Topological Darkness: How to Design a Metamaterial for Optical Biosensing with Virtually Unlimited Sensitivity

Due to the absence of labels and fast analyses, optical biosensors promise major advances in biomedical diagnostics, security, environmental and food safety applications. However, sensitivity of the most advanced plasmonic biosensor implementations has a fundamental limitation caused by losses in the system and or geometry of biochips. Here, we report a scissor effect in topologically dark metamaterials which is capable of providing virtually unlimited bona fide sensitivity to biosensing thus solving the bottleneck sensitivity limitation problem. We explain how the scissor effect can be realized via a proper design of topologically dark metamaterials and describe strategies for their fabrication. To validate the applicability of this effect in biosensing, we demonstrate the detection of folic acid (vitamin important for human health) in the wide 3-log linear dynamic range with the limit of detection of 0.125 nM, which is orders of magnitude better than previously reported for all optical counterparts. Our work opens possibilities for designing and realising plasmonic, semiconductor and dielectric metamaterials with ultra-sensitivity to binding events.Comment: 22 pages, 4 figure

Biocompatibility of Bare Nanoparticles Based on Silicon and Gold for Nervous Cells

This work aimed to investigate the biocompatibility of bare (ligand-free) lasersynthesized nanoparticles (NPs) based on silicon (Si) and gold (Au) with primary hippocampal cultures. 1%, 5% and 7% of culture medium were replaced by 0.1 mg/mL NP solution on day 14 of culture development in vitro. Our studies revealed that the NPs caused a dose-dependent cytotoxic effect, which was manifested by an increase the number of dead cells and a decrease of the spontaneous functional calcium activity of neural networks. Au NPs revealed less pronounced cytotoxic effect than Si ones and it can be explained by larger size and better solubility of Si NPs. Keywords: bare nanoparticles, primary hippocampal cultures, neurotoxicit

Giant and tunable excitonic optical anisotropy in single-crystal CsPbX3_3 halide perovskites

During the last years, giant optical anisotropy demonstrated its paramount importance for light manipulation which resulted in numerous applications ranging from subdiffraction light guiding to switchable nanolasers. In spite of recent advances in the field, achieving continuous tunability of optical anisotropy remains an outstanding challenge. Here, we present a solution to the problem through chemical alteration of the ratio of halogen atoms (X = Br or Cl) in single-crystal CsPbX$_3$ halide perovskites. It turns out that the anisotropy originates from an excitonic resonance in the perovskite, which spectral position and strength are determined by the halogens composition. As a result, we manage to continually modify the optical anisotropy by 0.14. We also discover that the halide perovskite can demonstrate optical anisotropy up to 0.6 in the visible range -- the largest value among non-van der Waals materials. Moreover, our results reveal that this anisotropy could be in-plane and out-of-plane, depending on perovskite shape -- rectangular and square. Hence, it can serve as an additional degree of freedom for anisotropy manipulation. As a practical demonstration, we created perovskite anisotropic nanowaveguides and show a significant impact of anisotropy on high-order guiding modes. These findings pave the way for halide perovskites as a next-generation platform for tunable anisotropic photonics.Comment: 18 pages, 3 figure

Giant optical anisotropy in transition metal dichalcogenides for next-generation photonics

Large optical anisotropy observed in a broad spectral range is of paramount importance for efficient light manipulation in countless devices. Although a giant anisotropy was recently observed in the mid-infrared wavelength range, for visible and near-infrared spectral intervals, the problem remains acute with the highest reported birefringence values of 0.8 in BaTiS3 and h-BN crystals. This inspired an intensive search for giant optical anisotropy among natural and artificial materials. Here, we demonstrate that layered transition metal dichalcogenides (TMDCs) provide an answer to this quest owing to their fundamental differences between intralayer strong covalent bonding and weak interlayer van der Walls interaction. To do this, we carried out a correlative far- and near-field characterization validated by first-principle calculations that reveals an unprecedented birefringence of 1.5 in the infrared and 3 in the visible light for MoS2. Our findings demonstrate that this outstanding anisotropy allows for tackling the diffraction limit enabling an avenue for on-chip next-generation photonics.Comment: 20 pages, 5 figure

Phase-sensitive plasmonics biosensors: from bulk to nanoscale architechtures and novel functionalities

Conference on Synthesis and Photonics of Nanoscale Materials XIII, San Francisco, CA, FEB 15-17, 2016International audienceWe 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)

Tungsten disulfide nanoparticles produced by femtosecond laser ablation in water for nanophotonic applications

International audienceWe demonstrate nearly spherical nanoparticles of tungsten disulfide (WS2) produced by femtosecond pulsed laser ablation of bulk target in deionized water. Structural and optical analysis reveals that produced nanospheres preserve the crystalline structure, high refractive index and support strong excitons and Mie resonances in the spectral range 400-700 nm, resulting in enhanced photothermal response probed by Raman spectroscopy