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In this paper, we described a novel sensor based on tiron-doped polypyrrole and carbon nanotubes (CNTs) fabricated on low resistance monolayer-modified glassy carbon electrode. First, the dodecylamine monolayer was chemically modified. Second, CNTs were controllably adsorbed onto dodecylamine. Then, tiron doped polypyrrole was electro-deposited on the CNTs film. The layer-by-layer modified electrode was sensitive to dopamine, while it made no response to even high concentration of ascorbic acid. Parameters influencing the dopamine response were optimized. High performance of the sensor was obtained, such as wide concentration range, low detection limit (3 nM), low background current, high stability, and reproducibility.

A new composite film comprising cationic gemini surfactant butane-α,ω-bis(dimethyl dodeculammonium bromide) (BDDA, C12-C4-C12) and poly (allylamine) hydrochloride(PAH) have been prepared. The composite film showed good biocompatibility and could promote the direct electron transfer between hemoglobin (Hb) and glassy carbon (GC) electrode. The immobilized Hb exhibited a pair of well-defined, quasi-reversible, and stable redox peaks with a formal potential of −0.158 V (vs. SCE) in 0.10 M pH 7 phosphate buffer solutions, and showed high affinity to hydrogen peroxide. The cathodic peak current of the electrode was linear with increasing concentration of H2O2 in the range of 5.14 to 200 μM.

The interaction between urea and guanidinium chloride (GuHCl) on lysozyme refolding was investigated in this work. Live micrococcus lysodeikticus was successfully introduced into a refolding system. Lysozyme can be refolded from the GuHCl-denatured, DTT-reduced state in a good yield of 96.54% at final protein concentration as high as 0.2 mg·mL−1. A model could be employed to elucidate refolding kinetics behavior and the kinetics constants were studied. In the coexistence of GuHCl and urea, the aggregation rate decreased by increasing urea concentration to a proper value. The cooperation of GuHCl and urea not only suppressed the competition of the aggregation reaction but also increased the yield of refolding efficiently.

A new method for monitoring Pseudomonas aeruginosa growth with dimethoate (DMA) as sole carbon using the series piezoelectric quartz crystal (SPQC) and high-performance liquid chromatography (HPLC) was described. Compared with the general methods, SPQC gives real-time, multidimensional information. The determination limit of HPLC was 1.08 ng. A combined novel response model for Pseudomonas aeruginosa degrading DMA was derived. By fitting DMA reducing data, the value of the reduction rate constant (k) was obtained and in line with the actual trend. The proposed kinetic model was successfully applied to Pseudomonas aeruginosa degrading DMA.

Pseudomonas aeruginosa immobilized multiwalled carbon nanotubes were used as a novel kind of solid-phase extraction adsorbents of heavy metals, and the concentration of copper ions in the aqueous solution was obtained with the use of linear sweep anodic stripping voltammetry (LSASV). The adsorption of copper ions was rapid, and equilibrium was attained within 30 min. The combination technique provides fast, real-time information for adsorption process. Based on the electrochemical results, the kinetics and equilibrium were systematically examined. The pseudo-second-order kinetic model was used to correlate the kinetic experimental data, and the kinetic parameters were evaluated. The Langmuir and Freundlich models were applied to describe the adsorption isotherms.

An electrochemical sensor for hydroquinone (HQ) using β‐cyclodextrin/poly(N‐acetylaniline)/carbon nanotube composite (β‐CD/PAA/MWNTs) modified glassy carbon electrode has been successfully developed. Based on the synergistic effect of MWNTs and conducting PAA polymer and the accumulation effect of β‐CD, the analytical response of the β‐CD/PAA/MWNTs film to the electrochemical behavior of HQ was better than that of a β‐CD/PAA film, a PAA/MWNTs film, a PAA film, or a bare glassy carbon (GC) electrode. Under the conditions chosen, the anodic currents increased linearly with HQ concentration from 1×10−6 to 5×10−3 mol l−1 and the detection limit was 8×10−7 mol l−1. This electrochemical sensor showed excellent reproducibility, stability and recovery for the determination of HQ.

A new nanocomposite was developed by combination of prussian blue (PB) nanoparticles and multiwalled carbon nanotubes (MWNTs) in the matrix of biopolymer chitosan (CHIT). The PB and MWNTs had a synergistic electrocatalytic effect toward the reduction of hydrogen peroxide. The CHIT/MWNTs/PB nanocomposite‐modified glassy carbon (GC) electrode could amplify the reduction current of hydrogen peroxide by ∼35 times compared with that of CHIT/MWNTs/GC electrode and reduce the response time from ∼60 s for CHIT/PB/GC to 3 s. Besides, the CHIT/MWNTs/PB nanocomposite‐modified GC electrode could reduce hydrogen peroxide at a much lower applied potential and inhibit the responses of interferents such as ascorbic acid (AA) uric acid (UA) and acetaminophen (AC). With glucose oxidase (GOx) as an enzyme model, a new glucose biosensor was fabricated. The biosensor exhibited excellent sensitivity (the detection limit is down to 2.5 µM), fast response time (less than 5 s), wide linear range (from 4 µM to 2 mM), and ...

A novel approach for the voltammetric determination of Pb2+, Cu2+, and Hg2+ in the presence of macromolecule contaminants was developed. An Au nanoparticles array was directly electrodeposited onto the gold electrode surface followed by a further modification of a mercaptoethanesulfonate (MES) monolayer. Square wave stripping voltammetry (SWSV) of Pb2+, Cu2+, and Hg2+ was performed on the doubly modified electrode. The electrodeposited gold nanoparticles provided a significantly improved sensitivity. Simultaneously, the MES monolayer efficiently prevented the macromolecules accessing the electrode surface. Compared with the bare gold electrode, the doubly modified electrode has the ability to detect metal ions in the presence of macromolecule contaminants, even when their concentration reach 100 ppm. Under the optimal conditions, the detection limits of 0.16, 0.15, and 0.14 ppb for Pb2+, Cu2+, and Hg2+ were obtained, respectively. The calibration graphs were linear in the concentration range of 1...

A new artificial receptor layer was successfully electrosynthesized on the gold electrode to fabricate a chemosensor. Based on the molecular imprinting technique and capacitive transduction, the sensor was applied for herbicide detection. The dielectric property of the receptor layer was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The relative capacitive shift depended on the concentration of mefenacet at the range of 1–50 µM. The kinetic aspects of the recognition process were evaluated. A two‐step kinetic model was derived to describe the recognition process. Fitted results were well in agreement with the corresponding experimental results. The selectivity was evaluated by capacitance selective coefficient of mefenacet and other herbicides. The chemosensor exhibited a selective response to herbicide mefenacet. The nonimprinted polymer modified electrode did not show selective response to mefenacet, thus, indicating that the imprinted polymer acts as recogniti...

A novel process analysis method, with a piezoelectric quartz crystal impedance technique based on the mass effect, for real-time monitoring the activated Bleomycin-induced cleavage of DNA process was proposed. The DNA-coated piezoelectric sensor was in contact with Bleomycin solution at the existence of H2O2 and Fe3+. The optimized experimental condition was determined through the experiments about the effect of pH and ionic strength. The experimental results indicated that activity of Bleomycin is maximal when pH = 8.0 and the ionic strength is low. Under the chosen experimental condition, Bleomycin concentration, which was in the range of 40–250 µg mL−1, had an effect on the interaction, while Fe3+ concentration did not. And then the results about other antibiotics, Cefradine, Streptomycin, Benzylpenicillin, Doxycycline, Acetylspiramycin, showed that these antibiotics did not show the same behavior like Bleomycin.

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.

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.

The hydrolysis of starch by the catalysis of α-amylase was monitored by a network analysis method, resulting in a new method for determination of α-amylase with a Bulk Acoustic Wave (BAW) viscosity sensor. The response of the sensor to the viscosity and density change of this process are measured. The frequency shift during a certain time interval is linearly related to the concentration of α-amylase in the range of 20-500 U.L−1. This method is simple, as no extra reagent such as chromogen or fluorescein is needed. It is fit for the continuous monitoring of the catalytic process and it may also be used to study the dynamics of the process.

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 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.