks for heme Fe(III)/Fe(II) with a formal potential of -0.284 V (vs. Ag/AgCl). Additionally, the Hb immobilized on the MCM-41 modified carbon ionic liquid electrode showed excellent electrocatalytic activity toward H(2)O(2). The electrocatalytic current values were linear with increasing concentration of H(2)O(2) in a wide range of 5-310 microM and the corresponding detection limit was calculated to be 5 x 10(-8)M (S/N=3). The surface coverage of Hb immobilized on the MCM-41 modified carbon ionic liquid electrode was about 2.54 x 10(-9) molcm(-2). The Michaelis-Menten constant K(m)(app) of 214 microM indicated that the Hb immobilized on the modified electrode showed high affinity to H(2)O(2). The proposed electrode had high stability and good reproducibility due to the protection effect of MCM-41 and ionic liquid, and it would have wide potential applications in direct electrochemistry, biosensors and biocatalysis.

A novel technology to obtain highly efficient biosorbent from the endophytes of a hyperaccumulator is reported. This technology is more convenient than the traditional method of obtaining biosorbents by experimentally screening many types of biomass by trial and error. Using this technology, endophytic fungus (EF) LSE10 was isolated from the cadmium hyperaccumulator Solanum nigrum L. It was identified as Microsphaeropsis sp. When cultured in vitro, the biomass yield of this EF was more than twice that of none-endophytic fungus (NEF) Rhizopus cohnii. Subsequently, it was used as a biosorbent for biosorption of cadmium from the aqueous solution. The results showed that the maximum biosorption capacity was 247.5 mg/g (2.2 mmol/g) which was much higher than those of other adsorbents, including biosorbents and activated carbon. Carboxyl, amino, sulphonate and hydroxyl groups on EF LSE10 surface were responsible for the biosorption of cadmium.

In this paper, DNA functionalized SWCNTs were used to immobilize horseradish peroxidase (HRP) on glassy carbon (GC) electrode. Cyclic voltammetry showed that the direct electrochemistry of HRP immobilized on DNA-SWCNTs hybrids was achieved. The DNA interlayer between the SWCNTs and HRP could be used to keep the activity of HRP. Compared with HRP-SWCNTs/GC and HRP-DNA/GC electrodes, the prepared HRP-DNA-SWCNTs/GC electrode exhibited more excellent electrochemical properties. Thus, the prepared HRP-DNA-SWCNTs/GC electrode was proposed as a third-generation H 2 O 2 biosensor. The effect of pH and applied potential on the performance of the biosensor was discussed in detail. Under the optimal conditions, a wide linear range of the propose biosensor for the detection of H 2 O 2 was observed from 6.0 × 10 −7 to 1.8 × 10 −3 M. The detection limit was found to be 3.0 × 10 −7 M at a signal-to-noise ratio of 3. Furthermore, the proposed biosensor displayed rapid response, high stability, very good reproducibility and high sensitivity for the detection of H 2 O 2 . Determination H 2 O 2 concentration in disinfector sample by the proposed biosensor also showed satisfactory result.

An array of four piezoelectric crystals, each working at a certain pH, was constructed for the simultaneous determination of o- and m-cresol in water. As there are differences in the reaction of o- and m-cresol with iodine under different pH conditions and because iodine in water can be adsorbed by quartz sensors coated with silver, the two cresols can be determined when excess of iodine is added to solutions containing the compounds and a crystal array is used to measure the remaining iodine. The data obtained were treated by two calibration techniques: multiple linear regression (MLR) and partial least-squares (PLS). With the use of this array of sensors, collinearity may occur, which affects the regression results. The experiments and computations indicated that better concentration estimates can be obtained with PLS than with MLR and the average relative prediction errors for o- and m-cresol in five unknown samples were 10.0% and 4.8%, respectively, with MLR and 5.2% and 3.4%, respectively, with PLS.

A sensitive glucose biosensor was fabricated by electrodepositing chitosan-ionic liquid-glucose oxidase biocomposite onto nano-gold electrode. First, nano-gold electrode was constructed by electrochemically depositing gold nanoparticles onto a flat gold electrode surface. Then the nano-gold electrode was immersed in the bath containing p-benzoquinone (BQ), chitosan (CS), glucose oxidase (GOD) and ionic liquid (IL) for electrodeposition of enzymatic electrode. The proton consumption during electroreduction of BQ increased the local solution pH near the electrode surface and led to the deposition of CS hydrogel on the electrode surface. Co-deposition of GOD and IL with the CS hydrogel was achieved. The proposed biosensor exhibited a fast amperometric response (5 s) to glucose. Under the optimal conditions, the proposed biosensor exhibited a high current sensitivity (14.33 microA mM(-1) cm(-2)), which was 2.8 times of the biosensor prepared by electrodepositing CS-IL-GOD biocomposite on flat gold electrode. The detection limit for glucose was 1.5 microM, which was 20-fold lower compared to the biosensor prepared on flat gold electrode. The linear range for glucose detection was wide from 3.0 microM to 9.0 mM. Moreover, the proposed biosensor exhibited high reproducibility, long-time storage stability and satisfactory anti-interference ability. The applicability of the proposed biosensor to serum samples analysis was also evaluated.

Multilayer films of multiwalled carbon nanotubes (MWCNTs) with molecule recognition function were assembled on glassy carbon (GC) electrode with lower capacitive background current by two steps: first, MWCNTs interacted with beta-cyclodextrin (beta-CD) with the aid of sonication to form beta-CD-MWCNTs nanocomposite, then the beta-CD-MWCNTs nanocomposite was assembled on GC electrode using layer-by-layer (LBL) method based on electrostatic interaction of positively charged biopolymer chitosan and negatively charged MWCNTs. The assembled beta-CD-MWCNTs multilayer films were characterized by scanning electron microscopy (SEM) and cyclic voltammetry. The SEM indicated that the MWCNTs multilayer films with beta-CD were somewhat more compact than that of the MWCNTs multilayer films without beta-CD. The cyclic voltammetric results indicated that the assembled MWCNTs with beta-CD on GC electrode exhibited lower capacitive background current than the assembled MWCNTs without beta-CD. The MWCNTs multilayer films with beta-CD were studied with respect to the electrocatalytic activity toward dopamine (DA). Compared with the MWCNTs multilayer films without beta-CD, the MWCNTs multilayer films with beta-CD possesses a much lower capacitive background current and higher electrocatalytic activity in phosphate buffer, which was ascribed to the relatively compact three-dimensional structure of the MWCNTs multilayer films with beta-CD and the excellent molecule recognition function of beta-CD.

A new method was proposed for studying antimutagenic characteristics of Tea Polyphenols (TP) using piezoelectric impedance analysis during the Salmonella typhimurium strain TA100 growth process in the presence of mutagen 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (abbreviated NNK). Compared with the general method of antimutagenic investigation, the proposed method provided real-time, multidimensional response information about the antimutagenic characteristics during the bacterial growth process. The results showed that TP was allowed to be antimutagenic at the lowest concentration of 0.25 μg/ml, and the inhibitory effect of TP presented a linear relationship with its dosage in the range of 0.25–2.5 μg/ml. And the relationship between the bacterial growth kinetic parameters and the TP dosage was also obtained. The present method provided a new approach for studying microbial antimutagenic characteristics.

A novel modified electrode was constructed by electropolymerization of bromophenol blue at a multi-walled carbon nanotubes modified glassy carbon electrode. The electrode developed was used for the simultaneous determination of the isomers of dihydroxybenzene in environmental samples using a voltammetry method. There was a linear relationship over the range 10(-6)-10(-4 )mol L(-1) of hydroquinone, catechol and resorcinol; the detection limits was 3 x 10(-7) mol L(-1). The constructed electrode showed excellent reproducibility and stability. Actual water samples were analyzed and satisfactory result was obtained.

Semi-interpenetrating polymer network (semi-IPN) hydrogel based on polyacrylamide (PAM) and chitosan was prepared to immobilize redox protein hemoglobin (Hb). The Hb-PAM-chitosan hydrogel film obtained has been investigated by scanning electron microscopy (SEM) and UV-VIS spectroscopy. UV-VIS spectroscopy showed that Hb kept its secondary structure similar to its native state in the Hb-PAM-chitosan hydrogel film. Cyclic voltammogram of Hb-PAM-chitosan film-modified glass carbon (GC) electrode showed a pair of well-defined and quasi-reversible redox peaks for Hb Fe(III)/Fe(II), indicating that direct electron transfer between Hb and GC electrode occurred. The electron-transfer rate constant was about 5.51 s(-1) in pH 7.0 buffers, and the formal potential (E degrees ') was -0.324 V (vs. SCE). The dependence of E degrees ' on solution pH indicated that one-proton transfer was coupled to each electron transfer in the direct electron-transfer reaction. Additionally, Hb in the semi-IPN hydrogel film retained its bioactivity and showed excellent electrocatalytic activity toward H(2)O(2). The electrocatalytic current values were linear with increasing concentration of H(2)O(2) in a wide range of 5-420 microM. The unique semi-IPN hydrogel would have wide potential applications in direct electrochemistry, biosensors and biocatalysis.

A novel method for real-time investigating the binding interaction between human serum albumin (HSA) and salicylic acid with capacitive sensing technique was successfully proposed. HSA was immobilized on the surface of a gold electrode modified with an insulating poly (o-phenylenediamine) (o-PD) film and colloid Au nanoparticles layers. The bioactivity of HSA was remained and major binding sites were available because of the excellent biocompatibility of gold nanoparticles. The capacitance and interfacial electron resistance of the sensor were altered, owing to the binding of HSA to salicylic acid. The time courses of the capacitance change were acquired with capacitive sensing technique during the binding process. Based on the capacitance response curves with time, the response model for the binding was derived in theory and the corresponding regression parameters were determined by fitting the real-time experimental data to the model. The binding and the dissociation rate constants (k(1) and k(-1)) were estimated to be 54.8 (mol l(-1))(-1) s(-1) and 2.9 x 10(-3) s(-1), respectively. And the binding equilibrium constant (K(a)) was calculated to be 1.89 x 10(4) (mol l(-1))(-1).

A simple, sensitive, and reliable method based on a combination of multi-walled carbon nanotubes with incorporated beta-cyclodextrin (beta-CD-MWNTs) and a polyaniline (PANI) film-modified glassy-carbon (GC) electrode has been successfully developed for determination of dopamine (DA) in the presence of ascorbic acid (AA). The PANI film had good anti-interference properties and long-term stability, because of the permselective and protective properties of the conducting redox polymer film. The acid-treated MWNTs with carboxylic acid functional groups promoted the electron-transfer reaction of DA and inhibited the voltammetric response of AA. Sensitive detection of DA was further improved by the preconcentration effect of formation of a supramolecular complex between beta-CD and DA. The analytical response of the beta-CD-MWNTs/PANI film to the electrochemical behavior of DA was, therefore, better than that of a MWNTs/PANI film, a PANI film, or a bare glassy-carbon (GC) electrode. Under the conditions chosen a linear calibration plot was obtained in the range 1.0 x 10(-7)-1.0 x 10(-3) mol L(-1) and the detection limit was 1.2 x 10(-8) mol L(-1). Interference from AA was effectively eliminated and the sensitivity, selectivity, stability, and reproducibility of the electrodes was excellent for determination of DA.

Electrochemical impendence spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed to investigate the barrier properties and electron transfer of derivatized thiol self-assembled monolayers (SAMs) on gold in the presence of surfactants. The thiol derivatives used included 2-mercaptoethanesulfonic acid (MES), 2-mercaptoacetic acid (MAA), and N-acetyl-L-cysteine (NAC). A simple equivalent circuit was derived to fit the impedance spectra very well. The negative redox probe [Fe(CN)6](3-/4-) was selected to indicate the electron-transfer efficiency on the interface of the studied electrodes. It was found that by changing the surface structure of SAMs, different surfactants could regulate the barrier properties and electron-transfer efficiency in different ways. A positively charged surfactant lowered the electrostatic repulsion between the negative redox probe and negatively charged surface groups of a monolayer, while enhancing the reversibility of electron transfer by virtue of increasing the redox probe concentration within the electric double-layer region. A neutral surfactant showed no significant effect, while a negative surfactant hindered the access and reaction of redox probe by electrostatic repulsion of same-sign charges.

The inhibitive effect of static magnetic field on the activity of lysozyme was studied using acoustic wave impedance analysis technique. Equivalent circuit parameters of piezoelectric quartz crystal (PQC) were obtained and discussed. The results showed that the activity of lysozyme was inhibited due to the effect of static magnetic field and the inhibitive effect becomes greater with an increase in magnetization time or magnetic field intensity. According to the response characteristics of motional resistance change (deltaR1), which is related to the change in the bacterial number, a quantitative response model reflecting the activity of lysozyme was theoretically derived. By fitting deltaR1 versus time curves under a specific magnetic field intensity but different magnetic time to the model, the relationship between K1 reflecting the activity of lysozyme and magnetic time t(m) was established. Based on the relationship, a new impedance response model that indicates the inhibitive influence of the magnetization time on the activity of lysozyme was derived as follows: deltaR1 = R0((K4(exp[K0exp(-0.26t(m))]t - 1) + 1)1/2 - 1). Similarly, another response model that indicates the effect of magnetic field intensity was derived as follows: deltaR1 = R0((K4(exp(K0 exp(- 5.17B)t) - 1) + 1)1/2 - 1).

A new antibody immobilization strategy was proposed for the fabrication of a label-free capacitive immunosensor based on electrodeposition of nanometer-sized bioactive hydroxyapatite (HAP). By a procedure of constant current cathodal electrodeposition, a nano-HAP film with bioactivity was formed on a self-assembled β-mercaptoethanol monolayer-modified gold electrode. A suitable amount of chitosan was added into the electrodeposition solution with the aim of obtaining a strong and homogeneous HAP-coating film. After blocking with long-chain alkylthiol and then embedding antibody by coupling with divinylsulphone, the electrode was possessed of a higher initial capacitance value, which was suitable for capacitive transduction. The sensitive layer was characterized by Fourier transform infrared spectrum, scanning electron microscopy and electrochemical method. Human transferrin immunoassay was selected as the testing system. The linear response range of the sensor for transferrin was between 1 and 100 ng/mL with a detection limit of 0.15 ng/mL. After simply rinsing with subacidity solution, the regenerated sensor achieved up to 10 assay cycles without significant loss of sensitivity.

A novel voltammetry with a modified gold electrode for the direct determination of copper in environmental samples, without any pretreatment, is proposed in this paper. A porous disorganized monolayer was formed on the surface of the gold electrode by the self-assembly of mercaptoacetic acid (MAA), which could selectively permeate small molecules. Subtractive square wave anodic stripping voltammetry (SASV) was applied to determine copper, in which the underpotential deposition (UPD) of copper was used as the deposition step. The linear range was from 8 x 10 - 7 to 1 x 10 - 5 mol I-' by the modified electrode in the presence of human serum albumin, and the determination was not interfered with common metal ions. Copper in a real environmental sample was successfully detected.

A sensitive and selective amperometric glucose biosensor based on platinum microparticles dispersed in nano-fibrous polyaniline (PANI) was investigated. Poly (m-phenylenediamine) (PMPD), which was employed as an anti-interferent barrier and a protective layer to platinum microparticles, was deposited onto platinum-modified PANI in the presence of glucose oxidase. The morphology of PANI, Pt/PANI and PMPD-GOD/Pt/PANI were investigated by scanning electron microscopy. The results show that PANI has a nano-fibrous morphology. The enzyme electrode exhibits excellent response performance to glucose with linear range from 2 x 10(-6) to 12 x 10(-3) M and fast response time within 7s. Due to the selective permeability of PMPD, the enzyme electrode also shows good anti-interference to uric acid and ascorbic acid. The Michaelis-Menten constant km and the maximum current density imax of the enzyme electrode were 9.34 x 10(-3) M and 917.43 microA cm(-2), respectively. Furthermore, this glucose biosensor also has good stability and reproducibility.

The effect of magnetic field on the growth of bacteria was studied with the series piezoelectric quartz crystal (SPQC) sensing technique. The growth situations of Escherichia coli (E. coli) in the absence and presence of different intensities of static magnetic fields were examined and analyzed. The results showed that the growth of E. coli was inhibited due to the presence of magnetic fields. By fitting frequency shift (deltaD) versus time curves according to the frequency shift response equation of SPQC, the relationships between three kinetic growth parameters, i.e., the asymptote A, the maximum specific growth rate mu(m) and lag time lambda, and magnetic field intensity were established. Based on these results, a new response model containing the magnetic field intensity was derived as: delta(f) = 167.7 (7.25 - 7.11B)/[1 + exp[4 x 2.46e(-3.97B)/(7.25 -7.1 IB)] x (4.42 + 16.46B - t) + 2]] The kinetic parameters of bacterial growth obtained from this model are close to those obtained from the logistics popular growth model, in which the concentration of the bacteria was determined by the traditional pour plate count method.

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.

A novel method for monitoring, in real time, the formaldehyde (FA)-induced DNA–protein cross-linking process with the piezoelectric quartz crystal impedance (PQCI) technique is proposed. The method was used to monitor FA-induced DNA–lysozyme cross-link formation. Lysozyme was directly immobilized on the silver electrode surface of a piezoelectric quartz crystal by adsorption. The lysozyme-coated piezoelectric sensor was in contact with FA and DNA solutions. The time courses of the resonant frequency and equivalent circuit parameters of the sensor during the cross-linking were simultaneously obtained and are discussed in detail. On the basis of the feature of the multi-dimensional information provided by the PQCI technique, it was concluded that the observed frequency decrease could be mainly ascribed to the mass increase resulting from the cross-linking. According to the frequency decrease with time, the kinetics of the cross-linking process were quantitatively studied. A piezoelectric response model for the cross-linking was theoretically derived. Fitting the experimental data to the model, the kinetic parameters, such as the binding and dissociation rate constants (k1 and k−1) and the cross-linking equilibrium constant (Ka), were determined. At 37 °C, the k1, k−1 and Ka values obtained were 7.0 (±0.1) × 10−5 (μg ml−1)−1 s−1, 6.6 (±0.1) × 10−3 s−1 and 1.06 (±0.02) × 10−2 (μg ml−1)−1, respectively.

The adsorption of human serum albumin (HSA) and bovine serum albumin (BSA) from PBS (pH 7.4) onto bare and polystyrene (PS)-modified silver electrodes was in situ monitored using quartz crystal impedance analysis. The adsorption characteristics of HSA and BSA were discussed by analyzing piezoelectric parameter simultaneous responses. Experimental results indicated that for both HSA and BSA, the amount adsorbed on bare silver was more than that on PS-modified surface. The BSA amount adsorbed on the two surfaces was more than that of adsorbed HSA. A kinetic model was developed to describe the adsorption process and fitted to the experimental data of frequency shift. It was shown that HSA adsorption could be described by a kinetic equation involving two consecutive reactions. At lower concentration, BSA adsorption only involved the first reaction. At higher concentration, BSA adsorption on PS-modified surface involved two consecutive reactions. All fitted results were well in agreement with the corresponding experimental results. The regression values of reaction rate constants for the HSA and BSA adsorption were obtained. These data exhibited difference in adsorption kinetics under different conditions.

A new quartz crystal impedance hyaluronidase sensing technique, which is based on the changes in viscosity and density during the enzymatic hydrolysis of chondroitin sulfate (CS) by hyaluronidase (HAse), is established in this paper. The variations of equivalent circuit parameters of the piezoelectric quartz crystal (PQC) during the enzymatic degradation are discussed. The initial hydrolysis rate of CS by HAse is obtained from the changes in viscosity and density with incubation time. Kinetic parameters (the Michaelis constant K m and the maximum hydrolysis rate V max ) of the degradation process are estimated by using a linear method of Lineweaver-Burk plot. K m is 2.73 ± 0.20 mg·ml −1 and V max is -(5.43 ± 0.38) × 10 −4 kg·m −2 ·s −1/2 ·min −1.