Single-mode nanoparticles-doped optical fibers: opportunities for high-performance biosensing

The possibility to control Rayleigh scattering in glass single-mode optical fibers opens important perspectives in the field of distributed sensing. Optical backscatter reflectometry (OBR), operating in the time domain, makes use of scattering events occurring in optical fibers as sensing methods. The possibility of forming nanoparticles during the fiber drawing process, which results in an increase of the backscattered power even up to 50 dB over standard single-mode fibers, increments the backscattered power and enables multi-fiber sensing architectures, suitable in medical devices. In this contribution, we turn our attention to the possibility of using the augmented elastic scattering in novel systems for biosensing, characterized by a simple fabrication. We present two methods based on reflector-less sensing, and on distributed interferometry, to achieve biosensing and we discuss the application in the detection of cancer biomarkers. Reflector-less biosensors make use of a fiber taper or etching without the need to fabricate any reflector; so far, sensitivity ratings up to ~1 nm/RIU (refractive index units) have been reported; however, detection limits of sub-picomolar levels are reported, due to the precise tracking of the OBR. Distributed interferometers turn a high-scattering fiber into a series of mirrors, which can be simply terminated by a fiber cleave. Even with a simple fabrication, we show the possibility to achieve sensitivity in the order of 60-100 dB/RIU and detection limit as low as few attomolars.