Tunable Surface Plasmon Resonance Research Articles

Fabrication of nanoparticles with precisely controllable plasmonic properties as tools for biomedical applications.

Metal nanoparticles are established tools for biomedical applications due to their unique optical properties, primarily attributed to localized surface plasmon resonances. They show distinct optical characteristics, such as high extinction cross-sections and resonances at specific wavelengths, which are tunable across the wavelength spectrum by modifying the nanoparticle geometry. These attributes make metal nanoparticles highly valuable for sensing and imaging in biology and medicine. However, their widespread adoption is hindered due to challenges in consistent and accurate nanoparticle fabrication and functionality as well as due to nanotoxicological concerns, including cell damage, DNA damage, and unregulated cell signaling. In this study, we present a fabrication approach using nanoimprint lithography in combination with thin film deposition which yields highly homogenous nanoparticles in size, shape and optical properties with standard deviations of the main geometry parameters of less than 5% batch-to-batch variation. The measured optical properties closely match performed simulations, indicating that pre-experimental modelling can effectively guide the design of nanoparticles with tailored optical properties. Our approach also enables nanoparticle transfer to solution. Particularly, we show that the surface coating with a PEG polymer shell ensures stable dispersions in buffer solutions and complex cell media for at least 7 days. Furthermore, our in vitro experiments demonstrate that these nanoparticles are internalized by cells via endocytosis, exhibit good biocompatibility, and show minor cytotoxicity, as evidenced by high cell viability. In the future, our high-precision nanoparticle fabrication method together with tunable surface plasmon resonance and reduced nanotoxicity will offer the possibility to replace conventional nanomaterials for biomedical applications that make use of an optical response at precise wavelengths. This includes the use of the nanoparticles as contrast agents for imaging, as probes for targeted photothermal cancer therapy, as carriers for controlled drug delivery, or as probes for sensing applications based on optical detection principles.

Intervalence plasmons in boron-doped diamond

Doped semiconductors can exhibit metallic-like properties ranging from superconductivity to tunable localized surface plasmon resonances. Diamond is a wide-bandgap semiconductor that is rendered electronically active by incorporating a hole dopant, boron. While the effects of boron doping on the electronic band structure of diamond are well-studied, any link between charge carriers and plasmons has never been shown. Here, we report intervalence plasmons in boron-doped diamond, defined as collective electronic excitations between the valence subbands, opened up by the presence of holes. Evidence for these low-energy excitations is provided by valence electron energy loss spectroscopy and near-field infrared spectroscopy. The measured spectra are subsequently reproduced by first-principles calculations based on the contribution of intervalence band transitions to the dielectric function. Our calculations also reveal that the real part of the dielectric function exhibits a crossover characteristic of metallicity. These results suggest a new mechanism for inducing plasmon-like behavior in doped semiconductors, and the possibility of attaining such properties in diamond, a key emerging material for quantum information technologies.

Deposition of plasmonic ITO nanoparticles by near-infrared laser ablation

Compound nanoparticles (NPs) attract attention because of their unique electrical, optical, and catalytic properties. Among them, plasmonic tin-doped indium oxide (ITO) NPs are characterized by transparency in the visible wavelength range and tunable localized surface plasmon resonance (LSPR) in the near-infrared (NIR) range due to high electronic conductivity. To date, they have been usually synthesized by a chemical solution process. However, the chemically synthesized ITO NPs are capped with organic protecting agents, which often block exchange of charge carriers and access of chemical species to the NPs, limiting some applications. In the present study, we propose a method for direct deposition of ITO NPs on a glass or plastic substrate using commercially available ITO-coated glass via NIR laser ablation. The LSPR characteristics of the ITO NPs, thus, prepared were controlled by changing the ablation conditions such as laser power. In addition, the potential applications of the ITO NPs were also investigated through measurements of their refractive index sensitivity and magnetic circular dichroism.

Tunable localized surface plasmon resonance absorption in silver-based nanoplasmonics

Tunable localized surface plasmon resonance absorption in silver-based nanoplasmonics

Investigating SERS performance of controllable fabricated Ag periodic nanostructures with morphologies of nanoclaws and nanocones in detecting SARS-CoV-2 S protein

Surface-enhanced Raman scattering (SERS) spectroscopy plays an important role in enabling high-precision detection and non-invasive diagnostics. Periodic metallic nanostructures with strong electromagnetic fields and tunable localized surface plasmon resonance can achieve high SERS sensitivity, but fabricating such nanostructures remains a challenge. In this work, the anodic aluminum oxide (AAO) nanocavity template-assisted process of fabricating periodic nanostructures with modulating morphologies from Ag nanoclaws (AgNCWs) to Ag nanocones (AgNCEs) is proposed. The morphologies-related SERS performances of nanostructures are analyzed by using rhodamine 6 g (R6G) as a probe molecule and the optimized AgNCEs possess a limit of detection (LOD) of 1 × 10−9 M. A sandwich strategy is applied to detect SARS-CoV-2 S protein in phosphate-buffered saline (PBS) and pharyngeal swab solution (PSS). The ACE2-modified AgNCEs (ACE2/AgNCEs) structure is applied to bind to the SARS-CoV-2 S protein. The 4-MBA and SARS-CoV-2 S antibody functionalized Au nanoparticles (AuNPs) are used as nanotags. By forming the ACE2/AgNCEs-SARS-CoV-2 S protein-nanotags sandwich structure, characteristic peak intensities of 1580 cm−1 are used as the report signal, and the LOD for SARS-CoV-2 S protein in PBS and PSS solution are 10 fg/mL.

Design and Optimization of Encoded and Tunable Graphene-Silver Metasurface Surface Plasmon Resonance Sensor for Detection of Low Refractive Index Variation in Terahertz Regime

Design and Optimization of Encoded and Tunable Graphene-Silver Metasurface Surface Plasmon Resonance Sensor for Detection of Low Refractive Index Variation in Terahertz Regime

Surface Modification of Gold Nanorods: Multifunctional Strategies and Application Prospects.

Gold nanorods (AuNRs), as an important type of gold nanomaterials, have attracted much attention in the nano field. Compared with gold nanoparticls, AuNRs have broader application potential due to their tunable localized surface plasmon resonance properties and anisotropic shapes. Yet, conventional synthesis methods using surfactants have limited the use of AuNRs in a variety of fields such as biomedical applications, plasma-enhanced fluorescence, optics and optoelectronic devices. To solve this problem and improve the stability and biocompatibility of AuNRs, researchers in recent years have used surface modification and functionalization to modify AuNRs, among which the introduction of organic ligands to prepare organic/gold hybrid nanorods has become an effective strategy. Organic materials have better toughness and easy processing, and by introducing organic ligands into the surface of AuNRs, the molecular-level composite of organic and inorganic materials can be realized, thus obtaining hybrid nanorods with excellent properties. This paper reviews the research progress of hybrid nanocomposites, and introducing the synthesis methods of AuNRs and the development of surface ligand modification, then summarises the applications of a wide variety of ligands. Also, the advantages and disadvantages of different ligands and their roles in further self-assembly processes are discussed.

Seed‐Mediated Synthesis of Gold Nanobipyramids at Low CTAB Concentration Using Binary Surfactants

AbstractThe conventional method for synthesizing gold nanobipyramids (AuNBPs) is well established. However, the cytotoxicity resulting from the conjugates between hexadecyltrimethylammonium bromide (CTAB) and gold limits their biomedical applications. This study introduces a dual surfactant approach with CTAB and sodium oleate (NaOL) in the seed‐mediated synthesis of the AuNBPs, which can significantly reduce the CTAB concentration to 10 mM. Additionally, optimal growth conditions are achieved by varying the volumes of seed solution, AgNO3, and HCl. Under low CTAB concentrations, AuNBPs with tunable sizes and localized surface plasmon resonances between 600 and 1200 nm are successfully synthesized, as characterized by UV–vis‐NIR spectroscopy, transmission electron microscopy (TEM), and finite‐difference time‐domain (FDTD) simulations. This work demonstrates a method for synthesizing AuNBPs at low CTAB concentrations using binary surfactants and provides a framework applicable to the synthesis of other metallic nanomaterials.

Design of Encoded and Tunable Graphene-Gold Metasurface-Based Surface Plasmon Resonance Sensors for Glucose Detection in the Terahertz Regime

Design of Encoded and Tunable Graphene-Gold Metasurface-Based Surface Plasmon Resonance Sensors for Glucose Detection in the Terahertz Regime

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±0.4 nm) 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±2 nm, 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 allows effective nanorod elongation with tunable surface plasmon resonance beyond 1000 nm and CTAB-free functional coating for mTHPC conjugation.

Gold nanorods with small dimensions demonstrate better cellular uptake and absorption efficiency. The ability to synthesize gold nanorods while maintaining a tunable high aspect ratio is challenging as it requires careful control of reaction conditions, often employing additional steps such as pH modification or the use of polymeric additives. We demonstrate a seedless approach for the synthesis of mini (width < 10 nm) gold nanorods with tunable longitudinal surface plasmon resonance from ∼700 nm to >1000 nm and aspect ratios ranging from ∼3 to ∼7 without the use of any polymeric additives or pH modification. A single mild reducing agent, hydroquinone, allowed for up to ∼98% reaction yield from a gold precursor. A mechanism for elongation is proposed based on partial silver decoupling from the reaction. Finally, the particles were coated with various capping agents to allow functionalization and conjugation of mTHPC drug molecules, which are used in photodynamic treatments, and cytotoxic CTAB was removed to increase their biocompatibility.

Hyaluronic Acid-Modified and Doxorubicin-Loaded Au Nanorings for Dual-Responsive and Dual-Imaging Guided Targeted Synergistic Photothermal Chemotherapy Against Pancreatic Carcinoma.

Pancreatic carcinoma (PC) is a highly malignant digestive tumor. Nanotechnology-based minimally invasive techniques have been proposed to provide a new opportunity for PC treatment. A minimally invasive nanoplatform (named HA/DOX-AuNRs) is fabricated by HA modifying and DOX loading Au nanorings (AuNR). Because of their complicated geometric structure and tunable localized surface plasmon resonance peak in the second near-infrared laser window (NIR-II window), HA/DOX-AuNRs exhibit fluorescence/photoacoustic and photothermal properties, dual-responsive DOX release, and tumor-targeting ability. HA/DOX-AuNRs are expected to improve the tumor therapeutic efficiency and reduce undesirable side effects through fluorescence/photoacoustic dual-imaging guided targeted synergetic photothermal chemotherapy under NIR-II irradiation. The morphological and physicochemical properties of HA/DOX-AuNRs are well-examined at first. The cytotoxicity, cellular uptake, and in vitro therapeutic effect of fluorescence/photoacoustic dual-imaging guided targeted synergetic photothermal chemotherapy are evaluated in Panc-1 cells. The in vivo biodistribution, anticancer effects, and systemic toxicity are investigated using PC xenograft models. HA/DOX-AuNRs significantly improve the therapeutic efficacy in a dual-responsive and dual-imaging guided targeted synergy.

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.