Label-free glucose biosensor based on enzymatic graphene oxide-functionalized tilted fiber grating

A label-free biosensor based on graphene oxide (GO) and glucose oxidase (GOD) functionalized tilted fiber grating (TFG) with large tilted angle is proposed for low concentration glucose detection. Taking advantages of sufficient binding sites of the GO with oxygen-containing groups, the enzymes (GOD) are covalently immobilized onto GO-deposited TFG via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxyl succinimide cross-liner. Surface characterizations with optical microscopy, scanning electron microscopy, Raman and infrared spectroscopy provide detailed assessments and evidences about the homogeneity of GO deposition and the effectiveness of enzyme modification. Through the specific catalysis reaction of GOD on the glucose, a considerable refractive index change in local microenvironment around the TFG results in the resonant wavelength shifts of cladding modes. The detection results of the low-concentration glucose demonstrate that the resonant wavelength has a linear response to the glucose concentration in the range of 0–8 mM with a response coefficient of ∼0.24 nm/mM, showing an enhanced sensitivity and bio-selectivity compared with the pristine TFG. The miniaturized size and remote label-free sensing capacity of the proposed device permit a multitude of opportunities for single-point measurement in harsh conditions and hard-to-reach spaces, presenting a promising candidate for label-free glucose detection for disease diagnosis, pharmaceutical research and bioengineering applications.