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, in order to create a microchannel. The latter was then coated with a gold nanofilm in order 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 μm) allows to avoid microfluidic systems, typically adopted in this kind of SPR configurations. As a proof of concept, the plasmonic sensor has been tested as a refractometer using different water-ethanol solutions, with a refractive index range 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 × 10 -4 RIU, respectively. These values testify to the proposed sensor goodness and its suitability for biochemical sensing applications.