Optical property and adsorption isotherm models of glucose sensitive membrane based on prism SPR sensor

For the prism based SPR glucose sensors, glucose sensitive membrane (GSM) is a key factor that decides the performance of sensor. GSM consists of glucose oxidase (GOD) and matrix material (for example, polyacrylamide gel, PAM). As the prism based SPR glucose sensor coated with GSM is put in the glucose solution, some glucose and dissolved oxygen can diffuse into the GSM and produce by-products, then the by-products will change the refractive index (RI) of GSM and cause the spectrum shift of SPR sensor. In this paper, our proposes are to build the quantitative relationships among the resonance angle of SPR sensor, the RI of GSM, the concentration of glucose in GSM and the concentration of glucose in solution, and then to provide an efficient research method for the GSM of optical sensors. Firstly, we have reported the fabrication and characterization of GSM which is made of immobilized GOD on SiO2 nanoparticles and polyacrylamide gel. Secondly, we have finished a serial of SPR sensing experiments and obtained the resonance spectra of SPR sensors coated with pure PAM gel film, with free GOD@PAMfilm, and with immobilized GOD@PAM film in PBS solution, respectively, also displayed their variation relationship of resonance angle with the concentration of glucose in PBS solution. Thirdly, we have investigated the effects of solution pH and the content of immobilized GOD on the performance of the sensor, and obtained the optimum solution pH and the optimum content of GOD. Finally, we have related the resonance angle of SPR sensor and the RI of GSM by the combination of SPR experiment data and theoretical simulation, related the RI of GSM and the concentration of glucose in GSM according to Gladstone-Dale mixing rule, related the concentration of glucose in GSM and the concentration of glucose in solution by using the adsorption isotherm model of GSM.