Label-free sequence-specific DNA sensing using copper-enhanced anodic stripping of purine bases at boron-doped diamond electrodes

Stripping voltammetric determination of purine bases in the presence of copper ions at mercury, amalgam, or carbon-based electrodes has recently been utilized in analysis of DNA or synthetic oligodeoxynucleotides (ODNs). Here we report on copper-enhanced label-free anodic stripping detection of guanine and adenine bases in acid-hydrolyzed DNA at anodically oxidized boron-doped diamond electrode (AO-BDDE). The AO-BDDE was successfully applied in a three-electrode microcell in which an approximately 50 microL drop of the analyte solution can be efficiently stirred during the accumulation step by streaming of an inert gas. Accelerated mass transport due to the solution motion in the presence of copper resulted in enhancement of the guanine oxidation signal by about 2 orders of magnitude (compared to accumulation of the analyte from still solution not containing copper), allowing an easy detection of approximately 25 fmol of the ODNs. The proposed technique is shown to be suitable for a determination of purine (particularly guanine) content in DNA samples. Applications of the technique in magnetic bead-based DNA assays (such as hybridization with DNA sequences exhibiting asymmetrical distribution of purine/pyrimidine nucleotides between the complementary strands or monitoring of amplification of specific DNA fragments in a duplex polymerase chain reaction) are demonstrated.     

In situ measurements of aggregation and disaggregation of Cu(II) complex at liquid/liquid interface

Aggregation of Cu(II)-5-(octadecyloxy)-2-(2-thiazolylazo)phenol (TARC18) complex at the heptane/water interface was measured directly by a centrifugal liquid membrane spectrometry and a two-phase microflow API-MS method. When the pH of an aqueous phase was increased from 4 to 6, the 1:1 complex of Cu(II)-TARC18, which was formed as a positively charged complex at the interface, formed further an aggregate, accompanied by the change of spectra suggesting its aggregation. The MS spectra of the interfacial species indicated the formation of 2:3 complex for Cu(II) and TARC18 under the conditions that the aggregate was formed. This observation allowed us to analyze the interfacial aggregation stoichiometrically: the aggregate of the 2:3 complex was formed from a 1:1 complex at the interface. The addition of purine base of adenine or guanine into the system resulted in the disruption of the aggregate by the formation of a new three-element complex of 1:1:1 for Cu(II), TARC18, and the base, showing a bathochromic shift in the spectra. Thus, the disaggregation experiment showed an interfacial molecular recognition ability of the Cu(II)-TARC18 aggregate for hydrophobic bases.     

Luminescent CdS quantum dots as selective ion probes

Water-soluble luminescent CdS quantum dots (QDs) capped by polyphosphate, L-cysteine, and thioglycerol were synthesized in aqueous solution. The ligands were found to have a profound effect on the luminesence response of CdS QDs to physiologically important metal cations. Polyphosphate-capped CdS QDs were sensitive to nearly all mono- and divalent cations, showing no ion selectivity. Conversely, thioglycerol-capped CdS QDs were sensitive to only copper and iron ions. Similar concentrations of physiologically relevant cations, such as zinc, sodium, potassium, calcium, and magnesium ions did not affect the luminescence of thioglycerol-capped CdS QDs. On the other hand, L-cysteine-capped CdS QDs were sensitive to zinc ions and insensitive to other physiologically important cations, such as copper, calcium, and magnium ions. To demonstrate the detection capability of these new ion probes, L-cysteine and thioglycerol-capped CdS QDs were used to detect zinc and copper ions in physiological buffer samples. The detection limits were 0.8 microM for zinc (II) and 0.1 microM for copper (II) ions. The emission enhancement of the QDs by zinc (II) is attributed to activation of surface states, whereas the effective reduction of copper (II) to copper (I) may explain the emission decrease of the thioglycerol-capped CdS QDs when charged with copper ions. Unlike organic fluorescent dyes, the thioglycerol-capped luminescent CdS QDs discriminate between copper and zinc ions and are therefore suitable for the analysis of copper ions in biological samples in the presence of physiological concentrations of zinc ions. The interference of iron ions with zinc and copper ion detection is attributed to an inner filter effect, which is eliminated by adding fluoride ions to form the colorless complex FeF6(3-). To the best of our knowledge, this is first use of luminescent semiconductor quantum dots as selective ion probes in aqueous samples.     

镀铜废水中Cu2+含量的5,6-二氯-苯并噻唑偶氮苯甲酸显色光度法测定

利用5,6-二氯-苯并噻唑偶氮苯甲酸(5,6-diCl-BTAEB)与铜的显色反应,在pH值为5.0的NH4OAcHOAc缓冲溶液中,在乳化剂OP存在下,使5,6-diCl-BTAEB与Cu2+反应生成2:1稳定的配合物,可实现对Cu2+的测定.其最大吸收波长为650 nm,表观摩尔吸光系数为5.57×104L/(mo...     

Preconcentration and separation of nickel, copper and cobalt using solid phase extraction and their determination in some real samples

A solid phase extraction method has been developed to separate and concentrate trace amounts of nickel, cobalt and copper ions from aqueous samples for the measurement by flame atomic absorption spectrometry. By the passage of aqueous samples through activated carbon modified by dithioxamide (rubeanic acid) (DTO), Ni2+, Cu2+ and Co2+ ions adsorb quantitatively. The recoveries of analytes at pH 5.5 with 500 mg solid phase were greater than 95% without interference from alkaline, earth alkaline and some metal ions. The enrichment factor was 330. The detection limits by three sigma were 0.50 microg L(-1) for copper, 0.75 microg L(-1) for nickel and 0.80 microg L(-1) for cobalt. The loading capacity was 0.56 mg g(-1) for Ni2+, 0.50 mg g(-1) for Cu2+ and 0.47 mg g(-1) for Co2+. The presented procedure was applied to the determination of analytes in tap, river and sea waters, vegetable, soil and blood samples with successfully results (recoveries greater than 95%, R.S.D. lower than 2% for n=3).     

Direct detection of S-nitrosothiols using planar amperometric nitric oxide sensor modified with polymeric films containing catalytic copper species

The direct amperometric detection of S-nitrosothiol species (RSNOs) is realized by modifying a previously reported amperometric nitric oxide gas sensor with thin hydrophilic polyurethane films containing catalytic Cu(II)/(I) sites. Catalytic Cu(II)/(I)-mediated decomposition of S-nitrosothiols generates NO(g) in the thin polymeric film at the distal tip of the NO sensor. Three different species are examined to create the catalytic layer: (1) a lipophilic Cu(II)-ligand complex; (2) Cu(II)-phosphate salt; and (3) small (3-microm) metallic Cu(0) particles. All three catalytic layers yield reversible amperometric response in proportion to the concentration of S-nitrosothiols (e.g., nitrosocysteine, nitrosoglutathione, S-nitroso-N-acetylcysteine, S-nitrosoalbumin) present in the aqueous test solution. Sensitivity toward the different RSNO species is dependent on the respective catalytic rates of decomposition of the RSNO species by reactive Cu(I), accessibility of the species into the polyurethane layer containing the catalyst, the level of reducing agents (ascorbate) used in solution to help generate reactive Cu(I) species, and the concentration of metal ion complexing agents present in the test solution (e.g., EDTA). Under optimized conditions, all RSNO species can be detected at < or =1 microM levels, with sensor lifetimes of at least 10 days for the sensors based on Cu(II)-phosphate and Cu0 particles. It is further shown that the new RSNO sensors can be used to assess the "NO-generating" ability of fresh blood samples by effectively detecting the total level of reactive RSNO species present in such samples.     

Voltammetric quantification of adenine and guanine at C60 modified glassy carbon electrodes

Voltammetric determination of adenine and guanine has been carried out at C60 modified glassy carbon electrode at physiological pH. Well-defined oxidation peaks were observed with Ep at approximately 990 mV and 692 mV for adenine and guanine respectively. Good colinearity was obtained in the concentration range 0.5 microM to 100.0 microM for adenine and guanine with sensitivity of approximately 0.06 microA microM(-1) and approximately 0.03 microA /microM(-1), respectively. Simultaneous voltammetric determination of adenine and guanine has been described. Recovery studies for adenine and guanine in biological samples were also carried out. Interfering effect of some common metabolites including ascorbic acid has been evaluated. Analytical application of the developed protocol for determination of (G +C)/(A + T) ratio in DNA sample is also described.     

Reactivity and structure of the complex between thiol groups of a chelating resin and copper ion

The chelation of copper(II) ion with a hydrophilic resin prepared from a polyacrylamide matrix with attached thiol groups was compared with that of a low molecular weight analog. The formation of Cu(I) complexes through a redox reaction between Cu(II) ions and thiol groups was demonstrated by ESR spectroscopy and electrochemical measurements. The macromolecular structure of the resin allows Cu(I) to oxidize slowly through contact with air. The determination of ESR parameters suggests that the copper(II) environment at this time is S-S-O-O.     

Synthesis and characterization of copper ions surface-doped titanium dioxide nanotubes

Copper ions surface-doped titanium dioxide nanotubes were prepared via an assembly process based on the reactions between Cu(NH₂CH₂CH₂NH₂)₂(OH)₂ and hydroxide radicals on the surface of TiO₂ nanotubes, followed by the heat treatment in air at 723 K. The as-prepared samples were characterized with infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and fluorescence spectroscopy (FL). The photocatalytic activity of the copper ions surface-doped titanium dioxide nanotubes was investigated by photodegradation of Rhodamine B. The results showed that copper ions were successfully introduced onto the surface of TiO₂ nanotubes. And two kinds of copper species of Cu(I) and Cu(II) were found on TiO₂ surface. Copper ions act as electron trappers facilitating the separation of electrons and holes on the surface of TiO₂ nanotubes, which allows more efficiency for the photodegradation of Rhodamine B.     

Penicillium digitatum immobilized on pumice stone as a new solid phase extractor for preconcentration and/or separation of trace metals in environmental samples

This study presents a column solid phase extraction procedure based on column biosorption of Cu(II), Zn(II) and Pb(II) ions on Penicillium digitatum immobilized on pumice stone. The analytes were determined by flame atomic absorption spectrometry (FAAS). The optimum conditions such as: pH values, amount of solid phase, elution solution and flow rate of sample solution were evaluated for the quantitative recovery of the analytes. The effect of interfering ions on the recovery of the analytes has also been investigated. The recoveries of copper, zinc and lead under the optimum conditions were found to be 97+/-2, 98+/-2 and 98+/-2%, respectively, at 95% confidence level. For the analytes, 50-fold preconcentration was obtained. The analytical detection limits for Cu(II), Zn(II) and Pb(II) were 1.8, 1.3 and 5.8 ng mL(-1), respectively. The proposed procedure was applied for the determination of copper, zinc and lead in dam water, waste water, spring water, parsley and carrot. The accuracy of the procedure was checked by determining copper, zinc and lead in standard reference tea samples (GBW-07605).     

Electrochemical determination of dopamine based on self-assembled peptide nanostructure

Self-assembled peptide nanostructures are electronically insulating as are most biomaterials derived from natural amino acids. To obtain additional properties and increase the applicability of peptide nanomaterials, some chemical modifications can be performed and materials can be functionalized to form hybrid compounds. In this work, we described the formation of L-diphenylalanine nanotubes (PNTs) with cyclic-tetrameric copper(II) species containing the ligand (4-imidazolyl)ethylene-2-amino-1-ethylpyridine [Cu(4)(apyhist)(4)](4+) in the Nafion membrane on a vitreous carbon electrode surface. This copper complex has been studied as structural and functional models for the active centers of copper containing redox enzymes. Scanning electron microscopy was used to confirm the formation of the nanostructures. The electrochemical properties of the PNT-[Cu(4)(apyhist)(4)](4+)/Nafion film on a glassy carbon electrode were characterized using cyclic voltammetry and square-wave voltammetry and showed high electrocatalytic activity toward the oxidation of dopamine (DA). The detection sensitivity was found to be enhanced by the use of copper(II) complex in the PNTs/Nafion films. Under the optimum conditions, the square-wave voltammetry peak height was linearly related to the DA concentration over two concentration intervals, viz., 5.0-40 μmol L(-1) and 40-1000 μmol L(-1). The detection limit was 2.80 μmol L(-1) (S/N = 3), and ascorbic acid did not interfere with the DA detection. These results suggested that this hybrid bioinorganic system provides an attractive advantage for a new type of electrochemical sensors. The detection sensitivity was found to be enhanced by use of PNTs.     

Rapid Detection of Copper in Biological Systems Using Click Chemistry

A fast (1 min), straightforward but efficient, click chemistry‐based system that enables the rapid detection of free copper (Cu) ions in either biological fluids or living cells without tedious pretreatment is provided. Cu can quickly induce the conjugation between graphene oxide (GO) and a fluorescent dye via click reaction. On the basis of the high specificity of bioorthogonal reaction and the effective quenching ability of GO, the assay studied in this paper can respond to Cu ions in less than 1 min with excellent selectivity and sensitivity, which is the fastest sensor for Cu as far as it is known. In addition, the application of this system is verified by performing assays in living cells and untreated urine samples from patients suffering from Wilson's Disease. Such a Cu detection system shows great promises in both fundamental research and routine clinical diagnostics.     

Colorimetric detection of trace copper ions based on catalytic leaching of silver-coated gold nanoparticles

A colorimetric, label-free, and nonaggregation-based silver coated gold nanoparticles (Ag/Au NPs) probe has been developed for detection of trace Cu(2+) in aqueous solution, based on the fact that Cu(2+) can accelerate the leaching rate of Ag/Au NPs by thiosulfate (S(2)O(3)(2-)). The leaching of Ag/Au NPs would lead to dramatic decrease in the surface plasmon resonance (SPR) absorption as the size of Ag/Au NPs decreased. This colorimetric strategy based on size-dependence of nanoparticles during their leaching process provided a highly sensitive (1.0 nM) and selective detection toward Cu(2+), with a wide linear detection range (5-800 nM) over nearly 3 orders of magnitude. The cost-effective probe allows rapid and sensitive detection of trace Cu(2+) ions in water samples, indicating its potential applicability for the determination of copper in real samples.     

Separation of copper ions from iron ions using PVA-g-(acrylic acid/N-vinyl imidazole) membranes prepared by radiation-induced grafting

Acrylic acid (AAc), N-vinyl imidazole (Azol) and their binary mixtures were graft copolymerized onto poly(vinyl alcohol) membranes using gamma irradiation. The ability of the grafted membranes to separate Cu ions from Fe ions was investigated with respect to the grafting yield and the pH of the feed solution. The data showed that the diffusion of copper ions from the feed compartment to the receiver compartment depends on the grafting yield of the membranes and the pH of the feed solution. To the contrary, iron ions did not diffuse through the membranes of all grafting yields. However, a limited amount of iron ions diffused in strong acidic medium. This study shows that the prepared membranes could be considered for the separation of copper ions from iron ions. The temperature of thermal decomposition of pure PVA-g-AAc/Azol membrane, PVA-g-AAc/Azol membrane containing copper ions, and PVA-g-AAc/Azol membrane containing iron ions were determined using TGA analyzer. It was shown that the presence of Cu and Fe ions increases the decomposition temperature, and the membranes bonded with iron ions are more stable than those containing copper ions.     

Detection of toxic compounds in real water samples using a conductometric tyrosinase biosensor

A conductometric tyrosinase biosensor for the detection of some toxic compounds including diuron, atrazine, and copper ions was developed. The work of this biosensor is based on the principle of change of conductivity of the enzyme membrane when tyrosinase either interacts with 4-chlorophenol substrate or is inhibited by pollutants. The different samples tested were solutions containing diuron, atrazine, copper, lead and zinc ions, mixtures of copper/atrazine or copper/diuron and real water samples coming from a Vietnamese river. In the last case, classical techniques such as GC-MS or atomic absorption spectrometry were used in order to estimate exact concentration of these species in real water samples. Results have shown that such a biosensor could be used as an early warning system for the detection of these pollutants, as no matrix effect coming from the real sample was observed and no synergetic or antagonist effects were found for the mixture of toxic compounds. In addition, results were coherent with the content of the tyrosinase inhibitors.     

Fluorescence quenching of the europium tetracycline hydrogen peroxide complex by copper (II) and other metal ions

The europium-tetracycline complex [Eu(Tc)] is known to show only weak fluorescence with an emission maximum at 615 nm. On addition of hydrogen peroxide (HP), the strongly fluorescent [Eu(Tc)(HP)] complex is formed, which displays a 15-fold stronger luminescence intensity. This study describes the decrease in luminescence intensity of the [Eu(Tc)(HP)] complex in aqueous solution in the presence of Cu2+, Fe3+, Ag+, Al3+, Zn2+, Co2+, Ni2+, Mn2+, Ca2+, and Mg2+. Static and dynamic quenching can be induced by Cu2+, and these processes were quantified by means of their quenching constants. Stern-Volmer plots were also derived from lifetime imaging measurements accomplished by the rapid lifetime determination (RLD) technique based on microwell plate assays, and also by the time-correlated single photon counting (TCSPC) technique. According to those data, a time-resolved fluorescent method for copper determination can be proposed that is based on dynamic quenching of the [Eu(Tc)(HP)] complex by Cu2+ ions. The response to copper concentrations is linear up to 1.6 micromol L(-1), providing a detection limit of 0.2 micromol L(-1).     

Sorption of copper from dilute aqueous solutions onto poly(vinyl mercaptan)

A hydrophilic poly(vinyl mercaptan) (PVM) has been prepared from poly(vinyl alcohol) by partial conversion of the OH groups to SH groups. The resin with a free mercaptan content of 2.23 meq/g has a copper sorption capacity of 70 mg/g. The polymercaptan used as a sodium salt, PVM(Na), has several-fold higher sorption capacity for copper than the same resin used in thiol from, PVM(H). From a solution containing Cu(II), copper is sorbed mostly as Cu(II) by PVM(Na) and as Cu(I) by PVM(H). Significantly, there is a large increase in the copper sorption capacity of both PVM(H) and PVM(Na) in the presence of sodium chloride in solution. In the absence of added NaCl, the copper sorption capacities of PVM(H) and PVM(Na) are influenced in different ways by the type of coion in solution. Thus, PVM(H) takes up more copper from copper(II) chloride solution than from copper(II) sulfate solution under comparable conditions, while the opposite is true for PVM(Na). These features can be explained by the formation of copper(II) chloro complexes in the presence of added chloride, more efficient Donnan exclusion of multivalent coions, and greater degree of hydrolysis of copper(II) chloride than copper(II) sulfate. The copper sorption on PVM(Na) is highly sensitive to pH, decreasing rapidly both at lower and higher pH from a maximum at pH ≈ 5. In contrast, the sorption on PVM(H) is fairly constant in the mildly acidic pH range and increases rapidly above pH ≈ 9, approaching the sorption capacity of PVM(Na).     

X-ray absorption spectroscopy study of a copper-containing material after thermal treatment

Thermal immobilization of copper contaminant in a copper-containing solid material collected from local copper smelting and foundry area is investigated in the present work. X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are employed for copper speciation. XAS results indicate that cupric hydroxide is the major copper species in the solid material dried at 105 degrees C. After being subjected to a 500 degrees C thermal process, cupric hydroxide still remains as the main copper species, but some Cu(II) is chemically reduced to Cu(I). More cupric hydroxide is progressively converted to Cu(I) as the sample was heated at 1100 degrees C than that heated at 500 degrees C. The sample heated at 500 degrees C is in its original powder form. However, thermal treatment at 1100 degrees C transforms the powder into a hardened granule-like form that is much bigger in size and difficult to be ground into powders. The sample is sintered with the sparingly soluble cuprous oxide and elemental copper being encapsulated inside. Toxicity characteristic leaching procedure (TCLP) results depict that amount of copper leached from the sample (containing 133,000 mg copper kg-1) heated at 1100 degrees C for 2 h is considerably minor, being 367 mg copper kg-1.     

Comparison of the influence of copper micro- and nano-particles on the mechanical properties of polyethylene/copper composites

This article reports on the influence of copper content and particle size on the tensile properties of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE) mixed with up to 25 vol.% Cu micro-particles and up to 5 vol.% Cu nano-particles, and on the influence of Cu micro-particle content on the dynamic mechanical properties of these polymers. This influence depends upon the extent of branching and crystallinity in the particular polymer. The copper micro-particles seemed to have a negligible influence on the tensile strength of LDPE and HDPE, while there was quite a significant reduction in tensile strength when LLDPE was used as matrix. The elongation at break generally decreased with increasing copper content, but the effect was more significant in the case of LDPE and HDPE. The tensile modulus generally increased with increasing Cu content, but the extent of increase was lower in the case of the more crystalline HDPE. The nano-copper containing samples showed comparable properties at equivalent Cu contents. The storage and loss moduli generally increased with increasing Cu. For all three polyethylenes the β-transition (where present) was not significantly influenced by the presence and amount of copper, but the α-transition was strongly influenced, especially in the case of LDPE and LLDPE.     

The effect of copper ions on interaction of UV radiation with methacrylic matrix – EPR study

The role of metal ions introduced to polymer matrix in the photochemical degradation of material is not fully understood. In this paper, we considered the effect of copper ions on the photochemical changes in Methafilcon A after UV-irradiation. The presence of methacrylic acid in the structure of Methafilcon A increases the loading capacity of these ions. In result, there is observed the production much more radicals after UV-irradiation than in pure matrix, without copper ions. When the time of UV-exposure increases, the EPR signal of trapped Cu(II) ions in the material decreases. This proves the transformation of Cu(II) to a diamagnetic state of stable Cu(I)-intermediates or copper oxides. Simultaneously, in the first 5-min of UV-irradiation there is observed a rapid increase in intensity of the radical signal, which disappears when the exposure time is extended. This mechanism of radical generating is quite different than for Methafilcon A matrix without copper ions.