Carbon nanotubes (CNTs) are interesting building blocks for electrochemical sensors owing to their high surface area and excellent electrical conductivity. However, these advantageous properties are often lost during the fabrication of CNT-based electrodes because of the non-uniform alignment of the CNT constituents and the need for binders to attach the CNTs to a suitable supporting structure. Mustafa Musameh and colleagues from the Commonwealth Scientific and Industrial Research Organisation in Australia have now described a method to create ‘CNT webs’ that do not undergo any degradation of properties during preparation, providing a strong, flexible, highly conductive and electrochemically active material for electrochemical sensors and biosensors.1

Fig. 1: Scanning electron microscopy image showing how webs of carbon nanotubes can be spun from a forest of CNTs.© 2011 Wiley-VCH

“The CNT webs are drawn — or spun — horizontally from a vertically aligned ‘forest’ of CNTs grown on a silicon or similar substrate,” says Musameh. As the web is drawn, vertical CNTs at the leading edge of the forest are pulled in a horizontal direction but remain attached to the CNTs immediately following them (see image). The process relies on complex interactions between parameters such as the CNT length, diameter, areal density, purity, uniformity and alignment. This in turn influences the number and strength of attachment points between the nanotubes and the substrate.

The CNT webs prepared in the study were as thin as 50 nm, but could be built to reach almost any thickness. They are extremely strong and can be cross-laid, wound, twisted, laminated, knitted, woven and braided, thus allowing a wide range of sensor geometries and sizes. The webs show very good chemical stability in different solvents, owing to their extended length and well-packed structure in large bundles.

The CNT webs are also highly conductive, display high surface areas and are hydrophobic, allowing for the sensitive adsorption and detection of toxic hydrophobic organic compounds such as organophosphate pesticides. Electron-transfer processes between the adsorbed molecules and the CNT-web electrodes give rise to distinct current–voltage characteristics, which could be used, for example, to sense the presence of adsorbates with high sensitivity.

According to Musameh, these CNT webs also have a range of other interesting and industrially useful applications, such as in fuel cells, solar cells and batteries.