Surface Plasmon Resonance Absorption Band Research Articles

Gold nanoprism-nanorod face off: comparing the heating efficiency, cellular internalization and thermoablation capacity.

This work compares the synthesis, heating capability, cellular internalization and thermoablation capacity of two different types of anisotropic gold nanoparticles: gold nanorods (NRs) and nanoprisms (NPrs). Both particles possess surface plasmon resonance absorption bands in the near-IR, and their heating efficiency upon irradiation with a continuous near-IR laser (1064 nm) was evaluated. The cellular internalization, location and toxicity of these PEG-stabilized NPrs and NRs were then assessed in the Vero cell line by transmission electron microscopy and inductively coupled plasma mass spectrometry analysis, and their ability to induce cell death upon laser irradiation was then evaluated and compared. Although both nanoparticles are highly efficient photothermal converters, NRs possessed a more efficient heating capability, yet the in vitro thermoablation studies clearly demonstrated that NPrs were more effective at inducing cell death through photothermal ablation due to their greater cellular internalization.

Spectroscopic study of silver halides in montmorillonite and their antibacterial activity

In this study silver halides (AgX, X=Cl, Br, I) in montmorillonite (MMT) were prepared by dispersion method in dark. AgNO3 was used as a silver precursor. The nanocomposites (NCs) (AgX-MMT) were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and ultraviolet-visible diffuse reflectance spectroscopy (DRS). The powder X-ray diffraction showed intercalation of AgCl and AgBr nanoparticles (NPs) into the clay interlayer space. The diffuse reflectance spectra indicated a broad surface plasmon resonance (SPR) absorption band in the visible region for AgCl-MMT and AgBr-MMT NCs, resulting of metallic Ag nanoparticles (Ag NPs). But the results were opposite in case of AgI-MMT NC. The antibacterial activity of NCs was investigated against Gram-positive bacteria, i.e., Staphylococcus aureus and Micrococcus luteus and Gram-negative bacteria, i.e., Escherichia coli, Pseudomonas aeruginosa, by the well diffusion method. The antibacterial effects on Staphylococcus aureus, Micrococcus luteus and Escherichia coli decrease in the order: AgCl-MMT>AgBr-MMT>AgI-MMT. No antibacterial activity was detected for Pseudomonas aeruginosa.

Dithiocarbamate-calix[4]arene functionalized gold nanoparticles as a selective and sensitive colorimetric probe for assay of metsulfuron-methyl herbicide via non-covalent interactions

In this work, a distinct demonstration of sensitive and selective colorimetric detection of metsulfuron-methyl herbicide in real samples was carried out using dithiocarbamate-p-tertbutylcalix[4]arene capped Au NPs (DTC-PTBCA-Au NPs) as a probe via host-guest (non-covalent) interactions. A careful optimization of all potential factors, the performance of the probe was successfully applied to detect metsulfuron-methyl in real samples with unique features including high selectivity, and assay with minimal volume of samples. Metsulfuron-methyl induces the aggregation of DTC-PTBCA-Au NPs via host-guest interaction, resulting red-shift in the surface plasmon resonance (SPR) absorption band accompanied by color changes which could be distinguished by the naked-eye. There is a good linearity with metsulfuron-methyl in the range of 1.0–50μM, with a detection limit of 1.9×10−7M (S/N=3). The DTC-PTBCA-Au NPs showed selective sensing performance towards metsulfuron-methyl over other herbicides, insecticides and fungicides. The percentage recovery obtained by the proposed method in real-world examples such as environmental water and food samples were 97–99% with relative standard deviation (RSD) <3%. The probe has been successfully used to detect metsulfuron-methyl in environmental water and food samples.

Facet-Dependent Optical and Photothermal Properties of Au@Ag–Cu2O Core–Shell Nanocrystals

This study examines the facet-dependent optical properties of size-tunable Ag–Cu2O core–shell nanocrystals with 38, 42, and 50 nm cubic Ag cores. The Ag cores were prepared from octahedral Au seeds. The Cu2O shells are single-crystalline. In the case of Au@Ag–Cu2O nanocrystals with 42 nm Ag cores, the Ag surface plasmon resonance (SPR) absorption band at 485 nm has been widely red-shifted to 730, 755, and 775 nm for rhombic dodecahedra, truncated octahedra, and cuboctahedra, respectively, after forming the Cu2O shells. The Ag SPR band positions are mostly fixed despite large changes in the shell thickness, showing the presence of facet-dependent optical properties. Because of the strong Ag SPR band absorption, all samples exhibit a better photothermal activity than that of Au–Cu2O nanocrystals. Facet-dependent heat transmission may be present for particles with a Ag SPR band much deviated from the laser wavelength, but this phenomenon is lost for particles with an SPR band approaching the excitation wavel...

Collective Surface Plasmon Resonances in Two-Dimensional Assemblies of Au and Ag Nanocrystals: Experiments and Discrete Dipole Approximation Simulation

The UV–visible absorption spectra of two-dimensional (2D) assemblies of Ag or Au nanocrystals (NCs) are measured in transmission at variable incidence angles for different average NC diameters ranging from 7.0 to 3.9 nm. The absorption spectra dominated by the collective surface plasmon resonance (SPR) absorption band are compared to those calculated using the discrete dipole approximation (DDA) method. The anisotropy of the optical response is inherent to the planar geometry of the NC assembly because of the near-field coupling between nanocrystals. For Ag NCs, the absorption spectra reveal the splitting of the SPR band into two components, namely, the transverse and longitudinal modes. At variance, no SPR band splitting is observed for 2D assemblies of Au NCs with identical size and coating agent. These features were satisfactorily reproduced by DDA simulation even though the SPR mode energies deduced from our calculations slightly overestimate the measured ones. The influence of the coating dodecanethi...

The green synthesis of Ag/ZnO in montmorillonite with enhanced photocatalytic activity

The Ag/ZnO-MMT nanocomposite was prepared using urtica dioica leaf extract. To improve the photocatalytic properties of ZnO-MMT nanocomposite, silver metal nanoparticles was deposited over nanocomposite. Zn(CH3COO)2, AgNO3 and Urtica dioica leaf extract were used as a zinc, silver precursor and reducing agent, respectively. The nanocomposite was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and ultraviolet-visible diffuse reflectance spectroscopy (DRS). The powder X-ray diffraction showed that Ag/ZnO nanoparticles located on the surface MMT layers. The diffuse reflectance spectra of nanocomposite indicated a strong surface plasmon resonance (SPR) absorption band in the visible region, resulting from metallic Ag nanoparticles. TEM image demonstrated the presence of silver nanoparticles with an average size of 2–4nm over both MMT and flower-shape ZnO. The photocatalytic activity of nanocomposite was studied for destructive reaction methylene blue dye under visible light. In addition, the effects of different parameters such as amount of nanocomposite, concentration of the dye and pH of the solution were studied. The results showed that modiffication of ZnO-MMT nanocomposite with silver nanoparticles increased the percentage of discoloration methylene blue (MB) from 38.95 to 91.95. MMT matrix showed an important role in the reduction of recombination of electron-hole in nanocomposite.

Application of Direct Current Atmospheric Pressure Glow Microdischarge Generated in Contact with a Flowing Liquid Solution for Synthesis of Au-Ag Core-Shell Nanoparticles.

A direct current atmospheric pressure glow microdischarge (dc-μAPGD) generated between an Ar nozzle microjet and a flowing liquid was applied to produce Au-Ag core-shell nanoparticles (Au@AgCSNPs) in a continuous flow system. Firstly, operating dc-μAPGD with the flowing solution of the Au(III) ions as the cathode, the Au nanoparticles (AuNPs) core was produced. Next, to produce the core-shell nanostructures, the collected AuNPs solution was immediately mixed with an AgNO3 solution and passed through the system with the reversed polarity to fabricate the Ag nanoshell on the AuNPs core. The formation of Au@AgCSNPs was confirmed using ultraviolet-visible (UV-Vis) absorbance spectrophotometry, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Three localized surface plasmon resonance absorption bands with wavelengths centered at 372, 546, and 675 nm were observed in the UV-Vis spectrum of Au@AgCSNPs, confirming the reduction of both the Au(III) and Ag(I) ions. The right configuration of metals in Au@AgCSNPs was evidenced by TEM. The Au core diameter was 10.2 ± 2.0 nm, while the thickness of the Ag nanoshell was 5.8 ± 1.8 nm. The elemental composition of the bimetallic nanoparticles was also confirmed by EDS. It is possible to obtain 90 mL of a solution containing Au@AgCSNPs per hour using the applied microdischarge system.

Green synthesis of Ag nanoparticles in montmorillonite

The Ag-MMT nanocomposite, was formed from AgNO3/MMT suspension. AgNO3 and Urtica dioica leaf extract were used as a silver precursor and reducing agent, respectively. The nanocomposite was characterized by x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and UV–vis spectroscopy. The XRD showed the intercalation of Ag nanoparticles (Ag NPs) into the clay interlayer space. The UV–vis indicated a strong surface plasmon resonance (SPR) absorption band in the UV region, resulting from metallic Ag NPs. The intensity of the SPR band increased with time in the AgNO3/MMT suspension. But the result was opposite in case of Ag+ solution. The stability of Ag NPs in MMT was more than the stability without support. These results showed that Ag NPs can be used as effective growth inhibitors in different biological systems.

Photothermal effects from Au–Cu2O core–shell nanocubes, octahedra, and nanobars with broad near-infrared absorption tunability

Other than the display of purely optical phenomenon, the recently-discovered facet-dependent optical properties of metal-Cu2O nanocrystals have become useful by illuminating Au-Cu2O nanocubes and octahedra having a surface plasmon resonance (SPR) absorption band in the near-infrared (NIR) region from octahedral Au cores with 808 nm light for heat generation. After 5 min of light irradiation, a solution of Au-Cu2O nanocubes can reach 65 °C with their Au SPR band matching the illuminating light wavelength. Photothermal efficiency has been found to be facet-dependent. In addition, short gold nanorods were employed to synthesize {100}-bound rectangular Au-Cu2O nanobars with a tunable longitudinal Au SPR absorption band covering a broad NIR range from ∼1050 to 1400 nm. Because the Au SPR bands can become fixed with relatively thin Cu2O shells of less than 15 nm, ultrasmall nanobars having a size of 61 nm directly red-shift the Au SPR band to 1047 nm. And 73 nm nanobars can give a Au SPR band at 1390 nm. Truncated nanobars exposing {100}, {110}, and {111} facets give a very blue-shifted Au SPR band. The nanobars also exhibit photothermal activity when illuminated by 1064 nm light. These small Au-Cu2O nanocrystals represent the simplest nanostructure design to absorb light covering the entire NIR wavelengths.

Influence of Different Percentages of Copper on the Size and Optical Properties of Ag-Cu Nanoparticles Formed by Wet-Chemical Method

In this work, Ag-Cu nanoparticles (with different percentages of copper, 10%, 25%, 50%, 75% Cu) were synthesized by wet chemical method. Copper(II) sulfate and silver nitrate were taken as metal precursors, ascorbic acid as reducing agent and anhydride maleic (MA) as a modifier. The prepared nanoparticles were characterized by means of X-ray diffraction (XRD) technique and scanning electron microscopy (SEM-EDAX), Fourier transform infrared spectroscopy (FT-IR) and UV-Vis spectroscopy. SEM indicated the formation of uniform spherical crystalline nanoparticle in a well distributed size and morphology. It can be seen from these pictures that the particle size decreased with increasing of the copper percent. When the molar ratio of Cu2+/Ag+ is 75/25 (>50%), mixture of the spherical and hexagonal nanoparticles was prepared. Three pronounced Ag diffraction peaks (111), (200) and (220) appeared at 2θ = 38°, 43.9° and 64.1°, respectively. The three most intense peaks of the XRD pattern of sample showed a slight shifting of the center of the diffraction peaks toward a lower angle. No shifting was observed in XRD lines with the increase of Cu2+ to Ag+ ratio in the Cu2+/Ag+ mixed solution (> 50% Cu). Fourier transform infrared spectroscopy (FT-IR) showed that nanoparticles are coordination between oxygen atoms and nanoparticles, because functional unit C=O present in MA, shifts to 1652.69 cm-1 after embedding nanoparticles. The position of the surface plasmon resonance (SPR) absorption band on the nanoparticles could be shifted from 380-350 nm via the change of their percentage of Cu.

Arsenazo III-functionalized gold nanoparticles for photometric determination of uranyl ion

Gold nanoparticles (AuNPs) were functionalized with the indicator dye Arsenazo III via reductive synthesis of AuNPs in the presence of arsenazo III. The indicator dye is shown to be immobilized on the AuNPs via interaction between gold and sulfo groups. The functionalized AuNPs undergo aggregation in the presence of uranyl ion due to the coordination interaction between arsenazo III and uranyl ion. This is accompanied by a longwave shift of the surface plasmon resonance absorption band (from 535 nm to 548 nm) and an up to 46.8 % increase in absorbance. This finding forms the basis for a photometric assay for uranyl ion. It shows good selectivity and has a 0.5 μM detection limit. Applied to the determination of uranyl ion in spiked environmental water samples, the recoveries were between 97 and 106 %.

Photochemical synthesis, characterization, photoinduced electron transfer, charging and discharging in copper-titania colloid

Abstract One of major goals in photocatalysis and photochemistry is to understand photoinduced charge transfer. Colloidal solutions serve as convenient model systems for mechanistic studies of charge transfer. For the first time, colloid Cu(0)-V O -TiO 2 was prepared by the “one-pot” photochemical synthesis from copper nitrate and titanium isopropoxide precursors in ethanol under UV–vis light. The Cu(0)-V O -TiO 2 colloid shows the surface plasmon resonance (SPR) absorption band of metallic copper and contains oxygen vacancy V O . Kinetics of the synthesis of Cu(0)-V O -TiO 2 colloid follows the zeroth-order kinetic rate law, while synthesis of Cu 2 O colloid under the same conditions follows the first order rate law. Under UV–vis light, Cu(0)-V O -TiO 2 colloid undergoes repeated accumulation of negative charge on metallic copper after photoexcitation of TiO 2 , and discharge of electrons from metallic copper occurs in the dark.

Synthesis and photocatalytic properties of multi-morphological AuCu3-ZnO hybrid nanocrystals

Noble metal–semiconductor hybrid nanocrystals represent an important class of materials for many potential applications, especially for photocatalysis. The utilization of transition metals to form alloys with noble metals can not only reduce the preparation costs, but may also offer tunable optical and catalytic properties for a broader range of applications. In this study, we report on the solution synthesis of AuCu3–ZnO hybrid nanocrystals with three interesting morphologies, including urchin-like, flower-like and multipod-like nanocrystals. In the synthetic strategy, Au–Cu bimetallic alloy seeds formed in situ are used to induce the heteroepitaxial growth of ZnO nanocrystals on the surface of bimetallic alloy cores; thus different types of morphologies can be achieved by controlling the reaction conditions. Through high-resolution transmission electron microscopy observations, well-defined interfaces between ZnO and AuCu3 are observed, which indicate that ZnO has a (0001) orientation and prefers to grow on AuCu3 {111} facets. The as-prepared hybrid nanocrystals demonstrate morphology- and composition-dependent surface plasmon resonance (SPR) absorption bands. In addition, much higher photocatalytic efficiency than pure ZnO nanocrystals is observed for the hybrid nanocrystals in the degradation of methylene blue. In particular, the multipod-like AuCu3–ZnO hybrid nanocrystals show the highest catalytic performance, as well as more than three times higher photocurrent density than the pure ZnO sample. The reported synthetic strategy provides a facile route to the effective combination of a plasmonic alloy with semiconductor components at the nanoscale in a controlled manner.

An intensive study on the optical, rheological, and electrokinetic properties of polyvinyl alcohol-capped nanogold

Low-temperature-assisted wet chemical synthesis of nanogold (NG) using gold hydroxide, a new precursor salt in the presence of a macroscopic ligand poly(vinyl alcohol) PVA in water in the form of nanofluid, is reported for the first time in this article. In the absorption spectra, the surface Plasmon resonance absorption band in the range of 520–545 nm signifies the formation of NG via a controlled Au3+ + 3e → Au reaction grafted in small assemblies with polymer. Absorption maximum increases nonlinearly with Au-contents up to 100 µM Au in Au-PVA charge-transfer complex. Marked enhancement in the peak intensity of some of the vibration bands of PVA polymer such as C–H stretching, C=O stretching, CH2 bending, and C–C in-plane bending in the presence of NG reveals an interfacial interaction between NG and oxidized PVA via C=O group. Execution of shear thinning behavior regardless of the Au-content strongly suggests that crosslinking exists between NG and PVA in Au-PVA rheo-optical nanofluids. Hydrodynamic diameter and polydispersity index draw a nonlinear path with the Au doping with 30.0 g/L PVA in water over a wide region of 5–100 μM Au covered in this study. Enhancement in the zetapotential of Au-PVA nanofluid over bare PVA in water is ascribed to buildup of nonbonding electrons of “–C=O” moieties from the oxidized PVA on the NG surface. Displaying of lattice fringes in the microscopic image of core–shell Au-PVA nanostructure confirms that crystalline nature of NG core with inter planar spacing 0.235 nm corresponds to Au (111) plane.

Implantation-synthesized Cu/Cu–Zn core/shell nanoparticles in SiO_2 and their optical properties

Silica glasses were pre-implanted with 60 keV Zn ions at different fluences of 1 × 1016 and 1 × 1017 cm−2, respectively, and were then subjected to implantation of 45 keV Cu ions at a fluence of 5 × 1016 cm−2. The formation of metallic nanoparticles (NPs) as well as their optical properties has been studied in details. Our results clearly show that Zn ion preimplantation at a low fluence of 1.0 × 1016 cm–2 can give rise to the formation of large Cu NPs with a double-layer arrangement, which contribute a greatly enhanced surface plasmon resonance (SPR) absorption at about 572 nm. As the Zn ion fluence increases to 1.0 × 1017 cm–2, Cu/Cu–Zn core/shell NPs with a high particle density and a narrow size distribution can be obtained, resulting in a strong and broad SPR absorption band around 528 nm. Besides, the dually implanted samples also exhibit excellent third-order nonlinear optical properties comparing with the Cu solely implanted sample. The possible mechanisms for the nucleation and growth of NPs as well as for the enhancements of linear and nonlinear optical properties have been discussed.

Biological behaviour of thin films consisting of Au nanoparticles dispersed in a TiO2 dielectric matrix

In this work it was studied the possible use of thin films, composed of Au nanoparticles (NPs) embedded in a TiO2 matrix, in biological applications, by evaluating their interaction with a well-known protein, Bovine Serum Albumin (BSA), as well as with microbial cells (Candida albicans). The films were produced by one-step reactive DC magnetron sputtering followed by heat-treatment. The samples revealed a composition of 8.3 at.% of Au and a stoichiometric TiO2 matrix. The annealing promoted grain size increase of the Au NPs from 3 nm (at 300 °C) to 7 nm (at 500 °C) and a progressive crystallization of the TiO2 matrix to anatase. A broad localized surface plasmon resonance (LSPR) absorption band (λ = 580–720 nm) was clearly observed in the sample annealed at 500 °C, being less intense at 300 °C. The biological tests indicated that the BSA adhesion is dependent on surface nanostructure morphology, which in turn depends on the annealing temperature that changed the roughness and wettability of the films. The Au:TiO2 thin films also induced a significant change of the microbial cell membrane integrity, and ultimately the cell viability, which in turn affected the adhesion on its surface. The microstructural changes (structure, grain size and surface morphology) of the Au:TiO2 films promoted by heat-treatment shaped the amount of BSA adhered and affected cell viability.

Synthesis of Silver-Chitosan Nanocomposites Colloidal by Glucose as Reducing Agent

Silver-chitosan nanocomposites colloidal was successfully performed by chemical reduction method at room temperature using glucose as reducing agent, sodium hydroxide (NaOH) as accelerator reagent, silver nitrate (AgNO3) as metal precursor and chitosan as stabilizing agent. Compared to other synthetic methods, this work is green and simple. The effect of the amount of NaOH, molar ratio of AgNO3 to glucose and AgNO3 concentration towards Localized Surface Plasmon Resonance (LSPR) absorption band of silver nanoparticles was investigated using UV-Vis spectrophotometer. The stability of the colloid was also studied for the first 16 weeks of storage at ambient temperature. The formation of silver nanoparticles was confirmed by the appearance of LSPR absorption peak at 402.4–414.5 nm. It is also shown that the absorption peak of LSPR were affected by NaOH amount, ratio molar AgNO3/glucose and concentration of AgNO3. The produced silver nanoparticles were spherical with dominant size range of 6 to 18 nm as shown by TEM images. All colloidals were stable without any aggregation for 16 weeks after preparation. The newly prepared silver-chitosan nanocomposites colloidal may have potential for antibacterial applications.

Analyte-induced photoreduction method for visual and colorimetric detection of tyrosine

A new method based on photochemical formation of silver nanoparticles (AgNPs) was developed for detection of tyrosine (Tyr). To selectively detect Tyr and to simplify the detection procedure, the photoactivity of Tyr was utilized to trigger the photochemical reduction in production of AgNPs. The drastic change of solution color caused by the surface plasmon resonance (SPR) absorption band of the formed AgNPs was used to extract the quantitative information of Tyr. This developed method is simple in detection, while both the sensitivity and selectivity are significant improved. Meanwhile, the solution color was changed from colorless to dark yellow after the formation of AgNPs, which allows a much higher sensitivity in visual identification when compared with the SPR band shifting technique commonly, used in conventional colorimetric methods. To optimize the detection system and to understand the mechanism in this proposed method, parameters such as irradiation time, intensity of light source, and the concentration of Tyr were systematically examined. Results indicated that these factors mainly affected the reaction rate of photoreduction. The morphologies of the formed AgNPs were similar, but with small differences in particle sizes. In the examination of selectivity, sixteen other amino acids were examined. Results indicated that only amino acids of tryptophan, cysteine and histidine are photoactive and possess potential interferences in analysis of Tyr. Quantitative studies indicated that a linear response up to 10μM with a detection limit of 100nM could be obtained. For visually detection, color change could be observed with a concentration as low as 500nM of Tyr.

Microwave-assisted green synthesis of silver nanoparticles from Fraxinus excelsior leaf extract and its antioxidant assay

The biosynthesis of nanoparticles has been proposed as a cost effective and environmentally benevolent alternative to chemical and physical methods. In the present study, microwave assisted synthesis of silver nanoparticles (AgNPs) has been demonstrated using leaf extract of Fraxinus excelsior reducing aqueous AgNO3 solution. The synthesized nanoparticles have been characterized on the basis of fourier transform infrared spectroscopy (FT-IR), UV–Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis. The presence of a characteristic surface plasmon resonance (SPR) absorption band at 425 nm in UV–Vis reveals the reduction of silver metal ions into silver nanoparticles. FT-IR analysis was carried out to probe the possible functional group involved in the synthesis of AgNPs. Further leaf extracts and AgNPs were evaluated for antiradical scavenging activity by 1,1-diphenyl-2-picryl-hydrazyl (DPPH) assay.

Photochromism of azobenzene-thiol-1,3-diazabicyclo-[3.1.0]hex-3-ene on silver nanoparticles

The new azobenzene-thiol terminated photochromic derivatives is designed, synthesized and used to form self-assembled monolayers on silver nanoparticles. The photochromic behavior of 1,3-diazabicyclo-[3.1.0]hex-3-ene joined with surface plasmon resonance absorption band of silver nanoparticles and photoisomerisable azobenzene is presented. The ultraviolet–visible experiments demonstrated that electronic transitions of functionalized silver nanoparticles were shifted as a result of chemical bonding and overlap between absorption bands of photochromic ligands with surface plasmon resonance absorption band of silver nanoparticle. Furthermore, we have also observed that trans→cis and cis→trans photoisomerization rate by ultraviolet light and thermally induced condition for functionalized silver nanoparticles are noticeably faster than free ligands.