Electrochemistry of polystyrene intercalated vertically aligned single- and double-walled carbon nanotubes on gold electrodes

Spatially isolated redox processes enabled by ambipolar charge transport in multi-walled carbon nanotube mats

This work demonstrates a simple dual-well device which enables spatially isolated solutions to undergo complementary redox reactions. The device functions by the ambipolar transport of charge carriers between two spatially isolated poly(dimethylsiloxane) (PDMS) microwells through an underlying multi-walled carbon nanotube (MWCNT) mat. This MWCNT mat enables charge carriers, produced from the decomposition of an analyte in one solution, to drive a redox reaction in a spatially isolated second colorimetric read-out solution via a potential difference between the wells. As proof-of-concept a visible colorimetric read-out was shown using an enzyme, cytochrome c (reduced in 16 h), and the visualizing reagent 3,3',5,5'-tetramethylbenzidine (TMB) (oxidized in 2.5 h) for the detection of dithionite and hydrogen peroxide, respectively, without any external energy input. We discuss the origin of this phenomenon and highlight the ability of MWCNTs to accept and transport both electrons and holes efficiently between spatially isolated solutions giving rise to a highly versatile sensor suitable for use in simple, low-cost point-of-care diagnostics.

Carbonaceous Dye-Sensitized Solar Cell Photoelectrodes

High photovoltaic efficiency is one of the most important keys to the commercialization of dye sensitized solar cells (DSSCs) in the quickly growing renewable electricity generation market. The heart of the DSSC system is a wide bandgap semiconductor based photoelectrode film that helps to adsorb dye molecules and transport the injected electrons away into the electrical circuit. However, charge recombination, poor light harvesting efficiency and slow electron transport of the nanocrystalline oxide photoelectrode film are major issues in the DSSC's performance. Recently, semiconducting composites based on carbonaceous materials (carbon nanoparticles, carbon nanotubes (CNTs), and graphene) have been shown to be promising materials for the photoelectrode of DSSCs due to their fascinating properties and low cost. After a brief introduction to development of nanocrystalline oxide based films, this Review outlines advancements that have been achieved in the application of carbonaceous-based materials in the photoelectrode of DSSCs and how these advancements have improved performance. In addition, several of the unsolved issues in this research area are discussed and some important future directions are also highlighted.

A comparative study of different protein immobilization methods for the construction of an efficient nano-structured lactate oxidase-SWCNT-biosensor

We constructed lactate biosensors by immobilization of lactate oxidase (LOx) onto a single-walled carbon nanotube (SWCNT) electrode. The first step of the sensor construction was the immobilization of oxidized SWCNT onto a platinum electrode modified with 4-aminothiophenol (4-ATP). Two enzyme immobilization methods were used to construct the biosensors, i.e., covalent immobilization using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and physical adsorption. Atomic force microscopy (AFM) experiments confirmed the immobilization of SWCNT during the biosensor construction and X-ray photoelectron spectroscopy (XPS) experiments confirmed covalent immobilization of LOx onto the SWCNT in the first method. The biosensor based on covalent enzyme immobilization showed a sensitivity of 5.8 μA/mM, a linearity up to 0.12 mM of L-lactate, and a detection limit of 4.0 μM. The biosensor based on protein adsorption displayed a sensitivity of 9.4 μA/mM, retaining linearity up to 0.18 mM of L-lactate with a detection limit of 3.0 μM. The difference in the biosensor response can be attributed to protein conformational or dynamical changes during covalent immobilization. The stability of the biosensors was tested at different temperatures and after different storage periods. The thermostability of the biosensors after incubation at 60 °C demonstrated that the biosensor with covalently immobilized LOx retained a higher response compared with the adsorbed protein. Long-term stability experiments show a better residual activity of 40% for the covalently immobilized protein compared to 20% of residual activity for the adsorbed protein after 25 d storage. Covalent protein immobilization was superior compared to adsorption in preserving biosensor functionality over extended time period.

Dramatic change of water-cluster accessibility of highly pure double-walled carbon nanotubes with high temperature annealing

Highly pure double-walled carbon nanotubes (DWCNTs) synthesized by a catalytic chemical vapour deposition method have a well-ordered bundle structure giving explicit diffraction peaks by synchrotron X-ray diffraction measurement. The changes of nanopore structural properties and water adsorptivity of DWCNTs with high-temperature heat treatment were investigated using molecular probe adsorption methods. It was founded that their nanoporosities and apparent hydrophilicities decreased with thermal annealing. However, a specific surface area of 275 m(2) g(-1) and the residual microporosity of more than 60% even after heat treatment at 2673 K suggest their unique applications.