Reaction-Induced Fluorogenic Sensing of Benzodiazepines: A 3D-Printed Smartphone-Based Device with Multivariate RGB Optimization

Abstract

A low-cost fluorimetric platform fabricated by 3D printing was developed for benzodiazepine (BZD) detection using smartphone-based RGB image analysis. The method relies on hypochlorite-induced fluorogenesis of non-emissive BZDs, including clonazepam, diazepam, bromazepam, and midazolam. Spectroscopic and theoretical analyses indicated that hypochlorite oxidation promotes cleavage of the seven-membered diazepine ring, generating conjugated benzophenone-like products containing a rigid C=O group responsible for the enhanced fluorescence emission. Mass spectrometry further indicated chlorination of the oxidation products under concentrated NaOCl conditions. The 3D-printed device employs UV-A excitation coupled with smartphone RGB detection for quantitative analysis. For clonazepam, the individual RGB channels exhibited linear responses over the range of 0–100 μg mL⁻¹, with the green channel providing the best performance (R² = 0.9924). Multivariate analysis using multiple linear regression (MLR) of the RGB channels further improved the analytical performance, yielding R² = 0.9998 and a limit of detection of 0.05 μg mL⁻¹. The smartphone-based results showed good agreement with UV–Vis and photoluminescence measurements, demonstrating the applicability of the portable platform as a rapid and cost-effective alternative for benzodiazepine analysis.