Functional Single-Walled Carbon Nanotubes for Anion Sensing.

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 () was studied using H NMR and UV-vis titrations, which reveal a binding strength toward acetate ions (AcO) followed by Cl > Br > NO. These studies reveal that selector is deprotonated upon addition of AcO, whereas it undergoes hydrogen bonding associated with Cl, Br, and NO. The cationic pyridinium moiety improves anion binding affinity by lowering the p value of selector 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--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 NO. The sensitivity transition was attributed to the internal charge transfer of by deprotonation of the thiourea proton upon addition of AcO.