Lab-on-fiber optrodes based on all-dielectric fluorescence enhancing metasurfaces

The need for miniaturized biological sensors which can be easily integrated into medical needles and catheters for in vivo liquid biopsies with ever-increasing performances has stimulated the interest of researchers in Lab-on-Fiber (LOF) technology. In this framework, the integration of Metasurfaces (MSs) on the tip of the optical fiber (Optical Fiber Meta- Tip, OFMT) has represented a major breakthrough. Indeed, we showed that a suitably designed plasmonic OFMT biosensor significantly outperforms standard plasmonic ones due to the advanced light wave manipulation of MSs. Here, to further improve the sensing performances, we propose a novel class of LOF optrodes for labelled biosensing based on dielectric fluorescence enhancing OFMT. We envision a single fiber probe with integrated a Silicon MS on its tip as a light coupled substrate that illuminates the sample and simultaneously collects the enhanced emission from the dye molecules labeling the biological target. We present a numerical environment to compute the fluorescence enhancement factor collected by a multi-mode-fiber, when on its tip a Silicon MS is laid, consisting of an array of cylindrical nanoantennas. According to the numerical results, a suitable design of the dielectric MS allows for a fluorescence enhancement up to three orders of magnitudes. Moreover, a feasibility study is carried out to verify the possibility to fabricate the designed MSs on the termination of multimode optical fibers using electron beam lithography followed by reactive ion etching. This work provides the main guidelines for the development of advanced LOF devices based on the fluorescence enhancement for labeled biosensing.