Spectroelectrochemical Fiber-Optic Sensor Based on Localized Surface Plasmon Resonance for Simultaneous Multiselective Electroactive Species Detection

Herein, we report the development of a novel sensor combining electrochemistry, localized surface plasmon resonance (LSPR) in nanoparticles, and fiber-optic sensing for the first time. The sensor developed comprises an indium tin oxide (ITO)-coated multimodal optical fiber with gold nanoparticles immobilized on the ITO surface via electrostatic self-assembly. Two types of sensing methods are demonstrated: one based on shift in LSPR peak wavelength accompanying electrochemical oxidation–reduction of an analyte and the other based on potential scanning-based detection of refractive index change. Ru(NH₃)₆^2+/3+, methylene blue, and Fe(CN)₆^3–/4– are used as model analytes for the first method. Consequently, we observe that the optical responses caused by electrochemical reactions of the analytes are accompanied by a linear relationship between the LSPR peak shift and analyte concentration. In the second method, the LSPR peak potential is obtained via potential scanning in sucrose solutions with various refractive indexes. By means of avidin–biotin interaction on its surface, the sensor developed is successfully applied for biodetection of the protein NeutrAvidin.