Fabrication and Measurement of Fiber Optic Localized Surface Plasmon Resonance Sensor Based on Hybrid Structure of Dielectric Thin Film and Bilayered Gold Nanoparticles

Abstract

Localized surface plasmon resonance (LSPR) sensor with hybrid structure of dielectric thin film and bilayered gold nanoparticles (AuNPs) on an optical fiber is proposed to enhance the sensitivity. The increased number of nanoparticles per unit plane due to the bilayer structure contributes to the upgrade in the sensitivity by improving the LSPR effect and extending the sensing area. The bilayered AuNPs will be particularly important in the application of fiber optic LSPR (FO LSPR) sensors because the optical fiber has a small cross-sectional area. The Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin film by atomic layer deposition is inserted between the first and second layers of AuNPs. The dielectric spacer can also help to improve the sensitivity by concentrating the electric field due to its high refractive index and ensuring a nanometer gap between nanoparticles. The monolayer and bilayer with AuNPs are prepared on the optical fibers, respectively. In each FO LSPR sensor, refractive index sensitivities are also analyzed and compared. In the sensor with bilayered AuNPs, a sensitivity improvement of approximately 2.3 times is confirmed. This strategy can be a breakthrough to increase the sensing area of the FO LSPR sensor without modifying the structure of the optical fiber.