Soft Langmuir–Blodgett Technique for Hard Nanomaterials

Materials and their assemblies of dimensions down to a few nanometers have attracted considerable scientific interest in physical, chemical, and biological sciences because of unique properties not available in their bulk counterparts. The Langmuir–Blodgett (LB) technique allows rigid nanomaterials to be aligned in particular structures through a flexible assembly process at liquid interfaces. In this review, we summarize the development of assembly of hard nanomaterials using soft LB techniques. An initial summary of the basic features of nanomaterials will include dimension‐related effects, synthesis, characterization, and analysis, and will be followed by examples of LB assemblies of nanomaterials described according to their morphology: nanoparticles, nanorods, nanowires, nanotubes, and nanosheets. Some of the nanomaterials have been fabricated in orientation‐controlled morphologies, and have been incorporated into prototype devices for gas sensing and photocurrent transport. In the final part of this review, the challenges remaining for LB techniques of hard nanomaterials will be overviewed, and will include a comparison with the widely‐used LB technique involving soft materials.     

活性炭纤维对贵金属的吸附

活性炭纤维（ACF）具有优越的氧化还原吸附特性，通过创麻基活性炭纤维（水蒸气活化和磷酸化学活化）与硝酸银溶液反应而将银引入纤维中，X射线衍射分析表明ACF上负载的都是纳米银热处理可使它们的畸变减小且在高于150℃时才长大此外，用其它基体的ACF也可还原吸附贵金属离子（Au+、Pt4+、Pd2＋），并得到晶体生长有取向的纳先资金属粒子复合的活性炭纤维     

贵金属纳米线的模板法制备及应用研究进展

贵金属纳米线因独特的光学性质吸引了人们的普遍关注,已经被广泛应用于生物传感器、太阳能电池、纳米尺度光电器件领域。其光学性能主要来源于贵金属表面的区域等离子体共振,而区域等离子体共振主要由金属纳米线的形状、尺寸、组成以及电磁常数决定。简要地回顾了模板法合成贵金属纳米线的方法,讨论了影响纳米线光学性质的因素,最后简述了应用前景。     

控制剂中金属离子对制备高纯高产纳米银线的影响

以含有不同金属离子Fe~(3+)和Cu(2+)的Cl盐晶体为控制剂,采用多元醇热法制备高性能的纳米银线(AgNWs)。通过SEM、TEM、SAED和XRD测试,对不同金属离子条件下制备所得的纳米银产物微观形貌和晶体结构进行表征,研究了控制剂中不同金属离子对AgNWs一维生长均匀性和纯度的影响。实验结果表明,选用控制剂FeCl_3·6H_2O时,可将反应时间缩短至40min,就可以制得高纯度高长径比的AgNWs。AgNWs的长度为10μm,直径为60nm,长径比在160以上。说明强氧化性金属离子对制备高性能纳米银线有优化促进作用,从而提高AgNWs的合成效率。     

Bimetallic Nanostructures as Active Raman Markers: Gold‐Nanoparticle Assembly on 1D and 2D Silver Nanostructure Surfaces

It is demonstrated that bimetallic silver–gold anisotropic nanostructures can be easily assembled from various nanoparticle building blocks with well‐defined geometries by means of electrostatic interactions. One‐dimensional (1D) silver nanowires, two‐dimensional (2D) silver nanoplates, and spherical gold nanoparticles are used as representative building blocks for bottom‐up assembly. The gold nanoparticles are electrostatically bound onto the 1D silver nanowires and the 2D silver nanoplates to give bimetallic nanostructures. The unique feature of the resulting nanostructures is the particle‐to‐particle interaction that subjects absorbed analytes to an enhanced electromagnetic field with strong polarization dependence. The Raman activity of the bimetallic nanostructures is compared with that of the individual nanoparticle blocks by using rhodamine 6G solution as the model analyte. The Raman intensity of the best‐performing silver–gold nanostructure is comparable with the dense array of silver nanowires and silver nanoplates that were prepared by means of the Langmuir–Blodgett technique. An optimized design of a single‐nanostructure substrate for surface‐enhanced Raman spectroscopy (SERS), based on a wet‐assembly technique proposed here, can serve as a compact and low‐cost alternative to fabricated nanoparticle arrays.     

Well-defined nanoclusters as fluorescent nanosensors: a case study on Au(25) (SG)(18)

The fluorescence of nanoparticles has attracted much attention in recent research, but in many cases the underlying mechanisms are difficult to evaluate due to the polydispersity of nanoparticles and their unknown structures, in particular the surface structures. Recent breakthroughs in the syntheses and structure determinations of well-defined gold nanoclusters provide opportunities to conduct in-depth investigations. Devising well-defined nanocluster sensors based on fluorescence change is of particular interest not only for scientific studies but also for practical applications. Herein, the potential of the glutathionate (SG)-capped Au(25) nanocluster as a silver ion sensor is evaluated. The Ag(+) detection limit of approximately 200 nM, based on the fluorescence enhancement and good linear fluorescence response in the silver ion concentration range from 20 nM to 11 μM, in combination with the good selectivity among 20 types of metal cations, makes Au(25) (SG)(18) a good candidate for fluorescent sensors for silver ions. Further experiments reveal three important factors responsible for the unique fluorescence enhancement caused by silver ions: 1) the oxidation state change of Au(25) (SG)(18) ; 2) the interaction of neutral silver species (Ag(0) , reduced by Au(25) (SG)(18) (-) ) with Au(25) (SG)(18) ; and 3) the interaction of Ag(+) with Au(25) (SG)(18.) Experiments demonstrate the very different chemistry of hydrophobic Au(25) (SC(2) H(4) Ph)(18) and hydrophilic Au(25) (SG)(18) in the reaction with silver ions. This work indicates another potential application of gold nanoclusters, offers new strategies for nanocluster-based chemical sensing, and reveals a new way to influence nanocluster chemistry for potential applications.     

Vertical arrays of anisotropic particles by gravity-driven self-assembly

Anisotropic particles assemble to spontaneously form columnar arrays. Hybrid nanotube/nanowire particles (silica nanotubes partially filled with metallic cores) deposit with their denser metallic ends towards the surface, orienting them vertically. Up to 84% are observed to be standing over a 0.64 cm(2) area within 15 min. Standing percentage is found to be dependent on particle surface concentration.     

Ultrasmall Ag+-rich nanoclusters as highly efficient nanoreservoirs for bacterial killing

Metallic silver （Ag） and its ability to combat infection have been known since ancient history. In the wake of nanotechnology advancement, silver＇s efficacy to fight broad spectrum bacterial infections is further improved in the form of Ag nanoparticles （NPs）. Recent studies have ascribed the broad spectrum antimicrobial properties of Ag NPs to dissociation of Ag＊ ions from the NPs, which may not be entirely applicable when the size of Ag NPs decreases to the sub-2 nm range [denoted Ag nanoclusters （NCs）]. In this paper we report that ultrasmall glutathione （GSH）-protected Ag^＋-rich NCs （Ag^＋-R NCs for short, with a predominance of Ag＋ species in the NCs） have much higher antimicrobial activities towards both gram-negative and gram-positive bacteria than the reference NC, GSH-Ag^＋-R NCs. They have the same size and surface ligand, but with different oxidation states of the core silver. This interesting finding suggests that the undissociated Ag^＋-R NCs armed with abundant Ag^＋ ions on the surface are highly active in bacterial killing, which was not observed in the system of their larger counterpart, Ag NPs.     

Gold Nanowire Fabrication with Surface‐Attached Lipid Nanotube Templates

A high‐throughput approach to fabricate gold nanowires on surfaces with a lipid nanotube template is demonstrated. Streptavidin‐coated gold nanoparticles are attached to the biotin‐tagged lipid nanotubes. After the chemical fixation, the samples are dried and treated with oxygen plasma to remove the organic template and connect the particles. The created nanowires are characterized by cryo‐transmission electron microscopy, atomic force microscopy, and electrical measurements.     

Ideal Dimers of Gold Nanospheres for Precision Plasmonics: Synthesis and Characterization at the Single‐Particle Level for Identification of Higher Order Modes

Ideal dimers comprising gold nanoparticles with a smooth surface and high sphericity are synthesized by a substrate‐based assembly strategy with efficient cetyltrimethylammonium bromide removal. An unprecedented structural and plasmonic uniformity at the single‐particle level is observed since inhomogeneities resulting from variations in gap morphology are eliminated. Single ideal dimers are analyzed by polarization‐resolved dark‐field scattering spectroscopy. Contributions from transverse as well as quadrupolar and octupolar longitudinal plasmon coupling modes can be discriminated because of their orthogonal polarization behavior. The assignment of these higher order coupling modes is supported by computer simulations.     

A Deformable and Highly Robust Ethyl Cellulose Transparent Conductor with a Scalable Silver Nanowires Bundle Micromesh

Huge challenges remain regarding the facile fabrication of neat metallic nanowires mesh for high‐quality transparent conductors (TCs). Here, a scalable metallic nanowires bundle micromesh is achieved readily by a spray‐assisted self‐assembly process, resulting in a conducting mesh with controllable ring size (4–45 µm) that can be easily realized on optional polymer substrates, rendering it transferable to various deformable and transparent substrates. The resultant conductors with the embedded nanowires bundle micromesh deliver superior and customizable optoelectronic performances, and can sustain various mechanical deformations, environmental exposure, and severe washing, exhibiting feasibility for large‐scale manufacturing. The silver nanowires bundle micromesh with explicit conductive paths is embedded into an ethyl cellulose (EC) transparent substrate to achieve superior optoelectronic properties endowed by a low amount of incorporated nanowires, which leads to reduced extinction cross‐section as verified by optical simulation. A representative EC conductor with a low sheet resistance of 25 Ω □^?1, ultrahigh transmittance of 97%, and low haze of 2.6% is attained, with extreme deformability (internal bending radius of 5 µm) and waterproofing properties, opening up new possibilities for low‐cost and scalable TCs to replace indium‐tin oxide (ITO) for future flexible electronics, as demonstrated in a capacitive touch panel in this work.