Functional Single-Walled Carbon Nanotubes for Real-Time Wireless Chemical Sensors

Carbon nanotubes (CNTs) are attractive nanomaterials considering their high electrical conductivity and aspect ratio, leading to the development of innovative electronic devices. In particular, CNTs are widely employed as sensing layers for application in chemical sensors due to their efficient electrical transduction properties. Nevertheless, the stable surface chemical property of pristine CNTs with sp² bond hybridization hinders sensitive and selective detection of a target analyte. In this regard, various surface modification techniques are proposed by altering surface chemistry and imposing chemical reactivity toward analytes. There are two types of surface functionalization techniques of CNTs; covalent and non-covalent functionalization techniques. The covalent functionalization technique results in the disruption of the electrical property of CNTs by breaking sp² carbon bonds, which limits the degree of surface modification. On the other hand, the non-covalent functionalization of CNTs can induce a high degree of surface modification while maintaining high electrical conductivity, thereby leading to sensitive detection of analytes.<br/>In this presentation, I will introduce the recent progress of non-covalently functionalized single-walled carbon nanotubes (SWCNTs) for applications in chemiresistive sensors.[1-4] Functional polymers were synthesized by decorating selector groups, which can have a chemical interaction with target analytes such as gas molecules and ionic species in solution. In particular, a functional polymer of poly(4-vinylpyridine) (P4VP) was employed and further modified by introducing dual-hydrogen bond donors (e.g., thiourea, squaramide, and croconamide) as selectors. The chemiresistive sensing layer of SWCNTs was non-covalently functionalized by wrapping with functional polymers. As a result, real-time electrical transduction was achieved upon the injection of a chemical analyte with high sensitivity and selectivity. For example, a large resistance transition of functional P4VP-SWCNT composite was obtained with the sensitivity [(R−R₀)/R₀ (%)] of 120% at 16.7 mM toward acetate anion. The chemiresistive sensor was integrated with a wireless sensing module for application in real-time wireless detection. The proposed SWCNT-based sensing platform with functional polymers can be applied in various fields such as environmental monitoring and healthcare.<br/><br/>[1] S.J. Choi, B. Yoon, J.D. Ray, A. Netchaev, L.C. Moores, T.M. Swager, Chemiresistors for the Real-Time Wireless Detection of Anions, <i>Adv. Funct. Mater.</i>, 30(2020), 1907087.<br/>[2] S.J. Choi, B. Yoon, S.B. Lin, T.M. Swager, Functional Single-Walled Carbon Nanotubes for Anion Sensing, <i>ACS Appl. Mater. Interfaces</i>, 12, 25(2020), 28375-28382.<br/>[3] B. Yoon, S.J. Choi, Selective acetate recognition and sensing using SWCNTs functionalized with croconamides, <i>Sens. Actuators B</i>, 346(2021), 130461.<br/>[4] B. Yoon, S.J. Choi, T.M. Swager, G.F. Walsh, Flexible Chemiresistive Cyclohexanone Sensors Based on Single-Walled Carbon Nanotube-Polymer Composites, <i>ACS Sens.</i>, 6, 8(2021) 3056-3062.