Chemiresistors for the Real-Time Wireless Detection of Anions

Reported is an electrical transduction platform for real-time wireless anion sensing using single-walled carbon nanotubes (SWCNTs) noncovalently functionalized with squaramide-based anion binding selectors. Systematically studied are anion-binding properties and efficiency of the electrical transduction of the functionalized SWCNT composites using the squaramide-based selectors with two similar electron-withdrawing groups, 3,5-bis(trifluoromethyl)benzyl (1) and 3,5-bis(trifluoromethyl)phenyl (2), which induce hydrogen-bonding interaction with anions and deprotonation of a squaramide N-H proton upon addition of acetate (AcO-), respectively. Charge transduction occurs with AcO- as a result of charge transfer from the deprotonated selector 2, whereas less sensitive transduction is observed with selector 1 via hydrogen-bonding interaction. These results provide guidelines to efficiently transduce the chemical interaction between selectors and anions to create resistive transduction with functionalized SWCNTs. Electron-withdrawing groups adjacent to the squaramide as well as proximate cationic pyridyl groups, enhance the anion binding affinity and also lower the selector's pK(a). The chemiresistive sensor arrays are readily integrated with a wireless sensing module and demonstrated real-time sensing of multiple anions with a smartphone readout.