Design of carbon nanotube fiber microelectrode for glucose biosensing

BACKGROUND: Carbon nanotube (CNT) fiber directly spun from an aerogel has a unique, well-aligned nanostructure (nano-pore and nano-brush), and thus provides high electro-catalytic activity and strong interaction with glucose oxidase enzyme. It shows great potential as a microelectrode for electrochemical biosensors. RESULTS: Cyclic voltammogram results indicate that post-synthesis treatments have great influence on the electrocatalytic activity of CNT fibers. Raman spectroscopy and electrical conductivity tests suggest that fibers annealed at 250 °C remove most of the impurities without damaging the graphite-like structure. This leads to a nano-porous morphology on the surface and the highest conductivity value (1.1 × 10 5 S m -1). Two CNT fiber microelectrode designs were applied to enhance their electron transfer behaviour, and it was found that a design using a 30 nm gold coating is able to linearly cover human physiological glucose level between 2 and 30 mmol L -1. The design also leads to a low detection limit of 25 μmol L -1. CONCLUSIONS: The high performance of CNT fibers not only offers exceptional mechanical and electrical properties, but also provides a large surface area and electron transfer pathway. They consequently make excellent bioactive microelectrodes for glucose biosensing, especially for potential use in implantable devices. © 2011 Society of Chemical Industry.

Effects of preferential transport in turbulent bluff-body-stabilized lean premixed CH 4/air flames

Preferential species diffusion is known to have important effects on local flame structure in turbulent premixed flames, and differential diffusion of heat and mass can have significant effects on both local flame structure and global flame parameters, such as turbulent flame speed. However, models for turbulent premixed combustion normally assume that atomic mass fractions are conserved from reactants to fully burnt products. Experiments reported here indicate that this basic assumption may be incorrect for an important class of turbulent flames. Measurements of major species and temperature in the near field of turbulent, bluff-body stabilized, lean premixed methane-air flames (Le=0.98) reveal significant departures from expected conditional mean compositional structure in the combustion products as well as within the flame. Net increases exceeding 10% in the equivalence ratio and the carbon-to-hydrogen atom ratio are observed across the turbulent flame brush. Corresponding measurements across an unstrained laminar flame at similar equivalence ratio are in close agreement with calculations performed using Chemkin with the GRI 3.0 mechanism and multi-component transport, confirming accuracy of experimental techniques. Results suggest that the large effects observed in the turbulent bluff-body burner are cause by preferential transport of H 2 and H 2O through the preheat zone ahead of CO 2 and CO, followed by convective transport downstream and away from the local flame brush. This preferential transport effect increases with increasing velocity of reactants past the bluff body and is apparently amplified by the presence of a strong recirculation zone where excess CO 2 is accumulated. © 2011 The Combustion Institute.

Efficient numerical models for investigating the statistics of random dynamic systems

The study of random dynamic systems usually requires the definition of an ensemble of structures and the solution of the eigenproblem for each member of the ensemble. If the process is carried out using a conventional numerical approach, the computational cost becomes prohibitive for complex systems. In this work, an alternative numerical method is proposed. The results for the response statistics are compared with values obtained from a detailed stochastic FE analysis of plates. The proposed method seems to capture the statistical behaviour of the response with a reduced computational cost.