Ion-in-Conjugation Polymer Enables Detection of NO2 with Parts-Per-Trillion Sensitivity and Ultrahigh Selectivity

Abstract

Detection of nitric dioxide (NO2) at part-per-trillion (ppt) level is critical for both environmental monitoring and human health. However, none of chemiresistors could detect NO2 at the part-per-trillion (ppt) level, suffering from low sensitivity of the sensory materials. In this work, an ion-in-conjugation polymer para-polyphenylsquaraine (p-PPS) was designed and fabricated into an NO2 chemiresistor. The sensor has the highest sensitivity of 1450 ppm-1 (at 100 ppb) and the lowest detection limit of 40 ppt among all reported chemiresistors. In addition, p-PPS shows an ultrahigh selectivity that other interfering gases have less than 1/1887 of the signal to NO2 under the same concentration (10 ppm). The calculation and in-situ infrared spectra and the sum frequency generation spectra (SFG) reveal that the ion-in-conjugation inspired H-bonding between p-PPS and NO2 leads to such a high sensitivity. Our result highlighted the concept of ion-in-conjugation in design of highly sensitive gas sensory materials.