172 research outputs found
Trends in Nanophotonics-Enabled Optofluidic Biosensors
Optofluidic sensors integrate photonics with micro/nanofluidics to realize compact devices for the label-free detection of molecules and the real-time monitoring of dynamic surface binding events with high specificity, ultrahigh sensitivity, low detection limit, and multiplexing capability. Nanophotonic structures composed of metallic and/or dielectric building blocks excel at focusing light into ultrasmall volumes, creating enhanced electromagnetic near-fields ideal for amplifying the molecular signal readout. Furthermore, fluidic control on small length scales enables precise tailoring of the spatial overlap between the electromagnetic hotspots and the analytes, boosting light-matter interaction, and can be utilized to integrate advanced functionalities for the pre-treatment of samples in real-world-use cases, such as purification, separation, or dilution. In this review, the authors highlight current trends in nanophotonics-enabled optofluidic biosensors for applications in the life sciences while providing a detailed perspective on how these approaches can synergistically amplify the optical signal readout and achieve real-time dynamic monitoring, which is crucial in biomedical assays and clinical diagnostics
Metallic and All‐Dielectric Metasurfaces Sustaining Displacement‐Mediated Bound States in the Continuum
Bound states in the continuum (BICs) are localized electromagnetic modes within the continuous spectrum of radiating waves. Due to their infinite lifetimes without radiation losses, BICs are driving research directions in lasing, non-linear optical processes, and sensing. However, conventional methods for converting BICs into leaky resonances, or quasi-BICs, with high-quality factors typically rely on breaking the in-plane inversion symmetry of the metasurface and often result in resonances that are strongly dependent on the angle of the incident light, making them unsuitable for many practical applications. Here, an emerging class of BIC-driven metasurfaces is numerically analyzed and experimentally demonstrated, where the coupling to the far field is controlled by the displacement of individual resonators. In particular, both all-dielectric and metallic as well as positive and inverse displacement-mediated metasurfaces sustaining angular-robust quasi-BICs are investigated in the mid-infrared spectral region. Their optical behavior with regard to changes in the angle of incidence is investigated and experimentally shows their superior performance compared to two conventional alternatives: silicon-based tilted ellipses and cylindrical nanoholes in gold. These findings are anticipated to open exciting perspectives for bio-sensing, conformal optical devices, and photonic devices using focused light
Metallic and All-Dielectric Metasurfaces Sustaining Displacement-Mediated Bound States in the Continuum
Bound states in the continuum (BICs) are localized electromagnetic modes
within the continuous spectrum of radiating waves. Due to their infinite
lifetimes without radiation losses, BICs are driving research directions in
lasing, non-linear optical processes, and sensing. However, conventional
methods for converting BICs into leaky resonances, or quasi-BICs, with
high-quality factors typically rely on breaking the in-plane inversion symmetry
of the metasurface and often result in resonances that are strongly dependent
on the angle of the incident light, making them unsuitable for many practical
applications. Here, we numerically analyze and experimentally demonstrate an
emerging class of BIC-driven metasurfaces, where the coupling to the far field
is controlled by the displacement of individual resonators. In particular, we
investigate both all-dielectric and metallic as well as positive and inverse
displacement-mediated metasurfaces sustaining angular-robust quasi-BICs in the
mid-infrared spectral region. We explore their behavior with changes in the
incidence angle of illumination and experimentally show their superior
performance compared to two conventional alternatives: silicon-based tilted
ellipses and cylindrical nanoholes in gold. We anticipate our findings to open
exciting perspectives for bio-sensing, conformal optical devices, and photonic
devices using focused light.Comment: 27 pages, 7 figures, 1 tabl
Mirror‐Coupled Plasmonic Bound States in the Continuum for Tunable Perfect Absorption
Tailoring critical light-matter coupling is a fundamental challenge of nanophotonics, impacting fields from higher harmonic generation and energy conversion to surface-enhanced spectroscopy. Plasmonic perfect absorbers (PAs), where resonant antennas couple to their mirror images in adjacent metal films, excel at obtaining different coupling regimes by tuning the antenna-film gap size. However, practical PA applications require constant gap size, making it impossible to maintain critical coupling beyond singular wavelengths. Here, a new approach for plasmonic PAs is introduced by combining mirror-coupled resonances with the unique loss engineering capabilities of plasmonic quasi-bound states in the continuum. This novel combination allows to tailor the light–matter interaction within the under-coupling, over-coupling, and critical coupling regimes using flexible tuning knobs including asymmetry parameter, dielectric gap, and geometrical scaling factor. The study demonstrates a pixelated PA metasurface with optimal absorption over a broad range of mid-infrared wavenumbers (950–2000 cm−1) using only a single gap size and applies it for multispectral surface-enhanced molecular spectroscopy. Moreover, the asymmetry parameter enables convenient adjustment of the quality factor and resonance amplitude. This concept expands the capabilities and flexibility of traditional gap-tuned PAs, opening new perspectives for miniaturized sensing platforms towards on-chip and in situ detection
Multi-band metasurface-driven surface-enhanced infrared absorption spectroscopy for improved characterization of in-situ electrochemical reactions
Surface-enhanced spectroscopy techniques are the method-of-choice to
characterize adsorbed intermediates occurring during electrochemical reactions,
which are crucial in realizing a green sustainable future. Characterizing
species with low coverages or short lifetimes have so far been limited by low
signal enhancement. Recently, metasurface-driven surface-enhanced infrared
absorption spectroscopy (SEIRAS) has been pioneered as a promising narrowband
technology to study single vibrational modes of electrochemical interfaces
during CO oxidation. However, many reactions involve several species or
configurations of adsorption that need to be monitored simultaneously requiring
reproducible and broadband sensing platforms to provide a clear understanding
of the underlying electrochemical processes. Here, we experimentally realize
multi-band metasurface-driven SEIRAS for the in-situ study of electrochemical
CO2 reduction on a Pt surface. We develop an easily reproducible and
spectrally-tunable platinum nano-slot metasurface. Two CO adsorption
configurations at 2030 cm-1 and 1840 cm-1 are locally enhanced as a proof of
concept that can be extended to more vibrational bands. Our platform provides a
41-fold enhancement in the detection of characteristic absorption signals
compared to conventional broadband electrochemically roughened platinum films.
A straightforward methodology is outlined starting by baselining our system in
CO saturated environment and clearly detecting both configurations of
adsorption, in particular the hitherto hardly detectable CO bridge
configuration. Then, thanks to the signal enhancement provided by our platform,
we find that the CO bridge configuration on platinum does not play a
significant role during CO2 reduction in an alkaline environment. We anticipate
that our technology will guide researchers in developing similar sensing
platforms.Comment: 21 pages, 4 figure
Mirror-coupled plasmonic bound states in the continuum for tunable perfect absorption
Tailoring critical light-matter coupling is a fundamental challenge of
nanophotonics, impacting diverse fields from higher harmonic generation and
energy conversion to surface-enhanced spectroscopy. Plasmonic perfect absorbers
(PAs), where resonant antennas couple to their mirror images in adjacent metal
films, have been instrumental for obtaining different coupling regimes by
tuning the antenna-film distance. However, for on-chip uses, the ideal PA gap
size can only match one wavelength, and wide range multispectral approaches
remain challenging. Here, we introduce a new paradigm for plasmonic PAs by
combining mirror-coupled resonances with the unique loss engineering
capabilities of plasmonic bound states in the continuum (BICs). Our BIC-driven
PA platform leverages the asymmetry of the constituent meta-atoms as an
additional degree of freedom for reaching the critical coupling (CC) condition,
delivering resonances with unity absorbance and high quality factors
approaching 100 in the mid-infrared. Such a platform holds flexible tuning
knobs including asymmetry parameter, dielectric gap, and geometrical scaling
factor to precisely control the coupling condition, resonance frequency, and
selective enhancement of magnetic and electric fields while maintaining CC. We
demonstrate a pixelated PA metasurface with optimal absorption over a broad
range of mid-infrared frequencies (950 ~ 2000 1/cm) using only a single spacer
layer thickness and apply it for multispectral surface-enhanced molecular
spectroscopy in tailored coupling regimes. Our concept greatly expands the
capabilities and flexibility of traditional gap-tuned PAs, opening new
perspectives for miniaturized sensing platforms towards on-chip and in-situ
detection.Comment: Main text and supporting information, 31 pages, 5 Figures manuscript
+ 11 Supporting Figure
Plasmonic Bound States in the Continuum to Tailor Light-Matter Coupling
Plasmon resonances play a pivotal role in enhancing light-matter interactions
in nanophotonics, but their low-quality factors have hindered applications
demanding high spectral selectivity. Even though symmetry-protected bound
states in the continuum with high-quality factors have been realized in
dielectric metasurfaces, impinging light is not efficiently coupled to the
resonant metasurfaces and is lost in the form of reflection due to low
intrinsic losses. Here, we demonstrate a novel design and 3D laser nanoprinting
of plasmonic nanofin metasurfaces, which support symmetry-protected bound
states in the continuum up to 4th order. By breaking the nanofins out-of-plane
symmetry in parameter space, we achieve high-quality factor (up to 180) modes
under normal incidence. We reveal that the out-of-plane symmetry breaking can
be fine-tuned by the triangle angle of the 3D nanofin meta-atoms, opening a
pathway to precisely control the ratio of radiative to intrinsic losses. This
enables access to the under-, critical-, and over-coupled regimes, which we
exploit for pixelated molecular sensing. Depending on the coupling regime we
observe negative, no, or positive modulation induced by the analyte, unveiling
the undeniable importance of tailoring light-matter interaction. Our
demonstration provides a novel metasurface platform for enhanced light-matter
interaction with a wide range of applications in optical sensing, energy
conversion, nonlinear photonics, surface-enhanced spectroscopy, and quantum
optics.Comment: 33 pages, 4 figures, 9 supplementary figure
Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces.
Photonic bound states in the continuum (BICs) provide a standout platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs) but have so far mostly been implemented as traditional all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap and material integration. Here, we demonstrate intrinsic strong coupling in BIC-driven metasurfaces composed of nanostructured bulk tungsten disulfide (WS2) and exhibiting resonances with sharp, tailored linewidths and selective enhancement of light-matter interactions. Tuning of the BIC resonances across the exciton resonance in bulk WS2 is achieved by varying the metasurface unit cells, enabling strong coupling with an anticrossing pattern and a Rabi splitting of 116 meV. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our self-hybridized metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver fundamental insights and practical device concepts for polaritonic applications
Introducing a Symmetry-Breaking Coupler into a Dielectric Metasurface Enables Robust High-Q Quasi-BICs
Dielectric metasurfaces supporting quasibound states in the continuum (quasi-BICs) exhibit very high-quality factor resonances and electric field confinement. However, accessing the high-Q end of the quasi-BIC regime usually requires marginally distorting the metasurface design from a BIC condition, pushing the needed nanoscale fabrication precision to the limit. This work introduces a novel concept for generating high-Q quasi-BICs, which strongly relaxes this requirement by incorporating a relatively large perturbative element close to high-symmetry points of an undistorted BIC metasurface, acting as a coupler to the radiation continuum. This approach is validated by adding a ≈100 nm diameter cylinder between two reflection-symmetry points separated by a 300 nm gap in an elliptical disk metasurface unit cell, using gallium phosphide as the dielectric. It is found that high-Q resonances emerge when the cylindrical coupler is placed at any position between such symmetry points. This metasurface´s second harmonic generation capability in the optical range is further explored. Displacing the coupler as much as a full diameter from a BIC condition produces record-breaking normalized conversion efficiencies >102 W−1. The strategy of enclosing a disruptive element between multiple high-symmetry points in a BIC metasurface can be applied to construct robust high-Q quasi-BICs in many geometrical designs.Fil: Moretti, Gianni Quimey. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Tittl, Andreas. Ludwig Maximilians Universitat; AlemaniaFil: Cortés, Emiliano. Ludwig Maximilians Universitat; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Maier, Stefan A.. Imperial College London; Reino Unido. Ludwig Maximilians Universitat; AlemaniaFil: Bragas, Andrea Veronica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Grinblat, Gustavo Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin
Radial bound states in the continuum for polarization-invariant nanophotonics
All-dielectric nanophotonics underpinned by the physics of bound states in the continuum (BICs) have demonstrated breakthrough applications in nanoscale light manipulation, frequency conversion and optical sensing. Leading BIC implementations range from isolated nanoantennas with localized electromagnetic fields to symmetry-protected metasurfaces with controllable resonance quality (Q) factors. However, they either require structured light illumination with complex beam-shaping optics or large, fabrication-intense arrays of polarization-sensitive unit cells, hindering tailored nanophotonic applications and on-chip integration. Here, we introduce radial quasi-bound states in the continuum (radial BICs) as a new class of radially distributed electromagnetic modes controlled by structural asymmetry in a ring of dielectric rod pair resonators. The radial BIC platform provides polarization-invariant and tunable high-Q resonances with strongly enhanced near fields in an ultracompact footprint as low as 2 µm2. We demonstrate radial BIC realizations in the visible for sensitive biomolecular detection and enhanced second-harmonic generation from monolayers of transition metal dichalcogenides, opening new perspectives for compact, spectrally selective, and polarization-invariant metadevices for multi-functional light-matter coupling, multiplexed sensing, and high-density on-chip photonics
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