Localized Surface Plasmon Resonances of Simple Tunable Plasmonic Nanostructures

Plasmonics - We derive and present systematic relationships between the analytical formulas for calculation of the localized surface plasmon resonances (LSPR) of some plasmonic nanostructures which...     

Localized Surface Plasmonic Properties of Au and Ag Nanoparticles for Sensors: a Review

Plasmonics - In the last two decades, plasmonic resonance in metallic nanoparticles (Au, Ag NPs) has created intensive research efforts in nanoscale optics, photonics and sensors. When light...     

Preparation of Nanostructured Film Arrays for Transmission Localized Surface Plasmon Sensing

This article presents a concise review of preparation methods for transparent nanostructured films, with an emphasis on their current applications in transmission-localized surface plasmon resonance (T-LSPR) sensing. One of the first methods used for the fabrication of transparent nanostructured metal films is a direct vacuum evaporation of thin gold films. Self-induced formations of small gold islands result in transparent nanostructured gold arrays. The most well-established method is a nanosphere lithography developed by Van Duyne. Nanotriangular island arrays with controlled size and optical properties can be fabricated by this protocol. A different nanolithography method known as focused ion beam milling is reported and used for the fabrication of nanohole arrays. Simple assembly of solution-phase synthesized nanoparticles has also been utilized for the preparation of nanoparticle arrays capable of T-LSPR sensing. Lastly, this article also describes a new preparation strategy, in which self-assembly/thermolysis of nanoparticle multilayers is employed to obtain transparent nanoisland architectures on glass substrates.     

Ultrasmall Plasmonic Cavity for Chemical Sensing

We propose an ultrasmall plasmonic cavity based on the channel waveguides for chemical sensing. The plasmonic mode gap due to cutoff angular frequency enables strong optical confinement in a subwavelength volume and suppression of radiation loss. Due to strong field overlap of the surface plasmon polariton mode with environmental material, large sensitivity (1,100 nm/refractive index unit) and a high figure of merit (330) are achieved in the plasmonic cavity with a small physical size of 600?×?800?×?2,500 nm having a telecommunication resonant wavelength. This plasmonic cavity can introduce a broad range of applications including biochemical sensing and strong light–matter interactions.     

Spoof Localized Surface Plasmons Excited by Plasmonic Waveguide Chip with Corrugated Disk Resonator

We designed and fabricated a millimeter plasmonic chip consisted of coplanar waveguide (CPW) and plasmonic waveguide with one corrugated disk resonator (CDR). The spoof localized surface plasmon (LSP) resonance modes can be excited by the interaction between plasmonic waveguide and CDR. Fundamental and higher order sharp spoof LSP resonances (from dipole to dodecapole) were observed in the transmission coefficient spectrum. The Q-value as high as 268.3 (octupole) was experimentally obtained. Experimental results show good agreement with theoretical and simulated ones. All the results may have potential applications in microchip based sensing and filtering.     

Tunable Plasmonic Absorber Based on Propagating and Localized Surface Plasmons Using Metal-Dielectric-Metal Structure

We propose a metal-dielectric-metal super absorber based on propagating and localized surface plasmons which exhibits a near perfect absorption in the visible and near-infrared spectrum. The absorber consists of Ag/Al₂O₃/Al triple layers in which the top Al layer is a periodic nano disk array. The absorption spectrum can be easily controlled by adjusting the structure parameters including the period and radius of the nano disk and the maximal absorption can reach 99.62 %. We completely analyze the PSPs and LSPs modes supported by the MDM structure and their relationship with the ultrahigh absorption. Moreover, we propose a novel idea to further enhance the absorption by exciting the PSPs and high-order LSPs modes simultaneously, which is different from the previous works. This kind of absorber using stable inexpensive Al instead of noble metal Au or Ag is an appropriate candidate for photovoltaics, spectroscopy, photodetectors, sensing, and surface-enhanced Raman spectroscopy (SERS).     

Template-Stripping Fabricated Plasmonic Nanogratings for Chemical Sensing

Plasmonics - Template stripping has been applied to transfer one-dimensional nanograting structures fabricated by interference lithography (IL) onto planar supports (i.e., glass slides and...     

Analysis and Simulation of a Novel Localized Surface Plasmonic Highly Sensitive Refractive Index Sensor

Dividing a metal nanoparticle into smaller components and the occurrence of the plasmonic phenomenon in the gap between these components can improve the sensitivity of the detector to variation of the refraction coefficient of liquid. In this paper, in a constant volume of metal, a golden disk is divided into two rings and one smaller disk. With a proper arrangement of these components, the surface plasmon resonance phenomenon takes place at the wavelength of 945.7 nm. The occurrence of this phenomenon increases the field in the distance between nanoparticles surrounded by liquid. The sensitivity of the detector that designed using nanodisks is 300 nm/RIU while it increases to 500 nm/RIU for the new structure. The increase of LSPR displacement, for a variation of 0.01 in the liquid refraction coefficient, from 3 nm for a disk to 5 nm for a proposed structure verifies a 67% improvement in the sensitivity of the sensor.

     

Refractive-Index Sensing with Ultrathin Plasmonic Nanotubes

We study the refractive-index sensing properties of plasmonic nanotubes with a dielectric core and ultrathin metal shell. The few nanometer thin metal shell is described by both the usual Drude model and the nonlocal hydrodynamic model to investigate the effects of nonlocality. We derive an analytical expression for the extinction cross section and show how sensing of the refractive index of the surrounding medium and the figure of merit are affected by the shape and size of the nanotubes. Comparison with other localized surface plasmon resonance sensors reveals that the nanotube exhibits superior sensitivity and comparable figure of merit.     

Tuning the Fano Resonance Between Localized and Propagating Surface Plasmon Resonances for Refractive Index Sensing Applications

Localized and propagating surface plasmon resonances are known to show very pronounced interactions if they are simultaneously excited in the same nanostructure. Here, we study the Fano interference that occurs between localized surface plasmon resonance (LSPR) and propagating surface plasmon polariton (SPP) modes by means of phase-sensitive spectroscopic ellipsometry. The sample structures consist of periodic gratings of gold nanodisks on top of a continuous gold layer and a thin dielectric spacer, in which the structural dimensions were tuned in such a way that the dipolar LSPR mode and the propagating SPP modes are excited in the same spectral region. We observe pronounced anti-crossing and strongly asymmetric line shapes when both modes move to each other’s vicinity, accompanied of largely increased phase differences between the respective plasmon resonances. Moreover, we show that the anti-crossing can be exploited to increase the refractive index sensitivity of the localized modes dramatically, which result in largely increased values for the figure-of-merit which reaches values between 24 and 58 for the respective plasmon modes.     

Dipole-Nano-Laser Based Plasmonic Nano-Sensor for Sensing Photons and Bio-Chemical Analytes

We propose a new type of plasmonic nano-sensors that is based on the concept of the dipole nano laser (DNL). The DNL is made of a quantum dot (QD) coupled to a nano particle (NP). The very small size of the DNL renders the sensor one of the smallest proposed in literature. The system is embedded within a photonic band gap (PBG) material. The PBG material is shown to greatly narrow the DNL spectral width, which translates into a high and accurate sensibility for the proposed plasmonic nano sensor. The proposed system configuration can easily be adjusted to detect either photons or bio-chemical analytes.     

Design Optimisation of Plasmonic Metasurfaces for Mid-Infrared High-Sensitivity Chemical Sensing

In this paper, we report on a general method to optimise the optical characteristics of 2D-arrays of plasmonic gold nanoantennas performing as band-pass filter functionalised metasurfaces to be used as high-sensitivity mid-infrared spectroscopic sensors. We demonstrate that it is possible to increase their sensitivity in the detection of chemical and biological substances when the sensors are used in the surface-enhanced infrared absorption (SEIRA) technique. This technique allows revealing the presence of a substance adsorbed on the nanoantennas by measuring its optical absorption under the conditions for which the maximum value of the functionalised metasurface reflectivity occurs at the same wavelength of the substance maximum absorption peak. In particular, numerical simulations based on finite element method of the metasurface detection response demonstrate the possibility to increase the sensor sensitivity of more than four orders of magnitude with respect to that one achievable if the same amount of the substance is deposited on an unstructured planar metal surface. These results can be obtained by acting on the 2D-array periodicity, nanoantenna shape (i.e. rod and cross), size and thickness independently from the wavelength at which the substance absorption occurs. Moreover, in the case of cross-shaped nanoantennas, we report a complete numerical characterisation of the dependence of the metasurface maximum reflectivity and peak wavelength on the variation of the geometrical parameters of both the nanoantennas and the 2D-array.     

Shape-Controlled Synthesis of Silver Nanoparticles for Plasmonic and Sensing Applications

The localized surface plasmon resonance of a silver nanoparticle is responsible for its ability to strongly absorb and scatter light at specific wavelengths. The absorption and scattering spectra (i.e., plots of cross sections as a function of wavelength) of a particle can be predicted using Mie theory (for a spherical particle) or the discrete dipole approximation method (for particles in arbitrary shapes). In this review, we briefly discuss the calculated spectra for silver nanoparticles with different shapes and the synthetic methods available to produce these nanoparticles. As validated in recent studies, there is good agreement between the theoretically calculated and the experimentally measured spectra. We conclude with a discussion of new plasmonic and sensing applications enabled by the shape-controlled nanoparticles.     

Tunable Ultrahigh Order Surface Plasmonic Resonance in Multi-Ring Plasmonic Nanocavities

Optical properties of multi-ring with spatial symmetry breaking are investigated theoretically. Tunable ultrahigh order surface plasmonic resonance is achieved, which is found to be sensitive to geometric parameters. Certain high-order surface plasmonic resonances can be either suppressed or enhanced when geometrical parameters are adjusted. Moreover, more than one quadrupolar-dipolar, octupolar-dipolar, and hexadecapolar-dipolar mode of the surface plasmonic resonance can be achieved. The asymmetry also allows the generation of strong electric field enhancement with these nanostructures that can be applied in the field of surface-enhanced spectroscopy and biosensing.     

Coupled-Resonator-Induced Fano Resonances for Plasmonic Sensing with Ultra-High Figure of Merits

Fano resonances are numerically predicted in an ultracompact plasmonic structure, comprising a metal-isolator-metal (MIM) waveguide side-coupled with two identical stub resonators. This phenomenon can be well explained by the analytic model and the relative phase analysis based on the scattering matrix theory. In sensing applications, the sensitivity of the proposed structure is about 1.1?×?10³ nm/RIU and its figure of merit is as high as 2?×?10⁵ at λ?=?980 nm, which is due to the sharp asymmetric Fano line-shape with an ultra-low transmittance at this wavelength. This plasmonic structure with such high figure of merits and footprints of only about 0.2 μm² may find important applications in the on-chip nano-sensors.     

Novel Apolar Plasmonic Nanostructures with Extended Optical Tunability for Sensing Applications

This paper outlines the design of complex nanostructures with apolar behavior which pave the way to a wider range of plasmon resonance tuning and applications requiring higher enhancement. These new nanostructure families are simply defined by symmetry considerations. An irreducible decomposition of optical response tensor demonstrates that nanoparticles which belong to C _n , with n?≥?3, symmetry point group for at least one scale have an optical response insensitive on the light polarization. This is experimentally confirmed by extinction and surface-enhanced Raman-scattering measurements.     

Localized Plasmonic Photothermal Therapy as a Life-saving Treatment Paradigm for Hospitalized COVID-19 Patients

Plasmonics - Lung failure is the main reason for mortality in COVID-19 patients, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To date, no drug has been clinically...     

Plasmonic Metals for Nanohole-Array Surface Plasmon Field-Enhanced Fluorescence Spectroscopy Biosensing

Plasmonics - Gold (Au) is so far the most commonly used plasmonic metal in nanohole-array-based surface plasmon resonance biosensors, due to its excellent plasmonic properties in visible light...     

Optimizing the Sensing Efficiency of Plasmonic Based Gas Sensor

Plasmonics - This paper investigates the behavior of the surface plasmon polaritons (SPPs) on dielectric-metal interface using Ag thin film on glass substrate. The Kretschman configuration, which...