Chemi-Impeditive Sensing\nPlatform Based on Single-Walled\nCarbon Nanotubes

Chemical sensing methodology based on electrochemical\nimpedance\nspectroscopy (EIS) targeting analytes in aqueous samples on functionalized\nsingle-walled carbon nanotube (SWCNT) is reported. The SWCNT in contact\nwith electrolyte shows unique impedance spectra that cannot be analyzed\nwith classical equivalent circuit models. Inspired by the charge transport\nproperty of mixed ionic-electronic conductors, we propose an equivalent\ncircuit based on transmission line model (TLM), by which the impedance\nof the CNT-electrolyte system can be analyzed to track down all the\nequivalent circuit parameters. By combining multiple pieces of information,\nwhich are technically immeasurable with conventional chemiresistive\nor chemicapacitive techniques, several analyte species responding\nto the sensor can be differentiated from each other. We demonstrate\nthe “chemi-impeditive” concept on chemically modified\nSWCNTs for detecting perfluoroalkyl substances (PFAS) in aqueous solutions.\nThe EIS coupled with a fluorination chemistry on SWCNT surface provides\nunique changes in equivalent circuit components for each PFAS, i.e.,\nchanges in CNT and solution resistances, as well as interfacial CNT-solution\ncapacitance, through which perfluorooctanesulfonic acid, perfluorooctanoic\nacid, hexafluoropropylene oxide dimer acid, and perfluorobutanesulfonic\nacid are detected in a discriminative manner. The new impedimetric\nmethod opens up new vistas in chemical sensing in that the EIS analysis\nprovides an additional dimension of information beyond the single\nresistance or capacitance typically measured by many conventional\ntypes of sensors.