Realization of thermally durable close-packed 2D gold nanoparticle arrays using self-assembly and plasma etching

Realization of thermally and chemically durable, ordered gold nanostructures using bottom-up self-assembly techniques are essential for applications in a wide range of areas including catalysis, energy generation, and sensing. Herein, we describe a modular process for realizing uniform arrays of gold nanoparticles, with interparticle spacings of 2 nm and above, by using RF plasma etching to remove ligands from self-assembled arrays of ligand-coated gold nanoparticles. Both nanoscale imaging and macroscale spectroscopic characterization techniques were used to determine the optimal conditions for plasma etching, namely RF power, operating pressure, duration of treatment, and type of gas. We then studied the effect of nanoparticle size, interparticle spacing, and type of substrate on the thermal durability of plasma-treated and untreated nanoparticle arrays. Plasma-treated arrays showed enhanced chemical and thermal durability, on account of the removal of ligands. To illustrate the application potential of the developed process, robust SERS (surface-enhanced Raman scattering) substrates were formed using plasma-treated arrays of silver-coated gold nanoparticles that had a silicon wafer or photopaper as the underlying support. The measured value of the average SERS enhancement factor (2 x 10(5)) was quantitatively reproducible on both silicon and paper substrates. The silicon substrates gave quantitatively reproducible results even after thermal annealing. The paper-based SERS substrate was also used to swab and detect probe molecules deposited on a solid surface.

Porous Three Dimensional Arrays of Plasmonic Nanoparticles

Plasmonic interactions in a well-defined array of metallic nanoparticles can lead to interesting optical effects, such as local electric field enhancement and shifts in the extinction spectra, which are of interest in diverse technological applications, including those pertaining to biochemical sensing and photonic circuitry. Here, we report on a single-step wafer scale fabrication of a three-dimensional array of metallic nanoparticles whose sizes and separations can be easily controlled to be anywhere between fifty to a few hundred nanometers, allowing the optical response of the system to be tailored with great control in the visible region of the spectrum. The substrates, apart from having a large surface area, are inherently porous and therefore suitable for optical sensing applications, such as surface enhanced Raman scattering, containing a high density of spots with enhanced local electric fields arising from plasmonic couplings.

Microwave-assisted, surfactant-free synthesis of air-stable copper nanostructures and their SERS study

A simple, rapid, and surfactant-free synthesis of crystalline copper nanostructures has been carried out through microwave irradiation of a solution of copper acetylacetonate in benzyl alcohol. The structures are found to be stable against oxidation in ambient air for several months. High-resolution electron microscopy (SEM and TEM) reveals that the copper samples comprise nanospheres measuring about 150 nm in diameter, each made of copper nanocrystals similar to 7 nm in extension. The nanocrystals are densely packed into spherical aggregates, the driving force being minimization of surface area and surface energy, and are thus immune to oxidation in ambient air. Such aggregates can also be adherently supported on SiO2 and Al2O3 when these substrates are immersed in the irradiated solution. The air-stable copper nanostructures exhibit surface enhanced Raman scattering, as evidenced by the detection of 4-mercaptobenzoic acid at 10(-6) M concentrations.

Study of the Formation of Nano-Networks in Colloidal Particles

The authors studied the formation of a wafer-scale network of connected colloidal beads by reactive ion etching. The dimensions of the connections have been studied as a function of etching time for colloidal beads of different sizes, and could be well controlled. The authors have found that the nano-network forms and disappears for the same time of etching independent of the diameter of the polystyrene beads. With recent interest of connected colloidal networks in various optical sensing applications, such as photonic crystals, as surface-enhanced Raman scattering substrates, the studies have potential uses in the development of wafer-scale nanophotonic sensors.

Spontaneous formation of branched nanochains from room temperature molten amides: visible and near-IR active, SERS substrates for non-fluorescent and fluorescent analytes

Highly stable, branched gold nanoworms are formed spontaneously in an acetamide-based room temperature molten solvent without any additional external stabilizing or aggregating agent. The nanoworms can be anchored onto solid substrates such as indium tin oxide (ITO) without any change in morphology. The anchored nanoworms are explored as substrates for surface enhanced Raman scattering (SERS) studies using non-fluorescent 4-mercaptobenzoic acid (4-MBA) and fluorescent rhodamine 6G (R6G) as probe molecules. The anchored nanostructured particles respond to near IR (1064 nm) as well as visible (785, 632.8 and 514 nm) excitation lasers and yield good surface enhancement in Raman signals. Enhancement factors of the order 10(6)-10(7) are determined for the analytes using a 1064 nm excitation source. Minimum detection limits based on adsorption from ethanolic solutions of 1028 M 4-MBA and aqueous solutions of 1027 M R6G are achieved. Experimental Raman frequencies and frequencies estimated by DFT calculations are in fairly good agreement. SERS imaging of the nanostructures suggests that the substrates comprising of three dimensional, highly interlinked particles are more suited than particles fused in one dimension. The high SERS activity of the branched nanoworms may be attributed to both electromagnetic and charge transfer effects.

表面增强拉曼光谱术在生命科学及单分子研究中的应用与进展

本文介绍了表面增强拉曼散射的基本原理及其在生命科学研究中的应用；综述了最近十年来利用表面增强拉曼散射进行单分子和活细胞检测的研究进展以及在活体检测中的应用；对表面增强拉曼光谱术在生命科学研究中的独特优势及发展前景进行了介绍。

SERS的基底、机理及在分子组装和生物分析中的应用研究

自表面增强Raman散射（SERS）在粗糙化的银电极上被首次发现以来，对于SERS的研究取得了很大的进展。主要集中在对SERS基底的构筑、SERS机理的解释以及SERS的应用方面，包括在表面科学及生物分析中的应用。本论文主要通过纳米合成及组装技术构筑了具有高活性、稳定性及重现性好的SERS基底，研究了SERS的电磁增强机理以及SERS在分子组装体与生物分析中的应用。关于SERS基底的构筑，我们主要合成了中空的银金纳米结构，在玻碳表面构筑了高SERS活性的银纳米簇、在水汽界面构筑了二维金纳米阵列及金纳米棒的聚集体膜作为SERS基底。我们还研究了处于金属纳米粒子-耦联分子-金属纳米粒子以及银纳米片-耦联分子-宏观金银两种三明治结构中耦联分子的SERS谱，得出存在于这两种三明治结构中的局域电磁耦合效应LSP-LSP (Localized Surface Plasmon)及LSP与宏观金银表面的表面等离子极化SPP (Surface Plamon Polartion)之间的电磁耦合效应，即LSP-SPP耦合。对于SERS的应用，我们首先研究了SERS在分子组装体方面的应用，得出分子在金属表面的吸附行为；同时利用SERS所具有的独特特征，分别研究了SERS在活体细胞以及构建适配子传感器方面的应用。具体工作如下： 1. SERS基底的构筑 采用种子调控的置换反应制备了中空的银金双金属纳米结构，研究了探针分子在其上的SERS效应; 采用静电组装的方法在玻碳表面构筑了具有SERS活性的银纳米簇；在水汽界面构筑了具有高SERS活性的二维金纳米阵列及金纳米棒的聚集体膜，同时研究了这些纳米结构作为SERS基底的特征。 2. SERS的电磁耦合增强机理 通过构筑金/银纳米粒子-耦联分子-银纳米粒子的三明治结构，研究了处于该结构中的耦联分子的SERS谱，得出存在于金银纳米粒子间的局域的表面等离子之间的耦合效应，即LSP-LSP电磁耦合；研究了处于宏观金/银-耦联分子-银纳米片的三明治结构中耦联分子的SERS谱，得出存在于这种三明治结构中的银纳米片的局域表面等离子共振与宏观金、银表面的表面等离子极化之间的电磁耦合效应，即LSP-SPP电磁耦合。 SERS在分子组装体方面的应用 首先通过SERS研究了硫醇类分子如4,4’-二巯基苯硫醚(4,4’-TBBT)在金表面的吸附，同时辅助其它表征手段如电化学、原子力等得出金属表面分子单层膜的吸附行为；通过SERS研究了该分子在银电极及银溶胶表面吸附行为的差异，得出该分子在银电极及银溶胶表面不同的吸附取向。 4. SERS在生物分析中的应用 利用SERS所具有的独特的特征，研究了染料分子在银纳米粒子上的SERS光谱及其作为光学探针在活体细胞中的应用；通过对纳米金进行适配子及Raman探针的标记构筑了对蛋白进行高灵敏度及选择性识别的SERS的适配子传感器。

Environmentally friendly synthesis of highly monodisperse biocompatible gold nanoparticles with urchin-like shape

We report a facile and environmentally friendly strategy for high-yield synthesis of highly monodisperse gold nanoparticles with urchin-like shape. A simple protein, gelatin, was first used for the control over shape and orientation of the gold nanoparticles. These nanoparticles, ready to use for biological systems, are promising in the optical imaging-based disease diagnostics and therapy because of their tunable surface plasmon resonance (SPR) and excellent surface-enhanced Raman scattering (SERS) activity.

Self-assembly of lambda-DNA networks/Ag nanoparticles: Hybrid architecture and active-SERS substrate

In this article, highly rough and stable surface enhanced Raman scattering (SERS)-active substrates had been fabricated by a facile layer by-layer technique. Unique lambda-DNA networks and CTAB capped silver nanoparticles (AgNP) were alternatively self-assembled on the charged mica surface until a desirable number of bilayers were reached. The as-prepared hybrid architectures were characterized by UV-vis spectroscopy, tapping mode atomic force microscopy (AFM) and confocal Raman microscopy, respectively.

Ethanol-induced formation of silver nanoparticle aggregates for highly active SERS substrates and application in DNA detection

A controllable silver nanoparticle aggregate system has been synthesized by adding different amounts of ethanol to cetyltrimethylammonium bromide (CTAB) capped silver nanoparticles (Ag-nps), which could be used as highly efficient surface-enhanced Raman scattering (SERS) active substrates. This ethanol-induced aggregation can be attributed to preferential dissolution of CTAB into ethanol, which leads a partial removal of the protective CTAB layer on Ag-nps. The optical and morphological properties of these aggregates under various volumes of ethanol were explored via UV-vis spectroscopy and atomic force microscopy.

Large-Scale and Template-Free Growth of Free-Standing Single-Crystalline Dendritic Ag/Pd Alloy Nanostructure Arrays

Large-scale arrays consist of dendritic single-crystalline Ag/Pd alloy nanostructures are synthesized for the first time. A simple galvanic replacement reaction is introduced to grow these arrays directly on Ag substrates. The morphology of the products strongly depended on the reaction temperature and the concentration of H2PdCl4 solution. The mechanism of the formation of alloy and the dendritic morphology has been discussed. These alloy arrays exhibit high surface-enhanced Raman scattering (SERS) activity and may have potential applications in investigation of "in situ" Pd catalytic reactions using SERS. Moreover, electrocatalytic measurements suggest that the obtained dendritic Ag/Pd alloy nanostructures exhibit electrocatytic activity toward the oxidation of formic acid.

Synthesis of different gold nanostructures by solar radiation and their SERS spectroscopy

In this article, a simple and novel photochemical synthesis of different gold nanostructures is proposed using solar radiation. This method is rapid, convenient and of low cost, and can be performed under ambient conditions. By adjusting the concentration of sodium acetate (NaAc), different morphologies of the products can be easily obtained. Without NaAc, the products obtained are mainly polyhedral gold particles; lower concentration of NaAc (0.05 and 0.1 M) accelerates the formation of flowerlike gold nanostructures; while higher concentration of NaAc (0.5 M) facilitates the formation of a variety of gold nanowires and nanobelts. It is found that the morphology change of gold nanaostructures is the result of the synergistic effect of poly(diallyl dimethylammonium) chloride (PDDA), Ac- ions, and the pH value. In addition, the different gold nanostructures thus obtained were used as substrates for surface-enhanced Raman scattering (SERS) with p-aminothiophenol (p-ATP) as the probe molecule.

A General Route to Construct Diverse Multifunctional Fe3O4/Metal Hybrid Nanostructures

We have developed a simple, efficient, economical, and general approach to construct diverse multifunctional Fe3O4/metal hybrid nanostructures displaying magnetization using 3-aminopropyltrimethoxysilane (APTMS) as a linker. High-density Au nanoparticles (NPs) could be supported on the surface of superparamagnetic Fe3O4 spheres and used as seeds to construct Au shell-coated magnetic spheres displaying near-infrared (NIR) absorption., which may make them promising in biosensor and biomedicine applications. High-density flower-like Au/Pt hybrid NPs could be supported on the surface of Fe3O4 spheres to construct multifunctional hybrid spheres with high catalytic activity towards the electron-transfer reaction between potassium ferricyanide and sodium thiosulfate. High-density Ag or Au/Ag core/shell NPs could also be supported on the surface of Fe3O4 spheres and exhibited pronounced surface-enhanced Raman scattering (SERS), which may possibly be used as an optical probe with magnetic function for application in high-sensitivity bioassays.

An effective hydrothermal route for the synthesis of multiple PDDA-protected noble-metal nanostructures

In this Article, we demonstrate an effective hydrothermal route for the synthesis of multiple PDDA-protected (PDDA = poly(diallyl dimethylammonium) chloride) noble-metal (including silver, platinum, palladium, and gold) nanostructures in the absence of any seeds and surfactants, in which PDDA, an ordinary and water-soluble polyelectrolyte, acts as both a reducing and a stabilizing agent. Under optimal experimental conditions, Ag nanocubes, Pt and Pd nanopolyhedrons, and Au nanoplates can be obtained, which were characterized by transmission electron microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. More importantly, the nanostrucfures synthesized show potential applications in surface-enhanced Raman scattering and electrocatalysis, in which Ag nanocubes and Pt nanopolyhedrons were chosen as the examples, respectively.

A general route to prepare one- and three-dimensional carbon nanotube/metal nanoparticle composite nanostructures

Adsorption of polyethyleneimine (PEI)-metal ion complexes onto the surfaces of carbon nanotubes (CNTs) and subsequent reduction of the metal ion leads to the fabrication of one-dimensional CNT/metal nanoparticle (CNT/M NP) heterogeneous nanostructures. Alternating adsorption of PEI-metal ion complexes and CNTs on substrates results in the formation of multilayered CNT films. After exposing the films to NaBH4, three-dimensional CNT composite films embedded with metal nanoparticles (NPs) are obtained. UV-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy are used to characterize the film assembly. The resulting (CNT/M NP)(n) films inherit the properties from both the metal NPs and CNTs that exhibit unique performance in surface-enhanced Raman scattering (SERS) and electrocatalytic activities to the reduction of O-2; as a result, they are more attractive compared to (CNT/polyelectrolyte)(n) and (NP/polyelectrolyte)(n) films because of their multifunctionality.