Quantitative analysis of a III-V tapered horn-shaped metal-clad nano-cavity as an on-chip light source

A horn-shaped metal-clad InGaAsP nano-cavity with sloped sidewalls is proposed as a platform for nanoscale light sources. The nano-cavity’s physical dimensions are 350 × 350 × 350 nm^3, and its mode volume is 0.5 (λ_0/n)^3. In our numerical simulations and quantitative analysis, we have shown that the sloped sidewalls reduce metallic absorption and improve resonant mode confinement; and adjusting their slope from 0 to 16° increased the Q factor from 150 to 900 and laser modulation 3dB bandwidth from 4.3 to 36 GHz. The lasing threshold current was expected to be 35 μA at 16°. In a simulated feasibility study, we demonstrate 60 Gbps modulated laser signal (5 fJ/bit), producing 20 μW output power at the 1.5 μm wavelength with injection current 100 μA, as an implementation of horn-shaped nano-cavity platform to the low power and ultra-fast on-chip nano-laser

Bioinspired Disordered Flexible Metasurfaces for Human Tear Analysis Using Broadband Surface-Enhanced Raman Scattering

Flexible surface-enhanced Raman scattering (SERS) has received attention as a means to move SERS-based broadband biosensing from bench to bedside. However, traditional flexible periodic nano-arrangements with sharp plasmonic resonances or their random counterparts with spatially varying uncontrollable enhancements are not reliable for practical broadband biosensing. Here, we report bioinspired quasi-(dis)ordered nanostructures presenting a broadband yet tunable application-specific SERS enhancement profile. Using simple, scalable biomimetic fabrication, we create a flexible metasurface (flex-MS) of quasi-(dis)ordered metal–insulator–metal (MIM) nanostructures with spectrally variable, yet spatially controlled electromagnetic hotspots. The MIM is designed to simultaneously localize the electromagnetic signal and block background Raman signals from the underlying polymeric substrate—an inherent problem of flexible SERS. We elucidate the effect of quasi-(dis)ordering on broadband tunable SERS enhancement and employ the flex-MS in a practical broadband SERS demonstration to detect human tear uric acid within its physiological concentration range (25–150 μM). The performance of the flex-MS toward noninvasively detecting whole human tear uric acid levels ex vivo is in good agreement with a commercial enzyme-based assay

Bioinspired Disordered Flexible Metasurfaces for Human Tear Analysis Using Broadband Surface-Enhanced Raman Scattering

Flexible surface-enhanced Raman scattering (SERS) has received attention as a means to move SERS-based broadband biosensing from bench to bedside. However, traditional flexible periodic nano-arrangements with sharp plasmonic resonances or their random counterparts with spatially varying uncontrollable enhancements are not reliable for practical broadband biosensing. Here, we report bioinspired quasi-(dis)ordered nanostructures presenting a broadband yet tunable application-specific SERS enhancement profile. Using simple, scalable biomimetic fabrication, we create a flexible metasurface (flex-MS) of quasi-(dis)ordered metal–insulator–metal (MIM) nanostructures with spectrally variable, yet spatially controlled electromagnetic hotspots. The MIM is designed to simultaneously localize the electromagnetic signal and block background Raman signals from the underlying polymeric substrate—an inherent problem of flexible SERS. We elucidate the effect of quasi-(dis)ordering on broadband tunable SERS enhancement and employ the flex-MS in a practical broadband SERS demonstration to detect human tear uric acid within its physiological concentration range (25–150 μM). The performance of the flex-MS toward noninvasively detecting whole human tear uric acid levels ex vivo is in good agreement with a commercial enzyme-based assay

Aluminum Metasurface with Hybrid Multipolar Plasmons for 1000-Fold Broadband Visible Fluorescence Enhancement and Multiplexed Biosensing

Aluminum (Al)-based nanoantennae traditionally suffer from weak plasmonic performance in the visible range, necessitating the application of more expensive noble metal substrates for rapidly expanding biosensing opportunities. We introduce a metasurface comprising Al nanoantennae of nanodisks-in-cavities that generate hybrid multipolar lossless plasmonic modes to strongly enhance local electromagnetic fields and increase the coupled emitter’s local density of states throughout the visible regime. This results in highly efficient electromagnetic field confinement in visible wavelengths by these nanoantennae, favoring real-world plasmonic applications of Al over other noble metals. Additionally, we demonstrate spontaneous localization and concentration of target molecules at metasurface hotspots, leading to further improved on-chip detection sensitivity and a broadband fluorescence-enhancement factor above 1000 for visible wavelengths with respect to glass chips commonly used in bioassays. Using the metasurface and a multiplexing technique involving three visible wavelengths, we successfully detected three biomarkers, insulin, vascular endothelial growth factor, and thrombin relevant to diabetes, ocular and cardiovascular diseases, respectively, in a single 10 μL droplet containing only 1 fmol of each biomarker

Aluminum Metasurface with Hybrid Multipolar Plasmons for 1000-Fold Broadband Visible Fluorescence Enhancement and Multiplexed Biosensing

Aluminum (Al)-based nanoantennae traditionally suffer from weak plasmonic performance in the visible range, necessitating the application of more expensive noble metal substrates for rapidly expanding biosensing opportunities. We introduce a metasurface comprising Al nanoantennae of nanodisks-in-cavities that generate hybrid multipolar lossless plasmonic modes to strongly enhance local electromagnetic fields and increase the coupled emitter’s local density of states throughout the visible regime. This results in highly efficient electromagnetic field confinement in visible wavelengths by these nanoantennae, favoring real-world plasmonic applications of Al over other noble metals. Additionally, we demonstrate spontaneous localization and concentration of target molecules at metasurface hotspots, leading to further improved on-chip detection sensitivity and a broadband fluorescence-enhancement factor above 1000 for visible wavelengths with respect to glass chips commonly used in bioassays. Using the metasurface and a multiplexing technique involving three visible wavelengths, we successfully detected three biomarkers, insulin, vascular endothelial growth factor, and thrombin relevant to diabetes, ocular and cardiovascular diseases, respectively, in a single 10 μL droplet containing only 1 fmol of each biomarker

Colour formation on the wings of the butterfly Hypolimnas salmacis by scale stacking.

The butterfly genus Hypolimnas features iridescent blue colouration in some areas of its dorsal wings. Here, we analyse the mechanisms responsible for such colouration on the dorsal wings of Hypolimnas salmacis and experimentally demonstrate that the lower thin lamina in the white cover scales causes the blue iridescence. This outcome contradicts other studies reporting that the radiant blue in Hypolimnas butterflies is caused by complex ridge-lamellar architectures in the upper lamina of the cover scales. Our comprehensive optical study supported by numerical calculation however shows that scale stacking primarily induces the observed colour appearance of Hypolimnas salmacis.non

Scalable and controlled self-assembly of aluminum-based random plasmonic metasurfaces.

Subwavelength metal-dielectric plasmonic metasurfaces enable light management beyond the diffraction limit. However, a cost-effective and reliable fabrication method for such structures remains a major challenge hindering their full exploitation. Here, we propose a simple yet powerful manufacturing route for plasmonic metasurfaces based on a bottom-up approach. The fabricated metasurfaces consist of a dense distribution of randomly oriented nanoscale scatterers composed of aluminum (Al) nanohole-disk pairs, which exhibit angle-independent scattering that is tunable across the entire visible spectrum. The macroscopic response of the metasurfaces is controlled via the properties of an isolated Al nanohole-disk pair at the nanoscale. In addition, the optical field confinement at the scatterers and their random distribution of sizes result in a strongly enhanced Raman signal that enables broadly tunable excitation using a single substrate. This unique combination of a reliable and lithography-free methodology with the use of aluminum permits the exploitation of the full potential of random plasmonic metasurfaces for diagnostics and coloration.We thank M. Heiler (KIT) for metal evaporation and G. Kamita (University of Cambridge) for the help in optical measurement. Furthermore, we acknowledge fruitful discussions with all members of the Biomimetics group at KIT and Bio-inspired photonics group at University of Cambridge. R.H.S acknowledges the funding by the Karlsruhe House of Young Scientists for a research stay at Cambridge. This work was partly carried out with the support of the Karlsruhe School of Optics and Photonics (KSOP, www.ksop.idschools.kit.edu) and the Karlsruhe Nano Micro Facility (KNMF, www.kit.edu/knmf), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT, www.kit.edu). S.V. acknowledges the BBSRC David Phillips fellowship [BB/K014617/1] and the ERC-2014-STG H2020 639088, and J.M. acknowledges the EPSRC [EP/G060649/1]

Colour formation on the wings of the butterfly Hypolimnas salmacis by scale stacking

The butterfly genus Hypolimnas features iridescent blue colouration in some areas of its dorsal wings. Here, we analyse the mechanisms responsible for such colouration on the dorsal wings of Hypolimnas salmacis and experimentally demonstrate that the lower thin lamina in the white cover scales causes the blue iridescence. This outcome contradicts other studies reporting that the radiant blue in Hypolimnas butterflies is caused by complex ridge-lamellar architectures in the upper lamina of the cover scales. Our comprehensive optical study supported by numerical calculation however shows that scale stacking primarily induces the observed colour appearance of Hypolimnas salmacis

Enhanced broadband fluorescence detection of nucleic acids using multipolar gap-plasmons on biomimetic Au metasurfaces

Recent studies on metal–insulator–metal-based plasmonic antennas have shown that emitters could couple with higher-order gap-plasmon modes in sub-10-nm gaps to overcome quenching. However, these gaps are often physically inaccessible for functionalization and are not scalably manufacturable. Here, using a simple biomimetic batch-fabrication, a plasmonic metasurface is created consisting of closely-coupled nanodisks and nanoholes in a metal–insulator–metal arrangement. The quadrupolar mode of this system exhibits strong broadband resonance in the visible-near-infrared regime with minimal absorptive losses and effectively supresses quenching, making it highly suitable for broadband plasmon-enhanced fluorescence. Functionalizing the accessible insulator nanogap, analytes are selectively immobilized onto the plasmonic hotspot enabling highly-localized detection. Sensing the streptavidin–biotin complex, a 91-, 288-, 403- and 501-fold fluorescence enhancement is observed for Alexa Fluor 555, 647, 750 and 790, respectively. Finally, the detection of single-stranded DNA (gag, CD4 and CCR5) analogues of genes studied in the pathogenesis of HIV-1 between 10 pM–10 μM concentrations and then CD4 mRNA in the lysate of transiently-transfected cells with a 5.4-fold increase in fluorescence intensity relative to an untransfected control is demonstrated. This outcome promises the use of biomimetic Au metasurfaces as platforms for robust detection of low-abundance nucleic acids

Bio-inspired, large scale, highly-scattering films for nanoparticle-alternative white surfaces

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO_2 saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 µm-thick scattering layer feature a whiteness with a reflectance of 90%. Even 9 µm thin scattering layers appear white with a reflectance above 57%. The transport mean free path in the artificial films is between 3.5 µm and 4 µm being close to the evolutionary optimised natural prototype. The bio-inspired white films do not lose their whiteness during further shaping, allowing for various applications