Electrochemical oxidation of dihydronicotinamide adenine dinucleotide (NADH) : Comparison of highly oriented pyrolytic graphite (HOPG) and polycrystalline boron-doped diamond (pBDD) electrodes

The electro-oxidation of nicotinamide adenine dinucleotide (NADH) is studied at bare surfaces of highly oriented pyrolytic graphite (HOPG) and semi-metallic polycrystalline boron-doped diamond (pBDD). A comparison of these two carbon electrode materials is interesting because they possess broadly similar densities of electronic states that are much lower than most metal electrodes, but graphite has carbon sp2-hybridization, while in diamond the carbon is sp3-hybridised, with resulting major differences in bulk structure and surface termination. Using cyclic voltammetry (CV), it is shown that NADH oxidation is facile at HOPG surfaces but the reaction products tend to strongly adsorb, which causes rapid deactivation of the electrode activity. This is an important factor that needs to be taken into account when assessing HOPG and its intrinsic activity. It is also shown that NADH itself adsorbs at HOPG, a fact that has not been recognized previously, but has implications for understanding the mechanism of the electro-oxidation process. Although pBDD was found to be less susceptible to surface fouling, pBDD is not immune to deterioration of the electrode response, and the reaction showed more sluggish kinetics on this electrode. Scanning electrochemical cell microscopy (SECCM) highlights a significant voltammetric variation in electroactivity between different crystal surface facets that are presented to solution with a pBDD electrode. The electroactivity of different grains correlates with the local dopant level, as visualized by field emission-scanning electron microscopy. SECCM measurements further prove that the basal plane of HOPG has high activity towards NADH electro-oxidation. These new insights on NADH voltammetry are useful for the design of optimal carbon-based electrodes for NADH electroanalysis

Electrochemical determination of hydroquinone using hydrophobic ionic liquid-type carbon paste electrodes

Three types of carbon paste electrodes (CPEs) with different liquid binders were fabricated, and their electrochemical behavior was characterized via a potassium hexacyanoferrate(II) probe. 1-Octyl-3-methylimidazolium hexafluorophosphate ionic liquid (IL) as a hydrophobic conductive pasting binder showed better electrochemical performance compared with the commonly employed binder. The IL-contained CPEs demonstrated excellent electroactivity for oxidation of hydroquinone. A diffusion control mechanism was confirmed and the diffusion coefficient (D) of 5.05 × 10-4 cm2 s-1 was obtained. The hydrophobic IL-CPE is promising for the determination of hydroquinone in terms of high sensitivity, easy operation, and good durability

Large-scale gene-centric analysis identifies novel variants for coronary Artery disease

Coronary artery disease (CAD) has a significant genetic contribution that is incompletely characterized. To complement genome-wide association (GWA) studies, we conducted a large and systematic candidate gene study of CAD susceptibility, including analysis of many uncommon and functional variants. We examined 49,094 genetic variants in ∼2,100 genes of cardiovascular relevance, using a customised gene array in 15,596 CAD cases and 34,992 controls (11,202 cases and 30,733 controls of European descent; 4,394 cases and 4,259 controls of South Asian origin). We attempted to replicate putative novel associations in an additional 17,121 CAD cases and 40,473 controls. Potential mechanisms through which the novel variants could affect CAD risk were explored through association tests with vascular risk factors and gene expression. We confirmed associations of several previously known CAD susceptibility loci (eg, 9p21.3:p<10−33; LPA:p<10−19; 1p13.3:p<10−17) as well as three recently discovered loci (COL4A1/COL4A2, ZC3HC1, CYP17A1:p<5×10−7). However, we found essentially null results for most previously suggested CAD candidate genes. In our replication study of 24 promising common variants, we identified novel associations of variants in or near LIPA, IL5, TRIB1, and ABCG5/ABCG8, with per-allele odds ratios for CAD risk with each of the novel variants ranging from 1.06–1.09. Associations with variants at LIPA, TRIB1, and ABCG5/ABCG8 were supported by gene expression data or effects on lipid levels. Apart from the previously reported variants in LPA, none of the other ∼4,500 low frequency and functional variants showed a strong effect. Associations in South Asians did not differ appreciably from those in Europeans, except for 9p21.3 (per-allele odds ratio: 1.14 versus 1.27 respectively; P for heterogeneity = 0.003). This large-scale gene-centric analysis has identified several novel genes for CAD that relate to diverse biochemical and cellular functions and clarified the literature with regard to many previously suggested genes

Ionic liquid-carbon composite glucose biosensor.

The use of ionic liquids that are solid at room temperature such as n-octyl-pyridinium hexafluorophosphate (nOPPF(6)) is shown to be advantageous in the fabrication of new form of biocomposite materials with attractive performance over other types of composites and pastes involving non-conductive binders. The resulting IL/graphite material brings new capabilities for electrochemical devices by combining the advantages of ILs and "bulk" composite electrodes. The electrocatalytic properties of the ILs are not impaired by their association with the graphite powder. The marked electrocatalytic activity towards hydrogen peroxide permits effective amperometric biosensing of glucose in connection with the incorporation of glucose oxidase within the three-dimensional IL/graphite matrix. The accelerated electron transfer is coupled with low background current and improved linearity. The advantages of these IL-based biocomposite devices are illustrated from comparison to conventional mineral oil/graphite biocomposite. The influence of the IL and glucose oxidase (GOx) loading upon the amperometric and voltammetric data, as well as the electrode capacitance and resistance, is examined. The preparation of IL/graphite composites overcomes a major obstacle for creating IL-based biosensing devices and expands the scope of IL-based electrochemical devices