Dual-Port U-shaped optical microfiber Couplers via Flame/Pull-Immersion for glucose monitoring

The growing need for effective diabetes management is driving the advances in glucose monitoring technologies. Existing electrochemical sensors suffer from limited reliability, while optical fiber alternatives, despite their advantages, still face challenges such as single-point failure, non-uniform enzyme immobilization, and poor microfabrication reproducibility. To address these issues, we developed a dual-port U-shaped optical microfiber coupler (OMC) via an integrated hydrogen–oxygen flame/pull-immersion process and functionalized with a 3-aminopropyltriethoxysilane (APTES) and glucose oxidase (GOD) coating. The optimized sensor (waist diameter 7.4 μm, curvature diameter 1.5 mm) achieves a wide linear range (0–6 mg/mL, R 2 = 0.9994), a high sensitivity (2.75 ± 0.02 nm·mL/mg), fast response (0.29 ± 0.068 s), low limit of detection (0.0073 mg/mL) and excellent selectivity with less than 7 % cross-reactivity against common interfering substances. The sensor retains > 87 % sensitivity across the physiological pH range and demonstrates stable operation over 8 h of continuous immersion (78.5 % retention) and 7 days of storage (73.4 % retention). The dual-port design provides system-level redundancy for uninterrupted operation, and the integrated fabrication strategy ensures high manufacturing repeatability. Furthermore, a temperature compensation method effectively reduced temperature interference. This work establishes a novel, integrable platform for reliable glucose monitoring.