Enzyme-dispersed carbon-nanotube electrodes: a needle microsensor for monitoring glucose

The preparation of an enzyme-dispersed carbon-nanotube (CNT) electrode, based on mixing glucose oxidase (GOx) within CNT, is described. The new binderless biocomposite was packed within a 21-gauge needle and used for amperometric monitoring of glucose. The resulting microsensor offers a low-potential highly selective and sensitive detection of glucose. The high sensitivity and selectivity are coupled to a wide linear range, prolonged lifetime and oxygen independence. About 80% of the GOx activity is retained during a 24 h thermal stress at 90 degrees C, reflecting the enzyme-stabilization action of CNT. The marked electrocatalytic action towards hydrogen peroxide allows highly selective detection of the glucose substrate at -0.1 V (vs. Ag/AgCl) with no interferences from coexisting ascorbic acid, acetaminophen or uric acid. Linearity prevails up to 40 mM glucose (with analytically useful signals observed up to 0.1 M). Factors affecting the performance of the CNT-based glucose biosensor were assessed and optimized. The attractive performance of the new needle electrode offers great promise for continuous monitoring of glucose in connection to the management of diabetes, and for the biosensing of other metabolites.     

Synthesis of a chitin-based biocomposite for water treatment: Optimization for fluoride removal

The optimum composition of a chitin-based biocomposite was determined based on both its fluoride adsorption capacity and its chemical resistance in acid aqueous solution. Parameters such as the chitin content, additive content, catalyst content, chitin particle size, degree of acetylation of chitin and effect of pH on adsorption were evaluated. It was possible to chemically reinforce chitin while keeping an acceptable fluoride adsorption capacity onto the chitin-based biocomposites. Optimum chitin content (60%) was limited by the polymer-biopolymer anchoring capacity. An amine-based additive was used to improve the biocomposite adsorption capacity; however, its inclusion was not suitable in terms of biocomposite chemical resistance. The chitin particle size had no effect on adsorption capacity, and the degree of acetylation of chitin notably modified biocomposite adsorption capacity. On the other hand, the biocomposite chemical resistance was notably improved compared to pure chitin. The physicochemical properties of the optimum chitin-based biocomposite showed its potential for being used in continuous adsorption processes.     

Cell biosensor for detection of phenol in aqueous solutions

A microbial sensor for concentration measurement of phenol in aqueous solutions has been developed. Phenol-utilizing cellsPseudomonas putida GFS-8 immobilized in poly(vinyl)alcohol cryogel were used as a biological transducer. Relationships between phenol concentration in the activating medium and endogenic cell respiration have been established. Cell respiration and phenol concentration in the assay solution positively correlated at a phenol concentration range of 0.1–2.0 mg/L and were linearly dependent in the range of 0.1–1.0 mg/L. A Clark membrane electrode was the physiochemical transducer. The assay may be completed within 5 min. The cells oxidize phenol, pyrocatechol, mesityl oxide, aniline, and do not react with a number of xenobiotics, sugars, and alcohol. With the exception of aniline, most components found in waste waters from phenol production affect neither the assay process nor the ability of these cells to use phenol as exogenic respiratory substrate. The immobilized cells retained their ability to utilize phenol as an exogenic respiratory substrate for up to 1 mo.     

An amperometric immunosensor based on a conducting immunocomposite electrode for the determination of Schistosoma japonicum antigen.

A renewable amperometric immunosensor based on a graphite-paraffin-Schistosoma japonicum antibody (SjAb) biocomposite electrode has been prepared for the detection of Schistosoma japonicum antigen (SjAg). Competitive ELISA was employed involving HRP-SjAg as a tracer and 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate. The product of an enzyme catalytic reaction was detected at +0.1 V (vs. Ag/AgCl reference electrode) for measuring the amount of HRP-labeled SjAg binding to the electrode surface. The assay conditions were optimized, including the amount of SjAb loading in the electrode and HRP-SjAg in the incubation solution, the pH of the measuring solution and the incubation time. The measuring range was 0.5-30 microg/ml under the optimum conditions. Rabbit serum samples of different infection degree were measured, which demonstrated that the immunosensor meets the demands of clinical analysis. It exhibits some advantages, such as simplicity of fabrication, rapidity of measurement, and satisfactory sensitivity and reproducibility.     

Aptamer-based determination of ATP by using a functionalized impedimetric nanosensor and mediation by a triangular junction transducer

Microchimica Acta - The authors describe an impedimetric nanosensor for aptamer-mediated detection of ATP. A triangular junction of polysilicon substrate is used as a transducer. The aptamer was...     

Enhancing the Efficiency of Anodic Stripping Voltammetry in Systems Permitting a Change of the Solution without Opening the Circuit

A new design for a transducer for voltammetric stripping analysis was proposed. It allows electroaccumulation and electrostripping stages to be carried out in the solutions of different compositions without opening a circuit. The potentialities of the transducer were demonstrated in the analysis of samples containing complex salt and organic matrices without their preliminary mineralization.     

An integrated on-chip sirtuin assay

A microchip-based assay to monitor the conversion of peptide substrates by human recombinant sirtuin 1 (hSIRT1) is presented. For this purpose a fused silica microchip consisting of a microfluidic separation structure with an integrated serpentine micromixer has been used. As substrate for the assay, we used a 9-fluorenylmethoxycarbonyl (Fmoc)-labeled tetrapeptide derived from the amino acid sequence of p53, a known substrate of hSIRT1. The Fmoc group at the N-terminus resulting from solid-phase peptide synthesis enabled deep UV laser-induced fluorescence detection with excitation at 266 nm. The enzymatic reaction of 0.1 U/μL hSIRT1 was carried out within the serpentine micromixer using a 400 μM solution of the peptide in buffer. In order to reduce protein adsorption, the reaction channel was dynamically coated with hydroxypropylmethyl cellulose. The substrate and the deacetylated product were separated by microchip electrophoresis on the same chip. The approach was successfully utilized to screen various SIRT inhibitors.     

Multiwalled Carbon Nanotube Coated on Stainless Steel Wire for Solid-Phase Microextraction of Organochlorine Pesticides in Water

A novel solid-phase microextraction (SPME) fiber was prepared by coating multiwalled carbon nanotube (MWCNTs) on a stainless steel wire, and its characteristics were studied. To evaluate the MWCNTs coating, the fiber was used for the extraction of some organochlorine pesticides (OCPs) from water samples by Headspace SPME (HS-SPME) mode. Potential factors affecting the extraction efficiency such as extraction time, extraction temperature, agitation, ionic strength, desorption temperature, and time were also optimized. Several experiments were carried out by water spiked with target compounds to evaluate the analytical characteristics of the proposed method under optimized conditions. The linearity was from 0.1 to 10 ug/L with the linear correlation coefficients (r) ranging from 0.9956 to 0.9995. The limits of detection (LOD, S/N = 3) for these pesticides were between 0.43 and 2.13 ng/L and the precision (RSD, n = 5) was 2.53–12.25%. When this method was applied for the spiked real river sample, the relative recoveries ranged from 72.4% to 134.7% for the tested OCPs.     

Thermoelectrical micro-calorimetry and microanalysis on free-standing membranes

The heat evolution of exothermic reactions and the thermal response to electrical and chemical heating of small volumes of solids and liquids were studied using thermopiles with free-standing thin-film membranes. Therefore, the adapted layout of a miniaturized absolute radiometer was used. The chosen arrangement is marked by the combination of highly sensitive thermopiles with an extreme reduction of parasitic heat capacity in comparison with conventional calorimeters or sensors. The sample is in contact with the free-standing membrane only, so a very small heat flow to the heat sink of the sensor substrate is guaranteed. A thermopile transducer made from 76 bismuth/antimony thin-film thermocouples was used for the measurement of temperature differences between sample and surroundings. Thin-film heaters of copper and silver were integrated into the microsystem. The average thickness of the whole thin-film system is less than 5 m. Microcalorimetric measurements were carried out in the temperature range 295–373 K, where thermoelectrical transducer signals up to 750 mV were observed. Evaporation, melting, solidification, redox reactions and enzymatic reactions were tested as examples, where a sample quantity in the nmole range was found to be sufficient.     

Electrochemical and microgravimetric studies of poly[3,4-ethylenedioxythiophene]-tyrosinase biocomposite material electrodeposited onto gold electrodes by a sinusoidal voltages method

The electrodeposition of poly(3,4-ethylenedioxythiophene)-tyrosinase (PEDOT-Ty) biocomposite material onto gold electrode has been achieved by means of a sinusoidal voltages (SV) method. The SV method consists in the superimposition of a sinusoidal voltage (sin wave) with fixed frequency and amplitude onto a d.c. potential. The influence of electrochemical parameters like frequency and amplitude of SV signal, d.c. potential value, deposition time, on the electrodeposition process has been investigated. The biocomposite material has been prepared as a thin layer onto quartz crystals coated with gold. The frequency change of the quartz crystal during the electrodeposition of the biocomposite material was recorded simultaneously with the measured current response. The morphology of the deposited PEDOT-Ty coatings was investigated by scanning electron microscopy. The electrochemical behavior of the biocomposite material in aqueous solution was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The use of d.c. potential value of 0.6 V revealed the contribution of the SV component to the electrodeposition process. The PEDOT-Ty modified electrode was used as an electrochemical biosensor in the voltammetric determination of dopamine in the presence of hydroquinone. The analytical performances of the prepared biosensors were also investigated.     

Finite concentration effects on diffusion-controlled reactions

The algorithm by Northrup, Allison, and McCammon [J. Chem. Phys. 80, 1517 (1984)] has been used for two decades for calculating the diffusion-influenced rate-constants of enzymatic reactions. Although many interesting results have been obtained, the algorithm is based on the assumption that substrate-substrate interactions can be neglected. This approximation may not be valid when the concentration of the ligand is high. In this work, we constructed a simulation model that can take substrate-substrate interactions into account. We first validated the model by carrying out simulations in ways that could be compared to analytical theories. We then carried out simulations to examine the possible effects of substrate-substrate interactions on diffusion-controlled reaction rates. For a substrate concentration of 0.1 mM, we found that the diffusion-controlled reaction rates were not sensitive to whether substrate-substrate interactions were included. On the other hand, we observed significant influence of substrate-substrate interactions on calculated reaction rates at a substrate concentration of 0.1M. Therefore, a simulation model that takes substrate-substrate interactions into account is essential for reliably predicting diffusion-controlled reaction rates at high substrate concentrations, and one such simulation model is presented here.     

Green biocomposites of chitosan dispersed in natural rubber matrices,and their urea controlled-release application

A green biocomposite comprising chitosan dispersed in partially cross-linked natural rubber matricesd was prepared. The starting materials and biocomposites were characterized by means of Fourier transform–infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Chitosan was found well dispersed in partially cross-linked natural rubber matrices indicating that natural rubber latex is successfully stabilized by sodium dodecyl sulfate. The swelling study of the biocomposites was carried out in several solvents. The biocomposites were used for the controlled-release of urea. The release behavior was found consistent, controlled, and prolonged over a period of 72 h. The Korsmeyer–Peppas model was applied to the experimental data and the possible release mechanism was found Fickian diffusion, which indicates that the polymer relaxation time is much greater than the characteristic solvent diffusion time.     

Cornstarch/Poly(vinyl alcohol) Biocomposite Blend Films: Mechanical Properties,Thermal Behavior,Fire Retardancy,and Antibacterial Activity

In the present study, biocomposite films of starch/poly(vinyl alcohol) (St/PVA) reinforced with delignified Grewia optiva fiber and methyl methacrylate (MMA) grafted fibers were prepared using citric acid as a plasticizer and glutaraldehyde as the cross-linker. The biocomposite films were subjected to evaluation of mechanical properties, biodegradability, and antibacterial properties. The biocomposite films were characterized by using Fourier transform-infrared (FT-IR) spectrophotometry, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA/DTA/DTG). SEM showed good adhesion between St/PVA blend matrix and fibers. The antimicrobial activity of biocomposite films against pathogenic bacteria such as Staphylococcus aureus and Escherichia coli was also explored. The results confirmed that the biocomposite films may be used for food packaging.     

Cyclizative radical carbonylations of azaenynes by TTMSS and hexanethiol leading to alpha-silyl- and thiomethylene lactams. Insights into the E/Z stereoselectivities

Free-radical mediated cyclizative carbonylations of azaenynes were carried out using TTMSS as a radical mediator to compare the efficiency and the stereochemistry with those using tributyltin hydride. Using a substrate concentration of 0.1 M, the reactions gave good yields of alpha-silylmethylene lactams having four to seven-membered rings. The observed E-diastereoselectivity of the resulting vinylsilane moiety is in sharp contrast to the Z-selectivity observed during the analogous carbonylation using tributyltin hydride. When hexanethiol was used as the radical mediator, alpha-thiomethylene lactams were formed with E-favoring stereoselectivity again. Ab initio and DFT molecular orbital calculations on the stability of E and Z products were carried out for a set of five-membered methylene lactams bearing SnH3, SiH3, and SMe groups. The distinct thermodynamic preference for the Z-isomer was only predicted for the Sn-bearing lactam. A steric effect due to the bulky (TMS)3Si group is proposed for the E-selectivity observed in the TTMSS-mediated reaction.     

电化学还原和羧化肉桂酸乙酯的研究

在一室型电解池中,以MeCN为溶剂,Mg为牺牲阳极,成功地实现了肉桂酸乙酯的电化学还原和羧化。直接电还原生成相应的氢化二聚物和饱和酯。而在CO2氛围下,可以实现相应的电羧化反应,反应的总产率和选择性受各个反应条件的影响,例如电极材料、电解电位、底物浓度和反应温度。在最佳条件（阴极为Ni,电位为-1.7 V,底物浓度为0.1 mol·L-1,温度为-10 ℃）下可以得到78 ％的羧酸化产率。     

In situ electrodeposited nanoparticles for facilitating electron transfer across self-assembled monolayers in biosensor design

Gold nanoparticles (AuNPs) were synthesized in situ and electrodeposited onto Au substrate. The AuNPs modified interface facilitates electron transfer across self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (MUA). After activation of surface carboxyl groups with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide, the interface displayed good stability for immobilization of biomolecules. These modification processes were characterized by contact angle measurement, cyclic voltammetry and electrochemical impedance spectra. The immobilized acetylcholinesterase (AChE), as a model, showed excellent activity to its substrate, leading to a stable AChE biosensor. Under the optimal experimental conditions, the inhibition of malathion on AChE biosensor was proportional to its concentration in two ranges, from 0.001 to 0.1 μg mL⁻¹ and from 0.1 to 25 μg mL⁻¹, with detection limit of 0.001 μg mL⁻¹. The simple method showed good reproducibility and acceptable stability, which had potential application in biosensor design.     

Structure and Properties of Polymer Biocomposite Materials

Results of studying the structure and properties of biocomposite materials are summarized. The materials in question include an enzyme (laccase, peroxidase), an ion- or electron-conducting polymer (Nafion, polymethylpyrrole), and a carbon substrate (compact, disperse). It is shown that the orientation of a large number of enzyme molecules in an enzyme/Nafion composite material on the substrate surface favors direct bioelectrocatalysis. During co-immobilization of an enzyme and polymethylpyrrole, conditions are realized under which the polymer takes part in the electron transfer between the active center of the enzyme and the surface of the electroconducting substrate. A fresh approach to constructing a biocomposite material is developed. The material is based on an extremely finely divided carbon material (colloidal graphite), which ensures a high specific activity of laccase immobilized on it. The size of colloidal-graphite particles is commensurate with that of the laccase molecule, owing to which the enzyme macromolecule is surrounded by carbon particles. As a result, practically all adsorbed enzyme molecules are electrochemically active and participate in direct bioelectrocatalysis.     

多壁碳纳米管固相萃取净化气相色谱法分析蔬菜中有机氯和拟除虫菊酯农药残留

建立了多壁碳纳米管为吸附剂的固相萃取(SPE)净化、气相色谱-电子捕获检测(GC-ECD)测定蔬菜中6种有机氯和7种拟除虫菊酯农药的方法。采用双柱(HP-50和HP-1色谱柱)双检测器进行定性和定量分析。蔬菜样品采用乙腈提取,多壁碳纳米管SPE柱净化,正己烷溶解上样,丙酮-正己烷(7:3, v/v)洗脱,13种农药中有11种农药的添加回收率高于70%。将该净化方法用于荷兰黄瓜、卷心菜、红圣女果、奶油生菜、紫甘蓝、韭菜、大葱和洋葱等样品的净化,与弗罗里硅土SPE柱相比较,净化效果更好,表明多壁碳纳米管具有较强的吸附去除色素的能力,可以避免色素对测定的干扰。     

Bacteria-modified amperometric immunosensor for a Brucella melitensis antibody assay.

A novel amperometric immunosensor setup is described which uses horseradish peroxidase (HRP) as a label in conjunction with a current-based Brucella sensor. The Bacteria modified immunosensor was constructed by using a biocomposite formed by dispersing graphite powder into a mixture of Brucella melitensis and silicate polymer gel. The enzyme-labeled antibody can readily diffuse toward the encapsulated antigen (Brucella melitensis), which retains its binding properties, and the association reaction is easily detected at the surface exposed to the solution. The use of an oaminophenol (o-AP) substrate and amperometric detection at -150 mV (vs. SCE) results in a relatively low detection limit of 3.5 ng/ml and a linear detection range of 3.5 ng/ml to 200 ng/ml. Based on an optimized parameter, the prepared sensor was used to detect the Brucella melitensis antibody in serum samples by using a competitive binding assay. The results demonstrate the feasibility of employing the proposed immunosensor for the detection for Brucella melitensis antibody in a clinical analysis.     

Uniform Surface Oxidation of an Si Substrate by a Planar Modulated Inductively Coupled Thermal Plasma with Molecular Gas Feed

A planar type of inductively coupled thermal plasma (ICTP) with coil current modulation was adopted for large-area rapid surface oxidation of a substrate. The planar ICTP has been developed by the authors for large-area surface modification processing. In addition, coil current modulation was used to control the temperature and chemical reaction fields in the planar ICTP. Firstly, a fundamental study of the operation of the planar modulated ICTP with a substrate was carried out by measuring its electrical properties and the visible light emission in this work. Secondly, spectroscopic observations were carried out to investigate the effect of the coil current modulation on the radiation intensity distribution of spectral lines from the planar ICTP on the substrate. Thirdly, surface oxidation tests were made for Si substrates by irradiation of the planar modulated ICTP at different modulation frequencies and different duty factors. Oxide layer thickness distribution fabricated on the substrate was measured to study the lateral uniformity of the oxidation processing by the modulated planar ICTP. Finally, it was found that adoption of the coil modulation can improve the uniformity of the oxidation processing by the planar modulated ICTP.