Electrochemical behavior of neomycin at DNA-modified gold electrodes

Deoxyribonucleic acid (DNA) modified gold electrodes are prepared by the dry adsorptive method and the electrochemical behavior of neomycin and the influence of Pb(II) are studied by cyclic voltammetry, chronocoulometry, differential pulse voltammetry. It is found that in 0.01 M phosphate-buffered saline (PBS) buffer solutions (pH 7.3) at DNA/Au electrode neomycin exhibits an irreversible cathodic peak (E_p = 0.489 V), which is more positive and less sensitive compared with that at bare gold electrodes (E_p = 0.423 V). In the presence of Pb(II) the peak shifts toward positive with its height increasing. Moreover, the peak height is linear to neomycin concentration over the range of 0.15-57 μM. The interaction of Pb(II)-neomycin complex with calf thymus DNA is also studied by calculating the binding constants (K) of the Pb(II)-neomycin complex to DNA and binding site size (s) from voltammetric data (1.0 × 10⁷ M⁻¹ and 4 bp, respectively).     

The electrochemiluminescence of ruthenium complex/tripropylamine systems at DNA-modified gold electrodes

The electrochemiluminescence (ECL) behavior of ruthenium complex/tripropylamine (TPA) systems at DNA-modified gold electrode was studied to understand the possible mechanism and to develop new detection platforms. DNA strand, especially double-stranded DNA (ds-DNA), can preconcentrate TPA and acts as the acceptor of the protons released from TPAH(+), therefore the improved ECL emission and the low potential ECL were observed. The intercalation of Ru(phen)(3)(2+) into ds-DNA was confirmed to be a sensitive and label-free DNA-related detection platform. The above results were validated by the analysis of lysozyme using anti-lysozyme aptamer-modified electrode. This work opens a new field by the use of DNA-modified electrode to develop novel sensing platforms, such as low potential ECL biosensors and Ru(phen)(3)(2+) intercalation-based ECL biosensors.     

Electrochemical characterization and application of azurin-modified gold electrodes for detection of superoxide

A novel biosensor for superoxide radical (O(2)(*-)) detection based on Pseudomonas aeruginosa azurin immobilized on gold electrode was designed. The rate constant of azurin reduction by O(2)(*-) was found to be 10(5)M(-1)s(-1) in solution and five times lower, i.e., 0.2 x 10(5)M(-1)s(-1), for azurin coupled to gold by 3,3'-dithiobis(sulfosuccinimidylpropionate) (DTSSP). The electron transfer rate between the protein and the electrode ranged from 2 to 6s(-1). The sensitivity of this biosensor to O(2)(*-) was 6.8 x 10(2)Am(-2)M(-1). The response to the interference substances, such as uric acid, H(2)O(2), and dimethylsulfoxide was negligible below 10 microM. The electrode was applied in three O(2)(*-) generating systems: (i) xanthine oxidase (XOD), (ii) potassium superoxide (KO(2)), and (iii) stimulated neutrophil granulocytes. The latter was compared with luminol-amplified chemiluminescence. The biosensor responded to O(2)(*-) in all three environments, and the signals were antagonized by superoxide dismutase.     

Electrochemical impedance immunosensor based on gold nanoparticles and aryl diazonium salt functionalized gold electrodes for the detection of antibody

Electrodes modified with passivating organic layers have been shown to, here and previously, to exhibit good Faradaic electrochemistry upon attachment of gold nanoparticles (AuNP). Due to their low background capacitances these constructs have good potential in electrochemical sensing. Herein is reported the application of these electrode constructs for impedance based immunosensing. The immunosensor was constructed by modifying a gold electrode with 4-thiophenol (4-TP) passivating layers by diazonium salt chemistry. Subsequently, the attachment of AuNP and then a biotin derivative as a model epitope to detect anti-biotin IgG were carried out. The interfacial properties of the modified electrodes were evaluated in the presence of Fe(CN)(6)(4-/3-) redox couple as a probe by cyclic voltammetry and electrochemical impedance spectroscopy. The impedance change, due to the specific immuno-interaction at the immunosensor surface was utilized to detect anti-biotin IgG. The increase in charge-transfer resistance (R(ct)) was linearly proportional to the concentration of anti-biotin IgG in the range of 5-500 ng mL(-1), with a detection limit of 5 ng mL(-1).     

Heterogeneous electron transfer of cytochrome c facilitated by polypyrrole and methylene blue polypyrrole film modified electrodes

Polypyrrole and methylene blue incorporated polypyrrole thin-film modified electrodes were prepared by the electrochemical polymerization method. These modified electrodes may facilitate heterogeneous electron transfer of cytochrome c with high electrocatalytic activity and good stability. Optical thin-layer spectroelectrochemical techniques were used to determine the characteristics of these electrochemical processes such as formal redox potential (E0), electron transfer number (n), and the apparent rate constant (ks.h0).     

Electrochemical endotoxin sensors based on TLR4/MD-2 complexes immobilized on gold electrodes

Even low concentrations of endotoxins can be life-threatening. As such, continuous effort has been directed toward the development of sensitive and specific endotoxin detection systems. In this paper, we report the design and fabrication of a new electrochemical endotoxin sensor based on a human recombinant toll-like receptor 4 (rhTLR4) and myeloid differentiation-2 (MD-2) complex. The rhTLR4/MD-2 complex, which specifically binds to endotoxin, was immobilized on gold electrodes through a self-assembled monolayer (SAM) technique involving the use of dithiobis(succinimidyl undecanoate) (DSU). The surface topography of the electrodes at each fabrication stage was characterized with a nanosurface profiler and atomic force microscope (AFM). The electrochemical signals generated from interactions between the rhTLR4/MD-2 complex and the endotoxin were characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). A linear relationship between the peak current and endotoxin concentration was obtained in the range of 0.0005 to 5 EU/mL with a correlation coefficient (R(2)) of 0.978. The estimated limit of detection (LOD) was fairly low, 0.0002 EU/mL. The rhTLR4/MD-2 based sensors exhibited no current responses to dipalmitoylphosphatidylcholine (DPPC) bearing two lipid chains, which is structurally similar to endotoxin, indicating the high specificity of the sensors to endotoxin.     

Electrochemical properties of hydrogenase on glass carbon electrodes modified with carbon nanotubes

Hydrogenase (H₂ ase) purified from phototropic bacteriumThiocapsa roseopersicina was coassembled with carbon nanotubes (CNTs) on glass carbon electrodes. Both oxidized CNTs and Nafion-CNT composites were used to modify the electrodes. The pure H₂ are formed dot-like domains, while the oxidized CNT-H₂ ase and Nafion-CNT-H₂ ase composites formed wire-like and large closely packed aggregates, respectively. The reductive potentials for the [4Fe-4S]^2+/1+ clusters of H₂ase were at about −500, −650, and −700 mV (vs Ag/AgCl) for the electrodes modified with pure H₂ase, Nafion-SWNT-H₂ase, and Nafion-MWNT-H₂ase composites, respectively. Potential step chronocoulometry measurements indicated a larger charge-transfer diffusion coefficient between the H₂ase and electrodes when the CNTs were co-assembled with H₂ase, suggesting that the CNTs can not only act as a supporting layer to immobilize enzymes, but also act as a highly conductive wire throughout the films.     

Electrochemical sensing of dihydrogen phosphate and adenosine-5′-triphosphate anions by self-assembled monolayers of (ferrocenylmethyl)trialkylammonium cations on gold electrodes

The effective electrochemical sensing of dihydrogen phosphate and adenosine-5′-triphosphate anions could be achieved in organic electrolytes using self-assembled monolayers of a (ferrocenylmethyl)trialkylammonium cation. The electrochemical response of these modified electrodes was found to be similar to that of the receptor in homogeneous solution. This observation showed that the electrochemical recognition properties of the redox active cationic receptor were fully retained after immobilization on the electrode surface. The recognition abilities of this redox assembly are based on strong ion pairing effects, further reinforced upon oxidation of the ferrocene centres to ferrocenium. The complexation events could be detected and amperometrically quantified through the emergence of new differential pulse voltammetric peaks corresponding to the electroactivity of the (ferrocenylmethyl)alkylammonium-anion complexes.     

Different photodynamic action of proflavine and methylene blue on bacteriophage

Summary Photodynamically induced DNA damage in Serratiaphase may be repaired by the host cell. The extent of this host cell reactivation (HCR) depends on the photosensitizing dye used: HCR of proflavine+visible light induced DNA damage appears to be more efficient than the one of DNA damage induced by methylene blue+visible light. This significant difference in HCR is not due to a preferential inhibition of the enzymes of DNA dark repair by either one of the dyes injected into the host cell along with the phage's genome.     

Different photodynamic action of proflavine and methylene blue on bacteriophage

Summary The irradiation with visible light (Li) of temperate Serratiaphage that is maximally sensitized with either proflavine (PF) or methylene blue (MB) induces—apart from lethal lesions—mutations which are phenotypically expressed as clear (c) or lightly turbid (l) plaques. The mutagenicity of the MB+Li and PF+Li treatment differs in several respects: (i) Up to an inactivation of 6 to 8 lethal hits MB+Li is a much more potent mutagen than PF+Li. (ii) at low levels of survival the dose curve of mutation frequency with MB+Li reaches a peak and then decreases drastically while the mutation frequency after PF+Li continues to increase in proportion to lethal hits induced. (iii) Mapping of 100 MB+Li and 77 PF+Li induced c or l mutants indicates significant difference in the electiveness of the four genomic regions of c or l mutants.     

Electrochemical characteristics of platinum electrodes coated with cytochrome b5-phospholipid monolayers

Platinum electrodes can be coated with cytochrome b5-phospholipid monolayers by the Langmuir-Blodgett technique. Cyclic voltammetry of a series of dyes shows that the coated electrodes become selective for certain electroactive species. The electron transfer reactions of negatively charged species are inhibited at the modified electrode, whereas positively charged species show enhanced reactivity compared with that at a bare metal electrode.