Single-walled Carbon Nanotube-Calixarene Based Chemiresistor for Volatile Organic Compounds

Calixarenes are exciting class of organic macromolecules and proved to be an excellent sensing material for optical and mass transaction based sensors. The limited conductivity of calixarenes is a major impediment for the development of calixarene-only chemiresistive sensors. The authors report on a calixarene-based chemiresistor that is based on a hybrid material obtained by non-covalent functionalization of SWCNTs with calixarene. This has two beneficial effects: (a) The use of SWCNT eliminates the conductivity issue, and this enables low-power chemiresistive sensing; (b) the excellent affinity of calixarenes for certain analytes improves sensitivity. The hybrid material was fabricated by solvent casting, and its formation was confirmed by structural (SEM and TEM), electrical (I-D-V-D and I-D-V-G), and spectroscopic (Raman and ATR-IR) characterizations. The resulting sensing device, operated typically at +1V, undergoes an increase in resistance upon exposure to successive increments in concentration from 50 to 250ppm for benzene, toluene, ethylbenzene and xylenes, commonly known as BTEX. Respective limits of detection are 25, 7.5, 6.5, and 4ppm. This is well below their Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) except for benzene. A mechanistic study for BTEX was performed via field-effect transistor measurements, and this suggested that the sensing mechanism is dominated by an electrostatic gating effect. In our perception, the availability of a wide variety of calixarenes generates wide perspectives for calixarene-only based SWCNT-calixarene hybrid sensor arrays for the realization of electronic nose application.