A Novel Microchannel-in-a-Fiber Plasmonic Sensor

In this work, a novel surface plasmon resonance (SPR) sensor has been designed, realized, and investigated. The SPR platform was created by using a D-shaped plastic optical fiber shell (POFS), obtained by removing the graded index core region from the fiber's protective jacket, to create a microchannel. The latter was then coated with a gold nanofilm to obtain the plasmonic-sensitive region. The sensor's structure includes an integrated measuring cell, being the solution under test injected into the microchannel using a peristaltic pump. The microchannel dimension ( $160 \mu \text{m}$ ) allows for avoiding microfluidic systems, typically adopted in this kind of SPR configuration. As a proof of concept, the plasmonic sensor has been tested as a refractometer using different water–ethanol solutions, with a refractive index (RI) ranging from 1.332 to 1.352. The experimental results have highlighted a sensitivity and a resolution equal to about 1026 nm/RIU and $1.95\times 10^{-{4}}$ RIU, respectively. These values testify to the proposed sensor's goodness and its suitability for biochemical sensing applications.