Regenerable PVA Hydrogel-Functionalized Optical Fiber Sensor for Ultra-Trace Detection of Berberine Hydrochloride

Most conventional methods for detecting pharmaceutical residues are limited by high operational cost, insufficient selectivity, or the requirement for harsh chemical regeneration that may damage sensing materials. In this study, a double-gourd-shaped Mach-Zehnder interferometric optical fiber sensor functionalized with a poly(vinyl alcohol) (PVA) hydrogel layer was developed for the sensitive and reusable detection of berberine hydrochloride (BBH) in aqueous media. The hydroxyl-rich hydrogel layer enables reversible BBH adsorption and induces wavelength shifts through local refractive-index (RI) variation. The sensor exhibited a sensitivity of 2.856 nm/μM within the linear calibration range of 0-1 μM, with a broad working response range extending to 1000 μM and a low limit of detection (LOD) of 0.04 μM. In addition, the sensor could be regenerated using 70% ethanol solution, maintaining stable performance over multiple adsorption-desorption cycles. It also demonstrated good selectivity, reproducibility, and stability, together with satisfactory applicability in real water samples and authentic BBH tablet samples. This work provides a simple and reusable platform based on mild ethanol-assisted regeneration for BBH monitoring in complex aqueous environments, particularly medical wastewater.