Functionalization and fabrication of single-walled carbon nanotube-based chemiresistors for sensory applications

Abstract

Chemical sensors that identify and monitor volatile organic compounds (VOCs) have an important role in assessing public security, food and water quality, industrial environment, and health. The fabrication of carbon-based sensors by printing, dip coating, drop casting, or drawing has advantages of being simple and low-cost without the need for highly specialized facilities. We have investigated the fabrication of sensors both by drop casting and drawing. Single-walled carbon nanotubes (SWCNT) electronic and spectroscopic properties for sensory applications are described. SWCNTs have unique properties wherein their conductance can be altered by environmental effects. These carbon nanomaterials can be easily integrated into a chemiresitive device to detect various analytes. In our studies using the drop cast method, we noncovalently functionalized SWCNT with a trifunctional selector that has three important properties: it noncovalently functionalizes SWCNTs with cofacial n-n interactions, it binds to cyclohexanone (a target analyte for explosive detection) via hydrogen bond, and it improves the overall robustness of SWCNT-based chemiresistors (e.g., humidity and heat). In our other studies, we fabricated sensors by drawing. Abrasion is a safe, simple, solvent-free, and low cost method for deposition of carbon-based materials onto a substrate. We successfully demonstrated fabrication on a wide variety of substrates (e.g., weighing paper, polymethyl methacrylate, silicon, and adhesive tape) of fully-drawn chemical sensors on a chip that can detect in real time parts-per-million (ppm) quantities of various vapors using SWCNTs as sensing materials and graphite as electrodes. This fabrication methodology does not require specialized facilities (e.g., clean room, thermal evaporator) and can be performed entirely on a desktop (with appropriate ventilation and safety precautions for handling nanomaterials). We also extended the abrasion method to detect anions such as fluoride (use to manufacture nuclear weapons) and cyanide (chemical warfare agent). These sensor are highly sensitive detecting the United State Environmental Protection Agency (EPA) maximum contaminant level (MCL) of fluoride and cyanide selectively.