Glucose oxidase-based enzyme immobilised on tapered optical fibre for reliability improvement in selective glucose sensing

Optical fibre-based sensing technology is considered as one of the uprising fields in photonics. Numbers of different fibre-based devices have been fabricated to systematically detect the element of interest, with the majority of the research works being focused on the selectivity and sensitivity of the sensor. In this research, a specific method of developing the sensor is demonstrated. The flame-brush technique was used on multimode fibre (MMF) to obtain an a tapered sensing structure with a waist diameter of 22.60 µm. The tapered region was coated with glucose oxidase (GOD) by silanisation and enzyme immobilisation processes. The surface was characterised by fluorescent microscopy, FTIR spectroscopy, FESEM, and EDX analysis. The optimisation of GOD-coating was done by comparing the GOD coated surface with bare (uncoated) fibre and second by differentiating the pH-value of the GOD enzyme. Coated fibre exhibited higher sensitivity compared to bare tapered fibre. The values are Scoated = (5.01 ± 0.72) × 10−3 a.u.(%)−1 for coated region, and Suncoated = (3.33 ± 0.59) × 10−3 a.u.(%)−1 for uncoated region. The highest sensitivity was obtained when the GOD has a pH-value of 5 where SpH5 = Scoated, followed by SpH7 = (1.73 ± 0.55) × 10−3 a.u.(%)−1 and SpH3 = (0.96 ± 0.10) × 10−3 a.u.(%)−1. The sensor offered good stability of ~8.384 × 10−6 a.u. s−1 retaining 0.4% of the original intensity. The sensor also provided good selectivity in glucose sensing, for which 11.595 nm redshift was observed in the transmitted spectrum.