No abstract

A novel optical label-free bio-sensing platform based on a new class of resonances supported in a photonic crystal metasurface is reported herein. Molecular binding is detected as a shift in the resonant wavelength of the bound states in the continuum of radiation modes. The new configuration is applied to the recognition of the interaction between protein p53 and its protein regulatory partner murine double minute 2 (MDM2). A detection limit of 66 nM for the protein p53 is found. The device provides an excellent interrogation stability and loss-free operation, requires minimal optical interrogation equipment and can be easily optimized to work in a wide wavelength range.

Plasmonic substrates play a crucial role in the confinement and manipulation of localized electromagnetic fields at the nanoscale. The large electromagnetic field enhancement at metal/dielectric interfaces is widely exploited in surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS) spectroscopies. Despite the advantage of near-field enhancement, unfortunately, in metals, the large absorption at optical frequencies induces local heating of the analyte fluid with possible damage of the biological material. In addition, in SEF plasmonic substrates, spacer layers are necessary to minimize undesired fluorescence quenching due to nonradiative decay, which strongly depends on the distance between molecules and metallic substrates. Therefore, the possibility of managing surface electromagnetic states mimicking surface-plasmon resonances in terms of spatial localization, high-field intensity, and dispersion characteristics, while avoiding metallic losses is of great interest. However, dielectric nanoantennas can currently provide limited possibilities in the visible range of optical frequencies. We present the realization of all-dielectric metasurfaces made of nanostructured transparent silicon nitride supporting bound states in the continuum (BICs). We show that this special kind of Fano resonances can be effectively used in standard microscopy for practical applications. We achieved concurrent enhancements of ∼10 3 fold of fluorescence emission and Raman scattering farfield intensities of molecules dispersed on these metasurfaces. In addition, we demonstrate that the gain of conventional SERS signals can be increased by more than one order of magnitude by resonant matching of the localized surface plasmon resonance with the BIC field. Our results can find significant applications for enhanced sensing, Raman imaging, and nonlinear processes.

Inspired by the concept of complementary media, we experimentally demonstrate that an engineered metamaterial made of alternating, stripe layers of negatively refracting (photonic crystals) and positively refracting (air) materials strongly collimates a beam of near-infrared light. This quasi-zero-average-index metamaterial fully preserves the beam spot size throughout the sample for a light beam traveling through the metamaterial a distance of 2 mm-more than 1000 times the input wavelength lambda=1.55 microm. These results demonstrate the first explicit experimental verification of optical antimatter as proposed by Pendry and Ramakrishna [J. Pendry and S. Ramakrishna, J. Phys. Condens. Matter 15, 6345 (2003)10.1088/0953-8984/15/37/004], using two complementary media in which each n(eff)=-1 layer appears to annihilate an equal thickness layer of air.