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At least 991 records · Page 55Linked to original sources
PubMed2003

Use of disposable gold working electrodes for cation chromatography-integrated pulsed amperometric detection of sulfur-containing amino acids.

We have prepared disposable thin-film gold working electrodes on polymeric substrates. Our microfabrication process allows for inexpensive and reproducible mass production of such electrodes. We utilize this new type of electrode in flow-through electrochemical cells to replace the conventional non-disposable gold working electrodes for integrated pulsed amperometric detection (IPAD) of compounds separated by high-performance cation-exchange chromatography. Using two S-containing amino acids (homocysteine and cysteine) as test compounds, we have modified a previously reported waveform for optimum performance with disposable gold electrodes. With the help of the same two test substances we have characterized the analytical performance of disposable gold electrodes under the new conditions. Compared to non-disposable working electrodes, the disposable working electrodes generated equal or better results in the limit of detection, linearity of calibration and reproducibility. When used with a new IPAD waveform, the disposable electrodes functioned reproducibly for 3 days. At the end of the specified usage period of 3 days, the disposable electrodes are simply replaced. Reconditioning by polishing is thus no longer required.

Calibration↗
PubMed2004

[Determination of trace platinum, palladium and gold in smples by ICP-AES and fire assay preconcentration].

A method of elemental determination is put forward in this paper. Namely, Pt, Pd, Au in 10-20 g samples were preconcentrated in milligram microgranular silver alloy by using fire assay. When compounded in solution, trace platinum, palladium, and gold in the solution were determined by ICP-AES. The detection limits of this method were 0.01, 0.005, and 0.01 microg x mL(-1) for Pt, Pd and Au, respectively. Recoveries of standard were more than 97% with precision of 0.1%, 0.12%, and 0.09% of RSD (n=10), respectively. It has proven that this analysis method is quick, simple and accurate. The method has been applied to the determination of contents of Pt, Pd and Au in samples.

Fires↗
PubMed2004

Mitochondrial permeability transition induced by dinuclear gold(I)-carbene complexes: potential new antimitochondrial antitumour agents.

Seven dinuclear gold(I) complexes of bidentate N-heterocyclic carbene ligands have been evaluated for their ability to induce mitochondrial membrane permeabilisation (MMP) in isolated rat liver mitochondria. Six of the compounds, at concentrations of 10 microM, induced Ca(2+)-sensitive MMP as evidenced by mitochondrial swelling. In the absence of low concentrations of exogenous Ca(2+), the compounds were either inactive or their activity was significantly decreased. The mitochondrial swelling was completely blocked by the addition of cyclosporin A, a well established inhibitor of the mitochondrial permeability transition pore (MPT) that is believed to be responsible for MMP. The rates and levels of uptake of these compounds into mitochondria were estimated by measuring mitochondrial Au levels using inductively coupled plasma optical emission spectroscopy. Significant differences were found in the levels at which the different compounds accumulated in the mitochondria, but these differences did not correlate with the rate at which they induced mitochondrial swelling. These results suggest that the mechanism by which MMP is induced by these lipophilic cationic Au(I)-carbene complexes is not purely a function of the level of compound accumulation. Instead, a more specific mechanism, possibly involving disruption of the function of a particular enzyme, or interaction with a MPT component, appears to be more likely.

Animals↗
PubMed2000

Affinity biosensor for avidin using a double functionalized dendrimer monolayer on a gold electrode.

We have developed an affinity biosensor system based on avidin-biotin interaction on a gold electrode. As the building block of an affinity-sensing monolayer, a fourth-generation (G4) poly(amidoamine) dendrimer having partial ferrocenyl-tethered surface groups was prepared and used. The unmodified surface amine groups from dendrimers were functionalized with biotinamidocaproate, and the biotinylated and electroactive dendritic monolayer was constructed on a gold electrode for the affinity-sensing surface interacting with avidin. An electrochemical signal from the affinity biosensor was generated by free glucose oxidase in electrolyte, depending on the degree of coverage of the sensing surface with avidin. The sensor signal decreased correlatively with increasing avidin concentration and approached a minimum level when the sensing surface was fully covered with avidin. The detection limit of avidin was about 4.5 pM, and the sensor signal was linear ranging from 1.5 pM to 10 nM under optimized conditions. From the kinetic analysis using the biotinylated glucose oxidase, an active enzyme coverage of 2.5 x 10(-12) mol/cm(2) on the avidin-pretreated surface was registered, which demonstrates the formation of a spatially ordered and compact protein layer on the derivatized electrode surface.

Animals↗
PubMed2006

Modification of gold nanorods using phosphatidylcholine to reduce cytotoxicity.

Hexadecyltrimethylammonium bromide (CTAB), which is necessary for the preparation of gold nanorods (NRs), was extracted from a NR solution into a chloroform phase containing phosphatidylcholine (PC). After three extractions, the zeta potential of the NRs remained positive, but its magnitude decreased from +67 +/- 1 to +15 +/- 1 mV. Transmission electron microscopy and energy-dispersive X-ray analysis indicated that the NRs were passivated with PC. The PC layer on the NR surface contributed to the prevention of NR aggregation. The PC-passivated NRs showed low cytotoxicity in comparison with twice-centrifuged NRs. It was shown that a negligible amount of CTAB was dispersed in the NR solution after the extraction. The extraction using a chloroform phase containing PC was found to be a convenient way of replacing the CTAB with alternative capping agents such as PC. This is a key technique for preparing functional NRs that can have practical applications.

Cell Survival↗
PubMed2005

Nanowiring of a redox enzyme by metallized peptides.

A molecular assembly consisting of a redox enzyme, NADH peroxidase, a metallized double-helical peptide, and a gold nanoparticle immobilized onto a gold wire derivatized with a benzenedithiol compound, initiated and conducted redox signals in the presence of H(2)O(2) and NADH. The current generated by the binding of NADH, the electron donor, was transduced through the molecular assembly with apparently little loss of signal to the solution. The currents measured correlate to an electron transfer rate constant on the order of 3,000 s(-1) within each assembly. This electron transfer rate is two orders of magnitude higher than the endogenous electron transfer rate from NADH to the native enzyme, 27 s(-1). This rate indicates that the metallized peptide is in a conformation conducive for electron transfer and, in conjunction with the redox enzyme, can form effective conduits of electrical signals. This work demonstrates the feasibility of utilizing designed and highly efficient biomolecular assemblies for the production of ultra-sensitive, in-situ biosensors.

Biosensing Techniques↗
PubMed2006

Hybridization probe for femtomolar quantification of selected nucleic acid sequences on a disposable electrode.

Mixed monolayers of electroactive hybridization probes on gold surfaces of a disposable electrode were investigated as a technology for simple, sensitive, selective, and rapid gene identification. Hybridization to the ferrocene-labeled hairpin probes reproducibly diminished cyclic redox currents, presumably due to a displacement of the label from the electrode. Observed peak current densities were roughly 1000x greater than those observed in previous studies, such that results could easily be interpreted without the use of algorithms to correct for background polarization currents. Probes were sensitive to hybridization with a number of oligonucleotide sequences with varying homology, but target oligonucleotides could be distinguished from competing nontarget sequences based on unique "melting" profiles from the probe. Detection limits were demonstrated down to nearly 100 fM, which may be low enough to identify certain genetic conditions or infections without amplification. This technology has rich potential for use in field devices for gene identification as well as in gene microarrays.

Algorithms↗
PubMed2006

Measurement of the azimuthal anchoring energy of liquid crystals in contact with oligo(ethylene glycol)-terminated self-assembled monolayers supported on obliquely deposited gold films.

We report measurements of the orientations and azimuthal anchoring energies of the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) on polycrystalline gold films that are deposited from a vapor at an oblique angle of incidence and subsequently decorated with organized monolayers of oligomers of ethylene glycol. Whereas the gold films covered with monolayers presenting tetra(ethylene glycol) (EG4) lead to orientations of 5CB that are perpendicular to the plane of incidence of the gold, monolayers presenting tri(ethylene glycol) (EG3) direct 5CB to orient parallel to the plane of incidence of the gold during deposition of the gold film. We also measure the azimuthal anchoring energy of the 5CB to be smaller on the surfaces presenting EG3 (3.2 +/- 0.8 microJ/m2) as compared to EG4 (5.5 +/- 0.9 microJ/m2). These measurements, when combined with other results presented in this paper, are consistent with a physical model in which the orientation and anchoring energies of LCs on these surfaces are influenced by both (i) short-range interactions of 5CB with organized oligomers of ethylene glycol at these surfaces and (ii) long-range interactions of 5CB with the nanometer-scale topography of the obliquely deposited films. For surfaces presenting EG3, these short- and long-range interactions oppose each other, leading to small net values of anchoring energies that we predict are dependent on the level of order in the EG3 SAM. These measurements provide insights into the balance of interactions that control the orientational response of LCs to biological species (proteins, viruses, cells) on these surfaces.

Biphenyl Compounds↗
PubMed1997

Bonding of silver-palladium-copper-gold alloy with thiol derivative primers and tri-n-butylborane initiated luting agents.

This in vitro study elevated the effect of two primers on bond strengths and durability of luting agents joined to a silver-palladium-copper-gold alloy. One primer (Metal Primer) contained methacryloyloxyalkyl thiophosphate derivative (MEPS). The other primer (V-Primer) contained 6-(4-vinylbenzyl-n-propyl)amino-1,3,5-triazine-2,4-dithiol (VTD). The luting agent was a methyl methacrylate (MMA)-based adhesive resin that contained 4-methacryloyloxyethyl trimellitate anhydride (4-META) and was initiated with tri-n-butylborane derivative (TBB). In order to evaluate the function of 4-META, MMA-TBB resin without 4-META was used as a control. The alloy specimens were bonded with six combinations of two primers and two luting agents. Shear bond strengths were determined before and after thermocycling. Both primers significantly elevated the bond strengths of the luting agents joined to the alloy. For unprimed groups, 4-META resin showed a more durable bond than did MMA-TBB resin. Combined use of Metal Primer with 4-META resin reduced the bond strength, while combination of V-Primer and 4-META resin did not affect the bond strength.

Acrylic Resins↗
PubMed1997

Effects of adhesive primers for noble metals on shear bond strengths of resin cements.

OBJECTIVES: The purpose of this study was to evaluate the durability and shear bond strengths of the different combinations of two adhesive primers and three resin cements to two types of noble metal alloys, silver-palladium copper-gold and type IV gold alloys. METHODS: The adhesive luting agents Imperva Dual, Panavia 21 and Super-Bond C&B, and the adhesive primers Metal Primer and V-Primer were used. Two sizes of casting alloy disks were nonprimed or primed and cemented with each adhesive luting agent. The specimens were stored in 37 degrees C water for one day and then immersed alternately in 4 degrees C and 60 degrees C water baths for 1 min each for up to 100,000 thermal cycles before shear mode testing at a cross-head speed of 0.5 mm/min. RESULTS: The application of Metal Primer was effective for improving the shear bond strengths between each of the three resin cements and both noble metal alloys compared with nonprimed specimens. When each noble metal alloy was cemented with Super-Bond C&B, there were no significant differences between the bond strengths with the use of Metal Primer and those with the use of V-Primer at 100,000 thermal cycles. However, V-Primer was ineffective for enhancing the shear bond strengths of Imperva Dual and Panavia 21 to noble metals. CONCLUSION: Metal Primer and V-Primer are clinically useful for strongly bonding adhesive resin cements to noble metal alloys.

Analysis of Variance↗
PubMed2006

Selective recruitment of membrane protein complexes onto gold substrates patterned by dip-pen nanolithography.

Dip-pen nanolithography (DPN) is employed to develop a generic array platform for the selective recruitment of membrane protein complexes. An atomic force microscope tip inked with HS(CH2)16NH2 is used to generate amino-terminated domains on gold. These domains can be arranged into microscopic and submicroscopic patterns, and the untreated gold substrate is subsequently blocked with HS(CH2)2CONH(CH2CH2O)15CH3, a compound known to resist the unspecific binding of proteins and cells. The patterned gold substrate is exposed to an enriched membrane fraction from mutant Rhodobacter sphaeroides, which contains photosynthetic core complexes consisting of the reaction center and the light-harvesting complex LH1. The selective recruitment to the patterned domains, governed primarily by electrostatic interactions, is confirmed by contact mode atomic force microscopy.

Adsorption↗
PubMed2004

Toward a novel metal-based chemotherapy against tropical diseases. 7. Synthesis and in vitro antimalarial activity of new gold-chloroquine complexes.

A number of new Au(I) and Au(III) complexes of chloroquine (CQ) have been prepared, characterized, and evaluated in vitro against several strains of Plasmodium falciparum. [(CQ)Au(PPh(3))][NO(3)] (2) was synthesized by reaction of AuCl(PPh(3)) with AgNO(3) followed by treatment with CQ. Similar reactions of AuCl(PR(3)) (R = Me, Et) with KPF(6) and CQ yielded [(CQ)Au(PMe(3))][PF(6)] (3), and [(CQ)Au(PEt(3))][PF(6)] (4), respectively. KAuCl(4) reacted with CQ to produce the Au(III) complex [(CQ)(2)Au(Cl)(2)]Cl (5), which in turn formed [(CQ)Au(Cl)(SR)(Et(2)O)]Cl (6) by reaction with 1-thio-beta-d-glucose-2,3,4,6-tetraacetate (SRH). The new compounds were characterized by a combination of elemental analysis, fast atom bombardment mass spectrometry (FAB-MS), and NMR spectroscopy. All the complexes display in vitro activity against CQ-sensitive and CQ-resistant strains of Plasmodium falciparum. The highest activity for this series was obtained for complex 4, which is 5 times more active than chloroquine diphosphate (CQDP) against the CQ-resistant strain FcB1. On preincubation of noninfected red blood cells with complexes 1, 5, and 6, protection against subsequent infection was observed in some cases. No clear structure-activity correlations could be established for this series of compounds.

Animals↗
PubMed2000

Modulating fibroblast adhesion, spreading, and proliferation using self-assembled monolayer films of alkylthiolates on gold.

Ultrathin, highly organized functionalized alkylthiol monolayers were applied as model substrates for cell growth and protein adsorption studies. The aim of this approach was to improve the understanding of molecular surface determinants required for adhesion-dependent cell growth and proliferation using well-controlled surface chemistry. Carboxyl- and methyl-terminated alkylthiol monolayers on gold were used to monitor Swiss 3T3 fibroblast adhesion, spreading, and growth. Stress fiber and focal contact formation were determined by immunostaining of actin filaments and paxillin. Fibronectin deposition and conformation on these surface chemistries in the presence and absence of competing proteins were also determined. The relative levels of adsorbed fibronectin were assessed using radiolabeled proteins. Exposure of the 10th type III cell integrin binding domain of fibronectin was assessed using a radiolabeled monoclonal antibody. Distinct alkylthiol substrate chemistry-dependent differences were observed in fibroblast adhesion, spreading, and growth. The formation of focal contacts and stress fibers was enhanced on the carboxyl-terminated surface relative to the methyl surface. Relative deposition and conformations of adsorbed fibronectin were shown to be dependent on surface chemistry in both the presence and absence of competing proteins. The results indicated that well-controlled culture surfaces modulate differential cell adhesion, spreading, and growth through modulations of the amounts and conformations of adsorbed extracellular matrix molecules (e.g., fibronectin).

3T3 Cells↗
PubMed1992

Protein-gold transport in the endocytic complex of trophotaenial absorptive cells in the embryos of a goodeid teleost.

This paper reports adsorptive endocytosis of exogenous proteins by the trophotaenial absorptive cells (TACs) in the viviparous goodeid teleost, Ameca splendens. In vitro incubations were performed with gold conjugated to bovine serum albumin (Au-BSA), human transferrin (Au-HTf), fetuin (Au-Fet), and asialofetuin (Au-ASFet). Localization of gold label on the TAC surface was nearly exclusive to patches of an amorphous coat associated with part of the intermicrovillous plasma membrane. On addition of excess BSA, HTf, Fet, or ASFet to incubation media containing, respectively, Au-BSA, Au-HTf, Au-Fet, or Au-ASFet, the density of gold particles adsorbed on the TAC surface decreased drastically. Moreover, attachment of the four protein-gold complexes to the same plasma membrane sites was suggested by reciprocal inhibitory effects. Further proteins such as hemoglobin, myoglobin, and cytochrome c were as well potent inhibitors of Au-BSA and Au-HTf binding and uptake. Binding of TACs of native BSA or HTf was visualized by immunogold labeling. The interactions between proteins and binding sites required both the presence of Ca2+ and appropriate pH greater than 6.6. Analyses of the concentration-dependent BSA and HTf binding curves, plotted from morphometric data, resulted in apparent dissociation constants, Kds, of approximately 5 x 10(-7) M and 4 x 10(-7) M, respectively. Following binding at the TAC surface and internalization via clathrin-coated pits and vesicles the several ligands were routed along the lysosomal pathway with transit through the endosomal compartment. Prolonged incubation periods led to massive intracellular accumulation of tracer proteins. The effects of NH4Cl (10 mM) treatment on TACs included enormous cytoplasmic vacuolation, a reversible loss of protein binding sites on the plasma membrane, and a block in the transport of protein-gold complexes to lysosomes.

Absorption↗
PubMed2005

An Os(II)--bisbipyridine--4-picolinic acid complex mediates the biocatalytic growth of au nanoparticles: optical detection of glucose and acetylcholine esterase inhibition.

The complex Os(II)-bisbipyridine-4-picolinic acid, [Os(bpy)(2)PyCO(2)H](2+) (1), mediates the biocatalyzed growth of Au nanoparticles, Au NPs, and enables the spectroscopic assay of biocatalyzed transformations and enzyme inhibition by following the Au NP plasmon absorbance. In one system, [Os(bpy)(2)PyCO(2)H](2+) mediates the biocatalyzed oxidation of glucose and the growth of Au NPs in the presence of glucose oxidase, GOx, AuCl(4) (-), citrate and Au NP seeds. The mechanism of the Au NPs growth involves the oxidation of the [Os(bpy)(2)PyCO(2)H](2+) complex by AuCl(4) (-) to form [Os(bpy)(2)PyCO(2)H](3+) and Au(I). The [Os(bpy)(2)PyCO(2)H](3+) complex mediates the GOx biocatalyzed oxidation of glucose and the regeneration of the mediator 1. Citrate reduces Au(I) and enlarges the Au seeds by the catalytic deposition of gold on the Au NP seeds. In the second system, the enzyme acetylcholine esterase, AChE, is assayed by the catalytic growth of the Au NPs. The hydrolysis of acetylcholine (2) by AChE to choline is followed by the [Os(bpy)(2)PyCO(2)H](3+) mediated oxidation of choline to betaine and the concomitant growth of the Au NPs. The mediated growth of the Au NPs is inhibited by 1,5-bis(4-allyldimethylammonium-phenyl)pentane-3-one dibromide (3). A competitive inhibition process was demonstrated (K(M)=0.13 mM, K(I)=2.6 microM) by following the growth of the Au NPs.

2,2'-Dipyridyl↗
PubMed1988

Corrosion behavior of nickel-containing alloys in artificial sweat.

The corrosion resistance of various nickel-containing alloys was measured in artificial sweat (perspiration) using the Tafel extrapolation method. It was found that Ni, CuNi 25 (coin alloy), NiAl (colored intermetallic compounds), WC + Ni (hard metal), white gold (jewelry alloy), FN42 and Nilo Alby K (controlled expansion alloys), and NiP (electroless nickel coating) are in an active state and dissolve readily in oxygenated artificial sweat. By contrast, austenitic stainless steels, TiC + Mo2C + Ni (hard metal), NiTi (shape-memory alloy), Hastelloy X (superalloy), Phydur (precipitation hardening alloy), PdNi and SnNi (nickel-containing coatings) are in a passive state but may pit under certain conditions. Cobalt, Cr, Ti, and some of their alloys were also investigated for the purpose of comparison. Cobalt and its alloys have poor corrosion resistance except for Stellite 20. Chromium and high-chromium ferritic stainless steels have a high pitting potential but the latter are susceptible to crevice corrosion. Ti has a pitting potential greater than 3 V. Comparison between the in vitro measurements of the corrosion rate of nickel-based alloys and the clinical observation of the occurrence of contact dermatitis is discussed.

Alloys↗