Ultra-narrow surface lattice resonances in plasmonic metamaterial arrays for biosensing applications

Abstract

When excited over a periodic metamaterial lattice of gold nanoparticles (~ 100nm), localized plasmon resonances (LPR) can be coupled by a diffraction wave propagating along the array plane, which leads to a drastic narrowing of plasmon resonance lineshapes (down to a few nm full-width-at-half-maximum) and the generation of singularities of phase of reflected light. These phenomena look very promising for the improvement of performance of plasmonic biosensors, but conditions of implementation of such diffractively coupled plasmonic resonances, also referred to as plasmonic surface lattice resonances (PSLR), are not always compatible with biosensing arrangement implying the placement of the nanoparticles between a glass substrate and a sample medium (air, water). Here, we consider conditions of excitation and properties of PSLR over arrays of glass substrate-supported single and double Au nanoparticles (~ 100-200nm), arranged in a periodic metamaterial lattice, in direct and Attenuated Total Reflection (ATR) geometries, and assess their sensitivities to variations of refractive index (RI) of the adjacent sample dielectric medium. First, we identify medium (PSLR, PSLR for air and water, respectively) and substrate (PSLR) modes corresponding to the coupling of individual plasmon oscillations at medium- and substrate-related diffraction cut-off edges. We show that spectral sensitivity of medium modes to RI variations is determined by the lattice periodicity in both direct and ATR geometries (~ 320nm per RIU change in our case), while substrate mode demonstrates much lower sensitivity. We also show that phase sensitivity of PSLR can exceed 10 degrees of phase shift per RIU change and thus outperform the relevant parameter for all other plasmonic sensor counterparts. We finally demonstrate the applicability of surface lattice resonances in plasmonic metamaterial arrays to biosensing using standard streptavidin-biotin affinity model. Combining advantages of nanoscale architectures, including drastic concentration of electric field, possibility of manipulation at the nanoscale etc, and high phase and spectral sensitivities, PSLRs promise the advancement of current state-of-the-art plasmonic biosensing technology toward single molecule label-free detection.

Plasmonic Sensors Based on Funneling Light Through Nanophotonic Structures

“…To improve sensitivity and FOM, the incoming light has to couple efficiently to surface plasmon resonances (SPR) with the narrowest possible lineshape at the desired wavelength range. A wide variety of designs have been proposed to produce these features [15,[21][22][23].…”

Impact of substrate etching on plasmonic elements and metamaterials: preventing red shift and improving refractive index sensitivity

“…The improvement of the sensitivity exceeding 4 times by using substrate etching is attributed to the extension of accessible electric fields and low index environment around the structures before PMMA coating. Figure 8 [17][18][19][34][35][36] mainly due to degradation of Q-factors due to substrate etching. If reduction of the Q-factors by substrate etching is prevented as discussed before, higher FOM is expected.…”

Condition of excitation and sensitivity of diffractively-coupled surface lattice resonances over plasmonic nanoparticle arrays in ATR geometry

“…We recently showed 26 that the excitation of PSLR is possible in both direct and attenuated total reflection (ATR) geometries under oblique light incidence. In this paper, we provide extensive details on conditions of excitation and properties of PSLR in ATR geometry, excluding the propagation of pumping light through sample liquid medium.…”

“…One of them corresponds to the disappearance of the medium diffraction modes (when the diffraction wave crosses the sample boundary from air/water to the substrate) and other one is related to crossing the boundary in the opposite direction. Such two Rayleigh cut-off wavelengths for air/substrate interface can be presented as follows 18,26 :…”

“…2c. PSLR typically appear in reflection as narrow Fano-shape dips over a positive background spectrum 26 , presenting the combination of reflected and scattered light from glass-supported nanoparticle array system. However, when measured by ellipsometry and presented as a function of ellipsometric reflection Ψ, which describes a ratio of amplitudes of p-and s-components upon reflection tan = , the resonances can appear as both minima (inset to Fig.…”