Carbon nanotubes (CNTs) promise to advance a number of real-world technologies. Of these applications, they are particularly attractive for uses in chemical sensors for environmental and health monitoring. However, chemical sensors based on CNTs are often lacking in selectivity, and the elucidation of their sensing mechanisms remains challenging. This review is a comprehensive description of the parameters that give rise to the sensing capabilities of CNT-based sensors and the application of CNT-based devices in chemical sensing. This review begins with the discussion of the sensing mechanisms in CNT-based devices, the chemical methods of CNT functionalization, architectures of sensors, performance parameters, and theoretical models used to describe CNT sensors. It then discusses the expansive applications of CNT-based sensors to multiple areas including environmental monitoring, food and agriculture applications, biological sensors, and national security. The discussion of each analyte focuses on the strategies used to impart selectivity and the molecular interactions between the selector and the analyte. Finally, the review concludes with a brief outlook over future developments in the field of chemical sensors and their prospects for commercialization.

Covalent functionalization significantly enhances the utility of carbon nanomaterials for many applications. Herein we report an efficient method for the covalent functionalization of carbon nanotubes and graphite. This reaction involves the reduction of carbon nanomaterials with sodium naphthalide followed by the addition of diaryliodonium salts. Carbon nanotubes, including singlewalled, double-walled, and multi-walled variants (SWCNTs, DWCNTs, MWCNTs), as well as graphite, can be efficiently functionalized with substituted arene and heteroarene iodonium salts. The preferential transfer of phenyl groups containing electron-withdrawing groups was demonstrated by reactions with unsymmetrical iodonium salts. The lower reactivity of iodonium salts relative to the more commonly used diazonium ions, presents opportunities for greater diversity in the selective functionalization of carbon nanomaterials.

A shapeshifting organic molecule dynamically adjusts its equilibrium population of discrete structural isomers in response to an analyte. By incorporating a single 13 C-label into the bullvalene core, these changes can be read by a single 13 C NMR experiment. The shapeshifting nature and 13 C nucleus together act as a reporting element that generates a reproducible pattern from small changes in the chemical shifts and intensities of the carbon peaks.

A new series of sidewall modified single-walled carbon nanotubes (SWCNTs) with perfluorophenyl molecules bearing carboxylic acid or methyl ester moieties are herein reported. Pristine and functionalized SWCNTs (p-SWCNTs and f-SWCNTs, respectively) were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and scanning electron microscopy (SEM). The nitrene-based functionalization provided intact SWCNTs with methyl 4-azido-2,3,5,6-tetrafluorobenzoate (SWCNT-N-C6F4CO2CH3) and 4-azido-2,3,5,6-tetrafluorobenzoic acid (SWCNT-N-C6F4CO2H) attached every 213 and 109 carbon atoms, respectively. Notably, SWCNT-N-C6F4CO2H was sensitive in terms of the percentage of conductance variation from 5 to 40 ppm of ammonia (NH3) and trimethylamine (TMA) with a two-fold higher variation of conductance compared to p-SWCNTs at 40 ppm. The sensors are highly sensitive to NH3 and TMA as they showed very low responses (0.1%) toward 200 ppm of volatile organic compounds (VOCs) containing various functional groups representative of different classes of analytes such as benzene, tetrahydrofurane (THF), hexane, ethyl acetate (AcOEt), ethanol, acetonitrile (CH3CN), acetone and chloroform (CHCl3). Our system is a promising candidate for the realization of single-use chemiresistive sensors for the detection of threshold crossing by low concentrations of gaseous NH3 and TMA at room temperature