Harmonic Vernier effect-enabled optical fiber biosensor for ultra-sensitive detection of CA125

A highly economical fiber immunosensor with the harmonic Vernier effect (HVE) is reported for cancer antigen 125 (CA125) tumor marker detection. The sensor architecture is constructed using a special fiber fusion splicer to cascade three sections of single-mode fiber (SMF) in sequence with a large offset. This configuration yields a cascaded Fabry-Perot interferometer (FPI) architecture incorporating the HVE. The misalignment fusion design facilitates direct and seamless interaction between biochemical fluids and optical signals. Experimental results demonstrate that the refractive index sensitivities of the internal envelope and upper envelope reach −5236, and 1163 nm/RIU, respectively, when refractive index increases from 1.334 to 1.339. It has excellent consistency with the simulation results of −5375 nm/RIU and 1257 nm/RIU as refractive index increases from 1.334 to 1.335. Obviously, the refractive index sensitivity is significantly enhanced via the HVE. The designed sensor is further biologically modified with the 50 μg/mL ovarian cancer 125 monoclonal antibody, enabling varying cancer antigen 125 concentrations detection. The proposed biosensor has low detection limit with value of 44.12 fg/mL and a fast response time (<30 min). Therefore, the proposed biosensor has latent application as an ideal platform for disease diagnosis and medical detection.