Sensitivity adjustable biosensor based on graphene oxide coated excessively tilted fiber grating

Biosensors play a significant role in biomedical, clinical and disease diagnosis areas. Here, we proposed Langmuir adsorption model to explain sensing mechanism of biosensor based on excessively tilted fiber grating (Ex-TFG) functionalized with graphene oxide (GO). Due to GO containing plenty of six-membered rings and oxygen-containing groups, the biomolecules can be easily adsorbed through π-π interaction and hydrogen bond. The whole interaction process obeys the Langmuir adsorption model in which there always an equilibrium during detecting process, inducing the sensor with adjustable bio-sensitivity and detection range. Three biosensors based on Ex-TFG coated with three different amount of GO were investigated for hemoglobin (Hb) detection experiment, showing pronounced bio-interaction induced resonance shifts. The experiment results indicate that GO coating could enhance the surface biological activity of Ex-TFG, making the Ex-TFG sensitive to the Hb biomolecule solutions. The three GO coated Ex-TFG sensors have the bio-sensitivity of 3.83 nm/(mg/ml), 4.33 nm/(mg/ml), and 8.21 nm/(mg/ml), and the detection range of 0.8 mg/ml, 0.6 mg/ml and 0.4 mg/ml, respectively, which are in good agreement with the prediction from the Langmuir adsorption model. By controlling the amount of the bio-functionalized materials, the bio-sensitivity and detection range of the Ex-TFG based biosensors can be easily adjusted.