Electrochemical detection of DNA damage induced by acrylamide and its metabolite at the graphene-ionic liquid-Nafion modified pyrolytic graphite electrode

A new electrochemical biosensor for directly detecting DNA damage induced by acrylamide (AA) and its metabolite was presented in this work. The graphene-ionic liquid-Nafion modified pyrolytic graphite electrode (PGE) was prepared, and then horseradish peroxidase (HRP) and natural double-stranded DNA were alternately assembled on the modified electrode by the layer-by-layer method. The PGE/graphene-ionic liquid-Nafion and the construction of the (HRP/DNA)(n) film were characterized by electrochemical impedance spectroscopy. With the guanine signal in DNA as an indicator, the damage of DNA was detected by differential pulse voltammetry after PGE/graphene-ionic liquid-Nafion/(HRP/DNA)(n) was incubated in AA solution or AA+H(2)O(2) solution at 37°C. This method provides a new model to mimic and directly detect DNA damage induced by chemical pollutants and their metabolites in vitro. The results indicated that, in the presence of H(2)O(2), HRP was activated and catalyzed the transformation of AA to glycidamide, which could form DNA adducts and induce more serious damage of DNA than AA. In order to further verify these results, UV-vis spectrophotometry was also used to investigate DNA damage induced by AA and its metabolites in solution and the similar results were obtained.     

Pre-treatment of penicillin formulation effluent by advanced oxidation processes

A variety of advanced oxidation processes (AOPs; O3/OH-, H2O2/UV, Fe2+/H2O2, Fe3+/H2O2, Fe2+/H2O2/UV and Fe3+/H2O2/UV) have been applied for the oxidative pre-treatment of real penicillin formulation effluent (average COD0 = 1395 mg/L; TOC0 = 920 mg/L; BOD(5,0) approximately 0 mg/L). For the ozonation process the primary involvement of free radical species such as OH* in the oxidative reaction could be demonstrated via inspection of ozone absorption rates. Alkaline ozonation and the photo-Fenton's reagents both appeared to be the most promising AOPs in terms of COD (49-66%) and TOC (42-52%) abatement rates, whereas the BOD5 of the originally non-biodegradable effluent could only be improved to a value of 100 mg/L with O3/pH = 3] treatment (BOD5/COD, f = 0.08). Evaluation on COD and TOC removal rates per applied active oxidant (AOx) and oxidant (Ox) on a molar basis revealed that alkaline ozonation and particularly the UV-light assisted Fenton processes enabling good oxidation yields (1-2 mol COD and TOC removal per AOx and Ox) by far outweighed the other studied AOPs. Separate experimental studies conducted with the penicillin active substance amoxicillin trihydrate indicated that the aqueous antibiotic substance can be completely eliminated after 40 min advanced oxidation applying photo-Fenton's reagent (pH = 3; Fe(2+):H2O2 molar ratio = 1:20) and alkaline ozonation (at pH = 11.5), respectively.     

Cathodic detection of H2O2 using iodide-modified gold electrode in alkaline media

Oxidative chemisorption and cathodic stripping reductive desorption of iodide have been studied at a smooth polycrystalline gold (Au (poly)) electrode. Potential-dependent surface coverage of iodide has been controlled on the basis of its reductive desoprtion in 0.1 M KOH alkaline media and its quantitative oxidation to aqueous iodates in acidic media. The Au (poly) electrode surface catalyzes the decomposition of H2O2 to O2. Specific adsorption of iodide on the Au electrode inhibits fully the catalytic decomposition and electrochemical oxidation of H2O2 as well as the adsorption of unknown impurities and the oxidative degradation of the electrode surface by H2O2. A quantitative characterization/detection of H2O2 at the iodide-modified Au (poly) electrode in the alkaline media has, thus, been achieved. Performance of the electrode toward the detection of H2O2 with respect to response time and sensitivity as well as operational stability has been evaluated. It has a sensitivity of 0.272 mA cm(-2) mM(-1) in amperometric measurements with a detection limit of 1.0 x 10(-5) M H2O2, and the response time to achieve 95% of the steady-state current is <20 s. The effect of O2 in the air-saturated solution can be minimized by subtracting the additional current for the O2 reduction. Experimental measurements were based upon cyclic voltametric and amperometric techniques.     

抗盐性高吸水性树脂的研制

本文以淀粉为骨架 ,丙烯酸、丙烯酰胺为接枝单体 ,过硫酸钾为引发剂 ,采用高温快速聚合的方法进行高吸水性树脂的制备。通过正交实验确定了最优配方 ,产品吸水率达到 15 5 0 g/ g ,吸盐率为 95 g/ g。     

Electrochemical polymerization of aniline investigated using on-line electrochemistry/electrospray mass spectrometry

A thin-layer electrochemical flow cell coupled on-line with electrospray mass spectrometry (EC/ES-MS) was used to investigate the soluble products from the controlled-potential anodic polymerization of aniline in H(2)O and H(2)O/CH(3)OH (1/1 v/v) with ammonium acetate and acetic acid or ammonium hydroxide as electrolytes (pH 4, 6.5, or 9). At a working electrode (glassy carbon) potential of 1.0 V versus Ag/AgCl, singly protonated aniline oligomers containing as many as 10 aniline units (10-mer) were observed in the ES mass spectra when the polymerization in H(2)O/CH(3)OH at pH 4 was carried out. The abundance of the higher n-mers decreased at higher solution pH and in 100% H(2)O at pH 4. Most of the oligomers were observed in more than one redox state ranging from fully oxidized (all imine nitrogens) to fully reduced (all amine nitrogens). The number of different redox states observed for the n-mers increased with increasing n. The structures of the reduced (m/z 185) and oxidized (m/z 183) aniline dimer ions (head-to-tail, tail-to-tail, or head-to-head) produced from the polymerization of aniline at pH 4, 6.5, and 9 in H(2)O/CH(3)OH were revealed to vary as a function of pH by comparison of their tandem mass spectrometry product ion spectra with the product ion spectra of the dimer standards. EC/ES-MS potential scan experiments, in which the working electrode current and major n-mer ions for n = 2, 3, and 4 were monitored as a function of electrode potential, were used to probe the growth mechanism to higher aniline oligomers. Under the conditions used, the controlled-current electrolytic process inherent to the operation of the ES ion source did not significantly influence the formation or nature of the oligomers observed. Beyond the current application, the results presented here serve to demonstrate the utility of EC/ES-MS as a tool in identifying the initial products of electropolymerization and in studying the products of electrode reactions in general.     

A facile electrochemical method for simultaneous and on-line measurements of glucose and lactate in brain microdialysate with prussian blue as the electrocatalyst for reduction of hydrogen peroxide

This study demonstrates a facile electrochemical method for simultaneous and selective on-line measurements of glucose and lactate in the brain of freely moving rats through integration of selective electrochemical detection with in vivo microdialysis. The selective electrochemical detection is accomplished by using oxidases as the specific sensing unit and prussian blue (PB) as the electrocatalyst for the reduction and thus for the determination of H(2)O(2) generated from the oxidase-catalyzed reactions in terms of its excellent electrocatalytic activity toward H(2)O(2) reduction. The uses of "artificial peroxidase" (i.e., PB) in this work to replace "natural peroxidase" (i.e., horseradish peroxidase) used in the previous on-line electrochemical methods essentially enables the method developed here to be facile but selective for the simultaneous and on-line measurements of glucose and lactate virtually interference-free from ascorbic acid and other electroactive species coexisting in the brain. Moreover, the dual oxidase/PB-based biosensors suffer from little cross-talk and exhibit a good stability and reproducibility. The basal levels of glucose and lactate in the microdialysate from the striatum of the freely moving rats are determined to be 200 +/- 30 and 400 +/- 50 microM (n = 3), respectively. The method demonstrated here is facile but reliable and durable and may find some interesting physiological and pathological applications.     

Hydroquinone as a buffer additive for suppression of bubbles formed by electrochemical oxidation of the CE buffer at the outlet electrode in capillary electrophoresis/electrospray ionization-mass spectrometry

Hydroquinone was found to suppress bubble formation at the outlet electrode of a sheathless capillary electrophoresis/electrospray ionization-mass spectrometer by replacing the oxidation of water (2H2O(1)<-->O2(g) + 4H+ + 4e) with that of more easily oxidized hydroquinone (hydroquinone<-->p-benzoquinone + 2H+ + 2e). Formation of p-benzoquinone replaces the formation of oxygen gas, effectively suppressing gas bubble formation. Several electrode materials, including platinum, gold-coated stainless steel, and stainless steel wires, were tested. However, hydroquinone suppressed bubbles only at the platinum electrode. Combination of the in-capillary electrode sheathless interface using platinum wire, hydroquinone as a buffer additive, and pressure programming at the inlet of the capillary electrophoresis provided a rugged high efficiency interface for analysis of protein digests using CE/ESI-MS.     

Selective permeation of hydrogen peroxide through polyelectrolyte multilayer films and its use for amperometric biosensors.

A platinum electrode was coated with polyelectrolyte multilayer (PEM) films to prepare an amperometric hydrogen peroxide sensor which can be used in the presence of possible interferences such as ascorbic acid, uric acid, and acetaminophen. The PEM films were prepared on the surface of a Pt disk electrode by an alternate deposition of polycation and polyanion from the aqueous solutions through electrostatic force of attraction. The Pt electrodes coated with a poly(allylamine)/poly(vinyl sulfate) or poly(allylamine)/poly(styrenesulfonate) film were used successfully for detecting H2O2 selectively in the presence of the possible interfering agents. It was suggested that H2O2 can diffuse into the PEM film smoothly while the ascorbic acid, uric acid, and acetaminophen cannot penetrate the film by a size exclusion mechanism. On the other hand, the electrodes coated with PEM films containing poly(ethyleneimine) or poly(diallyldimethylammonium chloride) were not useful for the selective determination of H2O2. The results were rationalized based on the different permeability of the films due to the different molecular density or packing in the PEM films. The PEM film-coated electrode was useful for constructing glucose biosensors by coupling with glucose oxidase.     

Selective detection of a catecholamine against electroactive interferents using an interdigitated heteroarray electrode consisting of a metal oxide electrode and a metal band electrode

We developed an interdigitated array electrode (IDAE) consisting of a metal oxide electrode and a metal band heteroelectrode and employed it for the selective detection of catecholamines. We used an indium-tin oxide (ITO) film as the oxidation electrode of the IDAE because the ITO was able to suppress response currents from L-ascorbic acid (AA) and uric acid (UA), which are major electroactive interferents in biological fluids. However, the ITO film also suppresses the reduction of quinones including oxidized catecholamines. We developed a simple technique for fabricating our hetero IDAE, which also preserves the electrochemical properties of the ITO. When we compared hetero ITO-gold, homo ITO-ITO, and carbon-carbon IDAEs, we found that the hetero IDAE provided both high sensitivity and selectivity for DA detection. We achieved high selectivities for DA against AA and UA. The ratios of the response currents of AA and UA to DA were calculated as 6 and 5%, respectively.     

Electron transfer from diamond electrodes to heme peptide and peroxidase

Direct electron transfer from boron-doped diamond electrodes to heme undecapeptide and horseradish peroxidase (HRP) was examined and evaluated for the application to H2O2 biosensors. As-grown and oxygen plasma-treated diamond electrodes on which heme peptide is adsorbed exhibited cathodic current responses to H2O2 on the basis of the direct electron transfer. In a comparative study of carbon electrodes on which heme peptide was adsorbed, an oxygen plasma-treated diamond electrode exhibited responses comparable with those of an edge-oriented pyrolytic graphite (EOPG) electrode, despite much smaller roughness. However, electron transfer to compounds I and II of HRP from the diamond electrodes was much slower than that from EOPG or glassy carbon, suggesting that the pi electrons of an sp2 carbon may play an important role in the direct electron transfer to the heme moiety of HRP. To examine the applicability of heme peptide-modified diamond electrodes to oxidase-based biosensors, anodic current responses of the oxygen plasma-treated diamond electrode to possible interfering agents, ascorbic acid and uric acid, were examined and compared with those of EOPG. Since the diamond electrode exhibited much less sensitivity to those interfering agents, the heme peptide-modified diamond electrode should be a promising H2O2 biosensor for the application to oxidase-based biosensors.     

Polyeugenol-modified platinum electrode for selective detection of dopamine in the presence of ascorbic Acid

A platinum electrode was modified with electropolymerized films of 4-allyl-2-methoxyphenol (eugenol) by its oxidative polymerization from an alkaline solution by cyclic voltammetry. The modified electrode was than used to determine dopamine (DA) in an excess of ascorbic acid (AA) by differential pulse voltammetry. The peak positions as well as relative sensitivity DA/AA were affected by the potential window applied for the polymerization. For polymerization between 0 and 2.2 V, the peak potentials recorded in a phosphate buffer solution (pH 7.4) were -61 and +152 mV vs Ag/AgCl for AA and DA, respectively. After a 5-min equilibration, relative sensitivity DA/AA was 164 and the current sensitivity for DA was 7.9 nA μM(-)(1). The detection limit for S/N = 3 is 0.1 μM. The high selectivity and sensitivity for DA was found to be due to charge discrimination/analyte accumulation and an effect of catalytic mediation of redox sites. Chronocoulometric data reveal that DA is accumulated on the electrode as a monolayer. The electrode is stable, reversible, and free of fouling problems.     

Superoxide dismutase-based third-generation biosensor for superoxide anion

A third-generation biosensor for superoxide anion (O2-) was developed by immobilizing superoxide dismutase (SOD) on a self-assembled monolayer of cysteine on gold electrode; i.e., a SOD/cysteine-modified gold electrode (SOD/Cys/Au) was fabricated. A rapid and direct electron transfer of SOD was realized at the gold electrode by using the cysteine molecule as an electron-transfer promoter. The promoted direct electron transfer of SOD and biomolecular recognition by the exploitation of specific and significant enzyme-substrate reactivity of SOD toward O2- combined with the low operating potential enabled a sensitive measurement of O2-. At SOD/Cys/Au, O2- could be specifically oxidized and reduced to O2 and hydrogen peroxide, respectively, through the inherent catalytic reaction of SOD. This allowed us to measure O2- by polarizing the electrode both anodically and cathodically. We could successfully measure O2- by suitably polarizing the electrode, typically at 300 and -200 mV versus Ag/AgCl without the virtual interference from physiological levels of H2O2, ascorbic acid, uric acid, and metabolites of neurotransmitters. The response mechanism of SOD/Cys/Au to O2- and its sensor characteristics are also presented and discussed.     

Direct electrochemistry and electrocatalytic activity of cytochrome c covalently immobilized on a boron-doped nanocrystalline diamond electrode

Cytochrome c (Cyt c) was covalently immobilized on a boron-doped nanocrystalline diamond (BDND) electrode via surface functionalization with undecylenic acid methyl ester and subsequent removal of the protecting ester groups to produce a carboxyl-terminated surface. Cyt c-modified BDND electrode exhibited a pair of quasi-reversible and well-defined redox peaks with a formal potential (E(0)) of 0.061 V (vs Ag/AgCl) in 0.1 M phosphate buffer solution (pH 7.0) and a surface-controlled process with a high electron transfer constant (ks) of 5.2 +/- 0.6 s(-1). The electrochemical properties of as-deposited and Cyt c-modified boron-doped microcrystalline diamond (BDMD) electrodes were also studied for comparison. Investigation of the electrocatalytic activity of the Cyt c-modified BDND electrode toward hydrogen peroxide (H2O2) revealed a rapid amperometric response (5 s). The linear range of response to H2O2 concentration was from 1 to 450 microM, and the detection limit was 0.7 microM at a signal-to-noise ratio of 3. The stability of the Cyt c-modified BDND electrode, in comparison with that of the BDMD and glassy carbon counterpart electrodes, was also evaluated.     

Simultaneous potentiometric determination of peracetic acid and hydrogen peroxide

A rapid and highly selective potentiometric method for the simultaneous analysis of peracetic acid (PAA) and hydrogen peroxide (H2O2) has been proposed, for the first time, using glassy carbon (GC) as an indicator electrode and I2/I- potential buffer. On the basis of the large difference in the reaction rates of PAA and H2O2 with I-, which was confirmed using stopped-flow spectrophotometry, a transient potential response corresponding to the reactions of the two species with I- was observed. The response times were typically a few seconds and several minutes for PAA and H2O2, respectively. The effects of the concentrations of molybdate catalyst, H+, I2, and I- in the potential buffer on the selectivity as well as the sensitivity were examined. The potential response obtained using the GC indicator electrode was found to be Nernstian over a wide range of their concentrations (typically from micromolar to millimolar) with slopes of 30.5 and 29.5 mV for PAA and H2O2, respectively (in close agreement with the theoretical value, that is, 29.6 mV). O2 was found to have no substantial effect on the potential change at the GC electrode in the present potential buffer.     

A hydrogen peroxide biosensor based on peroxidase activity of hemoglobin in polymeric film

A Hydrogen peroxide (H2O2) biosensor, based on hemoglobin (Hb) and ortho-phenylenediamine (o-PD) gold electrode, was fabricated. Hb was immobilized onto the electrode surface by electrochemical polymerize method with o-PD. The designed biosensor showed a well defined redox peak which was attributed to the direct electrochemical response of Hb. The immobilized Hb exhibited an excellent electrocatalytical response to the reduction of hydrogen peroxide, enabling the sensitivity determination of H2O2. Factors and performances such as pH, potential, influencing the designed biosensor, were studied carefully. The amperometric detection of H2O2 was carried out at -300 mV in phosphate buffer solution (PBS) (0.1 M) with pH 6.0. This biosensor showed a fast amperometric response (less then 5 s) to H2O2. The levels of the (Relative standard deviation) RSDs (< 3.5%) for the entire analyses reflected a highly reproducible sensor performance. Using the optimized conditions, the detection limit of the biosensor was 1 x 10(-7) M and linear range was from 5 x 10(-6) to 1.25 x 10(-4) M. In addition, this sensor showed long-term stability and good sensitivity.     

Following the biocatalytic activities of glucose oxidase by electrochemically cross-linked enzyme-Pt nanoparticles composite electrodes

An integrated platinum nanoparticles (NPs)/glucose oxidase (GOx) composite film associated with a Au electrode is used to follow the biocatalytic activities of the enzyme. The film is assembled on a Au electrode by the electropolymerization of thioaniline-functionalized Pt NPs and thioaniline-modified GOx. The resulting enzyme/Pt NPs-functionalized electrode stimulates the O 2 oxidation of glucose to gluconic acid and H 2O 2. The modified electrode is then implemented to follow the activity of the enzyme by the electrochemical monitoring of the generated H 2O 2. The effect of the composition of the Pt NPs/GOx cross-linked nanostructures and the optimal conditions for the preparation of the electrodes are discussed.     

Electrochemistry and electrocatalytic activities of superoxide dismutases at gold electrodes modified with a self-assembled monolayer

In this article, the electrochemical properties and electrocatalytic activity of three kinds of superoxide dismutases (SODs), that is, bovine erythrocyte copper-zinc superoxide dismutase (Cu/Zn-SOD), iron superoxide dismutase from Escherichia coli (Fe-SOD), and manganese superoxide dismutase from E. coli (Mn-SOD), in the SOD family were studied. It was revealed that the direct electron transfer of the three kinds of SODs could be efficiently promoted by a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) confined on a gold electrode. The electrochemical properties of the SODs at the MPA-SAM electrode vary with the sort of SOD with respect to the formal potential, reversibility of electrode reactions, kinetic parameters, and pH dependence, suggesting different mechanisms for the electrode reactions of the individual SODs. A combination of the facilitated direct electron transfer and the bifunctional enzymatic catalytic activities of the SODs via a redox cycle of their active metals substantially offered a flexible electrochemical route to determination of O(2)(*)(-) where O(2)(*)(-) can be sensed with the SOD-based biosensors in both anodic and cathodic polarizations. Such an intrinsic feature of the SOD-based biosensors successfully enabled a sensitive determination scheme for O(2)(*)(-) free from the interference from some coexisting electroactive species, such as ascorbic acid (AA) and uric acid (UA). Further potential applications for in vivo determination of O(2)(*)(-) is also suggested.     

The chemistry of cements formed between zinc oxide and aqueous zinc chloride

A series of cements has been prepared from zinc oxide powder and aqueous zinc chloride, using solutions corresponding to concentrations of 20%, 30%, 40%, 50% and 60% and a ratio of ZnO powder to zinc chloride solution of 1:1. As with cements of the zinc oxide/zinc nitrate system, these ZnO/ZnCl2 cements were found to be weak in compression (not exceeding 10 MPa) with strength rising with increasing concentration of ZnCl2. The pH change as the reaction proceeded was monitored and generally showed a rapid increase, followed by a slight decrease, and a subsequent slower increase. This is assumed to arise because the doubly charged aquo-zinc cation, Zn(H2O)2+n (n=4 or 6) behaves as a weak acid, due to so-called salt hydrolysis: Zn(H2O)2+n+H2OZnOH(H2O)+(n-1)+H3O+ and reacts to form a salt, thus setting up a classic weak acid/salt buffer system. Finally, cements were stored in water for 1 month, and were generally found to increase in mass during the first week, with the greatest increase occurring in the cement made from 20% ZnCl2 solution. All cements lost mass between 1 week and 1 month, showing them to be sparingly soluble at room temperature. © 1998 Chapman & Hall     

Peroxidase model electrodes: heme peptide modified electrodes as reagentless sensors for hydrogen peroxide

A peroxidase model electrode was devised for reagentless sensing of hydrogen peroxide (H2O2). A small model molecule, which mimics the vicinity of the reaction center of a redox enzyme, can communicate electrochemically with an electrode. Heme nonapeptide (MW congruent to 1600) having peroxidase activity was adopted as a peroxidase model compound and was covalently immobilized on a tin oxide (SnO2) electrode as a roughly monomolecular layer. The modified electrode thus obtained responded to H2O2 at concentrations down to 10(-6) M without electron mediator or promoter, at a mild potential of +150 or +300 mV vs Ag/AgCl. In a batch system, the response reached a steady state in a few seconds. Measurements were possible also in a flow system with an assay time of 0.5-1.0 min/sample. The steady-state response of the electrode was kinetically analyzed.     

Carbon nanotube nanoweb-bioelectrode for highly selective dopamine sensing

A highly sensitive and selective dopamine sensor was fabricated with the unique 3D carbon nanotube nanoweb (CNT-N) electrode. The as-synthesised CNT-N was modified by oxygen plasma to graft functional groups in order to increase selective electroactive sites at the CNT sidewalls. This electrode was characterized physically and electrochemically using HRSEM, Raman, FT-IR, and cyclic voltammetry (CV). Our investigations indicated that the O(2)-plasma treated CNT-N electrode could serve as a highly sensitive biosensor for the selective sensing of dopamine (DA, 1 μM to 20 μM) in the presence of ascorbic acid (AA, 1000 μM).