Tunable Surface Plasmon Resonance Research Articles

Gold nanoparticle microemulsion films with tunable surface plasmon resonance signal

Composite films were prepared by the dip-coating method. An organosol of Au nanoparticles (6.3±0.4nm) was used as the reaction mixture. The nanoparticles were stabilized with sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The prepared films were formed of an AOT layer with encapsulated Au nanoparticles (i.e. Au@AOT films). The films demonstrated a stable plasmon effect. The variation of the immersion number of the glass substrate from 1 to 10 allowed the adjustment of the plasmonic properties. The absorption intensity and maximum wavelength of the surface plasmon resonance were found to change from 0.183 to 0.245 and from 529±2 to 539±2nm, respectively. The plasmonic properties were found to correlate with the film thickness, roughness, and morphology. An increase in the concentration of Au nanoparticles improves the film’s mechanical strength and wettability.

A review of recent advances in the use of complex metal nanostructures for biomedical applications from diagnosis to treatment.

Complex metal nanostructures represent an exceptional category of materials characterized by distinct morphologies and physicochemical properties. Nanostructures with shape anisotropies, such as nanorods, nanostars, nanocages, and nanoprisms, are particularly appealing due to their tunable surface plasmon resonances, controllable surface chemistries, and effective targeting capabilities. These complex nanostructures can absorb light in the near-infrared, enabling noteworthy applications in nanomedicine, molecular imaging, and biology. The engineering of targeting abilities through surface modifications involving ligands, antibodies, peptides, and other agents potentiates their effects. Recent years have witnessed the development of innovative structures with diverse compositions, expanding their applications in biomedicine. These applications encompass targeted imaging, surface-enhanced Raman spectroscopy, near-infrared II imaging, catalytic therapy, photothermal therapy, and cancer treatment. This review seeks to provide the nanomedicine community with a thorough and informative overview of the evolving landscape of complex metal nanoparticle research, with a specific emphasis on their roles in imaging, cancer therapy, infectious diseases, and biofilm treatment. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Diagnostic Tools > Diagnostic Nanodevices.

Ultra-Broadband Plasmon Resonance in Gold Nanoparticles Precipitated in ZnO-Al2O3-SiO2 Glass

Optical materials with a tunable localized surface plasmon resonance (LSPR) are of great interest for applications in photonics and optoelectronics. In the present study, we explored the potential of generating an LSPR band with an ultra-broad range of over 1000 nm in gold nanoparticles (NPs), precipitated through a thermal treatment in ZnO-Al2O3-SiO2 glass. Using optical absorption spectroscopy, we demonstrated that the LSPR band’s position and shape can be finely controlled by varying the thermal treatment route. Comprehensive methods including Raman spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy were used to study the glass structure, while computational approaches were used for the theoretical description of the absorption spectra. The obtained results allowed us to suggest a scenario responsible for an abnormal LSPR band broadening that includes a possible interparticle plasmonic coupling effect taking place during the liquid–liquid phase separation of the heat-treated glass. The formation of gold NPs with an ultra-broad LSPR band in glasses holds promise for sensitizing rare earth ion luminescence for new photonics devices.

Seedless synthesis of Au nanoplates with tunable plasmonic peaks

Au nanoplates with tunable in-plane dipolar localized surface plasmon resonance peaks in a broad range from the visible to near-infrared region were obtained in high yield using a seedless wet chemical growth method after purification. Cetyltrimethylammonium chloride was used as a surfactant, while hydrogen peroxide and sodium borohydride were used as the weak and strong reducing agents, respectively. The edge length and in-plane dipolar localized surface plasmon resonance peak of the Au nanoplates could be adjusted by varying the amounts of hydrogen peroxide and sodium borohydride. The Au nanoplates were further used as the saturable absorber to generate pulsed laser output in a passively Q-switched solid-state laser at approximately 2 µm. Our study offers a new method for obtaining Au nanoplates with tunable plasmonic peaks over a broad range.

Construction of the Au Nanoparticle/Graphene Oxide/Au Nanotube (AuNP/GO/AuNT) Sandwich Membrane for Surface-Enhanced Raman Scattering Sensing.

Au nanotube-based composite membrane served as surface-enhanced Raman scattering (SERS) substrate with an ultralarge aspect ratio possesses an excellent flexibility and widely tunable surface plasmon resonance, and by introducing graphene oxide (GO) as a spacer layer, the SERS enhancement of the composite membrane is obviously better than those from the individual blocks of the Au nanotubes (AuNTS) membrane and the Au nanoparticle/graphene oxide (AuNP/GO) membrane. Such a "sandwich" (AuNP/GO/AuNT) structured membrane has a high SERS sensitivity and a wide tunability by controlling the size of Au nanoparticles and the thickness of graphene oxide, and the detection limits of the AuNP/GO/AuNT substrate for R6G and NBA are as low as 10-12 and 10-7 M, respectively; the large enhancement is attributed to the adsorption and chemical mechanism of graphene oxide and the physical mechanism of the Au nanoparticles and nanotubes (the electromagnetic field coupling between them).

High Yield Seedless Synthesis of Mini Gold Nanorods: Partial Silver Decoupling Enabling Effective Nanorods Elongation With Tunable Surface Plasmon Resonance Beyond 1000 nm and CTAB-Free Functional Coating for mTHPC Conjugation

High Yield Seedless Synthesis of Mini Gold Nanorods: Partial Silver Decoupling Enabling Effective Nanorods Elongation With Tunable Surface Plasmon Resonance Beyond 1000 nm and CTAB-Free Functional Coating for mTHPC Conjugation

Advances in Gold Nanoparticles: Synthesis, Functionalization Strategies, and Theranostic Applications in Cancer.

Cancer is among the leading causes of mortality and morbidity in the world. Metallic nanoparticles, especially gold nanoparticles (AuNPs) have emerged to be attractive systems to circumvent the associated adverse effects. By the virtue of their unique properties of tunable size, shape, composition, optical properties, biocompatibility, minimal toxicity, multivalency, fluorescence-luminescence property and surface plasmon resonance; AuNPs have the potential to be used as drug delivery systems. It is vital to ensure that the drug reaches the target site of action for selective kill of cancer cells without harm to healthy cells. These AuNPs can be easily functionalized with a wide array of ligands like peptides, oligonucleotides, polymers, carbohydrates for active targeting to ensure site specific delivery and reduced systemic effects. AuNPs have been in-vestigated as carriers for gene delivery, drug delivery with or without photothermal therapy, in diagnosis based on radiation or spectroscopy. They have emerged as attractive theranostic approach in the overall management of cancer with superior benefit to risk features. In this review, we have discussed synthesis of different AuNPs (nanorods, spherical nanoparticles, and hollow AuNPs), their functionalization strategies and their applications in biomedical domain. Various research studies and clinical trials on application of AuNPs in diagnosis and therapeutics are highlighted.

Heterogeneous CNF/MoO3 nanofluidic membranes with tunable surface plasmon resonances for solar-osmotic energy conversion.

Two-dimensional (2D) nanofluidic membranes are competitive candidates for osmotic energy harvesting and have been greatly developed. However, the use of diverse inherent characteristics of 2D nanosheets, such as electronic or optoelectronic properties, to achieve intelligent ion transport, still lacks sufficient exploration. Here, a cellulose nanofiber/molybdenum oxide (CNF/MoO3) heterogeneous nanofluidic membrane with high performance solar-osmotic energy conversion is reported, and how surface plasmon resonances (SPR) regulate selective cation transport is revealed. The SPR of amorphous MoO3 endows the heterogeneous nanofluidic membranes with tunable surface charge and good photothermal conversion. Through DFT calculations and finite element modeling, the regulation of electronic and optoelectronic properties on the surface of materials by SPR and the influence of surface charge density and temperature gradient on ion transport in nanofluidic membranes are demonstrated. By mixing 0.01/0.5 M NaCl solutions using SPR and photothermal effects, the power density can achieve a remarkable value of ≈13.24 W m-2, outperforming state-of-the-art 2D-based nanofluidic membranes. This work first reveals the regulation and mechanism of SPR on ion transport in nanofluidic membranes and systematically studies photon-electron-ion interactions in nanofluidic membranes, which could also provide a new viewpoint for promoting osmotic energy conversion.

Theoretical Design of Near-Infrared Tunable Surface Plasmon Resonance Biosensors Based on Gate-Controlled Graphene Plasmons

A tunable near-infrared surface plasmon resonance (SPR) biosensor based on gate-controlled graphene plasmons is numerically investigated by using the finite element method (FEM) and the transfer matrix method (TMM). The novel properties of chemical potential sensing make the proposed sensor promising in the application of ultra-sensitive and highly specific biosensing technology. The sensitivity of chemical potential sensing in wavelength interrogation mode can be calculated to be 1.5, 1.89, 2.29, 3.21, 3.73 and 4.68 nm/meV, respectively, at the resonance wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The figure of merit (FOM) achieves 129.3, 101.1, 84.5, 67.7, 69.5 and 59.7 eV−1, respectively, at these resonance wavelengths. The sensitivity of chemical potential sensing in gate voltage interrogation mode also can be calculated to be 156.9822, 143.6147, 131.0779, 111.0351, 101.3415 and 90.6038 mV/meV, respectively, at the incident wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The FOM achieves 135.6, 103.0, 88.9, 62.2, 66.6 and 61.5 eV−1, respectively, at these incident wavelengths. Theoretical estimates suggest that the limit of detection (LOD) of the sensor’s DNA sensing can reach the level of femtomolar or even attomolar, comparable to and even lower than that of 2D nanomaterial-enhanced metal SPR sensors with AuNPs as a sensitivity enhancement strategy. The feasibility of preparation and operation of this new concept SPR biosensor is also analyzed and discussed.

Surface-Enhanced Raman Scattering Studies of Au-Ag Bimetallic Nanoparticles with a Tunable Surface Plasmon Resonance Wavelength Synthesized by Picosecond Laser Irradiation

Here, we present a simple and green method of preparing Au-Ag bimetallic nanoparticles (NPs) with a tunable surface plasmon resonance (SPR) wavelength by using picosecond laser irradiation. Au-Ag alloy NPs have been produced by irradiating the solutions containing respective metallic salts in a polyvinyl alcohol (PVA) matrix using a picosecond laser in a single-step process. The SPR wavelength of the Au-Ag bimetallic NPs is observed to be shifted/changed with the Au-Ag concentration and the laser irradiation parameters. The Au-Ag NPs embedded in the PVA matrix are advantageous for Surface-Enhanced Raman scattering (SERS) applications. The estimated enhancement factors (EFs) were observed to vary as a function of conditions of the Au-Ag bimetallic alloy NPs synthesis and also on the concentration of Au at a fixed input fluence of irradiation. The SERS active platforms of Au-Ag bimetallic NPs showed EFs as high as of the order of 108 for Crystal Violet (CV) dye samples at nano molar concentrations. The present study demonstrates a simple, single-step, and green method that fabricates Au-Ag alloy-based nanocomposites suitable for SERS investigations with significantly higher orders of EFs.

Chromogenic Mechanisms of Colorimetric Sensors Based on Gold Nanoparticles.

The colorimetric signal readout method is widely used in visualized analyses for its advantages, including visualization of test results, simple and fast operations, low detection cost and fast response time. Gold nanoparticles (Au NPs), which not only exhibit enzyme-like activity but also have the advantages of tunable localized surface plasmon resonance (LSPR), high stability, good biocompatibility and easily modified properties, provide excellent platforms for the construction of colorimetric sensors. They are widely used in environmental monitoring, biomedicine, the food industry and other fields. This review focuses on the chromogenic mechanisms of colorimetric sensors based on Au NPs adopting two different sensing strategies and summarizes significant advances in Au NP-based colorimetric sensing with enzyme-like activity and tunable LSPR characteristics. In addition, the sensing strategies based on the LSPR properties of Au NPs are classified into four modulation methods: aggregation, surface modification, deposition and etching, and the current status of visual detection of various analytes is discussed. Finally, the review further discusses the limitations of current Au NP-based detection strategies and the promising prospects of Au NPs as colorimetric sensors, guiding the design of novel colorimetric sensors.

Thermally generated Au–Ag nanostructures with tunable localized surface plasmon resonance as SERS activity substrates

Various Au–Ag bimetallic alloy nanostructures were obtained as sensitive surface-enhanced Raman scattering (SERS) substrates by changing the thermal annealing sequence. The atomic force microscopy (AFM) and scanning electron microscopy (SEM) results confirm that Au/Ag bimetallic clusters and Ag–Au core-shell like structures can be designed by thermal annealing. The absorption spectra showed that the localized surface plasmon resonance (LSPR) frequency of the annealed Au/Ag bimetallic alloy structure could effectively shift from the near ultraviolet to the visible region. At the same time, the Au/Ag bimetallic alloy films modified by thermal annealing have shown satisfactory performance as SERS substrates. Raman enhancement mechanism of Au–Ag bimetallic alloy films is verified by finite-difference time-domain (FDTD) simulation results.

Shaping the Plasmonic Response: Hollow Gold Elliptical Nanotubes

AbstractHighly tunable localized surface plasmon (LSP) resonances in metal nanostructures are of great importance for manipulating light waves and enhancing light–matter interactions at the nanoscale. Here, a new type of plasmonic resonators based on hollow elliptical nanotubes, which can generate highly tunable LSP resonances in the visible frequencies, are reported. High‐quality hollow gold (Au) elliptical nanotubes with fine controllable size and morphology are experimentally fabricated. Dark‐field scattering measurements reveal the presence of multiple plasmon resonances including longitudinal Fabry–Pérot resonances and transverse hybridized LSP resonances due to rotational symmetry breaking. Upon varying the ellipticity, the hybridized LSP resonances exhibit continuously spectral evolution behaviors, such as the hybridized modes shifting and crossing. The experimental results show good agreement with the rigorous electromagnetic modeling and Raman spectroscopic measurements. The hollow anisotropic geometries provide highly tunable plasmonic responses together with homogeneous field distributions and high surface‐to‐volume ratio, which hold great potential for practical applications in sensing, nonlinear optics, surface‐enhanced spectroscopies, and bio‐medicine.

Actively tunable graphene ribbon based multi-band THz polarizer with a high extinction ratio

An electrically tunable surface plasmon resonance based graphene ribbon (GR) terahertz (THz) polarizer with an adjustable operating frequency, high extinction ratio, and low insertion loss is reported here, and is simple and fabrication feasible. The proposed metasurface structure comprises a periodic array of graphene ribbons deposited on a quartz–silicon substrate. The operating frequency of the GR-polarizer can be tuned by varying the gap between GRs, GR pitch, GR width, and Fermi level in graphene. Beyond the available graphene-based polarizers, the proposed device exhibits a high extinction ratio (ER) of up to 75 dB with simultaneous insertion loss of ∼1.5dB at the optimized frequency of 1.69 THz. In addition, an average ER of ∼30dB with insertion loss of ∼2dB in the broad frequency range of 0.8–2.5 THz is demonstrated. Such metastructure polarizing devices, enriched with the nontrivial functionalities of graphene, would open up a fertile platform for designing a range of integrated photonic components for useful applications in THz optoelectronics, biomedical engineering, and microfluidics.

Triple-Band Surface Plasmon Resonance Metamaterial Absorber Based on Open-Ended Prohibited Sign Type Monolayer Graphene.

This paper introduces a novel metamaterial absorber based on surface plasmon resonance (SPR). The absorber is capable of triple-mode perfect absorption, polarization independence, incident angle insensitivity, tunability, high sensitivity, and a high figure of merit (FOM). The structure of the absorber consists of a sandwiched stack: a top layer of single-layer graphene array with an open-ended prohibited sign type (OPST) pattern, a middle layer of thicker SiO2, and a bottom layer of the gold metal mirror (Au). The simulation of COMSOL software suggests it achieves perfect absorption at frequencies of fI = 4.04 THz, fII = 6.76 THz, and fIII = 9.40 THz, with absorption peaks of 99.404%, 99.353%, and 99.146%, respectively. These three resonant frequencies and corresponding absorption rates can be regulated by controlling the patterned graphene's geometric parameters or just adjusting the Fermi level (EF). Additionally, when the incident angle changes between 0~50°, the absorption peaks still reach 99% regardless of the kind of polarization. Finally, to test its refractive index sensing performance, this paper calculates the results of the structure under different environments which demonstrate maximum sensitivities in three modes: SI = 0.875 THz/RIU, SII = 1.250 THz/RIU, and SIII = 2.000 THz/RIU. The FOM can reach FOMI = 3.74 RIU-1, FOMII = 6.08 RIU-1, and FOMIII = 9.58 RIU-1. In conclusion, we provide a new approach for designing a tunable multi-band SPR metamaterial absorber with potential applications in photodetectors, active optoelectronic devices, and chemical sensors.

Colorimetric sensing of Cu(II) ions in water on the basis of selective chemical etching of EDA-capped Ag nanoplates

Cu(II) ions are one of the essential mineral elements in the human body, but can pose a substantial health risk to people exposed to high concentrations of Cu(II) ions over a long period. Therefore, the ability to detect Cu(II) ions in drinking water is important. In this study, a novel colorimetric sensing probe for the easy and onsite detection of Cu(II) ions in drinking water was developed. The probe was constructed through selective chemical etching of triangular Ag nanoplates with tunable localized surface plasmon resonance (LSPR) properties. Ethylenediamine (EDA) was used as an organic capping agent to improve the chemical stability of triangular Ag nanoplates. Selective chemical etching of the EDA-capped Ag nanoplates in the presence of Cu(II) ions as a result of the formation of a coordination complex between the EDA and Cu(II) ions caused remarkable changes in the nanoplates’ LSPR characteristics. On the basis of this phenomenon, a novel colorimetric sensing probe capable of detecting Cu(II) ions in drinking water at concentrations above the safety limit was developed. Our findings were also extended to develop a portable and paper-based sensing probe with good long-term stability to overcome the shortcomings of liquid-phase colorimetric sensors without requiring a spectrometer. The proposed colorimetric sensing probes provide accurate results even with a real sample and offer numerous advantages over conventional sensing platforms, including clearly distinguishable color changes that can be observed by the naked eye; thus, the proposed probes can be used for the selective, reliable, and low-cost point-of-care detection of Cu(II) ions in water.

Demonstration of graphene-assisted tunable surface plasmonic resonance sensor using machine learning model

Demonstration of graphene-assisted tunable surface plasmonic resonance sensor using machine learning model

Facile Preparation of Monodisperse Silver Nanorods with Tunable Plasmon Resonances in the Near-Infrared Region: Implications for SERS-Based Sensing

The facile synthesis of silver nanorods with uniform size and tunable localized surface plasmon resonances is of great significance for plasmon resonance-related applications, such as surface-enhanced Raman spectroscopy (SERS)-based sensing, biomedical diagnostics, and photothermal therapy. However, improving reproducibility is difficult for nonexpert researchers since general synthesis methods involve multiple steps. Addressing this issue, this work develops a facile, effective synthetic strategy for monodisperse silver nanorods with tunable plasmon resonance in the near-infrared region assisted by in situ monitoring via an optical microfiber in the seed formation stage and surfactant-assisted purification of the final product. The optical microfiber monitoring ensures the formation of monodisperse bipyramid templates, guaranteeing the synthesis of the final product. The surfactant-assisted purification of the final product ensures the monodispersity of the final Ag nanorods. This study provides a flexible and alternative approach for nonexpert researchers and may present an opportunity for solving the reproducibility problem faced by nanomaterial synthesis.

Hot Spot Engineering in Hierarchical Plasmonic Nanostructures

The controllable nanogap structures offer an effective way to obtain strong and tunable localized surface plasmon resonance (LSPR). A novel hierarchical plasmonic nanostructure (HPN) is created by incorporating a rotating coordinate system into colloidal lithography. In this nanostructure, the hot spot density is increased drastically by the long-range ordered morphology with discrete metal islands filled in the structural units. Based on the Volmer-Weber growth theory, the precise HPN growth model is established, which guides the hot spot engineering for improved LSPR tunability and strong field enhancement. The hot spot engineering strategy is examined by the application of HPNs as the surface-enhanced Raman spectroscopy (SERS) substrate. It is universally suitable for various SERS characterization excited at different wavelengths. Based on the HPN and hot spot engineering strategy, single-molecule level detection and long-range mapping can be realized simultaneously. In that sense, it offers a great platform and guides the future design for various LSPR applications like surface-enhanced spectra, biosensing, and photocatalysis.

High‐Performance Hydrogel SERS Chips with Tunable Localized Surface Plasmon Resonance for Coordinated Electromagnetic Enhancement with Chemical Enhancement

AbstractHydrogel surface‐enhanced Raman scattering (SERS) chips with tunable localized surface plasmon resonance (LSPR) wavelength are prepared to coordinate the chemical enhancement (CM) and electromagnetic enhancement (EM) effects for molecules. When detecting different molecules, a laser with matched energy is selected according to energy intervals between the molecular energy levels and the Fermi level of Ag nanoparticles to obtain the strongest CM effect. Meanwhile, a hydrogel SERS chip with the LSPR wavelength matching with the laser is selected to gain the strongest EM effect. As a result, the constructed hydrogel SERS chips show outstanding activity to many molecules. Amoxicillin, pymetrozine, and chlorpyrifos are used as the model molecules to demonstrate the great importance of CM effect and the working principle of the obtained hydrogel SERS chips. Besides the ultrahigh activity, the obtained hydrogel SERS chips also show high uniformity, long‐term stability, and strong anti‐interference to the sample matrix, and thereby are highly practical. This work not only provides an efficient strategy for building high‐performance SERS substrates, but also sheds the light on the mechanism of wave selection of SERS.