Real-time monitoring of bio-interface assembly enables high-sensitivity glucose sensing via no-core fiber with biocompatible composite coating

We report a mechanism-driven no-core fiber (NCF) glucose sensor, which not only features a polydopamine/polyethylenimine (PDA/PEI) coating that enhances the evanescent field, but also enables real-time monitoring of the bio-interface assembly. For the first time, to the best of our knowledge, the dynamic PDA/PEI deposition and the successive glucose oxidase (GOx) immobilization were tracked by the NCF itself, thus providing unprecedented insight into the formation kinetics of the sensing layer. The physicochemical characterization reveals that the engineered PDA/PEI composite exhibits a high refractive index (RI) of ∼1.55 and a low extinction coefficient of ∼0.02 in the near-infrared region, which significantly enhances the evanescent field and thus RI sensitivity of the sensor by ∼19.8%. A peak sensitivity of ∼96 pm/mM was achieved at the optimized condition (PDA:PEI = 2:0.5, 6 h deposition), with a linear range of 1-12 mM, a limit of detection (LOD) of 0.19 mM, and a response time of ∼22 s. The sensor also demonstrated good selectivity toward glucose in a representative biomass hydrolysis system and showed potential applicability in pretreated hydrolysate samples. This work presents a high-performance fiber-optic glucose sensor and demonstrates the utility of real-time monitoring for understanding bio-interface assembly in optical biosensors.