A reflective cascaded microfiber optic sensor for low-level β-lactoglobulin detection in dairy products: Sensitization by QU@ZIF-8/PDA nanosphere interface.

Food allergies are now becoming a major global health concern, with β-lactoglobulin (B-LG) in milk recognized as a leading allergen. This study proposes a reflective temperature-compensated sensor based on a quercetin@zeolitic imidazolate framework-8/polydopamine-coated microfiber interferometer (MFI) cascaded with a tilted fiber Bragg grating (TFBG) for highly sensitive B-LG detection. The sensing region relies on two parts fitting: the interference wavelength shift of MFI and the power difference of the TFBG cladding mode overlapping resonance peak. As a self-calibration temperature region, the TFBG core mode serves to eliminate temperature cross-sensitivity. The reflective sensor achieves a wide detection range of 0.2-100 μg/mL, a low detection limit of 0.04 μg/mL, and high sensitivity of 6.64 dB/(μg/mL) [1.74 nm/(μg/mL)]. The reflective sensor demonstrates high recovery rates (88 %-104 %) in real sample tests, including milk powder, skim milk, and demuttony goat milk. Importantly, the fabrication process allows for low-cost production and moderate manufacturing difficulty, confirming the strong potential for practical food safety monitoring and allergy prevention.