Paper-based device for nanomolar detection of Cd 2+ using AIEE-active imidazolium ionic liquid functionalized phenothiazine based Schiff-Base

A highly green fluorescent phenothiazine-based imidazolium ionic liquid (IL) [PTZ-SB][Br] was synthesized and its structure was thoroughly elucidated by 1 H, 13 C NMR, FT-IR, UV–visible spectroscopy and Mass spectrometry. Furthermore, thermal resilience of the IL was established by TGA and DSC investigations. The novel molecule revealed a distinct recognition for Cd 2+ ions over eleven other transition metal ions. Moreover, the promising results obtained in the solution phase interested us to embed [PTZ-SB][Br] on paper strips to create a paper-based fluorescent sensor, which was examined by a portable UV light source for the on-site Cd 2+ detection. Interestingly, the device demonstrated exceptional fluorescence sensing behavior towards Cd 2+ with a limit of detection (LOD) of 0.16 nM. Thus, the probe has noteworthy distinct and sensitive detection ability towards Cd 2+, which might find practical and on-spot applications. Noticeably, [PTZ-SB][Br] demonstrated aggregation-induced enhanced emission (AIEE) phenomenon. In fact, an incredible 38.1-fold increase in fluorescence intensity was observed for 10:90 ratio of THF:water mixture as compared that for pure THF solution of [PTZ-SB][Br]. AIEE property was further supported by DLS studies. A paper-based device for Cd 2+ sensing by applying an Ionic Liquid based Schiff base is reported herein for the first time.