A U-Shaped Long-Range Surface Plasmon Resonance (LRSPR) Biosensor With Low Detection Limit

To improve the performance of optical fiber surface plasmon resonance (SPR) sensor, we proposed a novel method based on a U-shaped long-range SPR (LRSPR) sensor, with a low limit of detection (LOD) and high sensitivity when detecting low concentration biological analytes. A kind of UV glue with low refractive index and strong adhesion was used as a dielectric matching layer (DML) to stimulate LRSPR. This article compared the performance of conventional SPR (CSPR) sensor, U-shaped SPR sensor, U-shaped LRSPR sensor, and U-shaped symmetrical LRSPR (SLRSPR) sensor in the field of biosensing. Compared with the conventional U-shaped SPR sensors, the sensitivity of the U-shaped LRSPR and SLRSPR sensors in refractive index detection was increased by 7.85% and 16.17%, and the figure of merit (FOM) was increased by 12.62% and 32.93%. When modified with carbon nanotubes, the sensitivity of the sensor was further improved, up to 5948.57 nm/RIU. In the detection of human immunoglobulin G (IgG), the LOD of U-shaped LRSPR and SLRSPR sensors were reduced by 10.71% and 32.20% compared with U-shaped SPR sensors, and the lowest LOD reached 6.112 ng/mL. In this work, a new method to improve the performance of optical fiber SPR sensors was presented innovatively, U-shaped structure was applied to fabricate improved LRSPR sensor for the first time. Successful detection of IgG in traces verified the broad application prospects of the proposed method in the field of low concentration biological analytes detection.