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PubMed1999

Boldine action against the stannous chloride effect.

Peumus boldus extract has been used in popular medicine in the treatment of biliar litiase, hepatic insufficiency and liver congestion. Its effects are associated to the substance boldine that is present in its extract. In the present work, we evaluated the influence of boldine both in: (i) the structural conformation of a plasmid pUC 9.1 through gel electrophoresis analysis; and in (ii) the survival of the strain of Escherichia coli AB1157 submitted to reactive oxygen species (ROS), generated by a Fenton like reaction, induced by stannous chloride. Our results show a reduction of the lethal effect induced by stannous chloride on the survival of the E. coli culture in the presence of boldine. The supercoiled form of the plasmid is not modified by stannous chloride in the presence of boldine. We suggest that the protection induced by boldine could be explained by its anti-oxidant mechanism. In this way, the boldine could be reacting with stannous ions, protecting them against the oxidation and, consequently, avoiding the generation of ROS.

Antioxidants↗
PubMed2003

HO-1 induction attenuates renal damage and oxidative stress induced by K2Cr2O7.

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme; its inducible isozyme HO-1 protects against some types of acute tissue injury. The expression and functional role of HO-1 in rats with renal injury induced by potassium dichromate (K(2)Cr(2)O(7)) was investigated in this work. Rats were studied 24 h after a single injection of K(2)Cr(2)O(7). To address the possible protective effect of HO-1 in this experimental model, this enzyme was induced by an injection of stannous chloride (SnCl(2)) 12 h before K(2)Cr(2)O(7) administration. The functional role of HO-1 in K(2)Cr(2)O(7) + SnCl(2)-treated animals was tested by inhibiting HO activity with an injection of zinc (II) protoporphyrin IX (ZnPP) 18 h before K(2)Cr(2)O(7). In K(2)Cr(2)O(7)-treated rats: (i) renal HO-1 content, measured by Western blot, increased 2.6-fold; and, (ii) renal nitrotyrosine and protein carbonyl content, markers of oxidative stress, increased 3.5- and 1.36-fold, respectively. Renal damage and oxidative stress were ameliorated and HO-1 content was increased in the K(2)Cr(2)O(7) + SnCl(2) group. The attenuation of renal injury and oxidative stress was lost by the inhibition of HO activity in K(2)Cr(2)O(7) + SnCl(2) + ZnPP-treated animals. Our data suggest that HO-1 overexpression induced by SnCl(2) is responsible for the attenuation of renal damage and oxidative stress induced by K(2)Cr(2)O(7).

Animals↗
PubMed2003

Solid-state NMR studies of the adsorption and photooxidation of ethanol on mixed TiO2--SnO2 photocatalysts.

In situ solid-state NMR methodologies have been used to investigate the photocatalytic oxidation of ethanol (CH3CH2OH) over a series of SnO2-based photocatalysts. The adsorption of ethanol on commercially available SnO2 powder was studied using both cross-polarization 13C NMR and REDOR experiments, and showed the formation of two surface ethanol species, hydrogen-bonded ethanol at surface hydroxyl groups and ethanol chemisorbed to the SnO2 surface (Sn--OCH2CH3). 13C NMR of the adsorbed ethanol was used to characterize the surface of monolayer SnO2--TiO2 coupled photocatalysts supported on porous Vycor glass. In situ solid-state NMR studies showed that the photooxidation of ethanol over the monolayer photocatalysts was slower than that over a supported TiO2 monolayer photocatalyst due to the build-up of reaction intermediates such as acetic acid on the catalyst surface. 119Sn NMR experiments characterized the tin species on the porous Vycor glass support.

Adsorption↗
PubMed2002

Voltage-induced inhibition of antigen-antibody binding at conducting optical waveguides.

Optical waveguides coated with electrically conducting indium-tin oxide (ITO) are demonstrated here as a new class of substrate for fluorescent immunosensors. These waveguides combine electrochemical control with evanescent excitation and image-based detection. Presented here are preliminary results utilizing these waveguides that demonstrate influence of waveguide voltage on antigen binding. Specifically, waveguide surfaces were bisected into electrically addressable halves, anti-ovalbumin immobilized in patterns on their surfaces, and a 1.3 V bias applied between waveguide halves in the presence of Cy5-labeled ovalbumin in 10 mM phosphate buffer (pH 7.4) containing 150 mM NaCl and 0.05% Tween-20. Fluorescence imaging indicated that binding of the antigen to positively biased waveguide halves was inhibited nearly 10-fold compared with negatively biased waveguide halves and unbiased controls. Furthermore, it is shown that ovalbumin binding to positively biased waveguide regions is regenerated after removal of applied voltage. These results suggest that electrochemical control of immunosensor substrates can be used as a possible strategy toward minimizing cross-reactive binding and/or nonspecific adsorption, immunosensor regeneration, and controlled binding.

Animals↗
PubMed2003

Optical-transparent and flexible glucose sensor with ITO electrode.

The glucose sensor was constructed by immobilizing glucose oxidase (GOD) with glutaraldehyde solution onto the sensitive area of the transparent oxygen electrode. The oxygen electrode was fabricated by sealing KCl electrolyte solution including the Indium-Tin Oxide (ITO)-electrode with both metal-weldable film and gas-permeable membrane coated with Ag/AgCl electrode. The sensor behavior was evaluated using standard glucose solutions in a batch measurement system with a computer-controlled potentiostat at a reduction potential of -900 mV. The sensor device has flexible structure and good optical transparency (less than 0.6 abs) at the visible wavelength from 400 to 700 nm. The sensor was possible to be used for measuring glucose from 0.06 to 1.24 mmol/l (correlation coefficient: 0.999), including the reported concentration of tear glucose in normal (0.14 mmol/l), with good reproducibility.

Adsorption↗
PubMed2003

A high-performance glucose biosensor based on monomolecular layer of glucose oxidase covalently immobilised on indium-tin oxide surface.

In this paper, a mediatorless amperometric glucose biosensor based on direct covalent immobilisation of monomolecular layer of glucose oxidase (GOx) on a semiconducting indium-tin oxide (ITO) is demonstrated. The abundance of surface hydroxyl functional group of ITO allows it to be used as a suitable platform for direct covalent immobilisation of the enzyme for sensor architecture. The anodic current corresponding to electrochemical oxidation of the enzymatic product, hydrogen peroxide, at a sputtered Pt electrode at 0.500 V (vs. SCE) was obtained as the sensor signal. It was found that the biosensor based on the direct immobilisation scheme shows a fast biosensor response, minimum interference from other common metabolic species and ease of biosensor miniaturisation. A linear range of 0-10 mM of glucose was demonstrated, which exhibits a high sensitivity as far as performance per immobilised GOx molecule is concerned. A detection limit as low as 0.05 mM and long-term stability were observed. Even more important, the biosensor design allows fabrication through a dry process. These characteristics make it possible to achieve mass production of biosensor compatible with the current electronic integrated circuit manufacturing technologies.

Adsorption↗
PubMed1997

Preparation of 188Re-RC-160 somatostatin analog: a peptide for local/regional radiotherapy.

Conditions are described for the preparation of 188Re-RC-160, a radiolabeled synthetic peptide derived from an analogue of somatostatin, using a lyophilized labeling kit containing RC-160 (200 micrograms) and stannous tartrate to which is added carrier-free 188Re (beta, Emax, 2.12 MeV; gamma, 155 keV, 10%; T1/2 = 16.7 h). The kits have been radiolabeled with > 2960 MBq (80 mCi) with a high labeling efficiency and no need for subsequent purification. Radiolabeling results in one major peak when analyzed by reverse-phase (RP) HPLC. Presumptive radiolysis was detected at 2.5 h post-labeling; however, a convenient method is described for stabilizing the kits against radiolysis by the post-labeling addition of ascorbic acid.

Antineoplastic Agents↗
PubMed1998

Determination of Sn(II) in technetium cold kits by voltammetry at the hanging mercury drop electrode (HMDE) and relevant radiopharmaceutical applications.

A novel approach for the determination of the stannous content in cold kits for labelling with 99mTc is described. The method is based on differential pulse polarography on the hanging mercury drop electrode in a methanol/water/perchloric acid mixture and is easy to perform. Examples for the determination of tin(II) in fractionated technetium cold kits are shown. The stability of tin(II) in solution was mainly dependent on the storage temperature and the kit composition. The low stability of stannous ions under certain conditions was shown to be the main reason for low radiochemical purity. Limits and dangers of fractionating kits are discussed and related to content and instability of tin(II).

Electrochemistry↗
PubMed2000

Fabrication and photoelectric properties of self-assembled bilayer lipid membranes on conducting glass.

Supported bilayer lipid membranes (s-BLMs with and without the doping of fullerene C60) self-assembled on indium-tin oxide (ITO) glass were fabricated and characterized by cyclic voltammetry and electrochemical impedance spectroscopy using a three-electrode system. The photoelectric properties of the ITO supported planar lipid bilayers were studied. Light intensity of irradiation, bias voltage, and concentration of donors have been found to be limiting factors of the transmembrane photocurrent. The facilitation effect of C60 doping in s-BLMs on the photoinduced electron transfer across s-BLM is discussed. This novel self-assembled ITO/s-BLM system may provide a simple and mechanically stable model for the study of the photoelectric and photodynamic properties of biomembranes.

Electric Conductivity↗
PubMed2002

Protective effect of HO-1 against oxidative stress in human hepatoma cell line (HepG2) is independent of telomerase enzyme activity.

Heme oxygenase-1 (HO-1) is a stress response protein and its induction is associated with protection against oxidative stress. Cell survival during exposure to environmental stresses is associated with elevation of HO-1. Telomerase plays an important role in cell proliferation and immortalization. Our objective was to determine whether the adaptive cellular response to survive exposure to environmental stresses is dependent on expression of HO-1 and telomerase activity in hepatoma cell line (HepG2). Exposure of HepG2 to oxidants, H(2)O(2) (100 microM), as well as HO-1 inducers, heme (10 microM) and stannic chloride (SnCl(2)) (10 microM), resulted in an increased HO-1 mRNA, protein and total HO activity. On the other hand, HO activity was inhibited by addition of stannic mesoporphyrin (SnMP) (10 microM). These effects were brought about without altering endogenous HO-2 protein levels. Telomerase activity was not affected by oxidants, inducers of HO-1 or inhibitors of HO activity. Similarly, the catalytic subunit of telomerase enzyme human telomerase reverse transcriptase (hTERT), which is considered as the major regulator of telomerase activity, was not affected by oxidants, heme and H(2)O(2), or downregulation of HO gene activity by SnMP. This study demonstrates, for the first time, that induction of HO-1 gene mediates protection against oxidants and increases cell survival by a mechanism independent of telomerase enzyme activity. Suppression of HO activity by SnMP decreased cell resistance to oxidant stressors without altering telomerase activity.

Blotting, Western↗
PubMed2003

Lead-tin mirror formation from mixtures of red lead and tin sulphide.

Mosaic gold, tin (IV) sulphide, is a yellow pigment which was known in antiquity but whose use was superseded by other more easily obtainable yellow pigments by the Renaissance. The identification of mosaic gold residues in a burnished golden mirror decoration on a XIIIth Century Spanish polychrome statue is important in that the first reference to the use of mosaic gold in the European literature dates from the XIVth Century, although the use of this material in China had been recorded some time before. In this paper, Raman spectroscopy, XRD and SEM are used in the analysis of the conditions required for the formation of golden mirrors using tin (IV) sulphide in admixture with dilead (II) lead (IV) tetroxide and mercury (II) sulphide. From these results, it is proposed that the major reactions are the reduction of Sn(IV) to Sn(0) with the accompanying oxidation of lead (II) oxide to lead (IV) oxide and the formation of lead (0) and lead (II) sulphide. From these results it was possible to explain the process of creation of the golden mirror from mosaic gold in the XIIIth Century.

Lead↗
PubMed2002

Effect of metal ion exchange on the photocurrent response from bacteriorhodopsin on tin oxide electrodes.

The transient photocurrent response from bacteriorhodopsin (bR) on tin oxide electrodes was strongly influenced by metal ions bound to bR molecules. The photocurrent polarity reversal pH, which corresponded to the pH value for the reversal of the proton release/uptake sequence in the bR photocycle, of cation-substituted purple membrane (PM) was shifted to lower pH with the increase in the cation affinities to carboxyl groups and a close correlation was noted between the two values. This suggests that the metal ion present in the extracellular region of a bR molecule modulates the pK(a) of proton release groups of bR by stabilizing the ionized state of the proton-releasing glutamic acids. The behavior of photocurrents at light-off in alkaline media, reflecting the proton uptake by bR, was unchanged by binding monovalent (Na(+) and K(+)) or divalent cations (Mg(2+) and Ca(2+)), but was drastically changed by binding La(3+) ions. This can be explained by invoking a substantial slowing of the proton uptake process in the presence of La(3+).

Bacteriorhodopsins↗
PubMed2001

Oxidation kinetics of guanine in DNA molecules adsorbed onto indium tin oxide electrodes.

Oligonucleotides containing the guanine nucleobase were adsorbed onto ITO electrodes from mixtures of DMF and acetate buffer. Chronocoulometry and chronoamperometry were performed on the modified electrodes in both phosphate buffer and buffer containing low concentrations of the inorganic complex Ru(bpy)3(2+) (bpy = 2,2' bipyridine), which catalyzes guanine oxidation. The charge and current evolution with and without the catalyst were compared to the charge and current evolution for electrodes that were treated with identical oligonucleotides that were substituted at every guanine with the electrochemically inert nucleobase hypoxanthine. Chronocoulometry over 2.5 s shows that roughly 2 electrons per guanine were transferred to the electrode in both the presence and absence of Ru(bpy)3(2+), although at a slower rate for the uncatalyzed process. Chronoamperograms measured over 250 ms can be fit to a double exponential decay, with the intensity of the fast component roughly 6-20 times greater than that of the slow component. First- and second-order rate constants for catalytic and direct guanine oxidation were determined from the fast component. The maximum catalytic enhancement for immobilized guanine was found to be i(cat)/i(d) = 4 at 25 microM Ru(bpy)3(2+). The second-order rate constant for the catalyzed reaction was 1.3 x 10(7) M(-1) s(-1), with an apparent dissociation constant of 8.8 microM. When compared to parallel studies in solution, a smaller value of the dissociation constant and a larger value of the second-order rate constant are observed, probably due to distortion of the immobilized DNA, an increase in the local negative charge due to the oxygen sites on the ITO surface, and redox cycling of the catalyst, which maintains the surface concentration of the active form.

Adsorption↗
PubMed2001

Modification of indium tin oxide electrodes with repeat polynucleotides: electrochemical detection of trinucleotide repeat expansion.

Genomic expansion of the triplet repeat sequences 5'-(CTG)n and 5'-(CGG)n leads to myotonic dystrophy and fragile X syndrome, respectively. Methods for determining the number of repeats in unprocessed nucleic acids would be useful in diagnosing diseases based on triplet repeat expansion. Electrochemical reactions based on the oxidation of guanine were expected to give larger signals per strand for expansion of repeats containing guanine. A novel PCR reaction was used to generate fragments containing 150, 230, 400, and 830 repeats of (CTG)n, which codes for myotonic dystrophy, and 130 and 600 repeats of (CGG)n, which codes for fragile X syndrome. These PCR fragments were immobilized to indium tin oxide electrodes, and oxidation of guanine in the fragments was realized using electrocatalysis by Ru(bpy)3(2+) (bpy = 2,2'-bipyridine). The catalytic currents due to oxidation of the immobilized guanines by Ru(bpy)3(3+) increased with the number of repeats and were a linear function of the repeat number when normalized to the number of strands immobilized. These results suggest a sensing strategy for repeat length based on the combination of the electrocatalytic strategy for determining the repeat length combined with existing methods for determining the number of strands.

DNA↗
PubMed2003

Development of an "electroptode" immunosensor: indium tin oxide-coated optical fiber tips conjugated with an electropolymerized thin film with conjugated cholera toxin B subunit.

We demonstrate that it is possible to create surface-conductive fiber optics, upon which may be electropolymerized a biotinylated polypyrrole thin film, which may then be used to affinity coat the fiber with molecular recognition probes. This fiber-optic electroconductive surface modification is done by the deposition of a thin layer of indium tin oxide. Thereafter, biotin-pyrrole monomers are electropolymerized onto the conductive metal oxide surface and then exposed to avidin. Avidin-biotin interactions were used to modify the fiber optics with biotin-conjugated cholera toxin B subunit molecules, for the construction of an immunosensor to detect cholera antitoxin antibodies. The biosensor was tested for sensitivity, nonspecificity, and overall practicality.

Antibodies↗
PubMed2004

Spectroelectrochemical sensing based on attenuated total internal reflectance stripping voltammetry. 2. Determination of mercury and lead.

Detection of lead and mercury by attenuated total internal reflectance spectroscopy coupled to stripping voltammetry is demonstrated. Changes in attenuation of light passing through an indium tin oxide optically transparent electrode (ITO-OTE) accompany the electrodeposition and stripping of lead and mercury on the electrode surface. The change in absorbance during stripping of electrodeposited metal constitutes the analytical response that enables detection over a range of 2.5 x 10(-7)-5 x 10(-5) and 5 x 10(-8)-5 x 10(-5) M for mercury and lead, respectively. The spectroelectrochemical responses of mercury and lead on the ITO surface are characterized and optimized with respect to solution conditions, the potential excitation signals used for deposition and stripping, and wavelength for detection. The deposited metals were examined by environmental scanning electron miscroscopy, and the electrodeposition pattern of lead and mercury was found to influence the optical response.

Electrochemistry↗
PubMed2004

Quantitative photoelectrochemical detection of biological affinity reaction: biotin-avidin interaction.

Quantitative detection of a biological affinity reaction, the biotin/avidin recognition, was achieved using our newly developed photoelectrochemical analytical system. The system is based on the operation mechanism of the well-developed dye-sensitized photoelectrochemical solar cells and comprises a ruthenium tris(2,2'-bipyridine) (Ru-bipy) derivative as the photoelectrochemical signal-generating molecule, oxalate as the sacrificial electron donor, and tin oxide nanoparticle as the semiconductor electrode material. To perform the affinity reaction, avidin was immobilized on SnO(2) electrode by passive adsorption. Biotin-linked bovine serum albumin (BSA) was labeled with an NHS-ester derivative of Ru-bipy. After binding of BSA to the surface-immobilized avidin through biotin, photoelectrochemical measurement was carried out in the presence of oxalate. Anodic photocurrent was turned on and off repeatedly by control of incidental light. The action spectrum of the photocurrent resembled the absorption spectrum of Ru-bipy, proving the photocurrent was generated from the metal complex. A linear relationship between photocurrent and BSA concentration was obtained in the range of 1-100 microg/mL. This is the first case of quantitative photoelectrochemical detection of a biological affinity interaction.

2,2'-Dipyridyl↗
PubMed2006

Dynamic, electronically switchable surfaces for membrane protein microarrays.

Microarray technology is a powerful tool that provides a high throughput of bioanalytical information within a single experiment. These miniaturized and parallelized binding assays are highly sensitive and have found widespread popularity especially during the genomic era. However, as drug diagnostics studies are often targeted at membrane proteins, the current arraying technologies are ill-equipped to handle the fragile nature of the protein molecules. In addition, to understand the complex structure and functions of proteins, different strategies to immobilize the probe molecules selectively onto a platform for protein microarray are required. We propose a novel approach to create a (membrane) protein microarray by using an indium tin oxide (ITO) microelectrode array with an electronic multiplexing capability. A polycationic, protein- and vesicle-resistant copolymer, poly(l-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG), is exposed to and adsorbed uniformly onto the microelectrode array, as a passivating adlayer. An electronic stimulation is then applied onto the individual ITO microelectrodes resulting in the localized release of the polymer thus revealing a bare ITO surface. Different polymer and biological moieties are specifically immobilized onto the activated ITO microelectrodes while the other regions remain protein-resistant as they are unaffected by the induced electrical potential. The desorption process of the PLL-g-PEG is observed to be highly selective, rapid, and reversible without compromising on the integrity and performance of the conductive ITO microelectrodes. As such, we have successfully created a stable and heterogeneous microarray of biomolecules by using selective electronic addressing on ITO microelectrodes. Both pharmaceutical diagnostics and biomedical technology are expected to benefit directly from this unique method.

Electrodes↗