Nanostructured carbon materials are potentially of great technological interest for the development of electronic, catalytic and hydrogen-storage systems. Here we describe a general strategy for the synthesis of highly ordered, rigid arrays of nanoporous carbon having uniform but tunable diameters (typically 6 nanometres inside and 9 nanometres outside). These structures are formed by using ordered mesoporous silicas as templates, the removal of which leaves a partially ordered graphitic framework. The resulting material supports a high dispersion of platinum nanoparticles, exceeding that of other common microporous carbon materials (such as carbon black, charcoal and activated carbon fibres). The platinum cluster diameter can be controlled to below 3 nanometres, and the high dispersion of these metal clusters gives rise to promising electrocatalytic activity for oxygen reduction, which could prove to be practically relevant for fuel-cell technologies. These nanomaterials can also be prepared in the form of free-standing films by using ordered silica films as the templates.

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The steady-state current that flows between the scanning tip (a disk ultramicroelectrode Imbedded In an Insulating sheath) and a planar sample substrate In a scanning electrochemical microscope (SECM) operating In the feedback mode is calculated by the finite element method with an exponentially expanding grid, for both conductive and Insulating samples. For conductive substrates the tip current, representing, for example, the oxidation reaction of R to O, Is enhanced by flow of R generated at the substrate to the tip and Is a function of tip/substrate distance, d, but not the radius of the Insulating sheath. For Insulating substrates, the tip current is decreased by blockage of the diffusion of R to the tip by the substrate and depends upon d and the Insulating sheath radius. The theoretical results are compared to experimental studies.

Real-time in situ spectroelectrochemical studies have been carried out in N,NЈ-dimethyl formamide containing lithium trifluoromethane sulfonate as an electrolyte and the results are reported. The results indicate that the primary reduction product of the cyclic form of sulfur, S 8c 2Ϫ , undergoes an equilibrium reaction to its linear chain counterpart, S 8l 2Ϫ , which then dissociates into various products. These two dianions and S 3 Ϫ• were produced along with a minor product, S 4 2Ϫ , at the potential corresponding to the first electron transfer. These products were further reduced or dissociated to species including S 7 2Ϫ , S 6 2Ϫ , S 5 2Ϫ , S 4 2Ϫ , S 3 2Ϫ , S 2 2Ϫ , and S 2Ϫ at the second electron-transfer step as evidenced by the spectral shifts observed during electrolysis. The reduction reactions are generally chemically reversible, making it possible to use sulfur reduction as a cathode reaction for Li/S batteries.

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By using specially constructed nanometer tips of sharpened Pt-Ir wire in a wax sheath, small numbers of molecules (1−10) can be trapped between the tip and a substrate. Repeated electron transfers of an electroactive molecule as it shuttles by diffusion between tip and substrate produce a current (∼0.6 pA/molecule) that can be used to detect the trapped molecules. The tip electrode size and shape can be found from the electrode approach curves (current vs tip-to-substrate distance) based on approximate equations and digital simulations. Analysis of the observed fluctuating currents by autocorrelation, spectral density, and probability density functions is also described.

We demonstrate the amplified detection of a target DNA based on the enzymatic deposition of silver. In this method, the target DNA and a biotinylated detection DNA probe hybridize to a capture DNA probe tethered onto a gold electrode. Neutravidin-conjugated alkaline phosphatase binds to the biotin of the detection probe on the electrode surface and converts the nonelectroactive substrate of the enzyme, p-aminophenyl phosphate, into the reducing agent, p-aminophenol. The latter, in turn, reduces metal ions in solutions leading to deposition of the metal onto the electrode surface and DNA backbone. This process, which we term biometallization, leads to a great enhancement in signal due to the accumulation of metallic silver by a catalytically generated enzyme product and, thus, the electrochemical amplification of a biochemically amplified signal. The anodic stripping current of enzymatically deposited silver provides a measure of the extent of hybridization of the target oligomers. This biometallization process is highly sensitive, detecting as little as 100 aM (10 zmol) of DNA. We also successfully applied this method to the sequence-selective discrimination between perfectly matched and mismatched target oligonucleotides including a single-base mismatched target.

We have developed a sandwich-type enzyme-linked DNA sensor as a new electrochemical method to detect DNA hybridization. A partially ferrocenyl-tethered poly(amidoamine) dendrimer (Fc-D) was used as an electrocatalyst to enhance the electronic signals of DNA detection as well as a building block to immobilize capture probes. Fc-D was immobilized on a carboxylic acid-terminated self-assembled monolayer (SAM) by covalent coupling of unreacted amine in Fc-D to the acid. Thiolated capture probe was attached to the remaining amine groups of Fc-D on the SAM via a bifunctional linker. The target DNA was hybridized with the capture probe, and an extension in the DNA of the target was then hybridized with a biotinylated detection probe. Avidin-conjugated alkaline phosphatase was bound to the detection probe and allowed to generate the electroactive label, p-aminophenol, from p-aminophenyl phosphate enzymatically. p-Aminophenol diffuses into the Fc-D layer and is then electrocatalytically oxidized by the electronic mediation of the immobilized Fc-D, which leads to a great enhancement in signal. Consequently, the amount of hybridized target can be estimated using the intensity of electrocatalytic current. This DNA sensor exhibits a detection limit of 20 fmol. Our method was also successfully applied to the sequence-selective discrimination between perfectly matched and single-base mismatched target oligonucleotides.