Micrometer level distributed cancer biomarker biosensing based on optical frequency domain reflectometry

We present a distributed cancer biomarker biosensing with a micrometer level spatial resolution by functionalized tapered fiber based on optical frequency domain reflectometry (OFDR). A Graphene oxide (GO) film is fixed on the surface of the tapered fiber. Carcinoembryonic antigen-related cell adhesion molecules 5 monoclonal antibody (CEACAM5 mAb) layer is coated on the entire GO fixed tapered region by polydopamine (PDA) assisted immobilization as the functionalized sensing element to achieve the sensing of carcinoembryonic antigen (CEA). To enhance the ability of localization for biochemical substances, we apply a differential relative phase method with a radius denoising method in OFDR to demodulate phase variations of Rayleigh backscattering caused by the biomolecular binding reaction. The measurable concentrations of CEA and phase variations have a good linearity in a range from 1 ng/ml to 8 ng/ml. The proposed distributed biosensor has a limit of detection (LOD) of is 1 ng/ml and a sensitivity of 0.0864 rad/(ng/mL). We also verify that the proposed distributed biosensor can locate the concentration changes of CEA with a sensing spatial resolution of 80 μm. The proposed distributed biosensor provides a potential tool to in situ detect and locate tumor cells at a spatial resolution of micrometer level.