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.