Ultrasensitive Plasmonics Sensors via Circular Surface Lattice Resonances

The sensitivity of plasmonic sensors can be radically enhanced by taking advantage of singular phase behavior under the excitation of the surface lattice resonance (SLR), which is one orders of magnitude better than propagating surface plasmon (PSP) sensitivity in the Kretschmann configuration. But the spectral sensitivity of SLRs in nanoperiodic array is typically much lower than that of PSP. Recently, a novel circular SLRs effect is proposed by applying the rotational symmetry instead of the translation symmetry, and extremely sharp resonance can be excited with less than ten nanoparticles. This paper extended this idea to explore its amplitude sensitivities, where the enhancement factor (EF) is simulated as a function of the refractive index (RI) of the surrounding medium and the incident wavelength. By optimized the structural arrangement, a circular array of only 8 nanoparticles illustrates a single SLR peak with EF as high as 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup>. The FWHM is less than 0.01nm, resulting an extremely high theoretical Q-factor of 105. For the RI detection, such high Q factor yields a sensitivity of 10–<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup>RIU.