Lossy Mode Resonance Fiber-Optic Biosensing Allowing Ultra-Low Detection Limit

Fiber-optic biosensors can offer great advantages over other optical technology platforms thanks to the typical features of optical fibers [1]. Moreover, the opportunity of depositing nm-thick overlays on optical fibers with a high degree of accuracy, repeatability and reproducibility has enabled spreading the application domains of this technology [2]. Recently, the concept of guided mode resonance has been exploited in thin film coated fiber-optic sensors, under the name of lossy mode resonance (LMR). LMR occurs when the real part of the thin film permittivity is positive and greater in magnitude than both its own imaginary part and the permittivity of the material surrounding the thin film. Therefore, metallic oxides and polymers can be used to generate LMRs, instead of the noble metals typically used in SPR devices. Instead of using multi-mode fibers, D-shaped single-mode fibers have been used to excite LMR [3], which enables tracking the spectral displacement of the 1st LMR, the most sensitive LMR, at wavelengths in the NIR, where the sensitivity is enhanced if compared to the visible region [1].