Investigation for terminal reflection optical fiber SPR glucose sensor and glucose sensitive membrane with immobilized GODs.

Glucose sensitive membrane (GSM) consists of glucose oxidases (GODs) and matrix material (for example, polyacrylamide gel). In this paper, we have investigated the optical property and adsorption isotherms of a GSM based on a terminal reflection optical fiber SPR sensor. Firstly, we reported the fabrication of one kind of GSM which was made of immobilized GODs on SiO nanoparticles and PAM gel. Then, we investigated the effects of GSM thickness, GOD content, solution pH and ambient temperature on the reflected spectrum of sensor, and the optimum parameters of the sensor, such as, GSM thickness of 12 times pulling, 4 mg/mL of GOD content in GSM, 7.0 of solution pH and 40 °C of measuring temperature were obtained. Thirdly, we measured the wavelength shifts of the optimized SPR sensor in the solutions with different glucose concentrations. As the glucose concentration increases from 0 to 80 mg/dL, the resonance wavelength decreases approximately linearly and the corresponding sensitivity is about 0.14 nm/(mg/dL). Finally, we investigated the RI of the GSM, the concentration of glucose into GSM and the adsorption isotherm of GSM by the combination of SPR experiment data, theoretical simulation and Gladstone-Dale mixing rule. As the glucose concentration is in the region of [0, 80] mg/dL, the adsorption of GSM for glucose can be explained by the Freundlich isotherm model. As the glucose concentration is in the region of [120, 500] mg/dL, the Langmuir isotherm model is more suitable to describe the adsorption process of GSM for glucose.