Robust, rapid, and ultrasensitive colorimetric sensors through dye chemisorption on poly-cationic nanodots.

Colorimetric sensors were fabricated by incorporation of anionic colorimetric probes on a hierarchical nanofibrous membrane containing poly-cationic nanodots through intense electrostatic interaction. Unique poly-cationic nanodots were covalently grown on poly (4-vinylpyridine)/polyacrylonitrile nanofibrous membrane through a self-propagation reaction of 2-diethylaminoethyl chloride (DEAE-Cl). The nanodots on the nanofiber surfaces possess strong adsorption affinity and high adsorption capacity toward anionic probes, which contributed to excellent detection sensitivity and sensor stability compared with the co-electrospun sensor. As a proof-of-concept study, phenol red was selected to functionalize the as-fabricated substrate (polyDEAE@P4VP/PAN NFM) to a colorimetric sensor, which shows responses to alkaline vapors. The as-fabricated sensor showed rapid color changes to ammonia and triethylamine (response time < 10 s), whose detection limits reached 1 ppm and 5 ppm, respectively. The sensor can be repeatedly used for at least 20 cycles by regenerating it in air for 1 min. Taking advantage of the intense attractive force between poly-cationic nanodots and anionic probes, polyDEAE@P4VP/PAN NFM is a promising media to be used for the development of robust, rapid, and ultrasensitive colorimetric sensors.