Multifactor-Controlled Non-Monotonic Plasmon Shift of Ordered Gold Nanodisk Arrays: Shape-Dependent Interparticle Coupling

Surface plasmon resonance (SPR) absorption spectra of gold nanodisks hexagonally arranged in planar arrays have been studied by using coupled dipole method and quasi-static approximation. The calculation results reveal that the increasing aspect ratio (AR) of gold disks in the close-packed nanoarray leads to SPR blue shift firstly and then red shift. The critical AR corresponding to the maximum blue shift can be controlled by tuning the interparticle distance and particle size. The physical mechanism of this non-monotonic SPR shift is investigated based on the competition between the influences from shape factor and arranging structure of the array. Although increasing the semi-minor axis of gold disk reduces the AR and leads to a blue shift of SPR, this increasing semi-minor axis also reduces the average gap between two neighboring disks and enhances their coupling. Furthermore, the coulombic attraction between two neighboring disks introduces an additional plasmon damping and results in a red shift of SPR. This competition between AR and interparticle coupling improves the tuning ability of SPR in anisotropic metallic nanoparticle arrays and presents a potential for design and fabrication of optical biochip based on SPR.     

Tailoring Plasmon Lifetime in Suspended Nanoantenna Arrays for High-Performance Plasmon Sensing

We demonstrate significantly longer plasmon lifetime and stronger electric field enhancement by lifting the nanoantenna arrays above the substrate by dielectric nanopillars. The role of the pillar is to offer a more homogeneous dielectric background allowing stronger diffraction coupling among plasmonic nanoantennas leading to a Fanolike asymmetric lineshape. It is found that the electric fields around the nanoantennas can be greatly enhanced when the Fanolike resonance is excited, and a 4.2 times enhancement is achieved compared with the pure resonance in individual nanoantennas. Furthermore, only a collective surface mode with its electric fields of the same direction as the induced electric moment in the nanoantennas could mediate the excitation of such a Fanolike resonance. More importantly, the sensitivity and the figure of merit (FOM) of this plasmonic structure can reach as high as 900 nm/RIU and 53, respectively. Our study offers a new, simple, and efficient way to design the plasmonic systems with desired electric field enhancement and spectral lineshape for different applications.     

Surface Plasmon Resonance Enhanced the Transverse Magneto-optical Kerr Effect in One-dimensional Magnetoplasmonic Nanostructure

Plasmonics - The properties of the optics and transverse magneto-optical Kerr effect (TMOKE) of one-dimensional magnetoplasmonic nanostructures are experimentally investigated. It shows that the...     

Sensitivity Enhancement of Ag-ITO-TMDCs-Graphene Nanostructure Based on Surface Plasmon Resonance Biosensors

Plasmonics - The novel configuration of surface plasmon resonance (SPR) based on Ag-indium tin oxide (ITO)-transition metal dichalcogenides (TMDCs)-graphene hybrid structures is proposed for highly...     

Manipulation of Microscale Fluid Using Laser-Irradiated Nanoparticle Arrays

The manipulation of microscale fluid has been widely used in biology, medicine, and chemistry. However, the traditional control systems are relatively large, complex, and costly. Optical driving micro- and nanofluid is a new trend of microfluidics, which combines the advantages of both optics and microfluidics in the micro-nano scale. In the present work, we investigated a method to drive microfluid by taking advantage of the localized surface plasmon resonance effect of gold nanoparticles, which can convert optical energy to fluid motion. First, numerical simulation was carried out to calculate the electromagnetic, temperature, and flow field around laser-irradiated gold nanoparticles. Then, the simplified heat source condition was verified. The nanoparticle array was regarded as heat source to induce convection flow. The influence of the spacing and number of nanoparticles in array was investigated. On this basis, the structural parameters of nanoparticle array that can be used to regulate the velocity of microfluidic were obtained.

     

On the Surface Plasmon Resonance Modes of Metal Nanoparticle Chains and Arrays

A method for estimating the surface plasmon resonance modes of metal nanoparticle chains and arrays within a multilayered medium is proposed. In this fully retarded point-dipole method, an inhomogeneous background is replaced with a homogeneous one, based on an effective refractive index approximation. The proposed method includes the effects of retardation, radiative damping, and dynamic depolarization due to the finite size of the nanoparticles. The use of diagonal terms of dyadic Green’s functions and different polarizability coefficients along the semi-axes of ellipsoidal nanoparticles provides a complete set of both longitudinal and transverse resonance modes. Numerical results are compared with experimental results found in the literature.     

Asymmetric Binary Plasmon Resonator Arrays for Perfect Trapping of Light

We propose to achieve perfect trapping of light with asymmetric binary plasmon resonator arrays on metal substrates, in which antisymmetrically coupled resonance modes are excited in each subwavelength period to eliminate any leaky radiation. The specific structure in the study is an ultrathin binary metal stripe array on a flat metal substrate interspaced with a dielectric layer. The antiphase resonance modes are excited underneath the binary metal stripes in each period, resulting in perfect trapping of light under appropriate difference of the metal stripe widths. The trapped light is fully absorbed by metals, accompanied with an improved enhancement of the local field compared to those in symmetric structures with equal metal stripe widths. The work suggests a new way in designing optical metamaterials to manipulate light for enhanced light-matter interactions.     

Tuning the Dipolar Plasmon Hybridization of Multishell Metal-Dielectric Nanostructure: Gold Nanosphere in a Gold Nanoshell

Because of the interaction between dipole resonances of the inner gold sphere and the outer gold shell, gold-dielectric-gold multishells with sub-50 nm diameter may at most have three hybridization modes of surface plasmon resonance (SPR). Theoretical calculations based on quasi-static theory indicate that there are blending and splitting of SPR bands in the absorption spectra, which makes the number of absorption peak tunable by changing the radius of inserted gold sphere, thickness of gold shell, dielectric constant of middle dielectric shell or outer environment. The two absorption peaks at longer wavelength, which correspond to the hybridization from the bonding shell plasmon and the sphere plasmon, are usually intense and well tunable. The absorption peak at shorter wavelength, which corresponds to the symmetric coupling between the anti-bonding shell plasmon and the sphere plasmon, is relative weak and only occurs with large dielectric constant of the middle shell, small dielectric constant of the outer surrounding, large inner radius of the gold shell, and small radius of the inner gold sphere. Furthermore, the physical origin of these plasmon hybridizations in gold-dielectric-gold multishells nanostructure has also been illuminated by analyzing the local electric field distributions.     

Localized Surface Plasmon Resonance in Gold Nanocluster Arrays on Opaque Substrates

Plasmonics - We report on the investigation of the localized surface plasmon resonance (LSPR) in periodical Au nanostructures. The arrays of Au nanoclusters and dimers were fabricated on Si and...     

Influences of Nanostructure Arrays on Light Absorption in Amorphous Silicon Thin-Film Solar Cells

By means of finite-difference time-domain (FDTD) numerical method, we investigate the possibility to enhance the light absorption in solar cells by employing different nanostructures. The solar cells are made of 100-nm-thick amorphous silicon (α-Si). The impacts of gold nanohole arrays, dielectric nanosphere arrays, and gold nanoparticle arrays on the light absorption are simulated, compared, and analyzed. The results show that gold nanohole arrays functioning as the back reflective layer, dielectric nanosphere arrays, and gold nanoparticle arrays can significantly enhance the light absorption for the solar cells, and the former two can increase the short-circuit current by more than 40 %, showing a great potential to improve the utilization efficiency of solar energy.     

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.     

Tunable Plasmonic Resonances in Hexagonally Ordered Gold Nanostructure Arrays with Increasing Interstice Size

Plasmonics - Gold nanostructure arrays were fabricated by combining colloidal lithography with inclined reactive ion etching and inclinded sputtering. Field emission scanning electron microscopy...     

Generation and Manipulation of Multiple Magnetic Fano Resonances in Split Ring-Perfect Ring Nanostructure

Plasmonics - The plasmon resonances and field enhancement in split ring-perfect ring (SR-PR) nanostructure are investigated numerically by using a finite element method. Multiple electric...     

Multiple Surface Plasmon Resonances in Compound Structure with Metallic Nanoparticle and Nanohole Arrays

The optical properties of a compound structure with metallic nanoparticle and nanohole arrays are numerically investigated by the means of finite-difference time domain method. We report on the observation of multi-valleys in the reflection spectra due to the excitation of surface plasmon (SP) resonant modes of the compound structure. Simulation results show that multiple SP resonances consist of surface plasmon polaritons on the gold film, localized surface plasmons on the nanoparticles, and coupling mode between them. These findings are important for applications utilizing multiple surface plasmon resonances.     

Spectral Shifting in Extraordinary Optical Transmission by Polarization-Dependent Surface Plasmon Coupling

Plasmonics - Nanoapertures in a metallic film exhibit extraordinary optical transmission (EOT) owing to the surface plasmon resonance. Their transmission properties are known to be dependent on the...     

Coupling Behaviors of Surface Plasmon Polariton and Localized Surface Plasmon with an InGaN/GaN Quantum Well

Plasmonics - Surface plasmon (SP) coupling behaviors of an InGaN/GaN quantum well (QW) with surface plasmon polariton (SPP) induced on a smooth Ag-film/GaN interface and localized surface plasmon...     

Detection of Deletion Mutants in Rice Via Overgo Hybridization Onto Membrane Spotted Arrays

Overlapping nucleotides or overgos were designed and used to detect deletions in rice mutants that had been generated by treatment with a chemical (diepoxybutane, DB) or irradiation (gamma ray, GR). As a proof of concept, DNA of three spotted leaf 11 (spl11) deletion mutants, GR5612, GR5717 and DB2487, and the wild-type DNA (IR64) were spotted onto nylon membranes in different concentrations and probed with radiolabeled overgos designed from different regions within the Spl11 gene. At least 3 μg per spot of DNA was required to show unambiguous and visible signals. Overgos designed from regions putatively deleted in GR5612 consistently did not hybridize to the GR5612 genomic DNA, whereas DNA from wild-type IR64 and from mutants in other regions consistently hybridized to the overgos. DNA of mutant DB2487 hybridized to all the overgos tested, suggesting the deletion is small and undetectable by the overgos. Overall, this study demonstrates that overgos can be employed to detect, verify, and characterize deletions, particularly in single copy genes, in mutant genomes. However, the technique requires careful adjustment of DNA concentration before spotting and the spotting of relatively high DNA concentrations onto the membranes.     

Plasmon Hybridization in Silver Nanoislands as Semishells Arrays Coupled to a Thin Metallic Film

We obtained experimentally strong plasmon interactions between localized surface plasmon with delocalized surface plasmon polaritons in a new nanosystem of silver semishells island film arrays arranged as a closed-packing structure coupled to an adjacent thin silver film. We show that plasmon interactions for such a nanosystem exhibits two pronounced resonances and interpret the coupling in terms of Fano resonances. The higher energy resonance is identified as a symmetric hybridization mode between localized plasmon resonances in the island semishell array and surface plasmon polaritons in the metal film and while the lower energy resonance is identified as a corresponding anti-symmetric hybridization mode. Increasing the size of the particle arrays enhances and red shifts the resonances. We show that adding a dielectric spacer between the semishell island array and the metal film results in a red shifting of the resonances and introduce an additional high energy spectral peak. The effect of the spacer layer is interpreted as a reduced hybridization and the generation of additional localized surface plasmon resonances.     

Surface Plasmon Coupling Effect of Gold Nanoparticles with Different Shape and Size on Conventional Surface Plasmon Resonance Signal

The labeling strategy with gold nanoparticles for the conventional surface plasmon resonance (SPR) signal enhancement has been frequently used for the sensitive determination of small molecules binding to its interaction partners. However, the influence of gold nanoparticles with different size and shape on SPR signal is not known. In this paper, three kinds of gold nanoparticles, namely nanorods, nanospheres, and nanooctahedrons with different size, were prepared and used to investigate their effects on the conventional SPR signal at a fixed excitation wavelength 670 nm. It was found that the SPR signal (i.e., resonant angle shift) was varied with the shapes and sizes of gold nanoparticles in suspension at a fixed concentration due to their different plasmon absorbance bands. For gold nanorods with different longitudinal absorbance bands, three conventional SPR signal regions could be clearly observed when the gold nanorod suspensions were separately introduced onto the SPR sensor chip surface. One region was the longitudinal absorbance bands coinciding with or close to the SPR excitation wavelength that suppressed the SPR angle shift. The second region was the longitudinal absorbance bands at 624 to 639 and 728 to 763 nm that produced a moderate increase on the SPR resonant angle shift. The third region was found for the longitudinal absorbance bands from 700 to 726 nm that resulted in a remarkable increase in the SPR angle shift responses. This phenomenon can be explained on the basis of calculation of the correlation of SPR angle shift response with the gold nanorod longitudinal absorbance bands. For nanospheres and nanooctahedrons, the SPR angle shift responses were found to be particle shape and size dependent in a simple way with a sustaining increase when the sizes of the nanoparticles were increased. Consequently, a guideline for choosing gold nanoparticles as tags is suggested for the SPR determination of small molecules with binding to the immobilized interaction partners.