Abstract

A cost-efficient fiber immunosensor based on an open-cavity Fabry–Perot interferometer (FPI) with the Vernier effect for tumor biomarker named carcinoembryonic antigen (CEA) detection is proposed and experimentally shown. A short single-mode fiber (SMF) with the length of 206 μm is spliced between a lead-in SMF and a 217 μm SMF with a large lateral offset to generate a compact open-cavity FPI configuration where a tightly connected open cavity and the silica cavity with slightly various free spectrum ranges are used as the sensing element and the reference element, respectively, to generate the Vernier effect. The refractive index (RI) liquids or biological materials can directly and easily interact with optical signals because of the presence of the open-cavity. The upper envelope's experimental RI sensitivities and open-cavity are −8535 and 1174 nm/RIU, respectively, with linear correlation coefficients of 0.99 and 0.998, respectively, at an RI range of 1.335–1.3388, which perfectly matches with theoretical simulation findings (−8247 and 1171 nm/RIU, respectively). RI sensitivity is enhanced by a factor of 7 using the Vernier effect. Furthermore, the fabricated open-cavity FPI is functionalized with the 50 μg /mL anti-CEA antibody for different concentrations of CEA detection with a limit of detection (LoD) of 36.14 fg/mL. The biosensor's response time is less than 30 min. Additionally, the proposed Fabry–Perot biosensor has low LoD, excellent stability, reproducibility, specificity, and high sensitivity for CEA detection, which allows it to function as a platform for diseases/medical diagnostics. More crucially, the robust biosensor provides the possibility for in situ detection.

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