Halochromic oxazolidine nanofibers as portable smart chemosensors for dual-mode colorimetric and fluorimetric detection of food spoilage: investigation of solid-state pH responsivity in polar microenvironments

Abstract

Today, the world increasingly depends on smart technologies, particularly in the realm of food safety. Among these innovations, one of the most significant solutions for addressing the challenges of timely and efficient visual detection of food spoilage is the use of intelligent tags in food packaging. In this study, an innovative class of intelligent sensors based on halochromic oxazolidine (hydroxyl and tertiary amine-functionalized) nanofibers was developed by electrospinning of functionalized copolymers based on methyl methacrylate (MMA) and functional comonomers that have various polar groups, including tertiary amine, sulfonic acid, and hydroxyl groups. Hence, the pH responsiveness of oxazolidine derivatives was examined across a pH range from 1 to 14, and in the presence of various types of aliphatic and aromatic amines, the most significant alkaline products generated during food spoilage. The pH responsiveness of halochromic nanofibers is primarily influenced by interactions between the functional groups of oxazolidine molecules and the polymer matrix, along with solvatochromic behavior, which together enable the fibers to change color in response to pH variations. Therefore, three pH-responsive sensor tags based on halochromic nanofibers were designed for precise and timely spoilage detection in milk, lamb, chicken, and fish foods by dual-mode fluorimetric and colorimetric monitoring of acidic and basic vapors by the protonation and deprotonation of oxazolidine molecules. The intelligent pH-indicator nanofibers effectively detected spoilage in milk, lamb, and chicken meat within 3 days, and in fish within 2 days, highlighting their potential for developing wireless, selective optical chemosensors responsive to microenvironmental polarity changes.