On Optical Properties of Dilute Colloidal Gold

Wavelength-dependent complex effective refractive index of dilute colloidal gold, i.e., spherical gold nanoparticles in water was measured using a reflectometer and a spectrophotometer. The spectral data obtained was used for the calculation of the wavelength-dependent complex permittivity of the gold nanoparticle with the aid of the Maxwell Garnett effective medium model for the colloid. It is shown that the wavelength-dependent complex permittivity of gold nanoparticle is different from the complex permittivity of bulk gold. Furthermore, Smakula’s formula is introduced for the calculation of the relative concentration of gold nanoparticles embedded in liquid using absorption data of the colloid.     

Comparative Theoretical Study of the Optical Properties of Silicon/Gold,Silica/Gold Core/Shell and Gold Spherical Nanoparticles

The scattering and absorption efficiencies of light by individual silicon/gold core/shell spherical nanoparticles in air are analysed theoretically in the framework of Lorenz-Mie formalism. We have addressed the influence of particle-diameter and gold-shell thickness on the scattering and absorption efficiencies of such nano-heterostructures. For comparison, we also considered the famous silica/gold core/shell nanoparticle and pure gold nanoparticle. Our simulation clearly shows that the optical response of the illuminated Si/Au core/shell nanoparticle differs markedly from that of the famous SiO₂/Au heterostructure which in turn does not show a significant difference with that of the pure gold nanoparticle. This difference is clearly evident for shell thickness to outer particle radius ratio of less than 0.5. It manifests itself essentially by the occurrence of a strong and sharp absorption resonance beyond the wavelength of 600 nm where the silica/gold and the pure gold nanoparticles never absorb. The characteristics of this resonance are found to be sensitive to the particle diameter and the shell thickness. In particular, its spectral position can be adjusted over a wide spectral range from the visible to the mid-IR by varying the particle diameter and/or the shell thickness.     

Review on the Optical Properties of Nanoparticle Aggregates Towards the Therapeutic Applications

Plasmonics - Nanoparticles are of potential use for therapeutic applications, and nowadays a variety of modalities involving optical characteristics of nanoparticles are in the clinical translation...     

基于纳米金光学性质的分子检测与应用

纳米金颗粒是近年研究最为广泛的纳米材料之一,它具有良好的生物相容性、化学稳定性以及独特的光学性质,在生物分子检测、诊断和治疗方面具有很大的发展潜力。尤其是纳米金显示出特殊的表面等离子体共振现象,导致了粒子表面产生强电磁场,并最终增强了诸如吸收和散射的辐射特性,其散射光强与粒子的尺寸和团聚状态有密切关系。而由于共振现象而产生的纳米金对光的强烈吸收并高效转换为热效应也被用于检测和治疗。此外,与纳米金尺寸相关的局域表面等离子体共振光学特性,能够在粒子附近产生很强的电磁场增强,从而构成表面增强拉曼散射的基础。纳米金在强光照射下也表现出良好的抗光漂白的荧光现象,其特有的荧光寿命也成为检测的一种有效手段。与其他荧光物质作用时,又表现出表面增强荧光特性以及荧光共振能量转移。综述中,在介绍纳米金这些特殊光学性质的基础上,回顾了其在生物分子检测方面的应用进展。     

Synthesis and Optical Properties of Highly Stabilized Peptide-Coated Gold Nanoparticles

Plasmonics - The interaction between peptide and gold nanoparticle surfaces has been increasingly of interest for bionanotechnology applications. To fully understand how to control such...     

Optical and Photocatalytic Measurements of Co-TiO2 Nanoparticle Thin Films

Plasmonics - Co-TiO2 nanoparticle thin films were synthesized by sol-gel method. The structural properties of the synthesized sample were studied using FTIR, XRD, and TEM. XRD confirmed the...     

Dichroic Optical Properties of Uniaxially Oriented Gold Nanorods in Polymer Films

Applications based on the optical excitation of the longitudinal surface plasmon resonance of gold nanorods (AuNRs) work at highest efficiency if all component AuNRs can be maximally excited simultaneously. This can be achieved in aligned AuNR structures, such as those embedded in uniaxially stretched polymer films. Since too high heating temperatures during film stretching cause reshaping and alteration of optical properties of the rods, a maximum allowable heating temperature is determined. The alignment of the rods is quantified by an orientational order parameter of 0.92 based on a statistically significant sample of assumed t distributed means and obtained by scanning electron microscopy. We show that a stretched AuNRs-PVA composite film has optical properties that approach the dichroic properties of an idealized ensemble of fully aligned, identical, and non-interacting AuNRs embedded in a PVA film. The idealized system is provided by FDTD simulations of a single AuNR, which we carried out using the size- and shape-adapted dielectric function of gold and the software RSOFT.     

Fluorescent (Au@SiO2)SiC Nanohybrids: Influence of Gold Nanoparticle Diameter and SiC Nanoparticle Surface Density

Gold@silica core–shell nanoparticles were prepared with various gold core diameters (ranging from 20 to 150 nm) and silica thicknesses (ranging from 10 to 30 nm). When the gold diameter is increased, the size dispersion became larger, leading to a broader plasmon band. Then, silicon carbide (SiC) nanoparticles were covalently immobilized onto silica to obtain hybrid (Au@SiO₂) SiC nanoparticles. The absorption properties of these hybrid nanoparticles showed that an excess of SiC nanoparticles in the dispersion can be identified by a strong absorption in the UV region. Compared to SiC reference samples, a blue shift of the fluorescence emission, from 582 to 523 nm, was observed, which was previously attributed to the strong surface modification of SiC when immobilized onto silica. Finally, the influence of several elaboration parameters (gold diameter, silica thickness, SiC concentration) on fluorescence enhancement was investigated. It showed that the highest enhancements were obtained with 10 nm silica thickness, low concentration of SiC nanoparticles, and surprisingly, with a 20-nm gold core diameter. This last result could be attributed to the broad plasmon band of big gold colloids. In this case, SiC emission strongly overlapped gold absorption, leading to possible quenching of SiC fluorescence by energy transfer.     

Plasmonic Effect on the Optical Properties in a Hybrid V-Type Three-Level Quantum Dot-Metallic Nanoparticle Nanosystem

We investigated theoretically the exciton–plasmon coupling effects on the population dynamics and the absorption properties of a hybrid nanosystem composed of a metal nanoparticle (MNP) and a V-type three-level semiconductor quantum dot (SQD), which are created by the interaction with the induced dipole moments in the SQD and the MNP, respectively. Excitons of the SQD and the plasmons of the MNP in such a hybrid nanosystem could be coupled strongly or weakly to demonstrate novel properties of the hybrid system. We also find that the gain happens in such a hybrid system, because of the coherent interaction between the SQD and the MNP. Our results show that the non-linear optical response of the hybrid nanosystem can be greatly enhanced or depressed due to the exciton–plasmon couplings.     

Optical Properties of Noncontinuous Gold Shell Engineered on Silica Mesosphere

The optical properties of individual noncontinuous shells with different gold coverage are investigated by the single-particle dark field scattering measurements and single-particle surface-enhanced Raman scattering (SERS) measurements at different excitation wavelengths. By controlling the growth of gold seeds, multi-metallic nanogaps/crevices with different optical responses are assembled on silica mesospheres forming noncontinuous shells that can be confirmed through the transmission electron microscope images. We find the surface plasmon resonance of single shell red-shifts from 510 to 680 nm with the increase of gold coverage. At the excitation of 532 and 785 nm, the best enhancements about 2.0?×?10⁵ and 1.1?×?10⁷ are obtained on spheres with ～60 and 83 % gold coverage, respectively. The weak polarization-dependent SERS indicates that the enhancement is from the multi-gaps on single noncontinuous shell. This optical tunable and SERS active noncontinuous gold shell can be applied in biosensing, ultra trace detection, and molecule analysis needing multi-wavelengths excitation.     

Naked Eye Detection of Cr3+ and Co2+ Ions by Gold Nanoparticle Modified with Azomethine

This paper reports the synthesis of azomethine-modified gold nanoparticles with azomethine (azomethine-AuNPs) in aqueous media, which were characterized by FT-IR spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The azomethine-AuNPs were employed as colorimetric for Cr³⁺ and Co²⁺ ions at pH 6.2–7.5 and 8.1–9.1, at room temperature in aqueous solution. In the presence of Cr³⁺ and Co²⁺, the azomethine-AuNPs induce aggregation of the nanoparticles. Upon aggregation, the surface plasmon absorption band red-shifts so that the nanoparticle solution appears a blue color. The sensitivity of azomethine-AuNPs towards other metal ions, Mg²⁺, Mn²⁺, Cr⁶⁺, Na⁺, Ni²⁺, Ag⁺, Al³⁺, Ca²⁺, Cd²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Hg²⁺, Cd²⁺, K⁺, Co³⁺, Ni²⁺, Pb²⁺, and Zn²⁺ are negligible. This highly selective sensor allows a direct quantitative assay of Co²⁺ and Cr³⁺ with colorimetric detection limits of 83.22 and 108 nM, respectively.

     

Modulation of Optical Properties of Gold Nanorods on Addition of KOH

Gold nanorods are known to exhibit two distinct surface plasmon oscillations namely, transverse and longitudinal bands corresponding to oscillations of conduction electrons along width and length of gold nanorods. Considerable changes in these surface plasmon resonance peak positions occurred when KOH was added to the nanorod solution. Nanorods with initial longitudinal plasmon band at 739, 796, and 895 nm are studied with variation in KOH concentration. While the longitudinal plasmon resonance peak showed blue shift, transverse plasmon resonance peak exhibited only intensity variations. Changes could be attributed to the shape transition of gold nanorods on variation of pH in the solution. Shape transition of gold nanorods is confirmed by transmission electron microscopy images.     

Influence of Material Properties on TiO2 Nanoparticle Agglomeration

Emerging nanomaterials are being manufactured with varying particle sizes, morphologies, and crystal structures in the pursuit of achieving outstanding functional properties. These variations in these key material properties of nanoparticles may affect their environmental fate and transport. To date, few studies have investigated this important aspect of nanoparticles'' environmental behavior. In this study, the aggregation kinetics of ten different TiO₂ nanoparticles (5 anatase and 5 rutile each with varying size) was systematically evaluated. Our results show that, as particle size increases, the surface charge of both anatase and rutile TiO₂ nanoparticles shifts toward a more negative value, and, accordingly, the point of zero charge shifts toward a lower value. The colloidal stability of anatase sphere samples agreed well with DLVO theoretical predictions, where an increase in particle size led to a higher energy barrier and therefore greater critical coagulation concentration. In contrast, the critical coagulation concentration of rutile rod samples correlated positively with the specific surface area, i.e., samples with higher specific surface area exhibited higher stability. Finally, due to the large innate negative surface charge of all the TiO₂ samples at the pH value (pH = 8) tested, the addition of natural organic matter was observed to have minimal effect on TiO₂ aggregation kinetics, except for the smallest rutile rods that showed decreased stability in the presence of natural organic matter.     

Controlled Fabrication of Gold Nanoparticle and Fluorescent Protein Conjugates

The unique optical properties of gold nanoparticles make them attractive for a wide range of applications which require optical detection and manipulation techniques. Here, we experimentally demonstrate the use of single femtosecond pulses at resonance wavelength for a controlled conjugation of gold nanoparticles and fluorescent proteins. This optically driven reaction is rigorously studied and analyzed using a variety of experimental techniques, and a detailed model is proposed which describes the adsorption of the proteins onto the nanoparticles' surface, as well as their subsequent desorption by a reducing agent. Potential applications of the resulting nanoparticle?Cprotein conjugates include controlled delivery of fluorescent markers and local sensing of biochemical processes.     

Gold Nanoparticle Interference Study during the Isolation,Quantification, Purity and Integrity Analysis of RNA

Investigations have been conducted regarding the interference of nanoparticles (NPs) with different toxicological assay systems, but there is a lack of validation when conducting routine tests for nucleic acid isolation, quantification, integrity, and purity analyses. The interference of citrate-capped gold nanoparticles (AuNPs) was investigated herein. The AuNPs were added to either BEAS-2B bronchial human cells for 24 h, the isolated pure RNA, or added during the isolation procedure, and the resultant interaction was assessed. Total RNA that was isolated from untreated BEAS-2B cells was spiked with various concentrations (v/v%) of AuNPs and quantified. A decrease in the absorbance spectrum (220–340 nm) was observed in a concentration-dependent manner. The 260 and 280 nm absorbance ratios that traditionally infer RNA purity were also altered. Electrophoresis was performed to determine RNA integrity, but could not differentiate between AuNP-exposed samples. However, the spiked post-isolation samples did produce differences in spectra (190–220 nm), where shifts were observed at a shorter wavelength. These shifts could be due to alterations to chromophores found in nucleic acids. The co-isolation samples, spiked with 100 µL AuNP during the isolation procedure, displayed a peak shift to a longer wavelength and were similar to the results obtained from a 24 h AuNP treatment, under non-cytotoxic test conditions. Moreover, hyperspectral imaging using CytoViva dark field microscopy did not detect AuNP spectral signatures in the RNA isolated from treated cells. However, despite the lack of AuNPs in the final RNA product, structural changes in RNA could still be observed between 190–220 nm. Consequently, full spectral analyses should replace the traditional ratios based on readings at 230, 260, and 280 nm. These are critical points of analyses, validation, and optimization for RNA-based techniques used to assess AuNPs effects.     

Single step Al2O3 chromatography for improved separation and recovery of Taxol

An improved method that uses a single alkaline Al₂O₃ chromatography step was developed both for separating Taxol from the extracts of Taxus cuspidate callus cultures, and meanwhile converting other taxanes to Taxol catalyzed by the Al₂O₃ adsorbent. Under the optimized operating conditions, a Taxol recovery of 170% was obtained. The final Taxol content was 29% starting from less than 1% in the initial extracts.     

Fe2O3 Nanoparticle Seed Catalysts Enhance Cyclability on Deep (Dis)charge in Aprotic LiO2 Batteries

Although the high energy density of Li?O₂ chemistry is promising for vehicle electrification, the poor stability and parasitic reactions associated with carbon‐based cathodes and the insulating nature of discharge products limit their rechargeability and energy density. In this study, a cathode material consisting of α‐Fe₂O₃ nanoseeds and carbon nanotubes (CNT) is presented, which achieves excellent cycling stability on deep (dis)charge with high capacity. The initial capacity of Fe₂O₃/CNT electrode reaches 805 mA h g^?1 (0.7 mA h cm^?2) at 0.2 mA cm^?2, while maintaining a capacity of 1098 mA h g^?1 (0.95 mA h cm^?2) after 50 cycles. The operando structural, spectroscopic, and morphological analysis on the evolution of Li₂O₂ indicates preferential Li₂O₂ growth on the Fe₂O₃. The similar d‐spacing of the (100) Li₂O₂ and (104) Fe₂O₃ planes suggest that the latter epitaxially induces Li₂O₂ nucleation. This results in larger Li₂O₂ primary crystallites and smaller secondary particles compared to that deposited on CNT, which enhances the reversibility of the Li₂O₂ formation and leads to more stable interfaces within the electrode. The mechanistic insights into dual‐functional materials that act both as stable host substrates and promote redox reactions in Li?O₂ batteries represent new opportunities for optimizing the discharge product morphology, leading to high cycling stability and coulombic efficiency.     

Synthesis, Conforming, Linear, and Non-linear Optical Properties of Gold Nanoparticles-sepiolite Compacts

Gold monodispersed nanoparticles (smaller than 10 nm) have been embedded into sepiolite fibres and sintered by spark plasma sintering (SPS) in order to preserve their nanometre size. The optical properties of these nanoparticles have been measured showing the surface plasmon resonance. Plasmon absorption curves have been successfully fitted by using the quasistatic approximation for gold nanoparticles. It has been observed that the sintering process decreases the plasmon width. SPS sintered nanostructured compacts present large values of the non-linear third-order dielectric susceptibility related to the gold concentration.