Design and Evaluation of N-Aryl-4-amino-1,8-naphthalimide Fluorescent Sensors for Nitrofurazone Antibiotic Detection

Nitrofurazone (NFZ) is a synthetic nitrofuran antibiotic commonly used to treat infections caused by both gram-positive and gram-negative microorganisms. Despite its effectiveness, NFZ is poorly biodegradable, and its accumulation in the environment and food chain can pose significant risks of teratogenicity and carcinogenicity to humans. Therefore, developing sensitive and selective methods for its trace-level detection is crucial. In this study, we introduce three small-molecule fluorescent sensors, Nap-1, Nap-2, and Nap-3, based on 4-amino-1,8-naphthalimide fluorophore integrated with bulky N-aryl substituents, for the selective detection of NFZ. These sensors can be synthesized easily in two steps and are fully characterized using standard spectroscopic techniques. All three sensors exhibit strong fluorescence arising from an internal charge-transfer (ICT) process and show notable positive solvatochromism across solvents of varying polarity. They exhibit excellent selectivity and high binding affinity toward NFZ, with detection sensitivities reaching the parts-per-billion (ppb) range. Importantly, their fluorescence emission is effectively quenched by NFZ, even in the presence of competing or structurally related antibiotics and complex environmental matrices, confirming NFZ's robust selectivity. Overall, Nap-1, Nap-2, and Nap-3 emerge as promising "turn-off" fluorescent chemosensors for rapid, accurate, and highly sensitive detection of NFZ in both analytical and environmental contexts.