Biofunctionalized Surface-Plasmon Optical Fiber Grating Sensors

Optical fiber refractometers coated by a nano-scale gold layer constitute a miniaturized counterpart to the Kretschmann prism and enable the exploitation of surface Plasmon resonance (SPR) for accurate (bio)chemical sensing purposes. We make use of tilted fiber Bragg gratings (TFBGs) photowritten in the core of a standard singlemode silica fiber to individually interrogate the cladding modes. TFBGs couple light to the fiber cladding in reflection and present a comb-like amplitude transmitted spectrum composed of the core mode resonance (so-called Bragg resonance) and several tens of cladding mode resonances. The Bragg resonance provides temperature-insensitivity while each cladding mode resonance finely probes a given range of surrounding refractive index values. Experiments conducted on gold-coated TFBGs immersed in calibrated liquids finally show that their ultimate refractometric sensitivity is of the order of 550 nm/RIU (refractive index unit). Thanks to this high sensitivity, we can consider this sensor for immunosensing. In this work, we use the antibody-antigen affinity mechanism to assess the unique protein detection and quantification capabilities of these SPR-TFBGs and evaluate their performances in terms of both sensitivity and limit of detection (LOD).