An international comparability study on quantification of total methyl cytosine content

Various methods have been developed for quantitative analysis of DNA methylation. However, there is currently no reference analysis system regarding DNA methylation with which other analytical approaches can be compared and evaluated. A standard measurement system that includes reference methods and reference materials may improve comparability and credibility of data obtained from different analytical environments. In an effort to establish a standard system for measurement of DNA methylation, the Korea Research Institute of Standards and Science (KRISS) coordinated an international comparison study among different national metrology institutes. An initial stage of the study involved an intercomparison regarding quantitative measurement of total methyl cytosine contents in artificially constructed DNA samples. The measurement principle involved measurement of dNMP contents following enzymatic hydrolysis of DNA samples. Results of the study showed good comparability among four of five participants and close agreement with reference values assigned by the coordinating laboratory. Conflicting data from one participant may have resulted from incomplete hydrolysis of samples due to use of insufficient amounts of enzymes. These results indicate that comparable and accurate results can be obtained from different measurement environments if digestion conditions are controlled appropriately and valid calibration systems are employed.     

Electrocatalysis and simultaneous determination of catechol and quinol by poly(malachite green) coated multiwalled carbon nanotube film

Electrochemically active composite film that contains multiwalled carbon nanotubes (MWCNTs), Nafion (NF), and poly(malachite green) (PMG) has been synthesized on glassy carbon electrode (GCE), gold, and indium tin oxide (ITO) electrodes by potentiodynamic method. The presence of MWCNTs in the composite film (MWCNT–NF–PMG) enhances the surface coverage concentration (Γ) of PMG by fivefold. Similarly, an electrochemical quartz crystal microbalance study revealed enhancement in the deposition of PMG at MWCNT–NF film when compared with bare and only NF modified electrodes. The surface morphology of the composite film was studied using atomic force microscopy, which revealed that the PMG incorporated on MWCNT–NF film. The composite film exhibited enhanced electrocatalytic activity toward the mixture of biochemical compounds catechol and quinol. The electrocatalytic responses of analytes at MWCNT–NF–PMG composite film were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From electrocatalysis studies, well-separated voltammetric peaks were obtained at the composite film for catechol and quinol with a peak separation of 147 mV. The sensitivity values of the composite film toward catechol and quinol by the DPV technique were 0.4 and 3.2 mA mM⁻¹ cm⁻², respectively, which are higher than the values obtained by the CV technique. Similarly, the above-mentioned values are better than the previously reported electroanalytical values for the same analytes.     

Nanocomposite of functionalized multiwall carbon nanotubes with nafion, nano platinum, and nano gold biosensing film for simultaneous determination of ascorbic acid, epinephrine, and uric acid

A unique bimetallic, nano platinum (Pt) with nano gold (Au) on nafion (NF) incorporated with functionalized multiwall carbon nanotubes (f-MWCNTs) composite film (f-MWCNTs-NF-PtAu) was developed by the potentiostatic method. The composite film exhibits promising efficient catalytic activity towards the oxidation of mixture of biochemical compounds and simultaneous measurement of ascorbate anion, epinephrine and urate anion in aqueous buffer solution (pH 6.75). Both, the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for the measurement of electroanalytical properties of neurotransmitters by means of composite film modified electrodes. Well-separated voltammetric peaks were obtained for ascorbate, epinephrine and urate anions with the peak separations of 0.222 and 0.131V. The composite film can also be produced on gold and transparent semiconductor indium tin oxide electrodes for different kinds of studies such as electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The incorporation of Pt and Au onto the f-MWCNTs-NF was revealed by the EQCM technique and the morphology of the film was studied using SEM, AFM and scanning electrochemical microscopy (SECM) techniques. Further, extensive studies were carried out using SECM for obtaining the surface current topographic images of composite film modified electrodes, and these indicated the presence of f-MWCNTs-NF-PtAu composite film on the electrode.     

An amperometric cholesterol biosensor based on multiwalled carbon nanotubes and organically modified sol-gel/chitosan hybrid composite film

A new type of amperometric cholesterol biosensor based on sol-gel chitosan/silica and multiwalled carbon nanotubes (MWCNTs) organic-inorganic hybrid composite material was developed. The hybrid composite film was used to immobilize cholesterol oxidase on the surface of Prussian blue-modified glass carbon electrode. Effects of some experimental variables such as enzyme loading, concentration of Triton X-100, pH, temperature, and applied potential on the current response of the biosensor were investigated. Analytical characteristics and dynamic parameters of the biosensors with and without MWCNTs in the hybrid film were compared, and the results show that analytical performance of the biosensor can be improved greatly after introduction of the MWCNTs. Response time, sensitivity, linear range, limit of detection (S/N=3), and apparent Michaelis-Menten constant Km are 25s, 0.54 microA mM(-1), 8.0 x 10(-6) to 4.5 x 10(-4) M, 4.0 x 10(-6) M, and 0.41 mM for the biosensor without MWCNTs and 13 s, 1.55 microA mM(-1), 4.0 x 10(-6) to 7.0 x 10(-4) M, 1.0 x 10(-6) M, and 0.24 mM for the biosensor with MWCNTs, respectively. The activation energy of the enzyme-catalyzed reaction was measured to be 42.6 kJ mol(-1). This method has been used to determine the free cholesterol concentration in real human blood samples.     

Vitamin B(12) incorporated with multiwalled carbon nanotube composite film for the determination of hydrazine

Electrochemically active composite film containing multiwalled carbon nanotubes (MWCNTs) and vitamin B₁₂ was synthesized on glassy carbon, gold, and indium tin oxide electrodes by the potentiodynamic method. The presence of MWCNTs in the composite film (MWCNT–B₁₂) modified electrode mediates vitamin B₁₂’s redox reaction, whereas vitamin B₁₂’s redox reaction does not occur at bare electrode. The electrochemical impedance spectroscopy studies reveal that MWCNTs present in MWCNT–B₁₂ film enhance electron shuttling between the reactant and electrode surface. The surface morphology of bare electrode, MWCNT film. and MWCNT–B₁₂ composite film was studied using atomic force microscopy, which reveals vitamin B₁₂ incorporated with MWCNTs. The MWCNT–B₁₂ composite film exhibits promising enhanced electrocatalysis toward hydrazine. The electrocatalysis response of hydrazine at MWCNT film and MWCNT–B₁₂ composite film was measured using cyclic voltammetry and amperometric current–time (i–t) curve techniques. The linear concentration range of hydrazine obtained at MWCNT–B₁₂ composite film using the i–t curve technique is 2.0 μM–1.95 mM. Similarly, the sensitivity of MWCNT–B₁₂ composite film for hydrazine determination using the i–t curve technique is 1.32 mA mM⁻¹ cm⁻², and the hydrazine’s limit of detection at MWCNT–B₁₂ composite film is 0.7 μM.     

Direct electrochemistry and electrocatalytic activity of catalase incorporated onto multiwall carbon nanotubes-modified glassy carbon electrode

The direct voltammetry and electrocatalytic properties of catalase, which was adsorbed on the surface of multiwall carbon nanotubes (MWCNTs), was investigated. A pair of well-defined and nearly reversible cyclic voltammetry peaks for Fe(III)/Fe(II) redox couple of catalase adsorbed on the surface of MWCNTs at approximately -0.05 V versus reference electrode in pH 6.5 buffer solution, indicating the direct electron transfer between catalase and electrode. The surface coverage of catalase immobilized on MWCNTs glassy carbon electrode was approximately 2.4x10(-10) molcm-2. The transfer coefficient (alpha) was calculated to be 0.4, and the heterogeneous electron transfer rate constant was 80 s-1 in pH 7, indicating great facilitation of the electron transfer between catalase and MWCNTs adsorbed on the electrode surface. The formal potential of catalase Fe(III)/Fe(II) couple in MWCNTs film had a linear relationship with pH values between 2 and 11 with a slope of 58 mV/pH, showing that the electron transfer is accompanied by single proton transportation. Catalase adsorbed on MWCNTs exhibits a remarkable electrocatalytic activity toward the reduction of oxygen and hydrogen peroxide. The value for calculated Michaelis-Menten constant (1.70 mM) was high, indicating the potential applicability of the films as a new type of reagentless biosensor based on the direct electrochemistry of the catalase enzyme.     

Electrochemical nitrite biosensor based on the immobilization of hemoglobin on an electrode modified by multiwall carbon nanotubes and positively charged gold nanoparticle

The report is on an electrochemical biosensor with remarkably improved sensitivity toward nitrite. In this strategy, positively charged gold nanoparticle (PCNA) is used in combination with multiwall carbon nanotubes (MWCNT) by electrostatic adsorption for fabricating PCNA/MWCNT films. Then hemoglobin (Hb) biocatalyst will easily be attached to the surface of the combination films aforementioned. After that, the Hb/PCNA films are immobilized onto the Hb/PCNA/MWCNT films through layer-by-layer assembly technique. The (Hb/PCNA)₂/MWNT/GC electrode thus prepared exhibits enhanced electrocatalytic behavior to the reduction of nitrite at −0.10 V versus SCE in 0.05 M H₂SO₄ solution_. On condition of the low detecting potential and low pH, interference caused by direct electrochemical oxidation or oxidizable substances can be prevented. Therefore, the modified electrode shows fast response time, very high sensitivity, good selectivity and stability. The current response of the sensor increases linearly with nitrite concentration from a range of 3.6 × 10⁻⁶ to 3.0 × 10⁻³ M with a detection limit(S /N = 3) of 9.6 × 10⁻⁷ M.     

Effect of electrode surface properties on enhanced electron transfer activity in microbial fuel cells

The influence of electrode surface chemistry over biofilm growth was evaluated for photo‐bioelectrocatalytic fuel cell. A consortium of photosynthetic bacteria was grown onto different electrodes designed with polyethylenimine (PEI) and multiwall carbon nanotubes as hydrophilic and hydrophobic modifier, respectively. The designed electrodes were loaded with 0.08, 0.17, and 0.33 μg/cm² of PEI to change the hydrophilicity. However, 0.56, 0.72, and 0.83 mg/cm² of multiwall carbon nanotubes were used to alter the hydrophobicity of the electrodes. The surface chemistry of electrode and bio‐interaction was evaluated as a function of contact angle and biofilm formation. The results were compared with those obtained with a carbon paper electrode. The contact angle on the untreated electrode (carbon paper) was 118°, whereas for hydrophobic and hydrophilic electrodes, the maximum and minimum contact angles were 170° and 0°, respectively. Interestingly, the maximum biofilm growth (0.2275 g, wet basis) was observed on highly hydrophobic surface; however, the maximum electrochemical performance (246 mV) was shown by the most hydrophilic electrode surface. PEI‐based electrode with good biofilm formation showed comparatively higher electrogenic activity.     

Effect of chirality,length and diameter of carbon nanotubes on the adsorption of 20 amino acids: a molecular dynamics simulation study

We carried out molecular dynamics simulations to study the adsorption of all the 20 amino acids (AAs; aromatic, polar and non-polar) on the surface of chiral, zigzag and armchair single-walled carbon nanotubes. The adsorption was occurring in all systems. In the aromatic AAs, the π–π stacking and the semi-hydrogen bond formation cause a strong interaction with the carbon nanotubes (CNTs). We also investigated the chirality, length and diameter dependencies on adsorption energies. We found that all AAs have more tendency to adsorption on the chiral and zigzag CNTs over the armchair. The results show that increasing both the diameter and the length causes the enhancement of the adsorption energy. But, the effect of the length is more than of the diameter. For example, the adsorption energy of Trp on the surface of CNT (4,1), with 2 nm length, is 20.4 kcal/mol. When the length of CNT becomes twice, the adsorption energy increases by 24 ± 0.3%. But by doubling the diameter, the adsorption energy increased only by 9.8 ± 0.25%.     

广西钩藤属植物中总生物碱含量变化研究

对广西不同品种、不同产地、不同部位、不同采收时间的钩藤进行了总生物碱含量变化研究 ,为充分开发利用广西钩藤资源提供了试验依据。     

降解剂对森林凋落物可溶性有机碳含量的影响及凋落物降解模式比较研究

森林凋落物是森林生态系统中可溶性有机碳(DOC)的主要来源,在生态系统碳循环过程中起重要作用。以帽儿山地区胡桃楸、兴安落叶松以及胡桃楸-兴安落叶松人工林凋落物为研究对象,通过液体发酵培养将纤维素高效降解真菌Peniophora intranata与Sarocladium strictum制成单一(A菌剂、B菌剂)及混合菌剂(C菌剂),测定野外条件下经降解剂处理的凋落物基质在不同时期的DOC含量,分析降解剂对不同类型森林凋落物DOC动态变化的影响,并比较各凋落物基质降解模式异同。结果表明：(1)凋落物基质DOC含量在降解剂处理后均随降解时间增加呈下降趋势,且下降幅度大小表现为混合基质>胡桃楸基质>落叶松基质;在最初的1个月,各凋落物基质DOC含量均显著高于其他降解时期DOC含量。(2)经混合菌剂处理后的胡桃楸基质DOC含量相较于2种单一菌剂处理后的胡桃楸基质DOC含量低,而经混合菌剂处理后的兴安落叶松基质与胡桃楸-兴安落叶松基质的DOC含量未表现出相同的显著性。(3)经3种菌剂处理后的胡桃楸基质降解模式均相同,经B菌剂与C菌剂处理的落叶松基质降解模式相同,经A菌剂与C菌剂处理...     

Electrochemical quartz crystal impedance study on the overoxidation of polypyrrole-carbon nanotubes composite film for amperometric detection of dopamine

The electrochemical quartz crystal impedance (EQCI) method was used to study the overoxidation of polypyrrole (PPy)–multiwalled carbon nanotubes (MWCNT) nanocomposite film in neutral and alkaline solutions. The values of molar mass per electron transferred (M/n) obtained during the overoxidation of PPy in 0.10 mol L⁻¹ Na₂SO₄ and 0.20 mol L⁻¹ NaOH aqueous solutions were estimated to be ca. 17 and 22 g mol⁻¹, respectively, suggesting the nucleophilic attack of solution OH⁻ to the pyrrole units during the overoxidation, and the possible partial formation of carboxylic groups after the overoxidation in the NaOH solution. Also, the overoxidized PPy–MWCNT composite film prepared in the NaOH solution showed a notably larger affinity to dopamine (DA) dissolved in a neutral phosphate buffer than that prepared in the Na₂SO₄ solution. The modification of the overoxidized nanocomposite film improved substantially the sensitivity for DA assay in a neutral phosphate buffer, as compared with the modification of overoxidized PPy or MWCNT alone. At a −6 kHz (201-nm thickness) nanocomposite film prepared in a polymerization bath containing 1.0 mg mL⁻¹ MWCNT and overoxidized in 0.20 mol L⁻¹ aqueous NaOH, the peak current response from differential pulse voltammetric assay of DA was linear with DA concentration from 4.0 × 10⁻⁸ to 1.4 × 10⁻⁶ mol L⁻¹, with a lower limit of detection of 1.7 nmol L⁻¹, good anti-interferent ability, as well as good stability and reproducibility.     

An empirical study on the dynamic effect of regional industrial carbon transfer in China

The dynamic trend of regional industrial carbon transfer along with industrial transfers in China is currently a hot topic. To explore this problem, the gravity model has been used to study the spatial distribution of industrial transfer and industrial carbon transfer. The results indicate that both barycenters are moving westward. Based on the STIRPAT model, a system-GMM model was then constructed that introduced the industrial transfer factor and its square to explore temporal changes in regional industrial carbon transfer in the course of industrial transfer. The estimated results revealed that the relationship between industrial transfer and industrial carbon transfer displays an inverted U-shaped pattern. For every 1% increase in industrial transfer, there was a 0.327% increase in industrial carbon transfer before the turning point, but industrial carbon transfer decreased by 0.07% when it passed the “peak”. Because no province had surpassed the turning point, carbon transfer during industrial transfer in China is currently in the growth phase. Moreover, real GDP per capita, industrial structure, and industrial carbon emission intensity promoted carbon emissions reduction in the course of industrial transfer.     

An amperometric biosensor based on horseradish peroxidase immobilized onto maize tassel-multi-walled carbon nanotubes modified glassy carbon electrode for determination of heavy metal ions in aqueous solution

A biosensor for trace metal ions based on horseradish peroxidase (HRP) immobilized on maize tassel-multiwalled carbon nanotube (MT-MWCNT) through electrostatic interactions is described herein. The biosensor was characterized using Fourier transform infrared (FTIR), UV–vis spectrometry, voltammetric and amperometric methods. The FTIR and UV–vis results inferred that HRP was not denatured during its immobilization on MT-MWCNT composite. The biosensing principle was based on the determination of the cathodic responses of the immobilized HRP to H₂O₂, before and after incubation in trace metal standard solutions. Under optimum conditions, the inhibition rates of trace metals were proportional to their concentrations in the range of 0.092–0.55 mg L⁻¹, 0.068–2 mg L⁻¹ for Pb²⁺ and Cu²⁺ respectively. The limits of detection were 2.5 μg L⁻¹ for Pb²⁺ and 4.2 μg L⁻¹ for Cu²⁺. Representative Dixon and Cornish-Bowden plots were used to deduce the mode of inhibition induced by the trace metal ions. The inhibition was reversible and mixed for both metal ions. Furthermore, the biosensor showed good stability, selectivity, repeatability and reproducibility.     

An international collaborative study of the effect of active pertussis toxin on the modified Kendrick test for acellular pertussis vaccines

Speculation that the Japanese modified intra-cerebral challenge assay, which is used in several countries for control of acellular pertussis vaccines, depends on the presence of small amounts of active pertussis toxin led to an assumption that it may not be appropriate for highly toxoided or genetically detoxified vaccines. Consequently, at the recommendation of a World Health Organisation AD Hoc Working Group on mouse protection models for testing and control of acellular pertussis vaccine, the effect of pertussis toxin on the modified intra-cerebral challenge assay (modified Kendrick, MICA) was evaluated in an international collaborative study. Results of this study showed that for genetically detoxified vaccines both with and without active pertussis toxin the MICA clearly distinguished mice vaccinated with acellular vaccines from unvaccinated mice and gave a significant dose–response relationship. However, vaccine samples containing active pertussis toxin (5 or 50 ng/single human dose) appeared to be more potent than the equivalent sample without active pertussis toxin. Similar results were also given by two respiratory infection models (intranasal and aerosol) included in the study. The results also indicated that the effect of pertussis toxin may vary depending on mouse strain.     

Comparison between standard culture and peptide nucleic acid 16S rRNA hybridization quantification to study the influence of physico-chemical parameters on Legionella pneumophila survival in drinking water biofilms

Legionella pneumophila is a waterborne pathogen that is mainly transmitted by the inhalation of contaminated aerosols. In this article, the influence of several physico-chemical parameters relating to the supply of potable water was studied using a L. pneumophila peptide nucleic acid (PNA) specific probe to quantify total L. pneumophila in addition to standard culture methods. A two-stage chemostat was used to form the heterotrophic biofilms, with biofilm generating vessels fed with naturally occurring L. pneumophila. The substratum was the commonly used potable water pipe material, uPVC. It proved impossible to recover cultivable L. pneumophila due to overgrowth by other microorganisms and/or the loss of cultivability of this pathogen. Nevertheless, results obtained for total L. pneumophila cells in biofilms using a specific PNA probe showed that for the two temperatures studied (15 and 20°C), there were no significant differences when shear stress was increased. However, when a source of carbon was added there was a significant increase in numbers at 20°C. A comparison of the two temperatures showed that at 15°C, the total cell numbers for L. pneumophila were generally higher compared with the total microbial flora, suggesting that lower temperatures support the inclusion of L. pneumophila in drinking water biofilms. The work reported in this article suggests that standard culture methods are not accurate for the evaluation of water quality in terms of L. pneumophila. This raises public health concerns since culture methods are still considered to be the gold standard for assessing the presence of this opportunistic pathogen in water.     

长期植稻年限序列水稻土团聚体有机碳分布特征

通过开展有机质物理分组试验,研究了杭州湾南岸不同植稻年限序列水稻土有机碳含量的粒级分布变化特征.结果表明: 各植稻年限耕层水稻土中,土壤团聚体主要分布在微团聚体(<0.25 mm)中,其中大微团聚体(0.053～0.25 mm)随着植稻年限的增加而减少;在微团聚体(0.053~0.25 mm,<0.053 mm)中,有机碳含量随着植稻年限的增加而增加,在0.053～2 mm粒径范围内,各粒级有机碳占总有机碳比例随着粒级的减小而增加,有机碳主要集中在大微团聚体(0.053～0.25 mm)中;随着种植年限的增加,颗粒有机碳含量减少.栽培年限长的水稻土比栽培年限短的水稻土碳封存量大,早期开垦的水稻土仍有很大的固碳潜力.     

基于挺水植物高光谱信息的再生水总氮含量估测——以北京市门城湖湿地公园为例

高光谱信息是探测植物体内氮素含量状况的重要手段,而植物体中的氮素与水体含氮量息息相关.本研究区为以再生水为主要补给水水源的北京门城湖湿地公园,通过获取区内典型的再生水氮净化挺水植物芦苇和香蒲叶片的高光谱数据,并在室内测定对应样点的水体总氮含量指标, 探讨基于典型湿地挺水植物高光谱数据对水体总氮进行遥感探测的可行性.采用4种高光谱参数(光谱指数、归一化差值指数、“三边”参数及吸收特征参数)分别建立一元线性模型、逐步多元回归模型和偏最小二乘模型,根据决定系数(R²)和均方根误差(RMSE)进行模型精度检验.结果表明: 逐步多元回归和偏最小二乘模型的预测精度高于一元线性模型. 3种模型对芦苇的拟合效果均优于香蒲.偏最小二乘模型对芦苇的拟合效果最优(R²=0.854,RMSE=0.647).500～700 nm是反映水氮含量的最佳波段范围,绿峰与红谷反射率的比值与水体总氮含量具有较强的相关性,尤其是吸收特征参数能够较好地预测水体总氮含量.