Short and long range surface plasmon polariton waveguides for xylene sensing

Abstract

Nanostructured plasmonic sensors are fabricated as sinusoidal surface plasmon metallic gratings (SPGs) embedded in a functional and porous hybrid sol-gel material, phenyl-bridged polysilsesquioxane (ph-PSQ). The metal layer is in contact with the environment through the sol-gel film, which works as sensitive element, changing its dielectric properties upon interaction with aromatic hydrocarbons. The combination of sensitivity, transparency and patternability offered by ph-PSQs gives the exceptional possibility to fabricate innovative optical sensors with straightforward processes. An embedded SPG is a thin metal slab waveguide, in which the surface plasmon polaritons (SPPs) at the two metal-dielectric interfaces superpose, resulting in two physical coupled modes: the long range SPPs (LRSPPs) and the short range SPPs (SRSPPs). An extended experimental and theoretical characterization of the optical properties of the plasmonic device was performed. The sensor performance was tested against the detection of 30 ppm xylene, monitoring the influence of the target gas on the SPPs modes. A reversible red-shift of the reflectance dips of both LRSPP and SRSPP resonances in the 1.9-2.9 nm range was observed and correlated to the interaction with the analyte. An enhancement in sensitivity associated with the rotation of the grating grooves with respect to the scattering plane (azimuthal rotation) was verified within the experimental errors. Collected data are compatible with theoretical predictions assuming a variation of the film refractive index of 0.011 ± 0.005.

Sol-Gel Thin Films for Plasmonic Gas Sensors

“…Recently, we further developed optical sensors based on extended plasmons by using a patternable sol-gel hybrid film to fabricate a dielectric-metal-dielectric (DMD) sinusoidal grating capable of coupling light and generating surface plasmon polaritons [ 28 ]. We used aryl-bridged polysilsesquioxane films similar to those described earlier thanks to their ability to undergo patterning and to their distinctive ability to detect aromatic hydrocarbons.…”

“…The glass prism can also be replaced by a diffraction grating: for a proper combination of the period of the grating, the angle and wavelength of the incident wave, a surface plasmon is generated [ 28 ].…”

Grating-coupled surface plasmon resonance gas sensing based on titania anatase nanoporous films

“…A postdeposition bake was applied to promote solvent evaporation and reach a stable cross-linking degree. [22] TiO 2 -based anatase TiO 2 nanoparticles (NPs) were synthesized starting from a solution containing water, HCl and methanol with molar ratios H 2 O/TiOPr=12.25 and HCl/ TiOPr=1.72. Following a previously described receipt, 10.5 mmol of Ti(OPri) 4 (Titanium Isopropoxide) were added drop wise into the solution, that was stirred for 60 min at room temperature afterwards, then heated in an oil bath at 70°C and kept at this temperature for 4 h under reflux.…”

“…Therefore, reflectance spectra could only be acquired at an incidence angle of 70°, varying the incident light frequency. [22] In order to test the sensor response to a specific analyte, the following procedure was adopted. First, a suitable reference reflectance spectrum was recorded in dry N 2 environment.…”

Grating-coupled Surface Plasmon Resonance (GC-SPR) Optimization for Phase-interrogation Biosensing in a Microfluidic Circuit

“…It is thus essential to find strategies to enhance the sensitivity of these sensors. It was demonstrated that a sensitivity enhancement can be achieved by working in "conical mounting", a configuration where the scattering plane is rotated of an azimuthal angle with respect to the grating wavevector [25][26][27][28]. It was also observed that the symmetry breaking, due to the azimuthal rotation, involves a fundamental role of the incident light polarization on SPP excitation [25,29].…”