Optical Plasmon Resonance Research Articles

Optical biosensors for food quality and safety assurance-a review.

Food quality and safety is a scientific discipline describing handling, preparation and storage of food in ways that prevent food borne illness. Food serves as a growth medium for microorganisms that can be pathogenic or cause food spoilage. Therefore, it is imperative to have stringent laws and standards for the preparation, packaging and transportation of food. The conventional methods for detection of food contamination based on culturing, colony counting, chromatography and immunoassay are tedious and time consuming while biosensors have overcome some of these disadvantages. There is growing interest in biosensors due to high specificity, convenience and quick response. Optical biosensors show greater potential for the detection of pathogens, pesticide and drug residues, hygiene monitoring, heavy metals and other toxic substances in the food to check whether it is safe for consumption or not. This review focuses on optical biosensors, the recent developments in the associated instrumentation with emphasis on fiber optic and surface plasmon resonance (SPR) based biosensors for detecting a range of analytes in food samples, the major advantages and challenges associated with optical biosensors. It also briefly covers the different methods employed for the immobilization of bio-molecules used in developing biosensors.

Manipulation of subwavelength optical fields and resonant field enhancements of a silver-shell nanocylinder pair and chain waveguides with different core–shell patterns

Near field optical properties and surface plasmon resonances on a pair of silver-shell nanocylinder and nanochain waveguides with different core–shell patterns which interact with incident plane wave along chain axis are numerically investigated by using the finite element method. Simulation results show that the peak wavelengths and resonant field enhancements are highly tunable by using the nanoshell particles instead of solid ones, revealing a critical relationship among the wavelengths and illuminated direction of incident light, interparticle spacing, radii, and medium of dielectric holes and the patterns of chain waveguides. Besides, nanochain waveguides with different patterns of core–shell that are operated on resonant multipolar modes can provide higher propagation intensities and the transmission ability can be increased by decreasing the size of nanocylinders along the chain axis.

OPTICAL PROPERTIES AND PLASMON RESONANCE OF COUPLED GOLD NANOSHELL ARRAYS

The optical properties and plasmon resonances coupling of ordered gold nanoshell arrays are investigated theoretically by means of finite-difference time-domain (FDTD) theory. We showed that the thickness, size and inter-shell distance of the nanoshells can tune the optical transmission of the system and the highly geometry-dependent plasmon response can be seen as an interaction between the essentially fixed-frequency plasmon response of a nanosphere and that of a nanocavity for the nanoshells. We also revealed the two different resonance modes by analyzing the spatial distributions of electric field component Ez. We proposed that the peaks of the lower energy mainly originate from the sphere plasmons coupling and the peaks of the higher energy are mainly attributed to the coupling between the sphere plasmons and the cavity plasmons.

Formation of metal nanoparticles in silicon nanopores: Plasmon resonance studies

We present a method for the formation of noble metal nanoparticle ensembles in nanostructured silicon. The key idea is based on the unique property of the large reduction potential of extended internal hydrogen-terminated porous silicon surfaces. The process of metal nanoparticle formation in porous silicon was experimentally traced using their optical plasmon resonance response. We also demonstrate that bimetallic compounds can be formed in porous silicon and that their composition can be controlled using this technique. Experimental results were found to contradict partially with considerations based on Mie theory.

Optical, Electrical and Surface Plasmon Resonance Methods for Detecting Telomerase Activity

Three different sensing platforms for the analysis of telomerase activity in human cells are described. One sensing platform involves the label-free analysis of the telomerase activity by a field-effect-transistor (FET) device. The telomerase-induced extension of a primer associated with the gate of the FET device, in the presence of the nucleotide mixture dNTPs, alters the gate potential, and this allows the detection of telomerase extracted from 65 ± 10 293T (transformed human embryonic kidney) cells/μL. The second sensing platform involves the optical detection of telomerase using CdSe/ZnS quantum dots (QDs). The telomerase-stimulated telomerization of the primer-functionalized QDs in the presence of the nucleotide mixture dNTPs results in the synthesis of the G-rich telomeres. The stacking of hemin on the self-organized G-quadruplexes found on the telomers results in the electron transfer quenching of the QDs, thus providing an optical readout signal. This method enables the detection of telomerase originating from 270 ± 20 293T cells/μL. The third sensing method involves the amplified surface plasmon resonance (SPR) detection of telomerase activity. The telomerization of a primer associated with Au film-coated glass slides, in the presence of telomerase and the nucleotide mixture (dNTPs), results in the formation of telomeres on the surface, and these alter the dielectric properties of the surface resulting in a shift in the SPR spectrum. The hybridization of Au NPs functionalized with nucleic acids complementary to the telomere repeat units with the telomeres amplifies the SPR shifts due to the coupling between the local plasmon of the NPs and the surface plasmon wave. This method enables the detection of telomerase extracted from 18 ± 3 293T cells/μL.

Novel D-type Fiber Optic Localized Plasmon Resonance Sensor Realized by Femtosecond Laser Engraving

A novel fiber optic localized plasmon resonance (FO-LPR) sensor composed of a D-shape optical fiber was proposed and demonstrated in the present study. The D-shape optical fiber was fabricated by a femtosecond laser micromachining system. The dimensions of the D-shape zone were 100 μm in depth measured from the surface of the polymer jacket layer, and the total length was 6 mm. After annealing treatment, the mean roughness of the surface was 231.7 nm as determined by AFM. The exposed surface of the D-shape fiber was modified with self-assembled gold nanoparticles to produce the FO-LPR sensor. The response of the sensor shows that the signal increases linearly with increasing refractive index. The sensor resolution of the sensor was determined to be 4.1×10 -4 RIU.

Development of near infrared responsive material based on silica encapsulated gold nanoparticles

In this research, the silica encapsulated gold nanoparticles with optical resonance located in 700–850 nm spectral region were synthesized by combining gold core and the silica shell. The synthesized composite particles can be potentially used in biological fields, due to the biocompatibility of gold, silica and biopolymers. Nano-gold, which can act a raw material of composite particles, was fabricated by stand citrate reduction method. Then, the polyvinyl pyrrolidone (PVP) and (3-mercaptopropyl)trimethoxysilane (MPTMS) are added to deposit silica shell and control particle size. Finally, a complete silica nanoshell was formed on the gold surface by the one-step method, without a repeated coating process. The controllable absorption wavelength of nano-composite particles can be easily controlled by the concentration ratio of PVP and MPTMS. Transmission electron microscopy (TEM) images and optical absorption spectra clearly showed that silica was successfully deposited onto the gold surface by this novel method. As the decreasing aggregation of gold core by adding PVP, the optical plasmon peaks became blue-shifted, but the optical plasmon resonance became red-shifted and the absorption spectra were functions of addition ratios by MPTMS. We expect to extend these functional nanoparticles for real sample applications in the near future.

Growth Kinetic of a Rod-Shaped Metal Nanocrystal

The crystallization dynamics in wet-chemical synthesis is the key parameter controlling nanoparticle morphology, which determines the frequency of the optical plasmon resonance in metal nanoparticles. Despite several in situ (dark-field microscopy) and ex situ (electron microscopy) studies of metal nanoparticle growth, the anisotropic growth kinetics are not well-understood mainly because the crystallization is a nonequilibrium process. Using simultaneous optical spectroscopy and time-resolved small-angle X-ray scattering at a synchrotron X-ray source, we directly monitor the anisotropic growth kinetics of gold and gold-copper nanorods and extract the growth parameters for both crystal directions (along the rod’s long and short axes) independently. We find a crossover from 1D to 3D growth modes at 8 and 12 min, respectively, where the nanorods attain their maximum aspect ratio. The growth model explains and predicts this crossover point without the need of a switch for the growth mode and allows for the f...

Low temperature self-agglomeration of metallic Ag nanoparticles on silica sol–gel thin films

A facile sol–gel synthesis for self-agglomeration of metallic silver nanoparticles, with fcc crystalline structure, on the silica surface in a low annealing temperature has been introduced. X-ray photoelectron spectroscopy (XPS) revealed initial agglomeration (∼30 times greater than the nominal concentration of Ag) of the nanoparticles on the surface of the dried film (100 °C) and also their oxidation as well as easy diffusion (with 0.08 eV required activation energy) into the porous silica thin films, by increasing the annealing temperature (200–400 °C). By raising the Ag concentration from 0.2 to 1.6 mol% in the sol, the average size of the Ag nanoparticles increased from ∼5 to 37 nm corresponding to a redshift of the optical plasmon resonance absorption peak from 404 to 467 nm. The high concentration of Ag (1.6 mol%) in the sol resulted in a rough surface containing compact nanoparticles. Using power spectral density analysis of the atomic force microscopy images, we have found that the highest contributions in the surface roughness of the dried silica films were caused by the particles ranging from ∼62 to 159 nm. The particles smaller than ∼39 nm did not show any detectable contributions in the surface roughness of the dried silica film. Based on the XPS analysis, a mechanism has also been proposed for the self-agglomeration of the Ag nanoparticles on the surface of the aqueous sol–gel silica thin films.

Multispecies ADI-FDTD Algorithm for Nanoscale Three-Dimensional Photonic Metallic Structures

The unconditionally stable alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is extended to model multispecies dispersive media for simulation of nanoscale three-dimensional metallic structures based on optical plasmon resonances. Examples involving modeling of Au nanoparticles show that the proposed ADI-FDTD yields improved computational performance versus standard FDTD in highly refined grids and for moderate Courant numbers

Ion synthesis and optical properties of gold nanoparticles in an Al2O3 matrix

Single-crystal Al2O3(0001) and Al2O3(1120) substrates are implanted by 160-keV Au+ ions with doses from 1015 to 1017 cm−2. Some of the implanted samples are air-annealed at 800–1200°C. The properties of the synthesized composite layers are studied by Rutherford backscattering and linear optical reflection measurements, and their nonlinear optical characteristics are examined by RZ-scanning using a picosecond Nd: YAG laser operating at a wavelength of 1064 nm. The Rutherford backscattering spectra indicate that the implanted impurity concentrates near the surface of the Al2O3. The formation of gold nanoparticles in the Al2O3 can be judged from the characteristic optical plasmon resonance band in the reflectance spectra of the samples irradiated to a dose higher than 6.0 × 1016 cm−2. The synthesized particles are shown to be responsible for nonlinear optical refraction in the samples. The nonlinear refractive index, n 2, and the real part of the third-order susceptibility, Rex(3), of the composite layers are determined.

Nonlinear optical properties of gold nanoparticles synthesized by ion implantation in sapphire matrix

Single crystal Al2O3 substrates have been implanted with 160-keV Au+ to a dose of 0.6 × 1017 or 1.0 × 1017 cm−2, with a postimplantation annealing for 1 h at 800°C in air. The obtained composite layers were studied by the method of linear optical reflection; the nonlinear optical characteristics were determined by the RZ-scan technique using picosecond radiation pulses of an Nd:YAG laser operating at 1064 nm. The appearance of a characteristic surface optical plasmon resonance band in the linear reflection spectra was indicative of the formation of gold nanoparticles in a subsurface layer of ion-irradiated Al2O3. It is shown that the synthesized particles are responsible for the observed manifestations of nonlinear refraction. The composite layers were characterized by the nonlinear refractive index (n2) and the real part of the third-order nonlinear susceptibility (Reϰ (3)).

Facile Methods to Coat Polystyrene and Silica Colloids with Metal

AbstractTo avoid the complex core surface functionalization or pretreatment that is necessary in order to coat latex and silica colloids with a uniform, complete metal shell, the solvent‐assisted route has been explored to prepare a complete metal (Ag or Au) shell with controlled thickness on polystyrene (PS) colloids and the electroless plating approach, based on electrostatic attraction, has been explored to prepare a complete silver shell with controlled thickness on silica colloids. Without any additional surface treatment, the as‐prepared complex core–shell colloids can be crystallized directly into long‐range‐ordered structures with photonic bandgaps, as reported here for the first time. These ordered structures may find potential applications as substrates or physical systems for the enhancement of Raman scattering studies, besides applications as photonic crystals. The optical plasmon resonance of the composite core–shell colloids changes with metal shell thickness, the wavelength varying over hundreds of nanometers. Our coating routes are facile and versatile, and can be extended to coat PS and silica colloids with any other metal whose ion or complex can be reduced in solution.

Application of ion implantation for synthesis of copper nanoparticles in a zinc oxide matrix for obtaining new nonlinear optical materials

We have obtained a layered composite material by implantation of single crystal zinc oxide (ZnO) substrates with 160-keV Cu+ ions to a dose of 1016 or 1017 cm−2. The composite was studied by linear optical absorption spectroscopy; the nonlinear optical characteristics were determined by means of Z-scanning at a laser radiation wavelength of 532 nm. The appearance of the optical plasmon resonance bands in the spectra indicated that ion implantation to the higher dose provides for the formation of copper nanoparticles in a subsurface layer of ZnO. The new nonlinear optical material comprising metal nanoparticles in a ZnO matrix exhibits the phenomenon of self-defocusing and possesses a high nonlinear absorption coefficient (β=2.07×10−3 cm/W).

Gold nanolayer-encapsulated silica particles synthesized by surface seeding and shell growing method: near infrared responsive materials

Gold nanolayer-encapsulated silica particles whose optical resonance is located in 750–900 nm spectral region were synthesized by combining Sn (tin)-surface seeding and a shell growing process. The synthesized composite particles can be potentially used in wide biological fields, due to biocompatibility and a well-known bioconjugation technique of gold layer. Sn atoms, which can act not only as a catalytic surface for reduction of gold but also as a linker between silica surface and gold nanoparticles, were chemically deposited on hydroxylated silica particles. Then, we introduced another reductant with gold chloride in order to produce a multilayer of Au shell. In the process, Au shells grew by the reduction of additional gold ions on the Sn-functionalized silica surface and resulted in the subsequent coalescence and growth of the deposited gold nanoparticles. Finally, a complete gold nanoshell was formed on the silica surface by the one-step method, without a repeated coating process. The deposition of a gold nanolayer on the silica particles was easily controlled by the concentration ratio of Sn-functionalized silica particles and gold chloride solutions. Transmission electron microscopy (TEM) images and optical extinction spectra clearly showed that gold nanolayers were successfully deposited on the silica surface by the novel method. As the gold colloids attached on the silica surface grew, their optical plasmon peak became red-shifted until complete a gold shell was formed. After the gold shell was completed, the optical plasmon resonance became blue-shifted and the extinction spectra were functions of a relative ratio of the core to shell thickness.