The electron/hole conduction of disordered bulk double-stranded (ds) calf thymus DNA and of one-dimensionally aligned 12-base pair single- and double-stranded oligonucleotide monolayers on gold was probed by testing for the occurrence of Faradaic processes. The disordered ds-DNA film was probed by doping it with soybean peroxidase, an easy to “wire” thermostable polycationic enzyme and measuring the current density of electroreduction of H2O2 to water at SCE potential. Although the current density in films with hydrophilic electron-conducting polymeric “wires” is ∼0.5 mAcm-2, when ds-DNA was used to “wire” soybean peroxidase, the current density was only 0.1 μA cm-2, similar to that in the absence of an electron-conducting enzyme-“wiring” polymer. We conclude that the diffusivity of electrons in unaligned and unstretched calf thymus DNA is less than 10-11 cm2 s-1. Nevertheless, the occurrence of a Faradaic reaction was observed in the Au−S−(CH2)2−ds-oligo-NH−PQQ/Au−S−CH2−CH2−OH monolayer on gold, in which the helices were one-dimensionally aligned and comprised a >30 Å ds-oligonucleotide segment. In these the rate constant for PQQ electrooxidation−electroreduction was 1.5 ± 0.2 s-1, only about 4-fold less than the 5 ± 1 s-1 constant for the reference Au−S−(CH2)2−NH−PQQ monolayer. When two mismatches were introduced in the 12 base-pair ds-oligonucleotide (by C → A and C → T substitutions) the constant decreased to 0.6 ± 0.2 s -1. In contrast, the rate for the Au−S−(CH2)2−ss-oligo-NH−PQQ/Au−S−CH2−CH2−OH monolayer was too small to be measured; no voltammetric waves were detected at a scan rate of 10 mV s-1. The anisotropic conduction in the one-dimensionally ordered solid ds-DNA films is attributed to the concerted movement of cations in the direction of the main axes of the ds-helices when an electric field is applied. Such movement causes the high-frequency longitudinal (not the high-frequency transverse optical) polarizability to be high and thereby makes the resolved component of the high-frequency dielectric constant high. The solid ds-DNA films also contain less water than their solutions, which reduces the static dielectric constant relative to that of water. As shown by Mott and Gurney, reduction of the difference between the static dielectric constant and the high-frequency longitudinal dielectric constant increases the mean free path and the mobility of electrons in an ionic solid and makes ds-DNA a one-dimensional semiconductor. The high frequency dielectric constant, as described in textbooks on solid-state physics, also decreases the ionization energies of donors and greatly extends their Bohr-radii, which are sausage-shaped in ds-DNA. A likely n-type dopant is the G-base in the GC base pair, a dopant ionized (“oxidized”) in the high-frequency dielectric constant medium. The proposed biological function of the insulator-to-semiconductor transition upon parallel alignment of the ds-DNA is protection against irreversible chemical change by oxidation or reduction. Removing or adding of an electron produces...

Enzyme electrodes based on complexing a water-soluble copolymer of acrylamide and vinylimidazole with [Os(dmebpy)2C1]+/2+ (dmebpy = 4,4'-dimethyl-2,2'-bipyridine) and cross-linking with oxidases by water-soluble cross-linkers are described. The potential of the polyacrylamide-based redox polymer is +55 mV (SCE), a typical electron diffusion coefficient (De) in the redox hydrogel that results from its cross-linking is (1.3 +/- 0.1) x 10(-9) cm2/s. The properties of the enzyme electrodes formed when this redox hydrogel "wired" horseradish peroxidase (HRP), lactate oxidase (LOx) or glucose oxidase (GOx) depended on the thickness of the hydrogel film, the chemistry of their cross-linking, and their enzyme content. At the wired HRP electrodes, H2O2 was electrocatalytically reduced to water at 0.0 V (SCE). Lactate and glucose were electrocatalytically oxidized at 0.16 V (SCE). The GOx electrodes, when made with 140 micrograms/cm2 thick polymer films, were selective for glucose in the presence of physiological concentrations of urate and ascorbate.

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Amplification of an 800-base template was verified in a 10-min test on a 2-microL sample of the PCR product solution. For verification, digoxigeninylated primers and biotinylated d-UTP-16-biotin were added to the amplification solution. The resulting amplified product was digoxigeninlabeled at its 3'-end and was also labeled with multiple biotin functions along its chain. The detecting electrode was coated with an electron-conducting redox hydrogel to which anti-digoxin monoclonal antibody was covalently bound. The amplified DNA was captured by the electrode through conjugation of its 3'-digoxigenin with the antibody. Exposure to a solution of horseradish peroxidase-labeled avidin led to capture of the enzyme and switched the redox hydrogel from a noncatalyst to catalyst for H2O2 electroreduction. The switching resulted in an H2O2 electroreduction current density of 2.1 +/- 0.9 microA cm-2 in 10-4 M H2O2 at Ag/AgCl potential and at 25 degrees C.