Multispectral plasmon induced transparency in coupled meta-atoms

Direct excitation of dark plasmonic resonances under visible light at normal incidence

Dark plasmon resonance modes are optical modes that have small scattering cross-sections and are thus difficult to excite directly by light at normal incidence. In this paper, we propose to excite quadrupolar and higher-order modes with normal incident light (in the visible regime) on a continuous plasmonic metallic surface covering a dielectric pillar array, hence resulting in narrow-band perfect absorption. Different from the general electromagnetic means of inducing dark modes, our dark modes are due to charge densities that are electrically induced by the standing-wave resonance of current on the thin metal sidewall of pillars. This new means of exciting dark modes can significantly improve the excitation efficiency and also provides an easy way to excite strong higher-order modes.

In-situ ultra-sensitive infrared absorption spectroscopy of biomolecule interactions in real time with plasmonic nanoantennas

Infrared absorption spectroscopy is a powerful biochemical analysis tool as it extracts detailed molecular structural information in a label-free fashion. Its molecular specificity renders the technique sensitive to the subtle conformational changes exhibited by proteins in response to a variety of stimuli. Yet, sensitivity limitations and the extremely strong absorption bands of liquid water severely limit infrared spectroscopy in performing kinetic measurements in biomolecules’ native, aqueous environments. Here we demonstrate a plasmonic chip-based technology that overcomes these challenges, enabling the in-situ monitoring of protein and nanoparticle interactions at high sensitivity in real time, even allowing the observation of minute volumes of water displacement during binding events. Our approach leverages the plasmonic enhancement of absorption bands in conjunction with a non-classical form of internal reflection. These features not only expand the reach of infrared spectroscopy to a new class of biological interactions but also additionally enable a unique chip-based technology.

Infrared absorption spectroscopy provides important information about molecules, but is hampered by the absorption of water. Adato and Altug exploit the plasmonic enhancement from nanoantennas to overcome this, enabling chip-based monitoring of biological samples in aqueous environments.

Fano resonances in a single defect nanocavity coupled with a plasmonic waveguide

Two Fano resonances are theoretically predicted in a single defect nanocavity, consisting of a rectangular cavity with a small stub defect, side-coupled with a plasmonic waveguide. These two Fano resonances are found to originate from two different mechanisms. One is caused by the excitation of a high-order resonant mode in the rectangular cavity owing to the structural breaking, and the other is attributed to the inherent resonant mode in the small stub defect. The narrow high-order mode and inherent mode couple with the broad low-order resonant mode in the rectangular cavity, giving rise to two Fano resonances. Because of the different origins, these two Fano resonances exhibit quite different responses to the variations of the structural dimensions. This has important applications in highly sensitive and multiparameter sensing in the complicated environments.

Plasmonic spectral splitting in multi-resonator-coupled waveguide systems

Spectral splitting is numerically investigated in a metal-insulator-metal plasmonic waveguide coupled with a series of disk cavities for the first time to our best knowledge. The finite-difference time-domain simulations find that, when an identical cavity is introduced into the single-cavity-coupled structure, a resonance peak emerges in reflection dip due to the plasmonic analogue of electromagnetically induced transparency. By cascading multiple cavities into the waveguide system, the resonance spectra are gradually split because of the phase-coupled effects. Particularly, the quality factors of splitting resonance spectra can be rapidly improved with increasing the number of coupled cavities. The proposed plasmonic systems may find potential applications in highly integrated optical circuits, especially for multichannel filtering, all-optical switching, and slow-light devices.

Metal nanoparticle plasmons operating within a quantum lifetime

We investigate the dynamics of a plasmonic oscillation over a metal nanoparticle when it is strongly coupled to a quantum emitter (e.g. quantum dot, molecule). We simulate the density matrix evolution for a simple model, a coupled classical-quantum oscillators system. We show that the lifetime of the plasmonic oscillations can be increased several orders of magnitude, up to the decay time of the quantum emitter. This effect shows itself as the narrowing of the plasmon emission band in the spaser (surface plasmon amplification by the stimulated emission of radiation) experiment [Nature, 2009, 460, 1110], where a gold nanoparticle interacts with the surrounding molecules. Enhancement of the plasmonic excitation lifetime enables stimulated emission to overcome the spontaneous one. The enhancement occurs due to the emergence of a phenomenon analogous to electromagnetically induced transparency (EIT). The effect can find applications in many areas of nanoscale physics, such as in quantum information with plasmons and in increasing solar cell efficiency.

Babinet to the half: coupling of solid and inverse plasmonic structures

We study the coupling between the plasmonic resonances of solid and inverse metallic nanostructures. While the coupling between solid-solid and inverse-inverse plasmonic structures is well-understood, mixed solid-inverse systems have not yet been studied in detail. In particular, it remains unclear whether or not an efficient coupling is even possible and which prerequisites have to be met. We find that an efficient coupling between inverse and solid resonances is indeed possible, identify the necessary geometrical prerequisites, and demonstrate a novel solid-inverse plasmonic electromagnetically induced transparency (EIT) structure as well as a mixed chiral system. We furthermore show that for the coupling of asymmetric rod-shaped inverse and solid structures symmetry breaking is crucial. In contrast, highly symmetric structures such as nanodisks and nanoholes are straightforward to couple. Our results constitute a significant extension of the plasmonic coupling toolkit, and we thus envision the emergence of a large number of intriguing novel plasmonic coupling phenomena in mixed solid-inverse structures.

Polarization and incidence insensitive dielectric electromagnetically induced transparency metamaterial

In this manuscript, we demonstrate numerically classical analogy of electromagnetically induced transparency (EIT) with a windmill type metamaterial consisting of two dumbbell dielectric resonator. With proper external excitation, dielectric resonators serve as EIT bright and dark elements via electric and magnetic Mie resonances, respectively. Rigorous numerical analyses reveal that dielectric metamaterial exhibits sharp transparency peak characterized by large group index due to the destructive interference between EIT bright and dark resonators. Furthermore, such EIT transmission behavior keeps stable property with respect to polarization and incidence angles.

Plasmonics in nanostructures

Plasmonics has developed into one of the rapidly growing research topics for nanophotonics. With advanced nanofabrication techniques, a broad variety of nanostructures can be designed and fabricated for plasmonic devices at nanoscale. Fundamental properties for both surface plasmon polaritons (SPP) and localized surface plasmons (LSP) arise a new insight and understanding for the electro-optical device investigations, such as plasmonic nanofocusing, low-loss plasmon waveguide and active plasmonic detectors for energy harvesting. Here, we review some typical functional plasmonic nanostructures and nanosmart devices emerging from our individual and collaborative research works.

Engineered absorption enhancement and induced transparency in coupled molecular and plasmonic resonator systems

Coupled plasmonic resonators have become the subject of significant research interest in recent years as they provide a route to dramatically enhanced light-matter interactions. Often, the design of these coupled mode systems draws intuition and inspiration from analogies to atomic and molecular physics systems. In particular, they have been shown to mimic quantum interference effects, such as electromagnetically induced transparency (EIT) and Fano resonances. This analogy also been used to describe the surface-enhanced absorption effect where a plasmonic resonance is coupled to a weak molecular resonance. These important phenomena are typically described using simple driven harmonic (or linear) oscillators (i.e., mass-on-a-spring) coupled to each other. In this work, we demonstrate the importance of an essential interdependence between the rate at which the system can be driven by an external field and its damping rate through radiative loss. This link is required in systems exhibiting time-reversal symmetry and energy conservation. Not only does it ensure an accurate and physically consistent description of resonant systems but leads directly to interesting new effects. Significantly, we demonstrate this dependence to predict a transition between EIT and electromagnetically induced absorption that is solely a function of the ratio of the radiative to intrinsic loss rates in coupled resonator systems. Leveraging the temporal coupled mode theory, we introduce a unique and intuitive picture that accurately describes these effects in coupled plasmonic/molecular and fully plasmonic systems. We demonstrate our approach's key features and advantages analytically as well as experimentally through surface-enhanced absorption spectroscopy and plasmonic metamaterial applications.

Tunable coupling-induced transparency band due to coupled localized electric resonance and quasiguided photonic mode in hybrid plasmonic system

A numerical and theoretical study is presented on the exhibition of tunable narrow band coupled-induced transparency phenomenon in a hybrid waveguide-plasmon system consisting of gold twin nanowires array embedded in a slab waveguide. We show that, at slightly non-normal incidence, a properly designed splitting of transmission with narrow transparency peaks may occur at a given wavelength, depending on the angle of incidence. This leads to the wavelength-selective high quality coupled-induced transparency resonance at optical frequencies. By adjusting the gap distance of the pair gratings, the coupled-induced transparency band can be switched between on-state and off-state, which provides us possibilities to develop controllable plasmonic functional devices employing plasmonic nanostructures.

Fano resonance in concentric ring apertures

We demonstrate a polarization-independent mid-infrared Fano resonance with extraordinary transmission when light passes through two concentric metallic ring apertures. A high-Q dark mode is indirectly excitated by coupling with a low-Q bright mode. A coupled optical resonator model is used to analyze the coupling process between the bright and dark modes. We find the Q of the dark mode is 3~6 times higher than that of the bright mode. We show that the dark mode can be selectively disabled without affecting the bright mode.

Multiple Fano resonances in single-layer nonconcentric core-shell nanostructures

Multiple plasmonic Fano resonances are generally considered to require complex nanostructures, such as multilayer structure, to provide several dark modes that can couple with the bright mode. In this paper, we show the existence of multiple Fano resonances in single layer core-shell nanostructures where the multiple dark modes appear due to the geometrical symmetry breaking induced by axial offset of the core. Both dielectric-core-metal-shell (DCMS) and metal-core-dielectric-shell (MCDS) configurations have been studied. Compared to the MCDS structure, the DCMS configuration provides higher modulation depth. Analytical studies based on transformation optics and numerical simulations have been performed to investigate the role of geometrical and material parameters on the optical properties of the proposed nanostructures. Refractive index sensing with higher-order Fano resonances has also been described, providing opportunity for multiwavelength sensing with high figure of merit.

Plasmonic diastereomers: adding up chiral centers

We construct chiral plasmonic molecules by assembling two individual chiral centers. Interestingly, depending on the exact arrangement of the centers, all combinations result in a chiral compound with a strong chiral optical response. Furthermore, we demonstrate that the overall circular dichrosim (CD) is determined by the response of the individual chiral centers. We find that the CD spectra of the composite molecules are then simply given as the sum of the CD spectra of the constituting building blocks. Interestingly, as soon as strong near-field coupling takes place between chiral centers, we find strong deviation from the simple additive chiral behavior. Most importantly, we demonstrate that the optical response of complex chiral plasmonic systems can be decomposed and understood in terms of fundamental building blocks, offering simple and straightforward design rules for future applications such as chiral optical elements and enantiomer sensors.

Optical properties of chiral three-dimensional plasmonic oligomers at the onset of charge-transfer plasmons

We demonstrate strong chiral optical response in three-dimensional chiral nanoparticle oligomers in the wavelength regime between 700 and 3500 nm. We show in experiment and simulation that this broad-band response occurs at the onset of charge transfer between the individual nanoparticles. The ohmic contact causes a strong red shift of the fundamental mode, while the geometrical shape of the resulting fused particles still allows for an efficient excitation of higher order modes. Calculated spectra and field distributions confirm our interpretation and show a number of interacting plasmonic modes. Our results deepen the understanding of the chiral optical response in complex chiral plasmonic nanostructures and pave the road toward broad-band chiral optical devices with strong responses, for example, for chiral plasmon rulers or sensing applications.

A plasmonic Fano switch

Plasmonic clusters can support Fano resonances, where the line shape characteristics are controlled by cluster geometry. Here we show that clusters with a hemicircular central disk surrounded by a circular ring of closely spaced, coupled nanodisks yield Fano-like and non-Fano-like spectra for orthogonal incident polarization orientations. When this structure is incorporated into an uniquely broadband, liquid crystal device geometry, the entire Fano resonance spectrum can be switched on and off in a voltage-dependent manner. A reversible transition between the Fano-like and non-Fano-like spectra is induced by relatively low (∼6 V) applied voltages, resulting in a complete on/off switching of the transparency window.

Multiple Fano resonances in plasmonic heptamer clusters composed of split nanorings

Fano resonances in plasmonic nanostructures are important for plasmon line shaping. Compared to a single Fano resonance, multiple Fano resonances can modify plasmon lines at several spectral positions simultaneously, but they often suffer from weak modulation depths. In this paper, plasmonic heptamer clusters comprising split nanorings are designed to form multiple Fano resonances. Three prominent Fano resonances are observed in the spectra due to the formation of multiple narrow subradiant resonances, and the multiple Fano resonances can be switched on and off by adjusting the polarization direction. Particularly, by modifying the geometry parameters, there is a large tunability of the modulation depth of each Fano resonance. Heptamer clusters comprising split nanorings are highly suitable for plasmon line shaping, and it is expected that they are useful for multiwavelength biosensing and surface-enhanced Raman scattering.

Generating and manipulating higher order Fano resonances in dual-disk ring plasmonic nanostructures

In this article, we investigate higher order (quadrupolar, octupolar, hexadecapolar, and triakontadipolar) Fano resonances generated in disk ring (DR) silver plasmonic nanostructures. We find that the higher order Fano resonances are generated when the size of the disk is reduced and falls into a certain range. With dual-disk ring (DDR) nanostructures, a rich set of tunable Fano line shapes is provided. More specifically, we report our observations on the optical behavior of the DDRs including asymmetric cases either in two disks with different sizes or their asymmetric locations inside the ring. In the case of symmetric dual-disk ring (SDDR) nanostructures, we demonstrate that the quadrupolar and the hexadecapolar Fano resonances are suppressed, which can reduce the cross-talk in spectroscopic measurements, while the octupolar and the triakontadipolar Fano resonances are enhanced. The potential of using the studied plasmonic nanostructures as biochemical sensors is evaluated with the figure of merit (FOM) and the contrast ratio (CR). The values of the FOM and the CR achieved using the triakontadipolar Fano resonance in the SDDR are 17 and 57%, respectively. These results indicate that the SDDRs could be developed into a high-performance biochemical sensor in the visible wavelength range.

Manipulating magnetic plasmon propagation in metallic nanocluster networks

Neighboring fused heptamers can support magnetic plasmons due to the generation of antiphase ring currents in the metallic nanoclusters. In this paper, we use such artificial plasmonic molecules as basic elements to construct low-loss plasmonic waveguides and devices. These magnetic plasmon-based complexes exhibit waveguiding functionalities including plasmon steering over large-angle bends, splitting at intersections, and Mach-Zehnder interference between consecutive Y-splitters. Our findings provide a strategy for circumventing significant challenges in the miniaturization and high-density integration of optical circuits in integrated optics, allowing for the development of ultracompact plasmonic networks for practical applications.

Plasmon-induced transparency in asymmetric T-shape single slit

By utilizing a dielectric-film-coated asymmetric T-shape single slit, comprising two grooves of slightly detuned widths immediately contacting with a single nanoslit, the plasmon-induced transparency was experimentally demonstrated. Because of the symmetry breaking in the unit-cell structure, the scattered lights from the two grooves with slightly detuned widths interfere destructively, leading to the plasmon-induced transparency. As a result, a response spectrum with nearly the same interference contrast but a much narrower bandwidth emerges in the unit-cell structure with the footprint of only about 0.9 μm(2), compared with that in the symmetric T-shape single slit. These pronounced features in the structure, such as the increased quality factor, ultracompact size, easy fabrication, and experimental observation, have significant applications in ultracompact plasmonic devices.

Three-dimensional chiral plasmonic oligomers

The living world is chiral. Chirality or the handedness of a structure or molecule is at the heart of life itself. Recently, it has been shown that plasmonic structures exhibit unprecedented and gigantic chiral optical responses. Here we show that truly three-dimensional arrangements of plasmonic "meta-atoms" only exhibit a chiral optical response if similar plasmonic "atoms" are arranged in a handed fashion as we require resonant plasmonic coupling. Moreover, we demonstrate that such particle groupings, similarly to molecular systems, possess the capability to encode their three-dimensional arrangement in unique and well-modulated spectra making them ideal candidates for a three-dimensional chiral plasmon ruler. Our results are crucial for the future design and improvement of plasmonic chiral optical systems, for example, for ultrasensitive enantiomer sensing on the single molecule level.

Classical analog of electromagnetically induced absorption in plasmonics

The ability to manipulate the phase shift between two resonantly coupled plasmonic oscillators in a controlled fashion has been unavailable up to now. Here we present a strategy to overcome this limitation by employing the benefits of near-field coupling on the one hand and retardation effects due to far-field coupling on the other hand. We theoretically and experimentally demonstrate that in the intermediate regime the coupling of a broad dipolar to a narrow dark quadrupolar plasmon resonance is possible while simultaneously allowing for a retardation-induced phase shift. This leads to constructive interference and enhanced absorption. The observed phenomenon can thus be termed a classical analog of electromagnetically induced absorption.

Plasmonic systems unveiled by Fano resonances

We show in detail how a derivation of Fano theory can serve as a new paradigm to study, understand, and control the interaction of nano-objects with light. Examples include a plasmonic crystal, a dolmen-type structure sustaining dark and bright plasmon modes, and a nanoshell heptamer. On the basis of only three coupling factors, a straightforward analytical formula is obtained, only assuming a plasmonic resonance for the continuum, and retaining the nonclassical character of the original formalism. It allows one to predict, reproduce, or decompose Fano interferences solely in terms of the physical properties of the uncoupled nanostructures when available, without the need of additional fitting parameters.

Analytical model of the three-dimensional plasmonic ruler

An electrostatic eigenmode method that describes the coupling between plasmonic nanoparticles is used to model the optical resonances of the 3D plasmonic ruler. The model provides a mathematical description of the ruler that enables us to identify the key resonance in the scattering spectrum that encodes the location of the central nanorod. The model demonstrates excellent agreement with experimentally measured spectra. We show that the spectra can uniquely encode the horizontal and vertical displacements of the central nanorod. From an understanding of the spatial dependence of the plasmonic coupling between the nanorods, we devise a method for estimating the position of the central nanorod and apply this to experimental data. Our method paves the way toward the use of high-resolution spectra from 3D plasmonic oligomers for structural analysis of single entities such as complex macromolecules, DNA scaffolds, proteins, and peptides.

From electromagnetically induced transparency to superscattering with a single structure: a coupled-mode theory for doubly resonant structures

We observe from simulations that a doubly resonant structure can exhibit spectral behavior analogous to electromagnetically induced transparency, as well as superscattering, depending on the excitation. We develop a coupled-mode theory that explains this behavior in terms of the orthogonality of the radiation patterns of the eigenmodes. These results provide insight in the general electromagnetic properties of photonic nanostructures and metamaterials.

Multi-band slow light metamaterial

In this paper, a multi-band slow light metamaterial is presented and investigated. The metamaterial unit cell is composed of three cut wires of different sizes and parallel to each other. Two transparency windows induced by two-two overlaps of absorption bands of three cut wires are observed. The multi-band transmission characteristics and the slow light properties of metamaterial are verified by numerical simulation, which is in a good agreement with theoretical predictions. The impacts of structure parameters on transparency windows are also investigated. Simulation results show the spectral properties can be tuned by adjusting structure parameters of metamaterial. The equivalent circuit model and the synthesis method of the multi-band slow light metamaterial are presented. It is seen from simulation results that the synthesis method accurately predicts the center frequency of the multi-band metamaterial, which opens a door to a quick and accurate construction for multi-band slow light metamaterial.

Designing and deconstructing the Fano lineshape in plasmonic nanoclusters

By varying the relative dimensions of the central and peripheral disks of a plasmonic nanocluster, the depth of its Fano resonance can be systematically modified; spectral windows where the scattering cross section of the nanocluster is negligible can be obtained. In contrast, electron-beam excitation of the plasmon modes at specific locations within the nanocluster yields cathodoluminescence spectra with no Fano resonance. By examining the selection rules for plasmon excitation in the context of a coupled oscillator picture, we provide an intuitive explanation of this behavior based on the plasmon modes observed for optical and electron-beam excitation in this family of nanostructures.

Hybridization induced transparency in composites of metamaterials and atomic media

We report hybridization induced transparency (HIT) in a composite medium consisting of a metamaterial and a dielectric. We develop an analytic model that explains HIT by coherent coupling between the hybridized local fields of the metamaterial and the dielectric or an atomic system in general. In a proof-of-principle experiment, we evidence HIT in a split ring resonator metamaterial that is coupled to α-lactose monohydrate. Both, the analytic model and numerical calculations confirm and explain the experimental observations. HIT can be considered as a hybrid analogue to electromagnetically induced transparency (EIT) and plasmon-induced transparency (PIT).

Plasmon induced transparency in cascaded π-shaped metamaterials

We experimentally and numerically demonstrate a planar metamaterial consisting of two asymmetrically positioned π-structures in a single unit that exhibits plasmonic analogue of electromagnetically induced transparency (EIT). Through the coupling of the constituent nanorod elements, the proposed structure enables fine spectral tuning of the EIT-like behavior and controlling the location of near field enhancement. Originated from the asymmetric cascaded π-structures, we introduce a more compact system which possesses the EIT-like characteristics and as well as much smaller mode volumes. Due to these properties, the proposed metamaterials can be utilized for a wide range of applications including bio-chemical sensors, optical filters and modulators and enhancement of non-linear processes.

Removing a wedge from a metallic nanodisk reveals a fano resonance

A wide variety of complex, multicomponent plasmonic nanostructures have been shown to possess Fano resonances. Here we introduce a remarkably simple planar nanostructure, a single metallic nanodisk with a missing wedge-shaped slice, that also supports a Fano resonance. In this geometry, the Fano line shape arises from the coupling between a hybridized plasmon resonance of the disk and a narrower quadrupolar mode supported by the edge of the missing wedge slice. As a consequence, both disk size and wedge angle control the properties of the resonance. A semianalytical description of plasmon hybridization proves useful for analyzing the resulting line shape.

Chiral metamaterial composed of three-dimensional plasmonic nanostructures

We introduce a top-down fabricated metamaterial composed of three-dimensional, chiral, plasmonic nanostructures for visible and near-infrared wavelengths. Based on a combined spectroscopic and interferometric characterization, the entire complex transmission response in terms of a Jones matrix is disclosed. Particularly, the polarization output state of light after propagation through the nanostructures can be decoded from the measurements for any excitation configuration. We experimentally found a rotation of the polarization azimuth of linearly polarized light exceeding 50° at wavelengths around 1.08 μm. This corresponds to a specific rotation which is significantly larger than that of any linear, passive, and reciprocal medium reported to date.

Directional double Fano resonances in plasmonic hetero-oligomers

We experimentally demonstrate for the first time a very compact plasmonic hetero-oligomer structure where the multiple radiant and subradiant modes can be tailored independently. Unlike previous approaches based on collective excitations in complex plasmonic systems, we show precise engineering of resonances leading to simultaneous spectral overlap of multiple plasmonic modes with opposite radiative character. This asymmetric behavior combined with inherent spatial features of the structure leads to directional double Fano resonances as shown with numerical analysis. A model based on temporal coupled mode theory is also provided to describe the double Fano behavior.

Real-space mapping of Fano interference in plasmonic metamolecules

An unprecedented control of the spectral response of plasmonic nanoantennas has recently been achieved by designing structures that exhibit Fano resonances. This new insight is paving the way for a variety of applications, such as biochemical sensing and surface-enhanced Raman spectroscopy. Here we use scattering-type near-field optical microscopy to map the spatial field distribution of Fano modes in infrared plasmonic systems. We observe in real space the interference of narrow (dark) and broad (bright) plasmonic resonances, yielding intensity and phase toggling between different portions of the plasmonic metamolecules when either their geometric sizes or the illumination wavelength is varied.

Plasmonic-induced optical transparency in the near-infrared and visible range with double split nanoring cavity

Plasmonic-induced optical transparency with double split nanoring cavity is investigated with finite difference time domain method. The coupling between the bright third-order mode of split nanoring with one gap and the dark quadrupole mode of split nanoring with two gaps leads to plasmonic analogue of electromagnetically induced transparency. The transparence window is easily modified to the near-infrared and visible range. Numerical results show a group index of 16 with transmission exceeding 0.76 is achieved for double split nanoring cavity. There is large cavity volume of double split nanoring, and the field enhancement inside the cavity is homogenous. Double split nanoring cavity could be a good platform for slow light and sensing applications.

Seeing protein monolayers with naked eye through plasmonic Fano resonances

We introduce an ultrasensitive label-free detection technique based on asymmetric Fano resonances in plasmonic nanoholes with far reaching implications for point-of-care diagnostics. By exploiting extraordinary light transmission phenomena through high-quality factor (Q(solution) ∼ 200) subradiant dark modes, we experimentally demonstrate record high figures of merits (FOMs as high as 162) for intrinsic detection limits surpassing that of the gold standard prism coupled surface-plasmon sensors (Kretschmann configuration). Our experimental record high sensitivities are attributed to the nearly complete suppression of the radiative losses that are made possible by the high structural quality of the fabricated devices as well as the subradiant nature of the resonances. Steep dispersion of the plasmonic Fano resonance profiles in high-quality plasmonic sensors exhibit dramatic light intensity changes to the slightest perturbations within their local environment. As a spectacular demonstration of the extraordinary sensitivity and the quality of the fabricated biosensors, we show direct detection of a single monolayer of biomolecules with naked eye using these Fano resonances and the associated Wood's anomalies. To fabricate high optical-quality sensors, we introduce a high-throughput lift-off free evaporation fabrication technique with extremely uniform and precisely controlled nanofeatures over large areas, leading to resonance line-widths comparable to that of the ideally uniform structures as confirmed by our time-domain simulations. The demonstrated label-free sensing platform offers unique opportunities for point-of-care diagnostics in resource poor settings by eliminating the need for fluorescent labeling and optical detection instrumentation (camera, spectrometer, etc.) as well as mechanical and light isolation.