Functional Single-Walled Carbon Nanotubes for Anion Sensing
Seon‐Jin Choi, Bora Yoon, Sibo Lin, Timothy M. Swager
Abstract
We report an anion-sensing platform wherein conductance changes are triggered by chemical interactions between selectors and anions. The selector design incorporates both a cationic moiety (i.e., pyridinium) and a thiourea-based dual-hydrogen-bond donor. Anion binding by a model selector (2) was studied using 1H NMR and UV–vis titrations, which reveal a binding strength toward acetate ions (AcO–) followed by Cl– > Br– > NO3–. These studies reveal that selector 2 is deprotonated upon addition of AcO–, whereas it undergoes hydrogen bonding associated with Cl–, Br–, and NO3–. The cationic pyridinium moiety improves anion binding affinity by lowering the pKa value of selector 2 and enhancing the hydrogen-bond donor capability as confirmed by spectroscopic titrations and DFT calculations. The selector is covalently attached to poly(4-vinylpyridine) (P4VP), which wraps single-walled carbon nanotubes (SWCNTs) (i.e., P4VP-2-SWCNT) to transduce an electrical signal. As a result, continuous anion sensing was achieved with high sensitivity represented by a normalized resistance change of 101.9 ± 10.3% toward 16.7 mM AcO–, whereas negligible sensitivity was observed toward Cl–, Br–, and NO3–. The sensitivity transition was attributed to the internal charge transfer of 2 by deprotonation of the thiourea proton upon addition of AcO–.