A Single-Point, Multiparameter, Fiber Optic Sensor Based on a Combination of Interferometry and LSPR

We demonstrate a new single-point, multiparameter, fiber optic sensor concept based on a combination of interferometric and plasmonic sensor modalities on an optical fiber end face. The sensor consists of an extrinsic Fabry-Perot interferometer in the form of a hemispherical stimuli-responsive hydrogel with immobilized gold nanoparticles (GNPs). The GNPs exhibit local surface plasmon resonance (LSPR) that is sensitive toward the local refractive index (RI) of the surrounding environment, whereas the stimuli-responsive hydrogel is sensitive toward specific chemical compounds. We evaluate the quality of the interferometric and LSPR signals as a function of GNP concentration and of hydrogel swelling degree stimulated by ethanol solutions. The GNPs have little influence on the visibility of the Fabry-Perot etalon. The swelling degree of the hydrogel, with corresponding bulk RI changes, has little influence on the local surface RI of the GNPs. We expect this novel sensor concept to be of great value for biosensors for medical applications.