Miniaturized Sensing Probes Based on Metallic Dielectric Crystals Self-Assembled on Optical Fiber Tips

We propose a novel fabrication process to realize optical sensing probes based on metal–dielectric crystals self-assembled on an optical fiber tip. The breath figure methodology has been adapted to work directly on nonconventional substrates, such as optical fibers, enabling the formation of regular and ordered metallo-dielectric crystals on optical fiber tips. Accurate morphological characterization was carried out to qualify the fabrication process. The reported results indicate that the proposed fabrication technique provides a method for rapid and cost-effective prototyping of photonic–plasmonic nanoprobes for sensing applications. To achieve this goal, we develop a technological platform via the addition of polymer–metal crystals onto the tip of a standard single optical fiber, which is able to support surface plasmon resonances in the near-infrared. A dedicated numerical tool was developed to study and analyze arbitrary subwavelength structures integrated on the optical fiber tip by taking into account finite-size effects. The numerical results are in good agreement with the observed experimental spectra and reveal that the fabricated sensing probes act as structured interferometers that are assisted by surface plasmon excitations at the metallo-dielectric interfaces. To prove the sensing capability of the proposed platform, refractive index measurements were carried out, revealing a sensitivity of up to 2300 nm/RIU, outperforming most plasmonic probes synthesized on optical fiber tips. The achieved performances, obtained using very small active areas, demonstrate the effectiveness of these self-assembled fiber-optic probes for label-free chemical and biological sensing applications.