NO-Affinitive Conjugated Polymer for Selective Sub-Parts-Per-Billion NO Detection in a Field-Effect Transistor Sensor.

Conjugated polymers (CPs) have provided versatile semiconducting implements for the development of soft electronic devices. When three CPs with the same conjugated framework but different side chains were adopted in the field-effect transistor (FET) sensor for NO detection, the response to NO showed an opposite tendency to the charge carrier mobility of each CP. Morphological and structural characterizations revealed that the flexible glycol side chain enhances NO affinity as well as prevents the formation of lamellar stacking of the CP chains, thereby providing routes for the facile diffusion of NO. Additionally, theoretical calculations for CP-NO complex formation at the molecular level support the relatively low energy barrier for inter-chain transition of NO between the glycol-based conjugated frameworks, which implies the spontaneous internal diffusion of NO to the semiconductor-dielectric interface in the FET-based sensor. As a result, the CP with a NO-affinitive morphology exhibited an exceptional sensitivity of 13.8%/ppb upon NO (100 ppb) exposure for 50 s and provided excellent selectivity to the FET-based sensor toward other environmentally abundant harmful gases, such as SO, CO, and NH. In particular, the theoretic limit of detection reached down to 0.24 ppb, which is the lowest value ever reported for organic FET-based NO gas sensors.