Polymer-decorated Plasmonic Nanoparticles

The preparation and characterization of noble metal nanoparticles that are coated by organic shells for the covalent immobilization of biopolymers were described. Plasmonic nanoparticles demonstrate unique size-dependent optical and photothermal properties due to the collective oscillation of free electrons in their conduction bands. The intensity of absorption and scattering of noble metal nanoparticles is significantly higher than most absorbing and scattering organic molecular dyes, which makes them excellent candidates as contrast agents in imaging. Cylindrical gold nanorods also demonstrate a tunable photothermal response to near infrared light as a function of nanoparticle aspect ratio. Organic functional groups on the nanoparticles allow the coupling of organic molecules to their shells. Several synthetic approaches to couple biomolecules to metal nanoparticles and to use the hybrid assemblies for various bioanalytical applications have been reported.     

Noble metals on the nanoscale: optical and photothermal properties and some applications in imaging, sensing, biology, and medicine

Noble metal nanostructures attract much interest because of their unique properties, including large optical field enhancements resulting in the strong scattering and absorption of light. The enhancement in the optical and photothermal properties of noble metal nanoparticles arises from resonant oscillation of their free electrons in the presence of light, also known as localized surface plasmon resonance (LSPR). The plasmon resonance can either radiate light (Mie scattering), a process that finds great utility in optical and imaging fields, or be rapidly converted to heat (absorption); the latter mechanism of dissipation has opened up applications in several new areas. The ability to integrate metal nanoparticles into biological systems has had greatest impact in biology and biomedicine. In this Account, we discuss the plasmonic properties of gold and silver nanostructures and present examples of how they are being utilized for biodiagnostics, biophysical studies, and medical therapy. For instance, taking advantage of the strong LSPR scattering of gold nanoparticles conjugated with specific targeting molecules allows the molecule-specific imaging and diagnosis of diseases such as cancer. We emphasize in particular how the unique tunability of the plasmon resonance properties of metal nanoparticles through variation of their size, shape, composition, and medium allows chemists to design nanostructures geared for specific bio-applications. We discuss some interesting nanostructure geometries, including nanorods, nanoshells, and nanoparticle pairs, that exhibit dramatically enhanced and tunable plasmon resonances, making them highly suitable for bio-applications. Tuning the nanostructure shape (e.g., nanoprisms, nanorods, or nanoshells) is another means of enhancing the sensitivity of the LSPR to the nanoparticle environment and, thereby, designing effective biosensing agents. Metal nanoparticle pairs or assemblies display distance-dependent plasmon resonances as a result of field coupling. A universal scaling model, relating the plasmon resonance frequency to the interparticle distance in terms of the particle size, becomes potentially useful for measuring nanoscale distances (and their changes) in biological systems. The strong plasmon absorption and photothermal conversion of gold nanoparticles has been exploited in cancer therapy through the selective localized photothermal heating of cancer cells. For nanorods or nanoshells, the LSPR can be tuned to the near-infrared region, making it possible to perform in vivo imaging and therapy. The examples of the applications of noble metal nanostructures provided herein can be readily generalized to other areas of biology and medicine because plasmonic nanomaterials exhibit great range, versatility, and systematic tunability of their optical attributes.     

Exploiting Size-Dependent Drag and Magnetic Forces for Size-Specific Separation of Magnetic Nanoparticles

Realizing the full potential of magnetic nanoparticles (MNPs) in nanomedicine requires the optimization of their physical and chemical properties. Elucidation of the effects of these properties on clinical diagnostic or therapeutic properties, however, requires the synthesis or purification of homogenous samples, which has proved to be difficult. While initial simulations indicated that size-selective separation could be achieved by flowing magnetic nanoparticles through a magnetic field, subsequent in vitro experiments were unable to reproduce the predicted results. Magnetic field-flow fractionation, however, was found to be an effective method for the separation of polydisperse suspensions of iron oxide nanoparticles with diameters greater than 20 nm. While similar methods have been used to separate magnetic nanoparticles before, no previous work has been done with magnetic nanoparticles between 20 and 200 nm. Both transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis were used to confirm the size of the MNPs. Further development of this work could lead to MNPs with the narrow size distributions necessary for their in vitro and in vivo optimization.     

Ultraviolet Extinction and Visible Transparency by Ivy Nanoparticles

Though much research has been conducted for nanoparticles, naturally occurring nanoparticles have not yet been well explored for their diverse properties and potential applications. This paper reports the optical absorption and scattering properties of nanoparticles secreted by English ivy. Both experimental and theoretical studies have been conducted. Strong ultraviolet extinction and excellent visible transparency are observed, compared to the inorganic TiO₂ and ZnO nanoparticles at similar concentrations. The contributions of absorption and scattering to the total extinction are quantified by simulation of the Mie scattering theory.     

NIR‐responsive nanomaterials and their applications; upconversion nanoparticles and carbon dots: a perspective

Near‐infrared (NIR) light responsive materials have received much attention for diverse applications due to their excellent optical properties. This type of material exhibits upconverted luminescence, a non‐linear optical process in which two or more low energy photons, usually from NIR light irradiation are transformed to high energy photons emission through energy transfer upconversion, excited state absorption, photon avalanche or multiphoton absorption. The NIR range of excitation source is favorable for biological imaging and cancer theranostic applications due to their high penetration depth, low autofluorescence, minimal light scattering, reduced photodamage, and negligible phototoxicity. Having these properties, NIR responsive materials such as upconversion nanoparticles (UCNPs) and carbon dots (CDs) which perform upconversion luminescence are actively exploited in a wide variety of applications such as display and sensory technology. While CDs are well known for their versatility in using different chemicals and green precursors to achieve tunable optical properties, UCNPs also have the advantage that a continuous‐wave NIR laser can be used as the excitation source. This article reviews the properties of these two materials in the aspects of luminescence mechanisms and their recent developments in cancer theranostics, display technology, biosensing and metal ions sensing applications. © 2018 Society of Chemical Industry     

Template-free synthesis of uniform hollow silica nanoparticles for controllable antireflection coatings

Antireflection coatings consisting of nanoparticles have promising applications in a wide range of UV optical fields, such as high-power laser systems and space telescopes. However, an open question for these coatings is how to minimize light scattering caused by the nanoparticles. Here, we utilize hollow silica nanoparticles to realize antireflection coatings, which largely diminish light scattering and, hence, exhibit excellent transmission even at UV wavelengths. The hollow silica nanoparticles were synthesized using a template-free approach and then dip coated onto fused silica substrates to form antireflection coatings. The coatings were found to exhibit nearly 100% transmission at any wavelength ranging from the UV to IR bands by variation of the coating thickness. Moreover, the coatings showed relatively high environmental stability because their hollow structures were insensitive to contaminants. This study provides a novel route to fabricate UV antireflection coatings with improved optical properties and good environmental stability, which will help promote the understanding, design and fabrication of optical coatings.     

A Study of Optical Properties of Soot Aggregates Composed of Poly-Disperse Monomers Using the Superposition T-Matrix Method

The diameters of soot monomers may not be constant in the single fractal aggregated soot particle. The optical properties of light absorbing soot particles aggregated with poly-disperse monomers were studied using the superposition T-matrix method. Soot aggregates were generated with different log-normal probability distribution functions (PDF) of soot monomer diameter, according to the same soot volumes and monomer numbers. The single scattering properties of soot particles were calculated at a wavelength of 550 nm, assuming a soot refractive index of 1.95 + 0.79i and a mass density of 1.8 g/cm³. The random-orientation averaging results indicated that the optical properties of soot aggregates were fairly varied for the different distributions of the monomer diameters. In these simulations, the extinction and absorption of soot aggregates were slightly (<10%) affected by the monomer poly-dispersity. The simulated mass absorption cross-sections (MAC) of fresh dry soot particles aggregated with poly-disperse monomers reached up to 6.62 ± 0.07 m²/g, which was closer to the measurement (7.5 ± 1.2 m²/g) than the assumption of volume-equivalent mono-disperse monomer (6.36 ± 0.06 m²/g). Moreover, the optical properties of soot coated with an organic shell were calculated, and the optical results showed that the absorption cross-sections of the internally mixed soot particles were also slightly (<8%) influenced by the monomer poly-dispersity. We found that the effect of the monomer poly-dispersity on the light scattering and the single scattering albedo may be considerably large (up to ?50% in extreme cases) for fresh dry soot aggregates. This effect on light scattering should be taken into account for those aggregates composed of monomers with widely distributed diameters.

Copyright 2015 American Association for Aerosol Research     

Influence of particle size distribution of calcium carbonate pigments on coated paper whiteness

The optical properties of pigments used for paper coating are linked to their morphology. The light scattering through coated layers depends upon the size and the size distribution of the pigments and their packing behavior. In this report the effect of particle packing of various calcium carbonate pigments on the whiteness of the final coated paper is studied. Different grades of calcium carbonate pigments of different particle size distribution and optics were used for coating applications on base papers. Base papers of different optics were also selected. The entire study was carried out at different coat weights. It was observed that the overall scattering from the coated sheet depends upon the light scattering from the base paper as well as through the coated layer. Higher light scattering through the coated layer will lower the effect of the base paper, whether it is dark or bright. So high bright and white pigments are not only the criteria for an enhancement in the optical properties of coated paper; the particle size and size distribution should also be considered before introducing any pigment into a coating formulation. The base optics should also be chosen on the bases of the pigments’ optics and their morphology.     

Synthesis and properties of near infrared-absorbing magnetic-optical nanopins

Novel near infrared-absorbing iron oxide-gold core-shell nanoparticles in pin shapes were synthesized. The nanopins are superparamagnetic, with 35-fold better surface enhanced Raman scattering activities than the conventional core-shell nanospheres and 50-fold greater photothermal properties than solid gold nanorods. The nanoparticles will have important impact on medical imaging, molecular diagnostics and disease treatment.     

Gold nanoparticles in biology: beyond toxicity to cellular imaging

Gold, enigmatically represented by the target-like design of its ancient alchemical symbol, has been considered a mystical material of great value for centuries. Nanoscale particles of gold now command a great deal of attention for biomedical applications. Depending on their size, shape, degree of aggregation, and local environment, gold nanoparticles can appear red, blue, or other colors. These visible colors reflect the underlying coherent oscillations of conduction-band electrons ("plasmons") upon irradiation with light of appropriate wavelengths. These plasmons underlie the intense absorption and elastic scattering of light, which in turn forms the basis for many biological sensing and imaging applications of gold nanoparticles. The brilliant elastic light-scattering properties of gold nanoparticles are sufficient to detect individual nanoparticles in a visible light microscope with approximately 10(2) nm spatial resolution. Despite the great excitement about the potential uses of gold nanoparticles for medical diagnostics, as tracers, and for other biological applications, researchers are increasingly aware that potential nanoparticle toxicity must be investigated before any in vivo applications of gold nanoparticles can move forward. In this Account, we illustrate the importance of surface chemistry and cell type for interpretation of nanoparticle cytotoxicity studies. We also describe a relatively unusual live cell application with gold nanorods. The light-scattering properties of gold nanoparticles, as imaged in dark-field optical microscopy, can be used to infer their positions in a living cell construct. Using this positional information, we can quantitatively measure the deformational mechanical fields associated with living cells as they push and pull on their local environment. The local mechanical environment experienced by cells is part of a complex feedback loop that influences cell metabolism, gene expression, and migration.     

Preparation, Characterization, and Photocatalytic Properties of CaNb2O6 Nanoparticles

CaNb₂O₆ nanoparticles with a size range of 30–50 nm were synthesized by heat treatment at 600°C after a solvothermal process and their optical and photocatalytic properties were investigated. The prepared powders were characterized by X-ray powder diffractometer, field-emission scanning electron microscope, transmission electron microscope, UV-Vis diffuse reflectance spectroscopy, Fluorescence spectroscopy, and Raman spectroscopy. Compared with a powder of the same material prepared by a solid-state reaction (SS) method, the nanoparticles exhibited a higher Brunauer–Emmett–Teller (BET) surface area, more efficient light absorption, and enhanced photocatalytic activity for producing H₂ from pure water under UV irradiation. The photoluminescence spectra revealed that a radiative recombination process is dominant in the powder prepared by the SS method (strong blue emission at 300 K) under UV light irradiation, while no obvious emission was observed in the nanoparticles. This decrease of the radiative recombination as well as the higher optical absorption ability and higher BET surface area resulting from the reduced dimensionality led to enhanced photocatalytic activity of the nanoparticles.     

Radiation synthesis and characterization of poly(vinyl alcohol)/poly(N-vinyl-2-pyrrolidone) based hydrogels containing silver nanoparticles

A series of PVA/PVP based hydrogels at different compositions were prepared by gamma irradiation. The gel fraction degree of swelling were investigated. Highly stable and uniformly distributed silver nanoparticles have been obtained onto hydrogel networks. The morphology and structure of (PVA/PVP) hydrogel and dispersion of the silver nanoparticles in the polymeric matrix were examined by scanning electron microscopy (SEM) and infrared spectroscopy (FT-IR), respectively. The formation of silver nanoparticles has been confirmed by ultraviolet visible (UV–vis) spectroscopy. A strong characteristic absorption peak was found to be around 420 nm for the silver nanoparticles in the hydrogel nanocomposite. The X-ray diffraction pattern confirmed the formation of silver nanoparticles with average particle size of 12 nm. The diameter distribution of silver nanoparticles was determined by dynamic light scattering DLS. Transmission electron microscope (TEM) showed almost spherical and uniform distribution of silver nanoparticles through the hydrogel network and the mean size of silver nanoparticles ranging is 23 nm. The good swelling properties and antibacterial of PVA/PVP-Ag hydrogel suggest that it can be a good candidate as wound dressing.     

Scattering and absorption coefficients vs. chemical composition of fine atmospheric aerosol particles under regional conditions in Hungary

The light scattering and absorption coefficients of aerosol particles with a dry diameter below 1 μm were recorded in the country air of Hungary. Concentrations of different inorganic and organic ions were measured in parallel to estimate the nature of particles causing light scattering. The sample air was heated gently to maintain a relative humidity of 30% and coarse particles were removed by a multi-jet impactor. The aerosol light scattering coefficient was monitored with an integrating nephelometer, while absorption was measured on the basis of the rate of blackening of a filter. Results gained during two time periods, mostly in the winter months, are presented in this paper. Data show that the winter average light scattering coefficient is 93 Mm⁻¹, while the corresponding figure for light absorption is 8.9 Mm⁻¹. This results in a single-scatter albedo of 0.91. Comparison of the optical data with chemical information indicates that there is a good correlation between light scattering coefficient and sulfate concentration. The relationship is significant, in particular, in the winter half-year. Regression calculations among the measured parameters suggest for summer and winter half-year a sulfate mass scattering efficiency of 6 and 8 m² g⁻¹, respectively. By using a mass absorption efficiency of 10 m² g⁻¹, the average winter absorption coefficient corresponds to an elemental carbon concentration of 0.9 μg m⁻³.     

Efficiency enhancements in Ag nanoparticles-SiO2-TiO2 sandwiched structure via plasmonic effect-enhanced light capturing

TiO₂-SiO₂-Ag composites are fabricated by depositing TiO₂ films on silica substrates embedded with Ag nanoparticles. Enhancement of light absorption of the nanostructural composites is observed. The light absorption enhancement of the synthesized structure in comparison to TiO₂ originated from the near-field enhancement caused by the plasmonic effect of Ag nanoparticles, which can be demonstrated by the optical absorption spectra, Raman scattering investigation, and the increase of the photocatalytic activity. The embedded Ag nanoparticles are formed by ion implantation, which effectively prevents Ag to be oxidized through direct contact with TiO₂. The suggested incorporation of plasmonic nanostructures shows a great potential application in a highly efficient photocatalyst and ultra-thin solar cell.     

微波合成(Au)_核·(Ag)_壳纳米粒子及其共振散射光谱研究

以柠檬酸化学还原法制备的金纳米粒子作晶种,采用微波高压液相合成技术,制备出分散性较好、规则球形的(Au)核·(Ag)壳复合纳米粒子。研究了(Au)核·(Ag)壳复合纳米粒子的紫外可见吸收光谱和共振散射光谱特性,在470nm处有最强共振散射峰,在404nm处产生一个吸收峰。结果表明,(Au)核·(Ag)壳复合纳米粒子的形成是导致470nm共振散射的根本原因。     

Effect of Cationic Surfactant Head Groups on Synthesis, Growth and Agglomeration Behavior of ZnS Nanoparticles

Colloidal nanodispersions of ZnS have been prepared using aqueous micellar solution of two cationic surfactants of trimethylammonium/pyridinium series with different head groups i.e., cetyltrimethylammonium chloride (CTAC) and cetyltrimethylpyridinium chloride (CPyC). The role of these surfactants in controlling size, agglomeration behavior and photophysical properties of ZnS nanoparticles has been discussed. UV–visible spectroscopy has been carried out for determination of optical band gap and size of ZnS nanoparticles. Transmission electron microscopy and dynamic light scattering were used to measure sizes and size distribution of ZnS nanoparticles. Powder X-ray analysis (Powder XRD) reveals the cubic structure of nanocrystallite in powdered sample. The photoluminescence emission band exhibits red shift for ZnS nanoparticles in CTAC compared to those in CPyC. The aggregation behavior in two surfactants has been compared using turbidity measurements after redispersing the nanoparticles in water. In situ evolution and growth of ZnS nanoparticles in two different surfactants have been compared through time-dependent absorption behavior and UV irradiation studies. Electrical conductivity measurements reveal that CPyC micelles better stabilize the nanoparticles than that of CTAC.     

Absorption and Scattering Properties of Dust Clouds at 10.5-μm

Mass-density-normalized absorption and extinction coefficients for arid region soil-based dust were measured at a wavelength of 10.5 μm using photoacoustical techniques, short-path transmissometry, and aerosol dosimetry. An environmental chamber incorporating strong circulation, as well as the various aerosol sampling systems, was specifically designed for aerosol size distributions with particles as large as 40 μm in radius.

The mass extinction coefficient was found to be 0.22 m²/g, while the single scattering albedo, determined from the absorption and extinction coefficients, was 0.5. Calculations of these properties were based on two approaches: analyses of size distributions from photomicrographs of filter samples and analyses of the results obtained using a mixed-medium settling theory. In both cases, Mie theory was applied despite the clearly irregular particle forms. Agreement was close to the measured value for both approaches. The expected overestimation of the optical properties for the former model did not occur. Larger particles in this range are included because of their relevance to arid region dust clouds.     

Fabrication and Characterization of Gradient Refractive Index Plastic Rods Containing Inorganic Nanoparticles

A novel method was developed for the preparation of GRIN plastic rods containing inorganic nanoparticles. Silver nanoparticles were prepared by using W/O (water in oil) reversed micelle technique in the presence of bis(2-ethylhexyl) sulpho-succinate (AOT) surfactant. The effects of w values (w=[H₂O]/[AOT]), silver nitrate concentration, AOT/isooctane/H₂O ratio, and initiator concentration on the nanoparticle size were investigated. Optical absorption spectra of the micellar samples were recorded on a spectrophotometer at room temperature in the range of 200–900 nm. The nanoparticle size was confirmed by TEM technique. To introduce the nanoparticles into the GRIN plastic rods, methyl methacrylate (MMA) was used instead of isooctane in the organic phase. Nanoparticles were found to increase the refractive index of plastic rods effectively. However, the existence of surfactant may cause the aggregation of nanoparticles leading to the occurrence of light scattering and becoming opaque. We estimated both real image transmission and the three dimensional refractive index distributions of the GRIN plastic rods prepared in this investigation. The results in this investigation suggest that nanoparticles could be used as a dopant to fabricate GRIN plastic rods and increase its refractive index effectively.     

INORGANIC NANOPARTICLES AS OPTICALLY EFFECTIVE ADDITIVES FOR POLYMERS

The transparency of polymer-particle composites can be markedly enhanced when nanoparticles are employed instead of larger particles, due to a reduction in light scattering. In addition, nanoparticles of metals (e.g., gold or silver) or semiconductors (e.g., TiO₂, ZnO, or PbS) can exhibit intrinsic optical properties that may be of interest per se or in combination with the enhanced transparency caused by the nanoparticles. For such reasons, inorganic nanoparticles have found special interest in studies devoted to optical properties in composites that look back to a long history. For instance, the size-dependent color of gold nanoparticles has been used to color glass for centuries. More recently, inorganic nanoparticles were investigated with regard to optical effects in polymeric nanocomposites such as very high or very low refractive index, reversible color switching in elastomers via swelling processes, dichroism in oriented polymers, reversible photochromic behavior, or UV absorption in visually transparent materials.