Dual Localized Surface Plasmon Resonance Sensors on a Single Optical Fiber

This letter reports a novel dual sensor based on localized surface plasmon resonance near the tip of an optical fiber. The sensor was fabricated by immobilizing two regions of the fiber with gold nanoparticles of different sizes. The evanescent field of the incident light interacted with the metal nanoparticles at the fiber tip and produced localized surface plasmon resonance at two distinct wavelengths. This multiplexing capability of a single fiber allows the detection of multiple analytes in a smaller footprint, reducing the number of fibers required for multianalyte sensing. The dual-coated fiber demonstrated localized surface plasmon resonance dips at 610- and 662-nm wavelengths, in contrast to the fiber coated with a single layer of gold nanoparticles, which exhibited a resonance dip at 620 nm. The performance of the dual sensor was tested with varying concentrations of ethanol (ranging from 0% to 100%). The resonance dips located at 610 and 662 nm showed variations in reflection intensities when ethanol was adsorbed onto the surface of the gold nanoparticles. In addition, the sensor performance was analyzed at different temperatures (at 25 °C, 40 °C, and 60 °C) and bending deformations (at 10° up to 30, 60, and 90 cycles). Temperature corrections were incorporated to compensate for variations in the sensor response caused by temperature changes. The sensor showed an excellent reproducible response under bending deformations. The presented design could be extended to implement multiple sensing regions on the same fiber, enabling the detection of multiple analytes with a single optical fiber.