Plasmon Resonance Wavelength Research Articles

Direct Observation of In-Focus Plasmonic Cargos via Breaking Angular Degeneracy in Differential Interference Contrast Microscopy.

Breaking the angular degeneracy arising from the 2-fold optical symmetry of plasmonic anisotropic nanoprobes is critical in biological studies. In this study, we propose differential interference contrast (DIC) microscopy-based focused orientation and position imaging (dFOPI) to break the angular degeneracy of single gold nanorods (AuNRs). Single in-focus AuNRs (39 nm × 123 nm) within a spherical mesoporous silica shell were characterized with high throughput and produced distinct doughnut-shaped DIC image patterns featuring two lobes in the peripheral region, attributed to the scattering contribution of the AuNRs with large scattering cross sections. Interestingly, rotation of the lobes was observed in the focal plane for a large AuNR (>100 nm) tilted by more than ∼20° from the horizontal plane as the rotational stage was moved by 10° in a rotational study. From the rotation-dependent characteristic patterns, we directly visualized counterclockwise/clockwise rotations without the angular degeneracy at the localized surface plasmon resonance wavelength. Therefore, our dFOPI method can be applied for in vivo studies of important biological systems. To validate this claim, we tracked the three-dimensional rotational behavior of transferrin-modified in-focus AuNRs during clathrin-mediated endocytosis in real time without sacrificing the temporal and spatial resolution. In the invagination and scission stage, one or two directed twist motions of the AuNR cargos detached the AuNR-containing vesicles from the cell membrane. Furthermore, the dFOPI method directly visualized and revealed the right-handed twisting action along the dynamin helix in dynamin-catalyzed fission in live cells.

Fabrication of Plasmonic Microcubes by Laser Ablation of Au‐Nanoparticles‐Loaded Acrylate

The fabrication of plasmonic 3D microstructures is still a challenge. In this study, the fabrication of gold‐nanoparticle (Au‐NP)‐filled acrylate‐based micron‐scale cuboids forming plasmonic 3D particles is investigated. UV curable acrylate is mixed with HAuCl4 and spin‐coated onto a fused silica wafer. UV light and heat treatment of the layer result in polymerization of the acrylate and formation of Au‐NPs with a plasmonic resonance ranging from 535 to 550 nm. The plasmonic resonance wavelength decreases slightly with increasing UV dose. The resonance wavelength can be shifted by a subsequent annealing process. The decreasing resonance wavelength with increasing annealing temperature is discussed as a result of the increasing Au‐NPs. The size and the distribution of the resulting gold particles in the acrylate matrix is investigated by transmission electron microscopy. The Au‐NPs‐filled acrylate layer is laser structured using a UV‐femtosecond laser, which allows the fabrication of adjustable micro‐cuboids with edge lengths down to 15 μm. The laser‐cut micro‐cuboids are transferred into isopropanol and the plasmonic properties of the structures in the liquid are successfully demonstrated. The presented concept allows easy and large‐scale fabrication of plasmonic microstructures with independently adjustable plasmonic properties and microstructural size and shape.

Effect of Geometric Parameters of Metallic Nanoprisms on the Plasmonic Resonance Wavelength

Effect of Geometric Parameters of Metallic Nanoprisms on the Plasmonic Resonance Wavelength

Mechanical Enhancement of the Strain‐Sensor Response in Dimers of Strongly Coupled Plasmonic Nanoparticles

AbstractDue to their particular optical and mechanical properties, plasmomechanical devices have become choice candidates in strain sensing applications. Using numerical simulation, a plasmomechanical system consisting of two gold nanoparticles with different shapes and separated by a small gap, deposited onto a deformable polydimethylsiloxane membrane, is investigated. With the aim of understanding the relationship between the plasmonic behavior of gold nanoparticles and induced mechanical deformations, mechanical extension ranging from 0% to 20% is applied to the polydimethylsiloxane membrane. In a first step, a mechanical calculation based on a hyperelastic model for polydimethylsiloxane shows that the interparticle spacing is enhanced nonlinearly by a percentage greater than the externally applied deformation, depending on the shape and size of the nanoparticles as well as the polydimethylsiloxane membrane thickness. Full optical simulation of the deformed nanosystems demonstrates that the plasmonic resonance wavelength is highly sensitive to the applied displacements and is enhanced compared to a basic approach where the gap deformation is taken as equal to the macroscopic applied deformation. The best figure of merit () is obtained for the disk–rod dimer near the strong coupling regime, larger than the values reported in the literature for localized nanoparticle systems.

Controlling Plasmon Resonance of Gold and Silver Nanoparticle Arrays with Help of Liquid Crystal

The tunability of plasmonic resonances in gold and silver nanosphere arrays on a glass substrate, embedded in a liquid crystal matrix, was explored. The calculations involving the finite element method revealed that the optical properties of these arrays can be modulated by reorienting the liquid crystal. When the liquid crystal director was reoriented between planar and homeotropic configurations in the plane containing the incident wave polarization vector, the plasmonic resonance wavelength shifted within an approximately 100 nm range. A reduced shift of about 40 nm was observed when the reorientation occurred in the plane perpendicular to the polarization. Both metal nanosphere arrays showed notable near-field amplification. Gold achieved up to 18 times the amplification of the incident wave electric field, while silver reached 16 times but showed a remarkable 40 times amplification at the inter-band transition resonance wavelength. This research underscores the potential of using liquid crystal reorientation for controlling the plasmonic lattice resonance in metal nanosphere arrays, opening up new possibilities for adaptable plasmonic devices.

Numerical study of a D-shaped optical fiber SPR biosensor for monitoring refractive index variations in biological tissue via a thin layer of gold coated with titanium dioxide

This study aims to explore the numerical analysis of the impact of integrating titanium oxide (TiO2) into a D-shaped optical fiber biosensor based on surface plasmon resonance (SPR). A thin layer of gold (Au) is applied to the flat section of the fiber, which is also coated with a thin layer of titanium dioxide (TiO2). The behavior and performance of the proposed biosensor for use in biological environments are evaluated using the finite element method (FEM). The optical response of SPR-based biosensors is highly dependent on the analyzed medium, enabling the detection of pathogenic cells and abnormalities in biological tissues. This provides high sensitivity and selectivity, as well as real-time detection accuracy and speed. In this study, the biosensor is incorporated into a biological medium with a refractive index that varies with wavelength. A series of simulations have been conducted to plot the spectra of transmissions, absorptions, and dielectric losses obtained in the output of the sensor instrument. From these spectra, the corresponding surface plasmon resonance (SPR) wavelength (λSPR) within the visible-near-infrared band can be determined. Taking into account the various parameters that influence plasmonic interactions, the biosensor's performance parameters, in particular sensitivity and refractive index resolution have been optimized. Our results show that the presence of the TiO2 layer improves the performance of the proposed sensor and offers the possibility of adjusting the resonance wavelength (λSPR). In addition, our proposed sensor can achieve a better resolution of 7.50×10-6[RIU] in 1.34-143 range of analyte refractive index, which notably exceeds that of current technologies. This opens up new prospects in the field of chemical and biological detection.

Influence of Au on the nucleation of Ag nanoparticles in GeO2-PbO glasses and characterization of their ultrafast third-order nonlinear responses within the plasmon resonance region

Germanate (GeO2-PbO) glasses doped with AgNO3 and co-doped with AgNO3 and Au2O3 were synthesized via melting-quenching technique. Silver nanoparticles were nucleated within the sample doped only with AgNO3 and its plasmon resonance was characterized. The influence of the addition of Au2O3 on the silver nanoparticles nucleation and on the spectroscopic properties of the produced composite materials were investigated using TEM, STEM and UV–Vis spectroscopy. Using the nonlinear ellipse rotation technique, the pure electronic contribution to the samples nonlinear refraction and absorption were characterized within the visible range, including the localized surface plasmon (LSP) resonance wavelength of the metallic nanoparticles. The real and imaginary parts of the third-order nonlinear susceptibility of the glass, composite samples and of the individual nanoparticles were also obtained. In addition, all-optical switching figures of merit of the samples were also calculated. From these results, the dispersion curves of the electronic contribution to the third-order susceptibility of the metallic nanoparticles were obtained and two figures of merit for all-optical switching of the composite materials were calculated. The studied samples are potential candidates for all-optical switching applications with exception to the one with the highest volume filling factor, whose linear and nonlinear absorption coefficients associated to the local field factor deplete the material performance around the LSP resonance wavelength. As far as we know nonlinear ellipse rotation technique was not used before to evaluate the influence of metallic nanoparticles on the nonlinear optical properties of glasses.

Silver-based SERS substrates fabricated using a 3D printed microfluidic device.

The detection of harmful chemicals in the environment and for food safety is a crucial requirement. While traditional techniques such as GC-MS and HPLC provide high sensitivity, they are expensive, time-consuming, and require skilled labor. Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical tool for detecting ultralow concentrations of chemical compounds and biomolecules. We present a reproducible method for producing Ag nanoparticles that can be used to create highly sensitive SERS substrates. A microfluidic device was employed to confine the precursor reagents within the droplets, resulting in Ag nanoparticles of uniform shape and size. The study investigates the effects of various synthesis conditions on the size distribution, dispersity, and localized surface plasmon resonance wavelength of the Ag nanoparticles. To create the SERS substrate, the as-synthesized Ag nanoparticles were assembled into a monolayer on a liquid/air interface and deposited onto a porous silicon array prepared through a metal-assisted chemical etching approach. By using the developed microfluidic device, enhancement factors of the Raman signal for rhodamine B (at 10-9 M) and melamine (at 10-7 M) of 8.59 × 106 and 8.21 × 103, respectively, were obtained. The detection limits for rhodamine B and melamine were estimated to be 1.94 × 10-10 M and 2.8 × 10-8 M with relative standard deviation values of 3.4% and 4.6%, respectively. The developed SERS substrate exhibits exceptional analytical performance and has the potential to be a valuable analytical tool for monitoring environmental contaminants.

Facile synthesis of silver-rhenium nanoparticles with plasmonic and mesoporous properties

Cetyltrimethylammonium bromide (CTAB) capped rhenium (Re0@CTA(aq)) NPs were prepared by using chemical reduction method at room temperature in aqueous solution. The resulting Re0@CTA(aq) sol was utilized as sacrificial template and silver ions (Ag+) for the synthesis of silver-rhenium bimetallic NPs (Ag0-Re0@CTA(aq)) under metal displacement galvanic cell reaction in aqueous solution with CTAB. Surface Plasmon resonance (SPR) band intensity and wavelength maxima of Plasmon band of Ag0-Re0@CTA(aq) depends on the concentration of CTAB. The Plasmon band was blue shifted from 434, 439, 519, 535, 465, and 445 nm, respectively, for 0.0, 0.75, 1.0, 1.25, 1.5, and 2.0 mM of CTAB. Oxidation states, crystalline nature, elemental composition, surface morphology, shape, size, and textural properties of as-prepared silver-rhenium were determined with X-ray photoelectron spectrometry (EDX), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and nitrogen adsorption-desorption isotherm (BET). Fourier transform infrared spectrometry (FTIR), 1H NMR, 13C NMR, and gas chromatography-mass spectrometry (GC-EIMS) analysis were used to establish the capping properties of CTAB. Application of FTIR, 1H NMR, 13C NMR and GC-EIMS analysis shows that the CTAB consistently remains adsorbed on Ag0-Os0 NPs. Optical properties of plasmonic nanomaterials can be tuned by using a suitable concentration of CTAB surfactant.

The plasmonic behaviours of gold nanoparticles with different thiol (n = 6, 10, 12) capping agents

The intense absorbance and scattering of incident light at the surface plasmon resonance wavelength of gold nanoparticles (AuNPs) is of paramount importance in its various and diverse applications. Being governed by their morphologies and surface chemistry, the optical property of AuNPs can be tuned to suit variety of applications by careful and systematic engineering of the particle surface. Among other variables, the nature of the ligands or capping agents employed and their concentrations play vital roles. Three different alkanethiols, namely 1-dodecanethiol (DDT), 1-decanethiol (DT) and 1-hexanethiol (HT) were investigated as capping agents in different concentration of gold/thiol ([Au]/[Thiol]) ratios of 7:1, 5:1, 3:1, 1:1, 1:3 and 1:5. First, the AuNPs with average particle sizes of 2 nm and characterised by 1H NMR, UV–visible, and TEM. The 1H NMR confirmed the capping of gold nanoparticles by the thiol. The TEM image confirmed the monodispersity of the nanoparticles with average size distributions of 2.4 nm, and plasmon absorption wavelength peaks at 505 nm was confirmed by the UV. There were variations in the values of the plasmonic peaks with the nature and concentrations of the capping agents.

Chiral metasurfaces of wavy rectangle resonators with tunable circular dichroism

Chiral metasurfaces operating at the mid-infrared frequencies are of great interest for chiral molecule vibrational sensing and other applications. Here, mid-infrared chiral metasurfaces of wavy rectangle resonators with strong chiroptical response and tunable circular dichroism (CD) are demonstrated. The chiral metasurface exhibits a high CD value of more than 0.57 as the chiral plasmonic resonance wavelength is tuned from 4.96 to 5.82 µm by enlarging the geometric dimensions of the unit cell. Furthermore, CD values can be continuously tuned from positive to zero and negative without altering the chiral plasmonic resonance wavelength, by simply relocating the cutting slot to change the geometric symmetry of the wavy rectangle structure. These results aim to advance the development of many promising applications in mid-infrared frequencies including protein molecule detection, thermal emission control, and infrared-light communication.

Symmetry-Breaking Effects of Near-Infrared II Thermoplasmonics of Gold–Silica–Cuprous Selenide Hybrid Nanoshells

This study presents a numerical investigation of the plasmonic and photothermal properties of Au-silica-Cu2–xSe hybrid nanoshells (Cu2–xSe HNSs) consisting of a silica-Cu2–xSe core–shell nanoshell embedded with a spherical Au core at varied core offsets. The plasmon modes in the symmetry-broken Cu2–xSe HNSs are explained by plasmon hybridization theory in combination with charge density distribution. Results unveil that the hybridized plasmon modes in a symmetry-broken Cu2–xSe HNS arise from the interaction of the primitive plasmon modes of the same angular momentum on the Au core and the Cu2–xSe nanoshell. An increase in the core offset redshifts and weakens the near-infrared II (NIR-II) plasmon band corresponding to the low-energy bonding dipolar mode but redshifts and enhances the low-energy bonding quadrupolar mode. At the NIR-II plasmon resonance wavelengths, the temperature increase distribution is uniform on the Au core but inhomogeneous on the Cu2–xSe nanoshell. The variation of the temperature increase with the core offset suggests spectral tunability of NIR-II thermoplasmonic properties in the Cu2–xSe HNSs through varying the core offset. Our work provides a paradigm for rational design of NIR-II plasmonic materials with optimal photothermal performances for in vivo biomedical applications through symmetry breaking.

A Review on Silver Nanoparticles

Nanoparticles are defined as particulate dispersions or solid particles with a size between 10 and 1000 nm. A one billionth of a metre scale is the simplest unit of measurement for nanotechnology. Silver nanoparticles superiority over silver in bulk forms is primarily due to the size, shape, composition, crystallinity, and structure of AgNPs. Silver nanoparticles synthesis can be achieved by physical, chemical and green methods. Evaporation-condensation and laser ablation processes are used in the physical synthesis of silver nanoparticle. Evaporation-condensation has been used to create a number of metal nanoparticles in the past, including fullerene, lead sulphide, cadmium sulphide, gold, and silver. Chemical reduction, photo-induced reduction, micro-emulsion, microwave-assisted synthesis, UV-initiated photo-reduction, electrochemical synthetic technique, and irradiation procedures are some of the chemical processes utilised to create nanoparticles. The temperature, pH, concentration, type of precursor, reducing and stabilising agents, and the molar ratio of surfactant and precursor are some of the reaction parameters that control how NPs form and grow in the chemical method. Utilizing biological organisms like bacteria, mould, algae, and plants allows for one-step synthesis. Proteins and enzymes found in plants and microbes are used in the reduction process to create nanoparticles. Silver nanoparticles function as nanoscale antennas at the plasmon resonant wavelength, boosting the strength of a nearby electromagnetic field. Raman spectroscopy, which uses molecules distinctive vibrational modes to identify them, is one spectroscopic method that benefits from the strengthened electromagnetic field. The plasmonic Au/Ag hollow-shelled NIR SERS probes were put together on silica nanospheres, which showed a redshift in the plasmonic extinction band in the NIR optical window region (700–900 nm). Animal tissues that were 8 mm deep showed a measurable signal in the NIR-SERS nanoprobe signals for single particle detection. Silver nanoparticles size-tunable absorption spectra can be used to multiplex optical attributes for point-of-care diagnostics. Silver nanoparticles have antimicrobial, anti-neoplastic, antioxidant, and antidiabetic activity. Silver nanoparticles also shows some kind of toxicity like Oral toxicity, Immunotoxicity, Neurotoxicity, Environmental toxicity, Reproductive toxicity etc.

Fluorescence Evolution of Gold Nanoclusters in the Presence of Shapely Silver Nanoparticles and UV-Vis Light

Gold nanoclusters (Au NCs) belong to a class of materials that is highly fluorescent and biocompatible. Bovine serum albumin (BSA) protected gold nanoclusters (BSA-Au NCs) have been extensively used in biological applications due to their easy synthesis and relatively high quantum yield. Therefore, understanding the behavior of BSA-Au NCs in different chemical and physical environments is essential to enhance their application in biological systems. In this study, we investigated the effect of plasmonic nanostructures with different localized surface plasmon resonance (LSPR) wavelengths on the behavior of BSA-Au NCs by recording time-dependent fluorescence spectra in the presence of silver nanoparticles (AgNPs) with various shapes. However, we did not observe any conclusive LSPR-wavelength-dependent fluorescent behavior. Additionally, the fluorescence intensity of BSA-Au NCs exhibited gradual decay under light excitation, even at several hundred μW/cm2 in a fluorescence spectrometer, indicating that they are not as photostable as previously assumed. We found further that the photostability of BSA-Au NCs is affected by the wavelength of the incident light (370, 420, 480, and 550 nm), which can be accurately described using bi-exponential decay functions. Our study provides an easy in situ method to evaluate the photostability of Au NCs under different-wavelength light irradiation using a commercial fluorescence spectrometer.

Plasmonic dual-parameter optical fiber sensor for cortisol and glucose detection

The concentration of cortisol in the human body is related to health. Research has shown that the cortisol level in the body correlates with glucose. Therefore, simultaneously and sensitively measuring cortisol and glucose levels is very important for diabetic patients. A combination of biomolecules and metal nanoparticle surfaces can change the refractive index and induce a shift in the surface plasmon resonance (SPR) wavelength. Therefore, a sensor for cortisol and glucose detection is designed and fabricated. The logarithmic sensitivity of cortisol and glucose concentrations reach 5.267 nm/log(ng ml-1) and 9.878 nm/log(mM), respectively. The limits of detection (LODs) for the cortisol and glucose concentrations reach 0.0126 ng ml-1 and 1.136 × 10−3 mM respectively. The detection range covers a concentration variation range of human saliva. The proposed sensor has a compact structure. In this work, it is proven that the sensor has good specificity and selectivity through experiments, and the technical methods of the sensor can be extended to applications in medical, biological and environmental detection.

Seed-mediated synthesis of gold nanorods by using dopamine as the weak reducing agent in a binary surfactant mixture

Gold nanorods were prepared by using a modified seed-mediated wet chemical growth method at reduced concentrations of hexadecyltrimethylammonium bromide and sodium oleate. The weak reducing agent used in the growth solution was dopamine. Gold nanorods with longitudinal surface plasmon resonance wavelength ranging from 780 to 1115 nm were obtained by varying the amounts of hexadecyltrimethylammonium bromide, silver nitrate, and hydrochloric acid in the growth solution. Moreover, the photothermal properties of the gold nanorods at 1064 nm were studied, indicating the potential applications of gold nanorods as photothermal agents in the second near-infrared window.

Flexible tuning of the peak wavelength and intensity of localized surface plasmon resonance by heat treatment of nanodisk structures fabricated by electron beam lithography

We demonstrate that the plasmonic properties of Au nanodisk structures fabricated by an electron beam lithography can be improved by very simple heat treatments, and that the resonance wavelength can be tuned by temperature. With a Ni adhesion layer, the resonance peak increased and blue-shifted due to improvement of metal quality without changing the sizes of nanostructures, while without the adhesion layer, the resonance wavelength can be tuned over a wider wavelength range by intentionally reducing the size of nanostructures through annealing. For Ag nanodisks with the adhesive layer, the plasmon resonance wavelength was blue-shifted due to the size reduction of nanodisks through thermal annealing. Full-color tuning of plasmonic resonance should be possible by controlling the diameter and height of Ag nanodisks under appropriate temperature conditions of heat treatment.

Dual enzyme induced colorimetric sensor for simultaneous identifying multiple pathogens

Rapid and accurate identification of foodborne pathogens improves public health. Currently employed methods are time-consuming, sensitive to environmental factors, and complex. This study develops a colorimetric sensor for detecting multiple bacteria with one probe using double-enzyme-induced colorimetry. Based on alkaline phosphatase (ALP) in bacteria decomposes L-ascorbic acid 2-magnesium phosphate salt hydrate into ascorbic acid (AA). Manganese dioxide flowers (MnO2 NFs) can oxidize TMB to etch gold nanorods (Au NRs), which can be inhibited by AA reduction to produce rich colors. Bacteria with varying ALP levels can be identified based on color changes and plasmon resonance wavelength signals produced from Au NRs. Furthermore, the conversion of RGB signals to digital signals and the use of linear discriminant analysis (LDA) allowed 99.57% accuracy in identifying multiple bacteria. It can simultaneously identify five foodborne pathogens across diverse environments (shrimp, meat, milk, etc.). This method may be useful for the rapid and simple identification of foodborne illnesses.

Quantitative Analysis of the Shape Effect of Thermoplasmonics in Gold Nanostructures.

The shape effect of thermoplasmonic properties of Au nanostructures remains largely unexplored. Herein, we report a systematic investigation on the photothermal effects of Au nanoparticles (NPs) of different shapes: nanosphere, nanocube, nanorod, nanostar, and nanobipyramid. The Joule (Jo) number (absorption cross section normalized by the particulate volume) is utilized for quantitatively assessing the photothermal properties of these different shaped Au NPs. It is shown that the Jo number of Au NPs greatly varies with the geometric shape and localized surface plasmon resonance (LSPR) wavelength. Specifically, the Jo number decreases with the red-shifting of the LSPR wavelength in these Au NPs, and the Au NPs of sharp structural features such as Au nanorod, nanostar and nanobipyramid have a much larger Jo number, indicative of their exceptional light-to-heat conversion ability. We further demonstrate the close correlation of the Jo number of Au NPs of different shapes with their optical absorption power density.

Evolutionary Plasmonic Properties of Single Truncated Ag Nanowire-on-Au Film Nanocavity

Noble metal nanocavities have been widely demonstrated to possess great potential applications in nano-optics and nanophotonics due to their extraordinary localized surface plasmon resonance. However, most metal nanocrystals synthesized by chemical methods often suffer from truncation with different degrees due to oxidation and dissolution of metal atoms at corner and edges. We investigate the influence of shape truncation on the plasmonic properties of single Ag nanowire on Au film nanocavity using the finite difference time domain method. When the Ag nanowire (the circumradius R 2 = 50 nm) is gradually truncated from pentagonal to circular geometry, the scattering peak position of the nanocavity shows prominent blue shift from 962 nm to 608 nm, suggesting a nonnegligible role of truncation on plasmonic properties. The electric field strength and charge distribution of the structure reveal the evolution from dipole mode to quadrupole mode. It is also found that the plasmon resonance wavelength is linearly dependent on the truncation ratio R 1/R 2 (R 1 is the inradius) and the modulation slope is also reliable to the size of Ag nanowire. Our observations could shed light on developing high-performance tunable optical nano-devices in future.