Electrocatalytic oxidation of guanine and DNA on a carbon paste electrode modified by cobalt hexacyanoferrate films

The electrochemical behavior of cobalt hexacyanoferrate complex adsorbed on a carbon paste electrode (CPE) and its application to the electrocatalytic oxidation of guanine and single-strand DNA (ss-DNA) in aqueous solution are investigated in this report. The modification of CPE by the adsorption of this complex results in excellent amplification of the guanine oxidation response of ss-DNA. The effects of paste composition, scan rate, DNA, and guanine concentration were studied. The detection limits of 52 and 920 ng mL(-)(1) were obtained for guanine and ss-DNA, respectively.     

Adsorption and co-precipitation behavior of arsenate, chromate, selenate and boric acid with synthetic allophane-like materials

Pollution caused by boric acid and toxic anions such as As(V), Cr(VI) and Se(VI) is hazardous to human health and environment. The sorption characteristics of these environmentally significant ionic species on allophane-like nanoparticles were investigated in order to determine whether allophane can reduce their mobility in the subsurface environment at circum-neutral pH condition. Solutions containing 100 or 150 mmol of AlCl₃·6H₂O were mixed to 100 mmol of Na₄SiO₄ and the pH were adjusted to 6.4 ± 0.3. The mineral suspensions were shaken for 1 h and incubated at 80 °C for 5 days. Appropriate amounts of As, B, Cr and Se solutions were added separately during and after allophane precipitation. The results showed that As(V) and boric acid can be irreversibly fixed during co-precipitation in addition to surface adsorption. However, Cr(VI) and Se(VI) retention during and after allophane precipitation is mainly controlled by surface adsorption. The structurally fixed As(V) and boric acid were more resistant to release than those bound on the surface. The sorption characteristics of oxyanions and boric acid were also influenced by the final Si/Al molar ratio of allophane in which Al-rich allophane tend to have higher uptake capacity. The overall results of this study have demonstrated the role of allophane-like nanoparticles and the effect of its Si/Al ratio on As, B, Cr and Se transport processes in the subsurface environment.     

Electrogenerated chemiluminescence DNA biosensor based on hairpin DNA probe labeled with ruthenium complex

A highly selective electrogenerated chemiluminescence (ECL) biosensor for the detection of target single-strand DNA (ss-DNA) was developed using hairpin DNA as the recognition element and ruthenium complex as the signal-producing compound. The ECL-based DNA biosensor was fabricated by self-assembling the ECL probe of thiolated hairpin DNA tagged with ruthenium complex on the surface of a gold electrode. In the absence of target ss-DNA, the ECL probe immobilized on the surface of the electrode was in the folded configuration in which its termini were held in close proximity to the electrode, and thus a strong ECL signal could be generated. In the presence of target ss-DNA, a stem-loop of the ECL probe on the electrode was converted into a linear double-helix configuration due to hybridization, resulting in the tag moving away from the electrode surface, which in turn decreased the ECL signal. The ECL intensity of the DNA biosensor generated a "switch off" mode, which decreased with an increase of the concentration of target DNA, and a detection limit of 9 x 10(-11) M complementary target ss-DNA was achieved. Single mismatched target ss-DNA was effectively discriminated from complementary target ss-DNA. The effect of different loop lengths of the hairpin DNA on the selectivity of the ECL DNA biosensor has been investigated. This work demonstrated that the sensitivity and specificity of an ECL DNA biosensor could be greatly improved using a hairpin DNA species which has an appropriate stem and loop length as the recognition element.     

DNA-decorated carbon nanotubes for chemical sensing

We demonstrate a new, versatile class of nanoscale chemical sensors based on single-stranded DNA (ss-DNA) as the chemical recognition site and single-walled carbon nanotube field effect transistors (swCN-FETs) as the electronic read-out component. swCN-FETs with a nanoscale coating of ss-DNA respond to gas odors that do not cause a detectable conductivity change in bare devices. Responses of ss-DNA/swCN-FETs differ in sign and magnitude for different gases and can be tuned by choosing the base sequence of the ss-DNA. ss-DNA/swCN-FET sensors detect a variety of odors, with rapid response and recovery times on the scale of seconds. The sensor surface is self-regenerating: samples maintain a constant response with no need for sensor refreshing through at least 50 gas exposure cycles. This remarkable set of attributes makes sensors based on ss-DNA decorated nanotubes very promising for "electronic nose" and "electronic tongue" applications ranging from homeland security to disease diagnosis.     

Allophane nanoclay for the removal of phosphorus in water and wastewater

We have assessed the capacity of an allophane nanoclay to take up phosphorus (P) from aqueous solutions and meatwork effluent. The data of adsorption in aqueous solutions were fitted to the Freundlich equation: q (g/kg) ¼ 5.620C(mg/L)^0.264. The nanoclay effectively removed P from a wide range of concentrations at high solution/nanoclay ratios. This finding together with the low cost and environmentally friendly nature of allophane make this material a superior candidate for the remediation of eutrophic water and the treatment of P-rich effluent and sewage. An added advantage is that allophane does not disperse in water, and hence can be recovered after use.     

Monitoring DNA immobilization and hybridization on surfaces by atomic force microscopy force measurements

DNA immobilization and hybridization was carried out on Au substrates that were modified with mercaptopropanoic acid and then treated with aluminum(III) solution. The positively charged AI(III) film can be used to immobilize both ds-DNA and ss-DNA. Atomic force microscopy (AFM) was used to monitor the process by force measurements between a negatively charged silica tip and the substrates while immersed in dilute electrolyte. Surface hybridization of ss-DNA produces an increase in the surface charge and surface potential of the substrates, which is reflected by the increasing repulsive force as determined from AFM force-separation curves. A single-base mismatch was detectable in surface hybridization. The AFM force measuring technique was also employed to investigate the interaction of Ru(phen)3(2+) with ss-DNA and ds-DNA. The force measurement results showed that there is a small interaction between Ru(phen)3(2+) and ss-DNA, which was ascribed to the electrostatic binding of Ru(phen)3(2+) to the ss-DNA surface. For ds-DNA, there is a strong interaction which is believed to be due to the association or intercalation of Ru(phen)3(2+) with ds-DNA.     

Influence of sulfur-crosslinking in vulcanized rubber chips on mercury(II) removal from contaminated water

The adsorption of Hg(II) by natural rubber chips was investigated. First, the effect of chip size (5 mmx5 mm and 10 mmx10 mm) on the adsorption kinetics was studied. The pseudo-second-order modeling was found to explain the kinetics well. The smaller chips had higher adsorption rate so they were used for the rest of the research. Next the effects of sulfur, zinc oxide and carbon black on the adsorption capacity of Hg(II) at equilibrium conditions were investigated. The effect of sulfur was studied through different standard vulcanizing systems. The amount of zinc oxide was varied to be 3, 4 and 5 part per hundred parts of rubber (phr) while the carbon black (N-330) loading was varied to be 0, 30 and 50 phr, respectively. It was found that adsorption capacity increased with the degree of crosslink density, generated by sulfur reacting with rubber molecules. In addition, the adsorption capacities of various amounts of zinc oxide corresponded with their crosslink densities while the addition of carbon black seemed to obstruct Hg(II) adsorption.     

A comparative study of natural, formaldehyde-treated and copolymer-grafted orange peel for Pb(II) adsorption under batch and continuous mode

Natural, formaldehyde-treated and copolymer-grafted orange peels were evaluated as adsorbents to remove lead ions from aqueous solutions. The optimum pH for lead adsorption was found to be pH 5. The adsorption process was fast, reaching 99% of sorbent capacity in 10 min for the natural and treated biomasses and 20 min for the grafted material. The treated biomass showed the highest sorption rate and capacity in the batch experiments, with the results fitting well to a pseudo-first order rate equation. In the continuous test with the treated biomass, the capacity at complete exhaustion was 46.61 mg g(-1) for an initial concentration of 150 mg L(-1). Scanning electronic microscopy and energy dispersive X-ray spectroscopy indicated that the materials had a rough surface, and that the adsorption of the metal took place on the surface. Fourier transform infrared spectroscopy revealed that the functional groups responsible for metallic biosorption were the -OH, -COOH and -NH(2) groups on the surface. Finally, the thermogravimetric analysis indicates that a mass reduction of 80% can be achieved at 600 degrees C.     

Direct DNA hybridization detection based on the oligonucleotide-functionalized conductive polymer

Electrochemical methods for DNA hybridization detection have many advantages that are very fast to detect hybridization and can be directly applied for a portable DNA sensor. In this paper, an electrochemical method to directly detect DNA hybridization was developed on the basis of a new conductive polymer, which was polymerized on the glassy carbon electrode with a terthiophene monomer having a carboxyl group (3'-carboxyl-5,2',5',2"-terthiophene). The ss-DNA probe was made by chemically bonding an amine-linked C6 alkyl group to the 5' terminus of oligonucleotide (19-mer). The probe moiety was immobilized on the polymer through covalent bonding with a catalyst, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. A difference in admittance was observed before and after hybridization as a result of the reduction of the resistance after hybridization. The highest difference in admittance was observed around 1 kHz before and after hybridization. Hybridization amounts of end two-base and center one-base mismatched sequences were obtained only in a 14.3% response when compared to that for the complementary matched sequence.     

Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution

An Australian natural zeolite was collected, characterised and employed for basic dye adsorption in aqueous solution. The natural zeolite is mainly composed of clinoptiloite, quartz and mordenite and has cation-exchange capacity of 120 meq/100g. The natural zeolite presents higher adsorption capacity for methylene blue than rhodamine B with the maximal adsorption capacity of 2.8 x 10(-5) and 7.9 x 10(-5)mol/g at 50 degrees C for rhodamine B and methylene blue, respectively. Kinetic studies indicated that the adsorption followed the pseudo second-order kinetics and could be described as two-stage diffusion process. The adsorption isotherm could be fitted by the Langmuir and Freundlich models. Thermodynamic calculations showed that the adsorption is endothermic process with Delta H(0) at 2.0 and 8.7 kJ/mol for rhodamine B and methylene blue. It has also found that the regenerated zeolites by high-temperature calcination and Fenton oxidation showed similar adsorption capacity but lower than the fresh sample. Only 60% capacity could be recovered by the two regeneration techniques.     

Thorium removal by different adsorbents

The removal of radiotoxic Th(4+) from aqueous solutions has been explored using two different groups of adsorptive materials (e.g. two activated carbons and four zeolites-two natural and two synthetic). The activated carbons were prepared from solvent extracted olive pulp (SEOP) and olive stone (OS) by a two-step physical activation method with steam. They were characterized by N(2) at 77K adsorption, Hg porosimetry and by determination of their iodine number. All carbons prepared are of the H-type (e.g. contain mainly basic surface oxides) confirmed by the results of the Boehm's method. The natural zeolites, clinoptilolite (NaCLI) and mordenite (NaMOR), were pretreated with Na(+) before the adsorption experiments, while the synthetic ones, NaX and NaA, were provided in their commercial sodium form.The natural zeolites, NaCLI and NaMOR, utilized 11.5 and 38.6% of the theoretical ion-exchange capacity, based on Al content, respectively, while NaX and NaA utilized 41.5 and 45.9%, respectively. The activated carbons showed better removal capability than NaCLI. NaMOR, showed comparable results to the carbon originated from OS, but lower removal capability than the carbon originated from SEOP. The synthetic zeolites showed the highest removal ability for thorium ions due to their increased ion-exchange capacity because of their cleaner and larger framework channels and their higher number of ion-exchange sites. The carbons adsorption capacity mainly depends on the content and nature of functional surface groups. The adsorption data were fitted to Langmuir and Freundlich models. The former achieved best fits and was further applied to obtain the respective Langmuir constant and maximum adsorption capacity for each system.     

微波模板交联壳聚糖吸附剂对镉离子的吸附机理

通过IR、XPS及化学分析方法研究了微波模板法交联壳聚糖吸附剂(CCTSCd)对Cd2+的吸附机理及其选择记忆性。IR谱图表明,模板法保护了一部分氨基,未与Cd2+发生配位作用的一部分活性氨基参与了交联反应。对比吸附前后CCTSCd的XPS谱图,CCTSCd中O1s和C1s的结合能基本没有变化,N1s和Cd(II)Cd3d 5/2和Cd3d 3/2的特征峰发生化学位移,通过分峰拟合分析,Cd2+与CCTSCd中-NH2基团发生了配位反应。CCTSCd对Cd2+吸附符合Freundlich吸附等温方程。     

The Effect of Mechanochemical Treatments on Clay Minerals and the Mechanochemical Adsorption of Organic Materials onto Clay Minerals

The present paper reviews investigations on the mechanochemical reactions occurring during the grinding of kaolinite and the mechanochemical adsorption of polar organic compounds by expanding and nonexpanding clay minerals, carried out in our laboratory by IR spectroscopy, supplemented by XRD and TG-DTA techniques. Kaolinite was ground in the absence and presence of diluents (alkali halides) and IR spectra were recorded after different grinding periods. The mechanochemical reactions can be classified into four groups, diffusion of atoms (mainly protons, "prototropy"), delamination, layer breakdown, and adsorption of atmospheric water by the amorphous product. In the mechanochemical adsorption study of phenol and dichlorophenol by smectites (montmorillonite, beidellite, saponite, and Laponite), the mineral was ground with excess phenol. Spectra of ground phenol–smectite mixtures were recorded in KBr disks, after leaving the disks for 3 days in a vacuum furnace at 115°C for the evolution of the excess phenol. In most cases, the first 5 min of grinding led to an increase in the adsorption of phenol. An additional 5 min of grinding resulted in a decrease of the phenol adsorption. In the mechanochemical adsorption study of stearic acid by nonexpanding clay minerals (sepiolite, playgorskite, talc, pyrophyllite, and allophane), the mineral was treated with molten acid. Disks were prepared with NaCl, KCl, and CsCl. Each disk was crushed, reground, and repressed an additional four times. Grinding the products converted some of the adsorbed acid into the stearate anion.     

Detection of human papilloma viruses using nanostructurated silicon support in microarray technology

In a typical microarray experiment, DNA is arrayed on a solid substrate as spots, the array being probed with a sample or a capture molecule of interest and the interaction monitored through different detection methods. The present study evaluates the possibility to use micro-array technology to genotype samples with Human Papilloma Viruses (HPV). The performance of DNA microarrays strongly depend on their surface properties. The efficiency of DNA immobilization in terms of sensitivity and specificity is one of the most important step in obtaining a microarray chip for diagnosis of HPV family viruses. Here we report the preparation and evaluation of nano-porous silicon surfaces for HPV detection based on DNA micro-array technique. Two different surfaces based on similar porous structure chemically modified in order to efficiently immobilize ss-DNA specific for HPV viruses were investigate.     

多功能壳聚糖水凝胶医用材料的功能性研究

作为一类兼具应用价值和经济效益的新型功能高分子材料,水凝胶越来越受关注。以天然可降解的壳聚糖为载体,通过自由基接枝共聚法制备了壳聚糖水凝胶,重点研究了其吸附性及药物控释性能。结果表明:该水凝胶20d左右可以完全降解,降解性能良好。在25℃条件下,铜离子浓度为1200mg/L时,壳聚糖水凝胶对铜离子的平衡吸附量可达225.8mg/g。以亚甲基蓝为药物模型的控释实验结果表明,温度以及初始药物投加量对控释性能影响较大,48h累积释放率达70%左右,可在一定程度上实现缓释控释效果。     

Electronic detection of target nucleic acids by a 2,6-disulfonic acid anthraquinone intercalator

A DNA hybridization biosensor based on long-range electron transfer that is capable of detecting DNA single-base mismatch is presented. A mixed self-assembled monolayer of single-stranded DNA (ss-DNA), thiolated at the 3' end, and 6-mercapto-1-hexanol was formed on a gold surface. This probe ss-DNA-modified gold surface was incubated in 2,6-disulfonic acid anthraquinone (AQDS) intercalator solution, rinsed, and placed in an AQDS-free buffer solution, whereupon voltammetric experiments were performed. No voltammetric peaks were observed for probe ss-DNA-modified gold electrodes. Upon DNA hybridization and incubation in AQDS, clear voltammetric peaks, consistent with the oxidation and reduction of AQDS, were observed. The absence of AQDS electrochemistry for ss-DNA-modified surfaces clearly shows the electrochemistry is due to long-range electron transfer through the DNA duplex. No peak currents were observed when the probe ss-DNA-modified surface was exposed to noncomplementary target DNA, but there was a diminution in current signal upon hybridization with C-A mismatched and a G-A mismatched targets.     

Separation of double- and single-stranded DNA restriction fragments: capillary electrophoresis with polymer solutions under alkaline conditions.

Capillary electrophoresis in buffers containing hydroxyethyl cellulose (HEC) was used to separate double- and single-stranded DNA restriction fragments under neutral and alkaline conditions in epoxy-coated capillaries. It was found that better resolution was achieved using highly entangled HEC solutions for a narrow range of DNA fragment sizes, while lower resolution was obtained over a wide separation range using diluted HEC solutions. Optimal resolution of these DNA fragments was obtained using buffers containing 0.5% HEC at pH 11 with plate numbers exceeding 3 x 10(6) plates/m. It was also found that the diffusion coefficients and electrophoretic mobilities of DNA fragments decreased with increasing pH. This may indicate a more extended DNA conformation and, therefore, enhancement of transient entanglement coupling between DNA and HEC polymers under alkaline condition. At pH 12, ss-DNA were well separated in entangled HEC solutions; however, the resolution of ss-DNA was significantly decreased in diluted polymer solution.     

Insights into isotherm making in the sorptive removal of fluoride from drinking water

The defluoridation research has thrown up many technologies, with adsorption as a popular alternative, especially among fluoride endemic habitations of the developing world. In the endeavor to develop novel adsorbents for defluoridation, the adsorption potential of hardened alumina cement granules (ALC) were examined through isotherm fitting. Though the adsorbent showed enhanced adsorption capacity at higher fluoride concentration ranges, the errors associated with linearization in isotherm fitting were also found to be increasing. The propagation of these errors was more prominent in Dubinin-Radushkevich and Langmuir models but negligible in Freundlich. The chi2 analysis, used to correlate the equilibrium experimental data and the isotherm models, also suggested poor correlations at higher fluoride concentration ranges for all the models. The procedure of linear and nonlinear regression through optimization of error functions rendered the 'best-fit' model and optimum model parameters, through sum of normalized error (SNE) values. Though ALC exhibited maximum monolayer adsorption capacity of 34.36 mgg(-1) in concentration variation studies of fluoride in the range of 2.5-100 mg l(-1) in synthetic water, it got reduced to 10.215 mgg(-1) in dose variation studies and further to 0.9358 mgg(-1) in natural ground water. Though Langmuir appeared as the best-fit model in terms of R2 in synthetic studies of different fluoride concentrations, the procedure of linear and nonlinear regression demonstrated that Freundlich was the best-fit. The nonlinear chi2 analysis together with minimum SNE values convincingly demonstrated that the equilibrium studies with dose variations of ALC offers more reliable isotherm parameters than those with high fluoride concentrations. The sorption of fluoride by ALC appeared endothermic with Freundlich adsorption capacity parameter increased from 0.5589 to 0.9939 lg(-1) in natural water and 3.980-7.5198 lg(-1) in synthetic water systems for a rise in temperature from 290 to 310 K. The study deviates from conventional methodologies of relying solely on R2 values in selecting 'best-fit' isotherm model, and basically demonstrates how the optimum model parameters like 'adsorption capacity' evolves through linear and nonlinear regression using error functions.     

Adsorption of duplex DNA on mesoporous silicas: possibility of inclusion of DNA into their mesopores

It is well known that a silica surface cannot adsorb duplex DNA in common aqueous solution (not chaotropic solution) because of the electrostatic repulsion of the silica surface and polyanionic DNA. However, we recently found that when duplex DNA in phosphoric acid form (or in acidic solution) was used, DNA was successfully adsorbed into mesoporous silicas even in low-salt aqueous solution. The adsorption behaviors of DNA into mesoporous silicas were influenced by the pore diameter sizes. Mesoporous silicas with 2.80- or 3.82-nm peak pore diameters adsorbed DNA the best in diluted NaCl solution. Formation of the hydrogen bond between P(O)OH groups in DNA and adsorbed water, SiOH groups, or both on silica surfaces is regarded as a main factor in this adsorption. The coincidence of the pore sizes and DNA diameter realizes this unique adsorption promoted by the effect of encompassing DNA with the inner surface of mesoporous silica. Although there is no clear direct evidence for including duplex DNA in the mesopores yet, this adsorption technique is expected to provide a new tool for DNA science, because DNA in the pore size 2-5 nm in diameter has to be in unusual disentangled thread form.     

Influence of ionic strength in the adsorption and during photocatalysis of reactive black 5 azo dye on TiO2 coated on non woven paper with SiO2 as a binder

Reactive black 5 (RB5), an azo dye, was degraded by using UV-irradiated TiO(2) coated on non woven paper with SiO(2) as a binder. The adsorption capacity of the photocatalyst was studied at natural pH, superior to pH(pzc) of the binder, for various ionic strengths. Different salts such as NaCl, KCl, CaCl(2), LiCl, Ca(NO(3))(2) were used to increase the ionic strength. The presence of salt increased the adsorption capacity. The electrostatic interactions between dye and oxide surface charges (TiO(2)/SiO(2)) is very important in the adsorption phenomena. The effect of the ionic strength of the solution on photocatalyst degradation was studied. The rate of degradation was increased by the presence of salts in the range of the experimental conditions. The increase of the initial decolorization rate was observed in the following order: Ca(2+)>K(+)>Na(+)>Li(+). Experiments with different anions (Cl(-), NO(3)(-)) had shown that nitrate was an indifferent electrolyte for the adsorption and photodegradation of the dye on SiO(2)/TiO(2).