Microsphere Sensitized Fiber Optic SPR Biosensor for Refractive Index Detection

In this paper, barium titanate glass microspheres were combined with optical fiber microspheres to enhance the surface plasmon resonance (SPR) effect of the optical fiber microspheres probe, and a probe type optical fiber sensor for detection was developed. The sensor adopts a reflective structure; the light source enters the tip of the probe by a single-mode fiber to stimulate the SPR effect and then returns through the single-mode fiber, and a spectrometer monitors the change of the reflected signal. Firstly, COMSOL Multiphysics was used for simulation to verify the sensitization effect of structure optimization using barium titanate microspheres at the theoretical level. To verify the actual detection effect of the sensor, this paper uses different concentrations of sodium chloride solution for refractive index detection experiments. It makes two kinds of fiber optic sensors for comparative experiments before and after structure optimization. The experimental results show that the refractive index sensitivity of the structure before and after optimization using barium titanate microspheres is 2486 nm/RIU and 6802 nm/RIU, respectively. Combined with different functionalization methods, the sensor can be used to detect a variety of parameters. Through the chemical modification of the gold film on the sensor's surface, the detection markers were captured on the surface of the microspheres, resulting in local refractive index changes, and the qualitative and quantitative detection of different parameters was realized. Alternatively, there is great potential in diagnosing major diseases by detecting the concentrations of specific biomarkers.