High-sensitive liquid crystal-based optical sensor for real-time detection of formaldehyde vapor

Abstract

In this study, we develop an optical liquid crystal (LC) sensor based on dodecylamine doped 4-cyano-4’-pentylbiphenyl (5CB) to accomplish real-time detection of formaldehyde (FA) vapor. When exposed to FA at ppm level, the LC sensor doped with 0.1 wt% dodecylamine shows a rapid dark-to-bright optical response within 10 s. The optical response of the LC sensor increases with the increasing concentration of FA vapor from 16.5 ppm to 824.1 ppm. This response is caused by the intermolecular force between dodecylamine and FA, which is verified by the Fourier transform infrared (FT-IR) spectrum. Meanwhile, the sensor demonstrates wide operational temperature range from 15℃ to 35℃, wide operational humidity range from 30% to 80% relative humidity (RH), high selectivity for FA vapor, excellent reversibility after 10 continuous tests, and reliable stability after storing at room temperature for 1 week. Overall, this LC sensor shows fast response, favorable specificity, excellent reversibility, and reliable stability, leading to a wider range of applications for FA detection.