Metallic versus Semiconducting SWCNT Chemiresistors: A Case for Separated SWCNTs Wrapped by a Metallosupramolecular Polymer

Abstract

As-synthesized single-walled carbon nanotubes (SWCNTs) are a mixture of metallic and semiconducting tubes, and separation is essential to improve the performances of SWCNT-based electric devices. Our chemical sensor monitors the conductivity of an SWCNT network, wherein each tube is wrapped by an insulating metallosupramolecular polymer (MSP). Vapors of strong electrophiles such as diethyl chlorophosphate (DECP), a nerve agent simulant, can trigger the disassembly of MSPs, resulting in conductive SWCNT pathways. Herein, we report that separated SWCNTs have a large impact on the sensitivity and selectivity of chemical sensors. Semiconducting SWCNT (S-SWCNT) sensors are the most sensitive to DECP (up to 10000% increase in conductivity). By contrast, the responses of metallic SWCNT (M-SWCNT) sensors were smaller but less susceptible to interfering signals. For saturated water vapor, increasing and decreasing conductivities were observed for S- and M-SWCNT sensors, respectively. Mixtures of M- and S-SWCNTs revealed reduced responses to saturated water vapor as a result of canceling effects. Our results reveal that S- and M-SWCNTs compensate sensitivity and selectivity, and the combined use of separated SWCNTs, either in arrays or in single sensors, offers advantages in sensing systems.

Chemiresistive Carbon Nanotube Sensors for N-Nitrosodialkylamines

“…The conductances of metallic CNTs are less perturbative to external stimuli as a result of the difficulty in quenching the metallic state. 36…”

Carbon Nanotube Chemical Sensors

“…105 Swager and co-workers showed that conjugated polymers attached to selector side chains can provide selectively for the detection specific analytes and even resolve very similar structural isomers. 47,73,97,106,107 CNTs can also be functionalized with polymeric surfactants containing long alkyl chains that interact via hydrophobic interactions. 108,109 Dai and co-workers demonstrated the adsorption of Tween 20 conjugates containing biotin, staphylococcal protein A (SpA), or human autoantigen U1A to CNTs.…”

Sensor Technologies Empowered by Materials and Molecular Innovations

“…Chemie pending upon the orientation of the graphene p-system with respect to the SWCNT axis,t he materials may be intrinsic metals or semiconductors.C hemiresistors with modes of action dominated by carrier injection/depletion/pinning will be most sensitive with semiconductive SWCNTs. [32] Metallic SWCNTs need not be charged to conduct, and as aresult are less susceptible to charge transfer processes,b ut also experience less interference from humidity.S ensors that operate solely on modulating the junctions between SWCNTs will be less sensitive to the nature of the carbon nanotubes.…”