Intense Surface Plasmon Resonance Research Articles

Sensitive spectrophotometric determination of ascorbic acid in drugs and foods using surface plasmon resonance band of silver nanoparticles

AbstractA simple and sensitive procedure was proposed for spectrophotometric determination of ascorbic acid. It was found that the reduction of Ag+ to silver nanoparticles (Ag-NPs) by ascorbic acid in the presence of polyvinylpyrrolidone (PVP) as a stabilizing agent produce very intense surface plasmon resonance peak of Ag-NPs. The plasmon absorbance of the Ag-NPs at λ = 440 nm allows the quantitative spectrophotometric detection of the ascorbic acid. The calibration curve was linear with concentration of ascorbic acid in the range of 0.5–60 μM. The detection limit was obtained as 0.08 μM. The influence of potential interfering substances on the determination of ascorbic acid was studied. The proposed method was successfully applied for the determination of ascorbic acid in some powdered drink mixtures, commercial orange juice, natural orange juice, vitamin C injection, effervescent tablet, and multivitamin tablet.

Plasma-induced brightening and coarsening of tarnished Ag nanoparticles

The recovery of the optical properties of tarnished silver nanoparticles (Ag NPs) has been demonstrated using exposure to plasma. As-prepared Ag NPs on a SiO2 substrate exhibited an intense localized surface plasmon resonance (LSPR) in the UV–vis optical extinction spectrum. The LSPR band weakened gradually when an Ag NP sample was stored in ambient air forming tarnished Ag. X-ray photoelectron spectroscopy (XPS) and ion-beam analysis revealed the presence of impurity elements, such as N and S. In addition, the shape of the valence-band XPS spectra changed significantly with exposure to ambient air. Ar plasma treatments recovered the intense LSPR and the XPS spectral shape. We conclude that both the reduction of Ag2S to Ag and the morphological change toward isolated Ag NPs most likely lead to their recovery. A simulation based on the Mie theory, as well as direct observation with an atomic force microscope, supports our findings.

Biogenic silver nanosols: Flavonol based green synthesis, and effects of stabilizers on their morphology

Extracellular biogenic silver-nanosols were prepared by treating aqueous solution of AgNO3 with Oriental plane leaves extract. Synthesized silver-particles shows an intense surface plasmon resonance band in the visible region at ca. 425nm. UV-visible spectroscopy was used to monitor the quantitative growth of silver-nanoparticles (AgNPs). X-ray diffractions (XRD), optical images, transmission electron microscopy (TEM) and selected area electron diffraction ring patterns (SAED) were used to determine morphology with and without CTAB. TEM images shows that the CTAB has significant effects on the shape, size and the size distribution, which changes from spherical arrangement to mixed anisotropic kind of morphology like triangular, spherical, rod, pentagonal, hexahedral nanodisks and/or nanoplates like structure with diameter ranging from 7nm to 235nm. Optical images also suggests that resulting silver sols has no any type of aggregation and are stable for more than two months.

Trace colorimetric detection of Pb2 + using plasmonic gold nanoparticles and silica–gold nanocomposites

A novel, simple and highly sensitive plasmonic colorimetric method is developed for the detection of Pb2+ in aqueous samples. The method is based on the aggregation of gold nanoparticles (AuNPs) or SiO2core–Aushell nanocomposites (SiO2@Au NCs) in the presence of Pb2+ ions. It was found that the colour of AuNPs or SiO2@Au NCs changes in the presence of Pb2+ ions and the intensity of surface plasmon resonance (SPR) peak of AuNPs or SiO2@Au NCs decreased. Thus, the synthesis of sensitive surface enhanced Raman scattering (SERS) materials; ~20nm spherical AuNPs and ~360nm SiO2@Au NCs leads to the development of nanosensor for the detection of Pb2+ ions. Both AuNPs and SiO2@Au NCs by virtue of their versatility show localized surface plasmon resonance (LSPR) peaks at 522nm and 541nm respectively. The synthesized AuNPs, SiO2@Au NCs and analyte samples prepared were characterised using a scanning electron microscope, a transmission electron microscope and a UV–vis spectrophotometer. The SERS study was also used to compare sensitivities of both AuNPs and SiO2@Au NCs towards Pb2+ ions using crystal violet (CV) as a target molecule. The analyte Pb2+ was detected as low as 500nM using 20nm AuNPs and 50nM using 360nm SiO2@Au NCs. It was confirmed that SiO2@Au NCs were found ten times more sensitive as compared to AuNPs for the detection of Pb2+ ions.

Development of an enhanced surface plasmon resonance sensor substrate by investigating a periodic nanohole array configuration

The sensor system utilizing a surface plasmon resonance (SPR) with nanoparticles and nanostructures measures a peak wavelength shift. In order to enhance the measurement accuracy, it is important to acquire the higher and sharper peak wavelength so as to identify accurately the position of the peak wavelength. We developed an enhanced SPR sensor substrate by investigating the configuration of a periodic nanohole array. We simulated the effects of the configuration parameters. The simulation results revealed that the proposed sensor substrate achieved the higher and sharper peak wavelength by strengthening the SPR intensity as the number of holes per unit structure was increased from one to three, and with allocation of the unit structure in a triangular lattice so as to have one rotational symmetry. We also verified our simulation results experimentally by fabricating nanohole array sensor substrates.

Formation of plasmonic silver nanoparticles by flavonoid reduction: A comparative study and application for determination of these substances

Formation of plasmonic silver nanoparticles by flavonoid reduction was studied. Effects of the nature and the concentration of a flavonoid and a stabilizer, composition of the solution and the interaction time were revealed. It was found that quercetin, dihydroquercetin, rutin and morin produced an intense surface plasmon resonance band of silver nanoparticles at 415nm which was linearly related to the concentration of a flavonoid, while chrysin, naringenin and naringin did not produce any remarkable changes. It was used for the spectrophotometric determination of the former four flavonoids with the detection limits of 0.03; 0.06; 0.09 and 0.1μgmL−1, respectively. The developed method was applied for the determination of flavonoids in biologically active food additives.

Biosynthesis of Gold Nanoparticles and Identification of Capping Agent Using Gas Chromatography-Mass Spectrometry and Matrix Assisted Laser Desorption Ionization-Mass Spectrometry.

In the present study, gold nanoparticles (AuNPs) were synthesized using leaf extract of Syzygium jambolanum and capping agent has been explored. The synthesized AuNPs have been characterized using UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HRTEM) and atomic force microscopic (AFM) analysis. The AuNPs show intense surface plasmon resonance (SPR) band at 528 nm and were found to be spherical and hexagonal in shape with particle size ranging from 20-30 nm. Transmission electron microscopy and atomic force microscopy were used to analyze the surface morphology of synthesized AuNPs. The capping ligand has been evaluated using matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) and gas chromatography-mass spectrometry (GC-MS) analysis.

Surface plasmon resonance and photoluminescence studies of Au and Ag micro-flowers

The surface plasmon resonance (SPR) and photoluminescence characteristics of gold and silver micro-flowers were compared to those of gold and silver nanoparticles. The micro-flower structures were grown under electron beam deposition using an alumina template. Both types of metallic micro-flowers showed systematic arrangements; they formed islands of flowers about 20 µm across, each one comprised of spikes ranging from 1 to 5 µm in length. A red shift in the SPR and enhancement intensity was observed for both micro-flowers and nanoparticles; the incremental increase was more than 50%. These results, which showed that gold and silver micro-flowers agglomerate at a micron size scale, are useful for the design of easier and more cost effective methods for large area fabrication, especially for particular plasmonic applications.

Tunable Plasmon Resonance and Fluorescence of Au/ZnS/CdS Core/Shell Nanorods

Au/ZnS/CdS core/shell nanorods were synthesized via layer-by-layer over-growing sulfide semiconductors ZnS and CdS onto Au-core nanorods, and the thickness of ZnS and CdS layers was tuned by adjusting the amounts of the added metal (Zn/Cd) salts. Owing to efficient interaction between the metal and semiconductor components in the multi-core/shell nanorods, we observed redshift of the surface plasmon resonance (SPR) band, enhancement of the SPR intensity, and generation of a new SPR band. Furthermore, the spectral redshift and enhancement were also observed in the excitonic fluorescence of the Au/ZnS/CdS core/shell nanorods, which is caused by the interaction between activated excitons in the CdS shell and the transverse SPR of the Au nanorod and can be tuned by adjusting the thickness of the middle shell (ZnS). These observations have prospective applications in active plasmonic nanodevices.

Highly sensitive colorimetric determination of amoxicillin in pharmaceutical formulations based on induced aggregation of gold nanoparticles

A novel, simple and highly sensitive colorimetric method is developed for determination of Amoxicillin (AMX). The system is based on aggregation of citrate-capped gold nanoparticles (AuNP) in acetate buffer (pH=4.5) in the presence of the degradation product of Amoxicillin (DPAMX). It was found that the color of gold nanoparticles changed from red to purple and the intensity of surface plasmon resonance (SPR) peak of AuNPs decreased. A new absorption band was appeared in the wavelength range of 600–700nm upon addition of DPAMX. The absorbance ratio at the wavelength of 660 and 525nm (A660/A525) was chosen as the analytical signal indirectly related to AMX concentration. The linearity of the calibration graph was found over the concentration range of 0.3–4.5μM AMX with a correlation coefficient of 0.9967. Under the optimum experimental conditions, the detection limit was found to be 0.15μM. The applicability of the method was successfully demonstrated by analysis of AMX in pharmaceutical formulations including capsules and oral suspensions.

Tailoring assemblies of plasmonic silver/gold and zinc–gallium layered double hydroxides for photocatalytic conversion of carbon dioxide using UV–visible light

In the search for novel efficient photocatalysts for the conversion of CO2 into fuels, plasmonic photocatalysts based on the self-assemblies of silver or gold nanoparticles with [Zn3Ga(OH)8]2CO3·mH2O layered double hydroxide (Zn3Ga|CO3 LDH) were prepared and tested for the photoreduction of CO2 by H2 under irradiation with UV–visible light. Ag and Au nanoparticles were obtained directly on the LDHs via the ion-exchange method or the reconstruction method of the LDHs. The catalysts exhibited intense surface plasmon resonance (SPR) effect at 411 and 555nm attributable to Ag and Au nanoparticles, respectively. The rate of CO2 photoreduction on Ag/Zn3Ga|CO3 increased by a factor of 1.69 than that of Zn3Ga|CO3 while the methanol selectivity also increased from 39 to 54mol%. On Au/Zn3Ga|CO3, the reduction rate of CO2 was 1.78 times higher than on Zn3Ga|CO3 LDH whereas the methanol selectivity decreased from 39 to 13mol%. Electron microscopy and UV–visible and X-ray spectroscopy detected particular interactions of the cationic layers of Zn3Ga|CO3 with Ag and Au nanoparticles. Results show that for Ag/Zn3Ga|CO3 catalysts, CO2 photoreduction by H2 under visible light was promoted by the SPR effect of Ag nanoparticles while for Au/Zn3Ga|CO3 catalysts Au nanoparticles might act as electron-trapping active sites.

Optimization Studies of Conditions for Biological Synthesis of AuNPs in Various Shapes Using Plant Extract (Ocimum sanctum).

We demonstrate the effects extract amount, pH and temperature on the formation of gold nanoparticles (AuNP) using Ocimum santum plant extract. The average AuNP size, shape, and particle number can be controlled by simply varying the pH, temperature and amount of plant extract in the reaction medium. Acidic pH was found to be ideal for the formation of AuNPs. UV-visible spectra for the reaction of the plant extract with 1 mM HAuCl4 solution showed that the highest intensity of surface plasmon resonance (SPR) occurred at pH 3. Transmission electron microscopy (TEM) showed that temperature can be used to control the aspect ratio and the relative amount of gold nanoplatelets (triangular and hexagonal). Increasing the temperature decreased the population of gold nanoplatelets and increased the number of spherical NPs, and nanoplatelet population was found to be highest at 20 degrees C and 30 degrees C.

Improve the surface-enhanced Raman scattering from rhodamine 6G adsorbed gold nanostars with vimineous branches

The surface-enhanced Raman scattering (SERS) activity of the gold nanostars with vimineous branches has been investigated by using rhodamine 6G (R6G) as the Raman active probe. The colloidal gold nanostars have two intense localized surface plasmon resonance (LSPR) peaks in the visible and infrared ranges, respectively. Besides the visible LSPR dependent local field effect induced Raman signal enhancement, the SERS ability also greatly depends on the infrared absorption from the plasmon resonance along the aligned branches. Whether increasing the peak intensity or wavelength of the infrared absorption leads to the efficient improvement of SERS. These correlations between plasmonic absorption and SERS indicate that the lightning rod effect and creation of hot spots have been enhanced with the length and number of gold branches.

Quantum Dot Thermometry Evaluation of Geometry Dependent Heating Efficiency in Gold Nanoparticles

Quantum dot based thermometry, in combination with double beam confocal microscopy, was used to investigate the absorption/heating efficiency of gold nanoparticles with different morphologies (nanorods, nanocages, nanoshells, and nanostars), all of them with an intense localized surface plasmon resonance within the first biological window, at around 808 nm. The heating efficiency was found to be strongly dependent on the geometry of the nanostructure, with the largest values found for gold nanorods and long-edge gold nanostars, both of them with heating efficiencies close to 100%. Gold nanorods and nanocages were found to have the largest absorption cross section per unit mass among all the studied geometries, emerging as optimum photothermal agents with minimum metal loading for biosystems.

Photothermal effect for localized desorption of primary lymphocytes arrayed on an antibody/DNA-based biochip.

This work proposes a miniaturized system able to perform multiple cell capture followed by cell-type selective release from a biochip surface. Unlabelled lymphocytes were first specifically captured onto a DNA array by antibody-DNA conjugates. The immobilized cells were subsequently released under spatiotemporal control within local heating generated by intense Surface Plasmon Resonance (SPR) produced by laser illumination.

Green synthesis of colloidal copper oxide nanoparticles using Carica papaya and its application in photocatalytic dye degradation

Copper oxide (CuO) nanoparticles were synthesized by treating 5mM cupric sulphate with Carica papaya leaves extract. The kinetics of the reaction was studied using UV–visible spectrophotometry. An intense surface Plasmon resonance between 250–300nm in the UV–vis spectrum clearly reveals the formation of copper oxide nanoparticles. The results of scanning electron microscopy (SEM) and dynamic light scattering (DLS) exhibited that the green synthesized copper oxide nanoparticles are rod in shape and having a mean particle size of 140nm, further negative zeta potential disclose its stability at −28.9mV. The Fourier-transform infrared (FTIR) spectroscopy results examined the occurrence of bioactive functional groups required for the reduction of copper ions. X-ray diffraction (XRD) spectra confirmed the copper oxide nanoparticles crystalline nature. Furthermore, colloidal copper oxide nanoparticles effectively degrade the Coomassie brilliant blue R-250 dye beneath the sunlight.

Extracellular biosynthesis of silver nanoparticles: effects of shape-directing cetyltrimethylammonium bromide, pH, sunlight and additives

The work reported in this paper describes the preparation, morphology, stability and sensitivity of Ag-nanoparticles towards sunlight using Allium sativum, garlic extract for the first time. The synthesized silver particles show an intense surface plasmon resonance band in the visible region at 410nm. The position of the wavelength maxima, blue and red shift, strongly depends on the sunlight and pH. TEM analysis revealed the presence of spherical, different size (from 5.0 to 30nm) and garlic constituents bio-conjugated, stabilized and/or layered silver nanoparticles. The concentrations of garlic extract, cetyltrimethylammonium bromide, Ag(+) ions and reaction time play vital roles for nucleus formation and the growth processes. Sulfur-containing biomolecules of extract, especially cysteine, are responsible for the reduction of Ag(+) ions into metallic Ag(0). The agglomeration number of the silver nanoparticles (N Ag) and the average number of free electrons per particle (n fe) are calculated and discussed.

Green Synthesis of a Gold Nanoparticle–Nanocluster Composite Nanostructures Using Trypsin as Linking and Reducing Agents

We report a green synthesis of novel gold nanoparticle–nanocluster composite nanostructures directly using trypsin as linking and reducing agents. Size exclusion chromatography (SEC) and transmission electron microscopy (TEM) reveals that the as-prepared gold nanocomposite (gold nanoparticles-trypsins-nanoclusters, GNPs-Trys-GNCs) is composed of GNPs (gold nanoparticles) with an average diameter of 5.5 nm and the GNCs (gold nanoclusters, about 1 nm)-embedded trypsins (Trys-GNCs), which are attached to the surface of the GNPs. The specific amino acids in the trypsin molecule, like cysteine, methionine, and tyrosine, combined with the unique spatial structures, enable trypsins to bind and reduce the AuCl4– ions, simultaneously forming GNPs and GNCs in one-pot synthesis. Similar to pure GNPs, the GNPs-Trys-GNCs nanocomposite also exhibits an intense surface plasmon resonance (SPR) absorbance at 520 nm. However, it shows an obvious different optical property in the interaction with Pb2+ ions. In the presence ...

Photocatalytic H2 Production from Ethanol–Water Mixtures Over Pt/TiO2 and Au/TiO2 Photocatalysts: A Comparative Study

Pt/TiO2 (Pt loadings 0-4 wt%) and Au/TiO2 (Au loadings 0-4 wt%) photocatalysts were synthesized, char- acterized and tested for H2 production from ethanol-water mixtures (80 vol% ethanol, 20 vol% H2O) under UV exci- tation. Average metal nanoparticle sizes determined by TEM were 1-3 nm for Pt in the Pt/TiO2 photocatalysts and 5-7 nm for Au in the Au/TiO2 photocatalysts. Au/TiO2 showed an intense localized surface plasmon resonance feature at *570 nm, typical for metallic Au nanoparticles of diameter *5 nm supported on TiO2. X-ray photoelectron spectros- copy and X-ray diffraction analyses established that Pt and Au were present in metallic form on the TiO2 support. X-ray fluorescence revealed close accord between nominal and actual Pt and Au loadings. The Au/TiO2 and Pt/TiO2 phot- ocatalysts both displayed very high activities for H2 pro- duction under UV irradiation, with the Au/TiO2 samples affording slightly superior rates of H2 production at most metal loadings. The 2 wt% Au/TiO2 and 1 wt% Pt/TiO2 photocatalysts showed the highest H2 production rates (32-34 mmol g -1 h -1 ). Photoluminescence studies confirmed that Pt and Au nanoparticles positively enhance the photocatalytic properties of P25 TiO2 for H2 production by acting as electron acceptors and thereby suppressing electron-hole pair recombination in TiO2.

A Magnetoplasmonic Imaging Agent for Copper(I) with Dual Response by MRI and Dark Field Microscopy

We present the design and synthesis of a responsive magnetoplasmonic assembly for copper(I) which allows monitoring of the concentration of the metal both in three dimensions by magnetic resonance imaging and with high spatial resolution by dark field microscopy. The probe consists of azide-functionalized iron oxide nanoparticles 11.6 nm in diameter and acetylene-terminated gold nanoparticles 44 nm in diameter that form three-dimensional networks of intermingled magnetic and plasmonic nanoparticles in the presence of copper. This aggregation results in a decrease in longitudinal relaxivity, and an initial increase followed by a sharp decrease in transverse relaxivity, a change observable both by T1- and T2-weighted images, concomitantly with a decrease of surface plasmon resonance intensity.