Tunable Localized Surface Plasmon Resonance Research Articles

Flexible tuning of hole-based localized surface plasmon resonance in roxbyite Cu1.8S nanodisks via particle size, carrier density and plasmon coupling

Semiconductor nanocrystals (NCs) heavily doped with cation/anion vacancies or foreign metal ions can support localized surface plasmon resonance (LSPR) in the near-infrared (NIR) and mid-infrared (MIR) spectral wavelengths. Typically, nonstoichiometric copper sulfide Cu2−xS NCs with different x values (0 < x ≤ 1) have attracted numerous attention because of hole-based, particle size, morphology, hole density and crystal phase-dependent LSPR. In spite of excited development of methodology for LSPR manipulation, systematic LSPR tuning of Cu2−xS NCs with a special crystal phase has been limited. Herein, roxbyite Cu1.8S nanodisks (NDs) were selected as a model and their LSPR was readily tuned by particle size, hole density via chemical oxidation and reduction, self-assembly and disassembly in solution and plasmon coupling in multilayer films. Particle size, hole density and plasmon coupling severely affect their LSPR peak position and absorption intensity. Therefore, the ability of flexible LSPR tuning gifts roxbyite Cu1.8S NDs great potential in plasmonic applications, including photocatalysis, photothermal agent, two-photon photochemistry and many others in NIR and MIR regions.

Novel color filters for the correction of red–green color vision deficiency based on the localized surface plasmon resonance effect of Au nanoparticles

Color filters are promising tools for the correction of color vision deficiency because a medical cure of this physiological deficiency is unattainable. After the introduction of organic-dye based color filters, however, no appreciable progress has been made. In this study, gold nanoparticle-based plasmonic color filter devices, that is, EyEye-lens and EyEye-film, were developed for the correction of color vision deficiency. The EyEye-lens was prepared by a simple immobilizing technique, and the EyEye-film was readily synthesized through a one-pot method. These color filter devices are based on tunable localized surface plasmon resonance in the visible and near-infrared spectral range. Plasmonic nanoparticles embedded in the color filter provide a specific spectral color range for the correction of color vision deficiency. Careful color vision tests using an Ishihara plate were performed on subjects with red–green color deficiency. Statistical analysis of the color vision tests revealed that the EyEye-lens and EyEye-film have similar or better performance in the correction of red–green color deficiency than a commercial ChromaGen lens. The newly developed color filter devices should be considered as alternative personalized color filter devices for practical applications.

Plasmonic Au nanorods stabilized within anodic aluminum oxide pore channels against high-temperature treatment

Au nanorods (Au NRs) are promising candidates for sensing applications due to their tunable localized surface plasmon resonance wavelength. At temperatures above 250 °C, however, these structures are morphologically unstable and tend to evaporate. We herein report a novel refractory plasmonic nanocomposite system comprising Au NRs entrapped in anodized aluminum oxide (AAO) scaffolds that are stable up to 800 °C. Au NRs were synthesized in the cylindrical pores of sapphire-supported AAO via in situ electroless deposition on catalytic Au nanoparticles (Au NPs) anchored on the pore walls. The morphological characteristics and surface-enhanced Raman scattering (SERS) functionality of Au NRs before and after heat treatment were evaluated using SEM, XRD and Raman spectroscopy. Compared to unconfined Au NRs that evolved into spherical particles at temperatures below 250 °C and subsequently evaporated from the substrate surface, the morphology of Au NRs in AAO was preserved upon heat treatment at temperatures up to 800 °C. Furthermore, by tuning the AAO scaffolds thickness and pore diameter, the aspect ratio (AR) of the entrapped Au NRs was varied from 2.4 to 7.8. The SERS sensitivity of Au NRs in AAO was found to increase with decreasing AR when the incident light was parallel to the rod longitudinal axis, in close agreement with the calculated fourth power of the local electromagnetic field using the finite-difference time domain method.

Fabrication of Various Plasmonic Pt Nanostructures via Indium Assisted Solid-State Dewetting: From Small Nanoparticles to Widely Connected Networks.

In this paper, the modified solid-state dewetting (MSSD) of well-defined and various uniform Pt nanostructures is demonstrated by the auxiliary diffusion enhancement. The MSSD utilizes the introduction of metallic indium (In) layers with high diffusivity in between sapphire and platinum (Pt) layer, through which the global diffusion and dewetting of metallic atoms can be significantly enhanced. Subsequently, the In atoms can be sublimated from the NP matrix, resulting in the formation of pure Pt NPs. By the systematic control of In and Pt bi-layer thickness, various areal density, size and configuration of Pt NPs are demonstrated. The In2 nm/Pt2 nm bilayers establish very small and highly dense NPs throughout the temperature range due to the early maturation of growth. Intermediate size of NPs is demonstrated with the In45 nm/Pt15 nm bilayers with the much improved interparticle spacings by annealing between 650 and 900 °C for 450 s. Finally, the In30 nm/Pt30 nm bilayers demonstrate the widely connected network-like nanostructures. In addition, the finite difference time domain (FDTD) simulation is employed to exploit the local electric field distributions at resonance wavelengths. The dewetting characteristics of In/Pt bilayers is systematically controlled by the modifications of layer thickness and annealing temperature and is systematically described based on the diffusion of atoms, Rayleigh instability and surface energy minimization mechanism. The optical properties demonstrate dynamic and widely tunable localized surface plasmon resonance (LSPR) responses depending upon the various surface morphologies of Pt nanostructures.

One-Dimensional Cuprous Selenide Nanostructures with Switchable Plasmonic and Super-ionic Phase Attributes.

Cuprous selenide nanocrystals have hallmark attributes, especially tunable localized surface plasmon resonances (LSPRs) and super-ionic behavior. These attributes of cuprous selenide are now integrated with a one-dimensional morphology. Essentially, Cu2 Se nanowires (NWs) of micrometer-scale lengths and about 10 nm diameter are prepared. The NWs exhibit a super-ionic phase that is stable at temperatures lower than in the bulk, owing to compressive lattice strain along the radial dimension of the NWs. The NWs can be switched between oxidized and reduced forms, which have contrasting phase transition and LSPR characteristics. This work thus makes available switchable, one-dimensional waveguides and ion-conducting channels.

One‐Dimensional Cuprous Selenide Nanostructures with Switchable Plasmonic and Super‐ionic Phase Attributes

AbstractCuprous selenide nanocrystals have hallmark attributes, especially tunable localized surface plasmon resonances (LSPRs) and super‐ionic behavior. These attributes of cuprous selenide are now integrated with a one‐dimensional morphology. Essentially, Cu2Se nanowires (NWs) of micrometer‐scale lengths and about 10 nm diameter are prepared. The NWs exhibit a super‐ionic phase that is stable at temperatures lower than in the bulk, owing to compressive lattice strain along the radial dimension of the NWs. The NWs can be switched between oxidized and reduced forms, which have contrasting phase transition and LSPR characteristics. This work thus makes available switchable, one‐dimensional waveguides and ion‐conducting channels.

Helium nanodroplet assisted synthesis of bimetallic Ag@Au nanoparticles with tunable localized surface plasmon resonance

Nanoparticles with tunable localized surface plasmon resonance have been prepared by synthesis in helium nanodroplets. Subsequent surface deposition allows for the formation of substrates which can be employed for surface-enhanced Raman spectroscopy (SERS). The assembly of Ag@Au core@shell clusters of about 5 nm diameter in helium droplets with different Ag:Au ratio allows to tune the surface plasmon resonance between the plain Ag resonance at 447 nm and the Au resonance at 555 nm. For the fabricated substrates only a single plasmon resonance is observed in the UV/vis absorption spectra. The prepared nanostructures have been functionalized with 4-methylbenzenethiol (4-MBT) molecules and SERS spectra have been recorded. The results demonstrate the potential of the helium droplet synthesis approach, opening up a new route to the formation of tailored plasmonic nanoparticles and functional nanostructures.Graphical abstract

Plasmonic responses of metallic/dielectric core-shell nanoparticles on a dielectric substrate

The effect of material selection on the plasmonic response and local absorption are evaluated for core–shell nanoparticles placed over a BK7 glass substrate. Eight different core–shell pairs are studied using the vectorized version of discrete dipole approximation with surface interactions (DDA-SI). Two classes of dielectric core-metallic shell and metallic core-dielectric shell particles are considered. It is shown that core–shell structures with dielectric materials can have absorption enhancement compared to the bare metallic nanoparticles. Moreover, it is observed that core–shell pairs yield multipeak localized surface plasmon resonance (LSPR) response due to their hybrid structure. Absorption enhancement and LSPR tuning ranges are shown with different dielectric materials that can be used in localized heating of designated core–shell NPs placed over a surface for nanomanufacturing purposes. In order to determine the optimum size configurations, a number of core–shell pairs are explored with specified volumetric filling ratio of core materials.

Tunable local surface plasmon resonance and refractive index sensitivity ability of three-layered dielectric-silver bimetallic nanoshells

Optical properties and refractive index sensitivity abilities of three-layered silver/gold-dielectric-silver bimetallic nanoshells are investigated based on quasi-static theory. The results show that absorption spectra of silver/gold-dielectric-silver bimetallic nanoshells can be well tuned by changing the inner core radius, middle dielectric radius and outer shell layer thickness. Local surface plasmon resonance (LSPR) shifts of |ω−−〉 mode show a red-shift with increasing the inner core radius and the thickness of middle dielectric layer, while a blue-shift with increasing the thickness of outer shell. It is interesting to find that the shifts of |ω−+〉 mode are related to the ratio ε2∕ε4, the component of core and nanoshell. In addition, the refractive index sensitivity abilities of three-layered silver/gold-dielectric-silver bimetallic nanoshells are also reported. A higher refractive index sensitivity ability can be obtained by adjusting its geometric size and component. |ω−−〉 mode gets more intensity with increasing the surrounding medium dielectric function, while |ω−+〉 mode fades down. The intensity difference between |ω−−〉 mode and |ω−+〉 mode is mainly effected by the surrounding medium dielectric function, its geometric parameter, middle layer dielectric function, the component of core and nanoshell. Our study provides a way to analyze sensitivity application of nanoshells and broadens the application of nanoshells in sensor ability.

Optical excitations of boron and phosphorous doped silicon nanoparticles: A computational study

Discovery of tunable localized surface plasmon resonances (LSPRs) in boron (B) and phosphorous (P) doped silicon (Si) nanocrystals has opened exciting possibilities for Si-based plasmonics. Here, using computationally efficient time-dependent density-functional theory calculations, we investigate the optical response modulations of B- and P-doped Si NPs as a function of dopant locations (incorporated in the bulk, sub-surface, and surface regions) and nanoparticle size. More specifically, we show that the optical features of doped Si NPs are critically depend on the location of the dopant atom and a maximal spectral intensity enhancement can be achieved via surface doping. We believe that our theoretical findings would help in the emerging field of doped Si-based plasmonics.

Synthesis and Properties of Plasmonic Boron‐Hyperdoped Silicon Nanoparticles

AbstractElectronic properties of silicon, the most important semiconductor material, are controlled through doping. The range of achievable properties can be extended by hyperdoping, i.e., doping to concentrations beyond the nominal equilibrium solubility of the dopant. Here, hyperdoping is achieved in a laser pyrolysis reactor capable of providing nonequilibrium conditions, where doping is governed by kinetics rather than thermodynamics. High resolution scanning transmission electron microscopy (TEM) with energy‐dispersive X‐ray spectroscopy shows that the boron atom distribution in the hyperdoped nanoparticles is relatively uniform. The hyperdoped nanoparticles demonstrate tunable localized surface plasmon resonance (LSPR) and are stable in air for periods of at least one year. The hyperdoped nanoparticles are also stable upon annealing at temperatures up to 600 °C. Furthermore, boron hyperdoping does not change the diamond cubic crystal structure of silicon, as demonstrated in detail by high flux synchrotron X‐ray diffraction and pair distribution function (PDF) analysis, supported by high‐resolution TEM analysis.

Plasmonic Gold Nanovesicles for Biomedical Applications

AbstractGold nanoparticles (GNPs), with tunable optical properties, bioinertness, and surface multivalent effect, have been widely explored for biomedical applications. As one classical type of GNPs‐based assemblies, plasmonic gold nanovesicles (GVs), with a hollow cavity, “solid skeleton” composed of GNPs cores and a “soft body” composed of functional polymers, have attracted considerable attention due to their tunable localized surface plasmon resonance, strong surface‐enhanced Raman scattering properties, and high photothermal conversion efficiency. This review summarizes recent advances in biomedical applications for plasmonic GVs. Firstly, the synthesis methods of GVs are mainly including self‐assembly and in situ gold growth methods. Secondly, the classification of GVs is described according to the morphology of GNPs cores. Thirdly, different biomedical applications of GVs are elaborated, including in vitro diagnosis, in vivo imaging, and in vivo therapy. Finally, the challenges and perspectives of GVs are discussed.

One-Pot Synthesis of Multi-Branch Gold Nanoparticles and Investigation of Their SERS Performance.

Gold nanoparticles with multiple branches have attracted intensive studies for their application in sensing of low trace molecules. A large number of the merits found on the gold nanoparticles for the above applications are attributed to the strong localized surface plasmon resonance excited by the incident radiation. However, a facile and flexible way of synthesizing the multi-branch gold nanoparticles with tunable localized surface plasmon resonance frequency is still a challenge for the plasmonic research field. Herein, we report an efficient one-pot synthesis of multi-branch gold nanoparticles method that resembles a seed-medicated approach while using no further chemicals except chloroauric acid, ascorbic acid and 4-(2-Hydroxyethyl)-1-piperazinyl]-ethanesulfonic acid. By controlling the amounts of ascorbic acid volumes in the reaction mixture, the morphology and the localized surface plasmon resonance frequency of the synthesized multi-branch gold nanoparticles can be manipulated conveniently. Moreover, using the 4-Mercaptobenzoic acid as the Raman reporter, the multi-branch gold nanoparticles show superior surface-enhanced Raman spectroscopy characteristics that can be potentially used in chemical and biological sensing.

Tunable Localized Surface Plasmon Resonance and Broadband Visible Photoresponse of Cu Nanoparticles/ZnO Surfaces.

Plasmonic Cu nanoparticles (NP) were successfully deposited on ZnO substrates by atomic layer deposition (ALD) owing to the Volmer-Weber island growth mode. An evolution from Cu NP to continuous Cu films was observed with an increasing number of ALD cycles. Real and imaginary parts of the NP dielectric functions, determined by spectroscopic ellipsometry using an effective medium approach, evidence a localized surface plasmon resonance that can be tuned between the visible and near-infrared ranges by controlling the interparticle spacing and size of the NP. The resulting Cu NP/ZnO device shows an enhanced photoresponse under white light illumination with good responsivity values, fast response times, and stability under dark/light cycles. The significant photocurrent detected for this device is related to the hot-electron generation at the NP surface and injection into the conduction band of ZnO. The possibility of tuning the plasmon resonance together with the photoresponsivity of the device is promising in many applications related to photodetection, photonics, and photovoltaics.

Investigation of compositionally tunable localized surface plasmon resonances (LSPRs) of a series of indium tin oxide nanocrystals prepared by one-step solvothermal synthesis

A series of novel nonmetallic plasmonic materials, indium tin oxide (ITO) nanocrystals (NCs), with tunable doping ratios of tin (from 0 up to 25%), were synthesized through a one-step solvothermal method. Cubic-shaped NCs with good crystallinity and uniform-size distribution (~ 17 nm), for all doping ratios, were confirmed through the X-ray diffraction patterns and transmission electron microscopy images. As inferred from X-ray photoelectron spectroscopy and inductively coupled plasma measurements, Sn is preferentially distributed close to the surface of ITO NCs. In particular, localized surface plasmon resonances (LSPRs) were tuned from near- to mid-infrared regions only by varying the doping ratios, which is of interest, for example, to avoid high-loss levels associated with metallic nanoparticles in LSPR biosensing applications. Our work provides a series of reliable and accessible materials for the researchers who need different wavelengths of LSPR frequencies in near-infrared and/or mid-infrared regions. It will benefit the research and development of nonmetallic plasmonic materials in a wider application scope.

Design of Gold Hollow Nanorods with Controllable Aspect Ratio for Multimodal Imaging and Combined Chemo-Photothermal Therapy in the Second Near-Infrared Window.

Gold nanoparticles (AuNPs) exhibit great potential for biological applications due to their good biocompatibility and tunable localized surface plasmon resonance (LSPR) properties. Currently, although tuning the aspect ratio of a solid structure or designing a hollow structure has been performed to regulate the LSPR properties of AuNPs, the method of preparing hollow anisotropic AuNPs has rarely been reported. In this study, we designed gold hollow nanorods (AuHNRs) with controllable aspect ratios by a Se-doping Te nanorod-templated method with the assistance of l-cysteine. UV-vis-NIR spectra showed that AuHNRs with an aspect ratio of about 3 could have a LSPR peak in the second near-infrared (NIR-II) window, which is only half of the value required by traditional Au nanorods. Moreover, AuHNRs are nontoxic and capable of loading drugs. In vivo experiment revealed that AuHNRs can be used as contrast agents in multimodal imaging, including photothermal imaging, photoacoustic imaging, and computed tomography imaging, as well as in chemo-photothermal combined therapy of tumor in the NIR-II window. Because light in the NIR-II window has remarkable advantages over that in the first near-infrared (NIR-I) window in biomedical applications, AuHNRs can be used as promising NIR-II-window-responsive multifunctional nanoagents.

Seed-Mediated Growth of Ag@Au Nanodisks with Improved Chemical Stability and Surface-Enhanced Raman Scattering.

Bimetallic Ag@Au nanoparticles (NPs) have received significant research interest because of their unique optical properties and molecular sensing ability through surface-enhanced Raman scattering (SERS). However, the synthesis of Ag@Au core–shell plasmonic nanostructures with precisely controlled size and shape remained a great challenge. Here, we report a simple approach for the synthesis of bimetallic Ag@Au nanodisks of about 13.5 nm thickness and different diameters through a seed-mediated growth process. The synthesis involves the conformal deposition of Au atoms at the corner sites of Ag nanoplate (AgNPL) seeds coupled with site-selective oxidative etching of AgNPL edges to generate Ag@Au nanodisks. The resultant Ag@Au nanodisks manifest significantly improved chemical stability and tunable localized surface plasmon resonance from the visible to the near-infrared spectral range. Moreover, in comparison to AgNPLs, the Ag@Au nanodisks showed greatly enhanced SERS performance with an enhancement factor up to 0.47 × 105, which is nearly 3-fold higher than that of the original AgNPLs (0.18 × 105). Furthermore, the Ag@Au nanodisks show a high sensitivity for detecting probe molecules such as crystal violet of concentration as low as 10–9 M and excellent reproducibility, with the SERS intensity fluctuation less than 12.5%. The synthesis route adapted for the controlled fabrication of Ag@Au nanodisks can be a potential platform for maneuvering other bimetallic plasmonic nanostructures useful for plasmonics and sensing applications.

Fabrication and application of substoichiometric tungsten oxide with tunable localized surface plasmon resonances

Substoichiometric tungsten oxide (WO3-x) has become one of the interesting candidates for localized surface plasmon resonance (LSPR) hosts because of its fascinating properties. Herein, we report that substoichiometric WO3-x can be fabricated via a facile solid phase reduction method, and at the same time it exhibits a strong LSPR in the near infrared region. Tunable plasmon resonances can be observed in a wide range by changing their stoichiometry. In the bovine serum albumin (BSA) based optical bio-sensing system, the plasmonic WO3-x displays superior sensitivity. Moreover, the hybrid nanocomposites combining the plasmonic WO3-x and plasmonic Ag can be also obtained, which show great potentials in heterogeneous catalysis. Specially, the WO3-x prepared at the reduction temperature of 350 °C (WO3-350) exerts improved photocatalytic performance toward methylene blue degradation, which is due to the synergistic effect of the strong plasmonic effect of WO3-350 and Ag nanoparticles.

Regulatory Mechanism of Localized Surface Plasmon Resonance Based on Gold Nanoparticles-Coated Paclitaxel Nanoliposomes and Their Antitumor Efficacy

To functionalize the advanced controlled drug delivery systems, gold nanomaterials have been explored as photothermal therapy agents owing to their tunable and strong localized surface plasmon resonance (LSPR). As the major tissue chromophores are barely absorptive in the near-infrared (NIR) region (650–900 nm), it is becoming particularly important to regulate the LSPR absorption of gold nanomaterials to the NIR region to minimize the absorption. The main factors for the LSPR absorption of nanomaterials, which decides the photothermal effects, drug release, and antitumor efficacy of gold-based drug carriers, include morphology, size, and dielectric constant of surrounding mediums. Herein, gold nanoparticles-coated paclitaxel nanoliposomes (PTX-Lips@AuNPs) with various morphologies, sizes, and dielectric constant of surrounding mediums were synthesized. We studied the regulatory mechanism of LSPR absorption and their antitumor efficacy. The results showed that the branched gold nanoshells-coated paclitaxel nanoliposomes (PTX-Lips@BGNs) with a big size (about 150 nm) in the medium of NaCl solution exhibit optimal antitumor efficacy among different parameters we have studied. Furthermore, the investigation of the regulatory mechanism endows a synthetic theoretical basis of the nanomaterials in the future.

Carrier Density-Dependent Localized Surface Plasmon Resonance and Charge Transfer Observed by Controllable Semiconductor Content

We discuss how the controllable carrier influences the localized surface plasmon resonance (LSPR) and charge transfer (CT) in the same system based on ultraviolet-visible and surface-enhanced Raman scattering (SERS) measurements. The LSPR can be easily tuned from 580 to 743 nm by changing the sputtering power of Cu2S in the Ag and Cu2S composite substrate. During this process, surprisingly, we find that the LSPR is proportional to the sputtering power of Cu2S. This observation indicates that LSPR can be accurately adjusted by changing the content of the semiconductor, or even the carrier density. Moreover, we characterize the carrier density through the detection of the Hall effect to analyze the Raman shift caused by CT and obtain the relationships between them. These fundamental discussions provide a guideline for tunable LSPR and the investigation of CT.