(298a) The Outlook for Chemical and Biochemical Sensors Made of Graphitic Nanodevices

The enormous sensitivity of carbon nanotubes to their chemical environment prompted substantial excitement about their promise for commercial sensors and detectors.  Subsequent research, using both nanotube and graphene electrodes, has generally demonstrated high sensitivity but poor stability and selectivity, as the electrodes are famously sensitive to most analytes including air, water, and noble gases.  Much ongoing research has focused on improving selectivity and reducing unwanted responses, though the direct physiochemical mechanisms responsible for sensing remain poorly understood.  In fact, the combination of possible interactions is daunting and remains under investigation on an analyte-by-analyte basis, as described in a recent review.[1]  Part of the difficulty is that very small amounts of disorder, such as from atomic defects, chemical adducts, or contaminants, enormously enhance electron transfer between the environment and the otherwise inert graphitic surfaces.  This enhancement is the underlying principle behind commercial carbon-based electrochemical sensors, after all, but it can be difficult to precisely control in a nanoelectrode of nanotubes or graphene.  From this standpoint, nanographite electrodes may be unable to successfully compete with existing sensor products, even when defects are present that enhance their sensitivity.[2]  An exception to this conclusion, and perhaps the main advantage of working with graphitic nanoelectrodes, appears to be their ability to monitor single molecule events.  Because nanoelectrodes, and particularly one-dimensional single-walled nanotubes (SWNTs), can operate in the limit of having one single active site, there are opportunities for monitoring single molecule dynamics that are normally obscured in ensemble measurements.  The direct interrogation of single molecule attachments, charge transfer events, or catalytic turnovers[4] provides truly new opportunities for electronic sensing and assaying of chemical and biochemical activity.

1. K.-J. Lee and J. Kong, "Chemical Sensing with SWNT-FETs," in Carbon Nanotube Electronics (A. Javey and J. Kong, Eds. New York: Springer, 2009).

2. V.R. Khalap, T. Sheps, A.A. Kane, P.G. Collins, Nano Lett. 10, 896 (2010).

4. B.R. Goldsmith, J.G. Coroneus, A.A. Kane, G.A. Weiss, P.G. Collins, Nano Lett. 8, 189 (2008).