LSPR- and SPR-Based Fiber-Optic Cholesterol Sensor Using Immobilization of Cholesterol Oxidase over Silver Nanoparticles Coated Graphene Oxide Nanosheets

Fabrication and characterization of a highly sensitive fiber-optic cholesterol sensor utilizing cholesterol oxidase (ChOx) have been carried out. The operation of the sensor is based on combined phenomenon of localized and propagating surface plasmons. Two different immobilization schemes of enzyme ChOx have been used. In one, the enzyme is entrapped in the hydrogel and in second the enzyme is immobilized over the graphene oxide (GO) nanosheets. The synthesis of GO is confirmed by XRD, TEM, and Raman spectroscopy and the binding between ChOx and GO is verified through the Raman spectroscopy and Fourier transform infrared spectroscopy techniques. Following three types of probes having different configurations are fabricated and compared: 1) enzyme entrapped gel layer over silver coated unclad fiber; 2) enzyme immobilized over silver and GO coated unclad fiber; and 3) enzyme immobilized over silver, GO, and silver nanoparticles coated unclad fiber. The performance of all these probes have been compared in terms of operating range, sensitivity and limit of detection. The sensors have many advantages, such as compact size, modest cost, high sensitivity, high selectivity, and capability of remote sensing.