Fabricating a hydroxynaphthalene benzophenone Schiff base into a wearable fluorescent sensor for point-of-care sensing of volatile organic compounds

Abstract

We herein present a donor-acceptor (D-A) luminogen, (E)-(3- (((2-hydroxynaphthalen-1-yl)methylene)amino)phenyl)(phenyl)methanone (HNPMO), with both intramolecular charge transfer and aggregation-induced emission (ICT + AIE) properties. It was developed into a film sensor by drop-casting, exhibiting sharp increase in emission when exposing to various volatile organic compounds (VOCs), such as benzene series (e.g., toluene), common organic solvents (e.g., ethyl acetate) and alcohols (e.g., methanol), etc. Spectral analysis and quantum chemical calculations confirmed that the turn-on response can be ascribed to the transition from the disordered molecular arrangement to the optimized conformation driven by VOCs in the gas phase, with some major influence factors including volatility, molecular size, structural compatibility and steric hindrance. In addition, the fluorescent response is quantified by well-established image technology, using RGB and Lab color space. In the sensitivity test, Lab color shift (ΔELab) was used to estimate the limit of detection (LOD) of the HNPMO film sensor, which gives a linear relation with VOC concentration. The resulting LOD value is as low as 7.04 mg/m3 (1.8 ppm), suggesting high sensitivity intrinsic to such turn-on type sensor. We further fabricate a wearable sensor device based on HNPMO film, employing a reference substance which is inert to VOCs. Thus the presence of VOCs can be confirmed by the Lab color shift between HNPMO and the inert reference. By cutting and shaping, the film sensor applies to gloves, labor suits and even nails. It is capable of point-of-care detection of VOCs, providing an early warning of air contamination in various scenarios.