Graphene oxide modified U-shaped polymer optical fiber biosensor for hemoglobin sensing

Background: Polymer optical fiber (POF)-based sensors are attracting increasing attention for biosensing applications due to their flexibility, cost-effectiveness, and compatibility with diverse functional coatings. While surface plasmon resonance (SPR) sensors with functionalization offer enhanced sensitivity, the integration of functional nanomaterials such as graphene oxide (GO) and polyvinyl alcohol (PVA) for hemoglobin detection remains underexplored. This study addresses this gap by demonstrating a sensitive, repeatable, and selective GO/PVA-coated U-bent POF sensor for hemoglobin detection in the early stage of cancer. Results: A 2 mm radius U-shaped uncladded POF coated with GO/PVA is experimentally demonstrated as a highly sensitive and easily fabricated hemoglobin sensor. The exposed U-bent core undergoes functionalization before sputter-coating with a 50 nm gold layer to facilitate SPR. Responsiveness to refractive index (RI) variations is confirmed over the range 1.3327 to 1.3418 with sensitivity measured at 3949.14 nm/RIU. The GO/PVA layer is thermally deposited onto the gold-modified surface to impart sensitivity toward the hemoglobin analyte. Three 2 mm radius probes are fabricated using identical coating procedures to ensure sensor reproducibility. The maximum sensitivity is found to be to be −16.10 nm/(mg/ml) with an average response time of 3 min. The sensor displays approximately five times greater selectivity for hemoglobin over other plasma proteins. The thermal response of the sensor is also investigated to minimize the measurement error. Significance: The proposed all-polymer U-shaped sensor demonstrates strong potential as a competitive optical biosensing platform for hemoglobin detection and advances optical fiber sensor applications.