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International audience; "Condition of excitation and sensitivity of diffractively-coupled surface lattice resonances over plasmonic nanoparticle arrays in ATR geometry ," Proc. ABSTRACT We investigate conditions of excitation and properties of Plasmonic Surface Lattice Resonances (PSLR) over glass substrate-supported Au nanoparticle dimers (~100-200 nm) arranged in a periodic metamaterial lattice, in Attenuated Total Reflection (ATR) optical excitation geometry, and assess their sensitivities to variations of refractive index (RI) of the adjacent sample dielectric medium. We show that spectral sensitivity of PSLR to RI variations is determined by the lattice periodicity (~ 320 nm per RIU change in our case), while ultranarrow resonance lineshapes (down to a few nm full-width-at-half-maximum) provide very high figure-of-merit values evidencing the possibility of ultrasensitive biosensing measurements. Combining advantages of nanoscale architectures, including a strong concentration of electric field, the possibility of manipulation at the nanoscale etc, and high phase and spectral sensitivities, PSLRs promise a drastic advancement of current state-of-the-art plasmonic biosensing technology. Keywords: plasmonic metamaterials for biosensing plasmonic surface lattice resonances, diffractive coupling, attenuated total reflection, plasmonic biosensing, improvement of sensitivity.

International audience; When excited over a periodic metamaterial lattice of gold nanoparticles (~ 100 nm), 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 (~100–200 nm), 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 (PSLRair, PSLRwat for air and water, respectively) and substrate (PSLRsub) 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 (~ 320 nm per RIU change in our case), while substrate mode demonstrates much lower sensitivity. We also show that phase sensitivity of PSLR can exceed 105 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 biosensors form the core label-free technology for studies of biomolecular interactions, but they still need a drastic improvement of sensitivity and novel nano-architectural implementations to match modern trends of nanobiotechnology. Here, we consider the generation of resonances in light reflected from 3D woodpile plasmonic crystal metamaterials fabricated by Direct Laser Writing by Multi-Photon Polymerization, followed by silver electroless plating. We show that the generation of these resonances is accompanied by the appearance of singularities of phase of reflected light and examine the response of phase characteristics to refractive index variations inside the metamaterial matrix. The recorded phase sensitivity (3*104 deg. of phase shift per RIU change) outperforms most plasmonic counterparts and is attributed to particular conditions of plasmon excitation in 3D plasmonic crystal geometry. Combined with a large surface for biomolecular immobilizations offered by the 3D woodpile matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology.

Plasmonic metamaterials for biosensing were designed as artificial materials, composed of gold/silver nanostructured blocks forming a nanolattice, which can provide improved sensing response in optical transduction compared to classical materials and additional sensing functionalities. 2D plasmonic nanoperiodic structures, including nanohole and nanodot arrays are prominent examples of such metamaterials, which can offer a series of novel functionalities, including size selectivity, spectral tuneability, drastical field enhancement etc., although spectral sensitivity of these structures is limited by spatial periodicity related to diffraction nature of plasmon coupling. Here, we consider metamaterials based on 3D plasmonic crystals and show the possibility of a delocalized plasmon mode, which can provide a drastic gain in spectral sensitivity (> 2600 nm/RIU compared to 200-400 nm/RIU for 2D structures). Combined with larger surface for bioimmobilization provided by the 3D matrix, the proposed metamaterial structure promises the advancement of plasmonic biosensing technology.

We explore the excitation of plasmons in 3D plasmon crystal metamaterials and report the observation of a delocalized plasmon mode, which provides extremely high spectral sensitivity (>2600 nm per refractive index unit (RIU) change), outperforming all plasmonic counterparts excited in 2D nanoscale geometries, as well as a prominent phase-sensitive response (>3*104 deg. of phase per RIU). Combined with a large surface for bioimmobilization provided by the 3D matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology.

Conference on Synthesis and Photonics of Nanoscale Materials XIII, San Francisco, CA, FEB 15-17, 2016; International audience; We overview our on-going activities on the improvement of physical sensitivity of plasmonic biosensors. Our approach is based on the employment of phase properties of light reflected from plasmonic transducer instead of amplitude ones in order to improve its detection limit in studies of biomolecular interactions between a target analyte and its corresponding receptor. Originally, phase-sensitive biosensing concept was demonstrated in conventional Surface Plasmon Resonance (SPR) geometry using a thin Au film in Kretschmann-Raether arrangement, but the resulting sensitivity had some limitations because of a rough relief of the gold film surface. We then demonstrate the possibility for the extension of this concept to novel nanoscale architectures of designed plasmonic metamaterials in order to further improve the sensitivity of plasmonic biosensing technology. The latter approach also profits from much enhanced electric field in coupled nanostructures exposed to illumination, therefore enabling spectroscopy analysis (Raman, Fluorescence, IR etc) methods to increase sensitivity level (potentially down to single molecule).