Longitudinal Surface Plasmon Band Research Articles

Photo-Driven Synthesis of Anisotropic Gold Nanoparticles Using Silk Fibroin—Cell Viability Activities in Lymphocyte and Jurkat Cancer Cells

A simple, environmentally benign and low-cost method for the synthesis of different-shaped gold nanoparticles using silk fibroin (SF) under ultraviolet (UV-B) radiation has been reported in this work. No additives such as organic solvents, surfactants, external reducing, stabilizing agents or high temperature were used for the synthesis of the particles. SF acts as a reducing and subsequently, stabilizing agent. The UV-Visible (UV-Vis) absorption spectra support the formation of different-shaped gold nanoparticles by displaying transverse and longitudinal surface plasmon bands at different wavelengths. The size and shape evolution of the nanoparticles was studied using the transmission electron microscope (TEM) to confirm the formation of different-shaped particles. Nano-crystalline structure and FCC crystal family of gold were confirmed by X-ray diffraction (XRD) measurement study. Furthermore, the proliferative activities of the synthesized colloidal gold nanoparticles were tested against lymphocyte and Jurkat cancer cell lines. The obtained results proved that the biogenic different-shaped AuNPs showed better activity in comparison with the spherical-shaped gold nanoparticles.

Field-assisted growth of magnetic nanoparticle supercrystals

We report on the organization of magnetic nanoparticles (Fe3O4 and Fe3O4@Au NPs) into two and three dimensional (2D and 3D) supercrystals (SCs) and which were imbedded in polyethylene glycol (PEG) matrix. The organization of NPs was induced by subjecting their dispersion (in chloroform) to an external magnetic field. The Fe3O4 NPs were prepared by the high temperature decomposition of an Fe-oleate complex. The core–shell Fe3O4@Au NPs were made by treating Fe3O4 seed NPs with chloroauric acid (HAuCl4). Both the bare and Au-coated Fe3O4 NPs dispersed in chloroform were treated, separately, with PEG (molecular weight 6000) and suspended in the presence of an external magnetic field. On evaporation of chloroform, flaky crystals having sizes on the order of tens of millimeters were formed. Examination of the crystals in a transmission electron microscope (TEM) revealed the formation of 2D and 3D stacked NP SCs. The magnetic properties, ascertained by using a vibrating sample magnetometer (VSM), were found to be similar to that due to NPs only. However, the optical signature due to Fe3O4@Au NP SCs indicated the presence of NPs in aggregated forms as displayed through the appearance of longitudinal surface plasmon band in addition to the transverse one.

Colloidal Dispersion of Gold Nanorods and Gold-Silver Core-Shell Nanorods in Polar Organic Solvents

Abstract Gold nanorods and gold-silver core-shell nanorods were colloidally dispersed in polar organic solvents, acetonitrile, dimethylsulfoxide, and dimethylformamide, and their water mixtures. The gold nanorods showed narrow longitudinal surface plasmon bands in 100% dimethylformamide, 25% dimethylsulfoxide, and 25% acetonitrile solutions, indicating that the gold nanorods were well dispersed in these solutions. For the core-shell nanorods, acetonitrile and its water mixtures gave well-dispersed colloidal solutions. Amphiphilic molecules in the dispersions did not influence the systems; however, thiol-terminated poly(ethylene glycol) (PEG-SH) strongly stabilized the colloidal dispersions. The nanorods in the organic dispersions with the addition of PEG-SH could be redispersed in phosphate buffer saline (PBS) solutions. The zeta potentials of the gold nanorods in 1/10 PBS solutions ranged from −7.5 to +3.3 mV. Steric effects of the bulky PEG chains attached to the nanorod surfaces stabilized their colloidal dispersions in PBS.

Facile synthesis of gold nanorods/hydrogels core/shell nanospheres for pH and near-infrared-light induced release of 5-fluorouracil and chemo-photothermal therapy

We described a facile synthesis of pH and near-infrared (NIR) light dual-sensitive core/shell hybrid nanospheres, consisting of gold nanorods (GNR) as the core and poly(N-isopropylacrylamide-co-methacrylic acid) as the shell, p(NIPAM-MAA). The resultant GNR/p(NIPAM-MAA) nanospheres showed a core/shell structure, with an average diameter of ∼110nm and a strong longitudinal surface plasmon band at NIR region. Due to the photothermal effect of GNR and pH/thermal-sensitive volume transition of p(NIPAM-MAA) hydrogels, the nanospheres with loading of 5-fluorouracil (5-FU) by electrostatic interactions were developed as a smart carrier for pH- and photothermal-induced release of 5-FU. Experimental results testified that the cumulative release of 5-FU from nanospheres was markedly increased in a mild acidic medium. Moreover, a NIR light (808nm) irradiation triggered a greater and faster release of 5-FU, which was further testified by relevant results from in vitro cytotoxicity assay, in vivo tumor growth inhibition and histological images of ex vivo tumor sections. These results revealed significant applications of GNR/p(NIPAM-MAA) nanospheres in controlled release of anticancer agents and photothermal ablation therapy of tumor tissues, accompanied by synergistic effect of chem-photothermal therapy.

In SituPlasmonic Counter for Polymerization of Chains of Gold Nanorods in Solution

Self-assembly of gold nanorods (NRs) in linear, polymer-like chains offers the ability to test and validate theoretical models of molecular polymerization. Practically, NR chains show multiple promising applications in sensing of chemical and biological species. Both areas of research can strongly benefit from the development of a quantitative tool for characterization of the structure of NR chains in the course of self-assembly, based on the change in ensemble-averaged optical properties of plasmonic polymers; however, quantitative correlation between the extinction spectra and the structural characteristics of NR chains has not been reported. Here, we report such a tool by a quantitatively correlating the red shift of the longitudinal surface plasmon band of gold NRs and the average aggregation number of NR chains. The generality of the method is demonstrated for NRs with different aspect ratios, for varying inter-rod distances in the chains, and for varying initial concentrations of NRs in solution. We modeled the extinction spectra of the NR chains by combining the theory of step-growth polymerization with finite-difference time-domain simulations and a resistor-inductor-capacitor model, and obtained agreement between the theoretical and experimental results. In addition to capturing quantitatively the ensemble physics of the polymerization, the proposed 'plasmonic counter' approach provides a real-time cost- and labor-efficient method for the characterization of self-assembly of plasmonic polymers.

Preparation and characterization of pH‐responsive and thermoresponsive hybrid microgel particles with gold nanorods

AbstractWe report on pH‐responsive and thermoresponsive hybrid materials based on the assembly of gold nanorods, Au NRs, into multiresponsive, crosslinked copolymer microgel particles. These microgel particles were prepared by the surfactant‐free emulsion polymerization of N‐isopropylacrylamide and acrylic acid using N, N′‐methylene bis‐acrylamide as a crosslinker, which produces particles measuring approximately 160 nm that are interconnected to one other. Cetyltrimethyl ammonium bromide‐stabilized Au NRs were also prepared independently using a seed‐mediated growth method and then loaded into swollen, deprotonated, acrylic acid‐containing microgel particles using the electrostatic interactions between the oppositely charged particles. Transmission electron micrographs of the as‐prepared hybrid Au NR–microgel particles confirmed that the Au NRs were attached to the surface of the microgel particles. The size‐dependent temperature‐responsive characteristics of the hybrid microgel particles were studied by dynamic light scattering, and it was found that as the temperature increased across the phase transition temperature, the particle size decreased to 56% of the original volume. The thermoresponsive and pH‐responsive optical properties of the hybrid microgel particles were also systematically investigated. The thermo‐ and pH‐induced shrinkage of the microgel led to an increase in the UV–vis absorption intensity and caused a significant blue shift in the longitudinal surface plasmon bands of the Au NRs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Silica-coated Au/Ag nanorods with tunable surface plasmon bands for nanoplasmonics with single particles

We present the synthesis and analysis of silica-coated Au/Ag bimetallic nanorods with controlled surface plasmon bands. Depending on the thickness of Ag shell deposited on the Au nanorod surface, there is a blue-shift on the longitudinal surface plasmon band of Au nanorods, which can be expressed by an approximate formula derived from the absorption profile of light in Ag films using finite difference time domain simulations. The subsequent coating of silica shell not only enhances the stability of the Au/Ag bimetallic nanorods but also provides a mesoporous host for optically active species. Minute red-shifts of the longitudinal resonance mode, induced by stepwise increased silica shell volumes, are shown. Application as carrier for fluorescent rhodamine B molecules is demonstrated by photoluminescence analysis. On the single-particle level, dark field microscopy of Au/Ag-silica nanorods was finally employed. This introduces a route towards revealing the relation between structure, shape, and optical (plasmonic) properties of complex composite metal particles as well as fabrication strategies for nanoassemblies of tailored structures in the field of nanoplasmonics.

Sensing of oligopeptides using localized surface plasmon resonances combined with Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Gold nanorods were fixed on an ITO plate and used for the spectroscopic sensing and Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SALDI-MS) of oligopeptides (angiotensin I). The longitudinal surface plasmon bands of the gold nanorods responded to the 10(-10) M angiotensin solution that was cast on the ITO plate. The SALDI-MS measurements had an ultra-high sensitivity to the angiotensin on the ITO plate. A very small surface density (5 × 10(-19) mol cm(-2)) of angiotensin could be detected at m/z = 1297 with a good signal/noise ratio (S/N = 11). The ITO plate, which was modified with gold nanorods, was found to be effective in collecting angiotensin molecules adjacent to the gold nanorods, and the SALDI processes that were induced by the photoabsorption of the gold nanorods efficiently contributed to the desorption and ionization of the angiotensin.

Label-free Biosensor Using Polyion-modified Gold Nanorods Adsorbed on a Glass Substrate

Abstract Gold nanorods (NRs), which were modified with polyions, were fixed on polycation-modified glass substrates. Adsorption of antibodies and antigens on the glass substrates induced large peak shifts (44 nm) of longitudinal surface plasmon bands in the near-infrared region. The shifts were assignable to changes of refractive indices of polyion layers at the glass surfaces.

Selective Aggregation of Polyanion-Coated Gold Nanorods Induced by Divalent Metal Ions in an Aqueous Solution

A simple, accurate method for detecting metal ions in an aqueous solution using functionalized gold nanorods (AuNRs) is described. The method involves the complexing of divalent metal ions with poly(acrylic acid) (PAA) and, the localized surface plasmon resonance (LSPR) phenomena of AuNRs. Changes in the longitudinal surface plasmon bands (LSPBs) were monitored using aggregates of PAA-coated AuNRs with various divalent metal ions via UV-vis spectroscope. Functionalized AuNRs underwent robust aggregate formation by chelation with divalent metal ions (e.g., Cu2+, Zn2+, Cd2+, and Fe2+). Copper ions formed largest aggregates within 2 h, because complexation between Cu2+ and dicarboxylate has the highest deltaH and -deltaG values. This process represents an easy and useful method for detecting certain divalent metal ions, and the aggregates are also, in some cases, clearly visible to the naked eye.

Polymer Membrane Stabilized Gold Nanostructures Modified Electrode and Its Application in Nitric Oxide Detection

Nafion polymer/gold nanostructures film that can be utilized as a proficient electrochemical sensor for nitric oxide was prepared by an electrochemical process, forming the gold nanostructures (Aunano) through infiltration into a Nafion (Nf) matrix preassembled on an electrode. The formation of gold nanostructures was monitored by the in situ spectroelectrochemical method. The in situ absorption spectra of Aunano showed systematic and uniform formation of gold nanostructures at the Nafion (Nf−Aunano)-modified electrode. The electrochemically formed Nf−Aunano was characterized by UV−visible spectroscopy, X-ray diffraction, scanning electron microscope, transmission electron microscope, and electrochemical techniques. The surface plasmon absorption spectra recorded for the wet and dry Nf−Aunano composite film showed the interaction between the gold nanostructures and the swelled polymer matrix. The longitudinal surface plasmon band and the TEM images observed for the Nf−Aunano showed the formation of nanorod-like and Y-shaped gold nanostructures in the Nafion matrix. In addition to the nanoparticles, the edge-to-edge interactions lead to the formation of 1D assembly. The electrical communication between the gold nanostructures embedded in the Nafion film improved the electrocatalytic properties of the modified electrode toward NO detection. The Nf−Aunano electrode showed excellent sensitivity for NO detection with the experimental detection limit of 1 nM. The present Nf−Aunano electrode is very simple to fabricate and is stable, sensitive, and reproducible.

Shape-Controlled Synthesis of Gold Nanoprism and Nanoperiwinkles with Pronounced Electrocatalytic Activity

We report the one-pot shape-controlled aqueous synthesis of triangular gold nanoprisms (GNPMs) and nanoperiwinkles (GNPWs) and their electrocatalytic activity toward reduction of oxygen and oxidation of methanol. The GNPMs and GNPWs were synthesized using 5-hydroxytryptamine (HT) as a reducing/stabilizing agent at room temperature. The UV−visible absorption spectrum of the nanostructured colloidal particles exhibits transverse and longitudinal surface plasmon bands at 535 and 900 nm, respectively. The transmission electron microscopy measurement shows that the nanostructured particles have prism and periwinkle-like morphology. The concentration of HT controls the shape and morphology of the nanostructured particles. The GNPMs have the size of 70−110 nm whereas GNPWs have the size of 150−230 nm. The X-ray diffraction profiles of GNPMs and GNPWs reveal that the nanoparticles are composed of mainly a Au(111) lattice plane. The GNPMs and GNPWs were self-assembled on a three-dimensional silicate network derived from (3-mercaptopropyl)trimethoxysilane, and their spectral and electrochemical properties have been investigated. The UV−visible diffuse reflectance spectral measurement shows that both GNPM and GNPW retain their morphology on the silicate network. The nanoparticles on the silicate network show excellent electrocatalytic activity toward oxidation of methanol and reduction of oxygen. The electrocatalytic activity of GNPMs and GNPWs is higher than the spherical gold nanoparticles.

Assembling covalently linked nanocrystals and nanotubes through click chemistry

The click reaction involving the Huisgen 1,3-cycloaddition reaction between azide and ethynyl groups has been employed to obtain assemblies of nanostructures. The click reaction between gold nanorods capped with azidoalkane- and alkyne-thiols yields chains and complex assemblies, accompanied by a large red shift of the longitudinal surface plasmon band. A similar reaction between CdSe nanocrystals results in a splitting of the photoluminescence band, possibly due to exciton splitting. Carbon nanotubes decorated by covalently linked gold nanoparticles have been obtained through click chemistry.

Selective Shortening of Single-Crystalline Gold Nanorods by Mild Oxidation

Gold nanorods (NRs) have received much attention due to their size-dependent surface plasmon-related optical properties. A seed-mediated approach has recently been developed for the synthesis of Au NRs with varying length-to-diameter aspect ratios. With the introduction of silver ions in the growth solution, Au NRs of narrow size distributions can be produced in high yields. Herein we describe an approach for the continuous and selective shortening of Au NRs synthesized by the silver ion-assisted seed-mediated method through oxidation with environmentally benign oxygen at slightly elevated temperatures. UV-visible extinction measurements indicate that the longitudinal surface plasmon band of Au NRs decreases in intensity and blue-shifts as a function of the oxidation time. Transmission electron microscopy (TEM) imaging shows that the length of Au NRs decreases with oxidation and their diameter stays almost constant, which suggests that oxidation starts at the ends of Au NRs. The size distributions of shortened Au NRs are similar to those of starting NRs. Further oxidation transforms Au NRs into nanospheres, which become smaller in diameter and finally completely disappear. It has been found that the oxidation rate of Au NRs can be controlled by temperature and acid concentration. Furthermore, high-resolution TEM studies reveal that Au NRs synthesized by the silver ion-assisted seed-mediated method are single crystalline and they stay single crystalline during oxidation. It is expected that Au NRs of any aspect ratio with narrow size distributions within the limit of that possessed by starting NRs can be produced by this mild oxidation approach.

How long does it take to melt a gold nanorod?: A femtosecond pump–probe absorption spectroscopic study

Using pump–probe femtosecond transient absorption spectroscopy, we determined the rate of the bleach of absorption around 700–800 nm due to the longitudinal surface plasmon band of gold nanorods. Using TEM of the spotted, completely irradiated solutions suggest that the dominant products of the photothermal conformation of the rods are spheres of comparable volume. This lead to the conclusion that the melting of the rods is at least 30–35 ps, independent of the power used (5–20 μJ) or the nanorod aspect ratio (1.9–3.7).

The Shape Transition of Gold Nanorods

We report a revised synthetic procedure based on an electrochemical method for preparing an aqueous solution containing suspended Au nanorods. The mean aspect ratios of the Au nanorods can be experimentally adjusted between 1 and 7. The evolution of the longitudinal surface plasmon bands shows an eminently sensitive dependence on the aspect ratios of the nanorods. Their dependence is accordingly described by classical-electrostatic-model predictions. The shape transition of the nanorod particles has been studied by varying some key influencing factors such as the wavelength, the laser fluence, and matrix effects. The nanorods were exposed to laser lines at 532 and 1064 nm, frequencies which correspond closely to the short- and long-axis plasmon resonances, respectively. A photon-induced shape transition process was evidenced, and the corresponding rod-to-sphere conversion contributed by a photoannealing process was observed in both cases. Meanwhile, we observed a new type of “φ-shaped” Au nanostructure in...