Near‐Infrared Active Lead Chalcogenide Quantum Dots: Preparation,Post‐Synthesis Ligand Exchange,and Applications in Solar Cells

Quantum dots (QDs) of lead chalcogenides (e.g. PbS, PbSe, and PbTe) are attractive near‐infrared (NIR) active materials that show great potential in a wide range of applications, such as, photovoltaics (PV), optoelectronics, sensors, and bio‐electronics. The surface ligand plays an essential role in the production of QDs, post‐synthesis modification, and their integration to practical applications. Therefore, it is critically important that the influence of surface ligands on the synthesis and properties of QDs is well understood for their applications in various devices. In this Review we elaborate the application of colloidal synthesis techniques for the preparation of lead chalcogenide based QDs. We specifically focus on the influence of surface ligands on the synthesis of QDs and their solution‐phase ligand exchange. Given the importance of lead chalcogenide QDs as potential light harvesters, we also pay particular attention to the current progress of these QDs in photovoltaic applications.     

The role of graphene‐based sorbents in modern sample preparation techniques

The application of graphene‐based sorbents in sample preparation techniques has increased significantly since 2011. These materials have good physicochemical properties to be used as sorbent and have shown excellent results in different sample preparation techniques. Graphene and its precursor graphene oxide have been considered to be good candidates to improve the extraction and concentration of different classes of target compounds (e.g., parabens, polycyclic aromatic hydrocarbon, pyrethroids, triazines, and so on) present in complex matrices. Its applications have been employed during the analysis of different matrices (e.g., environmental, biological and food). In this review, we highlight the most important characteristics of graphene‐based material, their properties, synthesis routes, and the most important applications in both off‐line and on‐line sample preparation techniques. The discussion of the off‐line approaches includes methods derived from conventional solid‐phase extraction focusing on the miniaturized magnetic and dispersive modes. The modes of microextraction techniques called stir bar sorptive extraction, solid phase microextraction, and microextraction by packed sorbent are discussed. The on‐line approaches focus on the use of graphene‐based material mainly in on‐line solid phase extraction, its variation called in‐tube solid‐phase microextraction, and on‐line microdialysis systems.     

Enzyme Mimics: Advances and Applications

Enzyme mimics or artificial enzymes are a class of catalysts that have been actively pursued for decades and have heralded much interest as potentially viable alternatives to natural enzymes. Aside from having catalytic activities similar to their natural counterparts, enzyme mimics have the desired advantages of tunable structures and catalytic efficiencies, excellent tolerance to experimental conditions, lower cost, and purely synthetic routes to their preparation. Although still in the midst of development, impressive advances have already been made. Enzyme mimics have shown immense potential in the catalysis of a wide range of chemical and biological reactions, the development of chemical and biological sensing and anti‐biofouling systems, and the production of pharmaceuticals and clean fuels. This Review concerns the development of various types of enzyme mimics, namely polymeric and dendrimeric, supramolecular, nanoparticulate and proteinic enzyme mimics, with an emphasis on their synthesis, catalytic properties and technical applications. It provides an introduction to enzyme mimics and a comprehensive summary of the advances and current standings of their applications, and seeks to inspire researchers to perfect the design and synthesis of enzyme mimics and to tailor their functionality for a much wider range of applications.     

Supported colloidal nanoparticles in heterogeneous gas phase catalysis: on the way to tailored catalysts

Using colloidally synthesized nanoparticles for the preparation of supported catalysts offers several advantages (e.g. precise control of particle size and morphology) when compared to traditional preparation techniques. Although such nanoparticles have already been very successfully used for catalytic applications in the liquid phase, applications in heterogeneous gas phase catalysis are still scarce. One aspect, usually considered as a problem, is organic stabilizers typically employed during the nanoparticle synthesis since they or their decomposition products are supposed to block catalytically active sites on the nanoparticle surface. Thus, in many studies so far, the removal of the organic ligands prior to use in gas phase catalysis has been proposed. In this perspective article, however, we will discuss a number of benefits such ligand shells may have for heterogeneous gas phase catalysis, including the protection against chemical modification, prevention of sintering and tuning of SMSI effects.     

Gold nanoparticle-modified ITO electrode for electrogenerated chemiluminescence: well-preserved transparency and highly enhanced activity

Although it is desirable to use transparent indium tin oxide (ITO)-coated glass substrates as working electrodes for electrogenerated chemiluminescence (ECL), their applications in ECL studies of the Ru(bpy)32+ (bpy, 2,2'-bipyridine)/tri-n-propylamine (TPrA) system have been limited because of the large overpotential of TPrA oxidation and the instability of the ITO surface at high anodic potentials. Here, we describe a simple method to achieve high ECL activity using ITO electrodes modified with gold nanoparticles (GNPs). The GNPs have been capped with fluorosurfactant ligands (i.e., Zonyl FSO). Much more facile TPrA oxidation was achieved by using the modified electrode, and an intense low-oxidation-potential (LOP) ECL signal was observed at approximately 0.88 V versus SCE. The electrode transmittance drop upon modification was generally less than 5% over the visible spectrum when small-sized GNPs (approximately 4 nm) were employed. The well-preserved transparency and highly enhanced activity make the modified electrode promising for ECL studies.     

Cellular Uptake of Gold Nanoparticles and Their Movement in 3D Multicellular Tumor Spheroids: Effect of Molecular Weight and Grafting Density of Poly(2‐hydroxyl ethyl acrylate)

It is known that the size of gold nanoparticles (GNPs) is not the only determining factor in the uptake by cells such as cancer cells. The surface functionalization plays a crucial role, in particular the nature of the ligand as well as the molecular weight and the grafting density. Here, poly(2‐hydroxy ethyl) acrylate (pHEA) with molecular weights ranging from 10, 20 to 39 g mol^?1 via reversible addition–fragmentation chain transfer polymerization is synthesized. These polymers are used directly to coat GNPs with sizes of 20, 40, and 70 nm as the trithiocarbonate functionality can strongly bind to the gold surface. The library of nine GNP is found to be nontoxic against lung carcinoma cells A549 and has negligible albumin protein absorption as determined by quartz crystal microbalance. Laser scanning confocal microscopy and flow cytometry reveal that GNP coated with medium length pHEA displays the highest cellular uptake while the effect of the size is not statistically significant. In contrast, multicellular tumor spheroids, which is a 3D model that simulates the tissue, enable the penetration of GNP coated with the longest pHEA chain while it also appears that smaller GNPs have now a clear advantage.     

Surface initiated‐atom transfer radical polymerization of a sugar methacrylate on gold nanoparticles

For development of surface‐functionalized gold nanoparticles (GNPs) as cellular probes, we report herein the synthesis of glycoconjugates of GNPs with cyclic sugar methacrylate, 2‐lactobionamidoethyl methacrylate (LAMA). The strategy involves the attachment of an initiator on the nanoparticle surface followed by surface initiated‐atom transfer radical polymerization (SI‐ATRP) of LAMA. SI‐ATRP of LAMA was achieved by reacting a mixture of copper (I) bromide (CuBr), 2,2′‐bipyridine (bpy) and initiator‐bound GNPs in methanol at 20 °C for 12 h. The resultant GNP glycoconjugates were characterized using Fourier‐transform infrared (FT‐IR) spectroscopy, X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The FT‐IR spectra of GNP glycoconjugates show IR peaks characteristic of LAMA demonstrating the formation of a LAMA layer on the GNPs' surface. The XPS spectrum of glycoconjugates shows signals due to the presence of carbon (C1s, 288 eV) and oxygen (O1s, 536 eV) along with gold (Au 4f, 100 eV; Au 4p, 743 eV). The increase in diameter of GNPs from 13 to 25 nm measured by SEM further confirms the presence of a LAMA layer on the surface of the GNPs. Considering the biological importance of glycoconjugates, such as cell recognition, cell adhesion and cell growth regulation, the method described herein would be beneficial in many areas such as pathogen detection and biosensors. Copyright © 2008 John Wiley & Sons, Ltd.     

Solution‐Processable Graphene Quantum Dots

This minireview describes recent progress in solution‐processable graphene quantum dots (SGQDs). Advances in the preparation, modification, properties, and applications of SGQDs are highlighted in detail. As one of emerging nanostructured materials, possible ongoing research related to the precise control of the lateral size, edge structure and surface functionality; the manipulation and characterization; the relationship between the properties and structure; and interfaces with biological systems of SGQDs have been speculated upon.     

Colloidal stability of gold nanoparticles modified with thiol compounds: bioconjugation and application in cancer cell imaging

Gold nanoparticles (GNPs) are attractive alternative optical probes and good biocompatible materials due to their special physical and chemical properties. However, GNPs have a tendency to aggregate particularly in the presence of high salts and certain biological molecules such as nucleic acids and proteins. How to improve the stability of GNPs and their bioconjugates in aqueous solution is a critical issue in bioapplications. In this study, we first synthesized 17 nm GNPs in aqueous solution and then modified them with six thiol compounds, including glutathione, mercaptopropionic acid (MPA), cysteine, cystamine, dihydrolipoic acid, and thiol-ending polyethylene glycol (PEG-SH), via a Au-S bond. We systematically investigated the effects of the thiol ligands, buffer pH, and salt concentrations of the solutions on the colloidal stability of GNPs using UV-vis absorption spectroscopy. We found that GNPs modified with PEG-SH were the most stable in aqueous solution compared to other thiol compounds. On the basis of the above results, we developed a simple and efficient approach for modification of GNPs using a mixture of PEG-SH and MPA as ligands. These biligand-modified GNPs were facilely conjugated to antibody using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide and N-hydroxysulfosuccinimide as linkage reagents. We conjugated GNPs to epidermal growth factor receptor antibodies and successfully used the antibody-GNP conjugates as targeting probes for imaging of cancer cells using the illumination of a dark field. Compared to current methods for modification and conjugation of GNPs, our method described here is simple, has a low cost, and has potential applications in bioassays and cancer diagnostics and studies.     

Metal–Organic Frameworks: From Molecules/Metal Ions to Crystals to Superstructures

Metal–organic frameworks (MOFs) are among the most attractive porous materials known today, exhibiting very high surface areas, tuneable pore sizes and shapes, adjustable surface functionality, and flexible structures. Advances in the formation of MOF crystals, and in their subsequent assembly into more complex and/or composite superstructures, should expand the scope of these materials in many applications (e.g., drug delivery, chemical sensors, selective reactors and removal devices, etc.) and facilitate their integration onto surfaces and into devices. This Concept article aims to showcase recently developed synthetic strategies to control the one‐, two‐ and three‐dimensional (1‐, 2‐ and 3D) organisation of MOF crystals.     

Single-step biofriendly synthesis of surface modifiable, near-spherical gold nanoparticles for applications in biological detection and catalysis

There is an increased interest in understanding the toxicity and rational design of gold nanoparticles (GNPs) for biomedical applications in recent years. Such efforts warrant reliable, viable, and biofriendly synthetic methodology for GNPs with homogeneous sizes and shapes, particularly sizes above 30 nm, which is currently challenging. In the present study, an environmentally benign, biofriendly, single-step/single-phase synthetic method using dextrose as a reducing and capping agent in a buffered aqueous solution at moderate temperature is introduced. The resulting GNPs are near-spherical, stable, catalytically active, place exchangeable, and water-soluble within the size range of 10-120 nm. The added advantage of the biologically friendly reaction medium employed in this new synthetic approach provides a method for the direct embedment/integration of GNPs into biological systems such as the E. coli bacterium without additional capping ligand or surface modification processes.     

Recent Advances in Preparation and Applications of Magnetic Framework Composites

Metal‐organic frameworks (MOFs) offer ample characteristics, such as easy synthesis, high surface area, tunable porosities, open metal sites, post‐synthesis modification, making them attractive for diverse applications. Since magnetic particles can be positioned and separated by a magnetic field, magnetic framework composites (MFCs) have attracted tremendous attention. In this review, different methods of preparing MFCs, including direct mixing, in‐situ growth of magnetic particles, embedding method, layer‐by‐layer growth method and encapsulation method, will be discussed in detail. Moreover, their applications in catalysis, adsorption, biomedicine and sensing will also be introduced.     

Mesoporous Silica Layer: Preparation and Opportunity

Periodic mesoporous silicas, which were prepared from silica‐surfactant mesostructured materials, have been investigated for a wide range of application due to their very large surface area, high porosity, pore size uniformity and variation, periodic pore arrangement and possible pore surface modification, after the pioneering papers on the formation of mesoporous silicas (MCM‐41 and FSM‐16). Morphosyntheses from such macroscopic morphologies as bulk monolith and film to nanoscopic ones, nanoparticles and their stable suspension, make mesoporous materials more attractive for applications and detailed characterization. Mesoporous silicas have been studied initially for such applications as adsorbent and catalyst, and more recently, optical, electronic, and bio‐related applications have been investigated. This review summarizes the studies on mesoporous silica film to highlight the present status and future of the preparation, characterization and application of the mesoporous silica film.     

Amphiphilic well-defined degradable star block copolymers by combination of ring-opening polymerization and atom transfer radical polymerization: Synthesis and application as drug delivery carriers

Atom transfer radical polymerization (ATRP) is one of the most popular advanced polymerization techniques in macromolecular science, allowing the synthesis of tailor-made polymers with controlled molecular weight, architecture, composition, and functionality. The combination of ATRP and ring-opening polymerization (ROP) provides a straightforward route for the preparation of polymers exhibiting both targeted and well-defined features and biodegradability, which is very interesting for the development of new materials for biomedical applications. Among the different types of polymer architectures, amphiphilic star block copolymers (BCPs) represent a very attractive one, due to their high degree of functionality at the molecular surface, low hydrodynamic volume and higher encapsulation ability, compared to molecular systems based on linear polymers. This review article highlights the research focused on the synthesis of amphiphilic well-defined degradable star BCPs by combination of ROP and ATRP, with particular focus on the development of polymers for biomedical applications, such as anticancer drug delivery, diagnosis therapy, or photodynamic therapy, which is the most investigated field regarding these polymers.     

Simultaneous Detection of Copper,Lead and Zinc on Tin Film/Gold Nanoparticles/Gold Microelectrode by Square Wave Stripping Voltammetry

In this work, three heavy metals (Cu(II), Pb(II) and Zn(II)) in wide potential window were simultaneously detected on tin film/gold nanoparticles/gold microelectrode (Sn/GNPs/gold microelectrode) by the method of square wave stripping voltammetry. The Sn/GNPs/gold microelectrode was fabricated by in situ plating of a Sn film on a gold nanoparticles (GNPs) modified gold microelectrode. The influence of hydrogen overflow on stripping of Zn(II) on the gold microelectrode was reduced by modification of GNPs, which made the stripping potential of target metals shift positively. The interference of sulfhydryl groups was reduced and the selectivity of the microelectrode was improved due to the addition of Sn in the detection solution. After accumulation at ?1.4 V for 300 s in acetate buffer solution (0.1 mol L^?1, pH 4.5), the Sn/GNPs/gold microelectrode revealed a good linear behavior in the examined concentration ranges from 5 to 500 µg L^?1 for Cu(II) and Pb(II), and from 10 to 500 µg L^?1 for Zn(II), with a limit of detection of 2 µg L^?1 for Cu(II), 3 µg L^?1 for Pb(II) and 5 µg L^?1 for Zn(II) (S/N=3). When compared with a Sb/GNPs/gold microelectrode and a Bi/GNPs/gold microelectrode, the Sn/GNPs/gold microelectrode showed the best stripping performance to Cu(II), Pb(II) and Zn(II). As a new type of environment‐friendly electrode, the Sn/GNPs/gold microelectrode has potential applications for detection of heavy metals.     

Multivalent Gold Glycoclusters: High Affinity Molecular Recognition by Bacterial Lectin PA‐IL

Multivalent protein‐carbohydrate interactions are involved in the initial stages of many fundamental biological and pathological processes through lectin–carbohydrate binding. The design of high affinity ligands is therefore necessary to study, inhibit and control the processes governed through carbohydrate recognition by their lectin receptors. Carbohydrate‐functionalised gold nanoclusters (glyconanoparticles, GNPs) show promising potential as multivalent tools for studies in fundamental glycobiology research as well as biomedical applications. Here we present the synthesis and characterisation of galactose functionalised GNPs and their effectiveness as binding partners for PA‐IL lectin from Pseudomonas aeruginosa. Interactions were evaluated by hemagglutination inhibition (HIA), surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC) assays. Results show that the gold nanoparticle platform displays a significant cluster glycoside effect for presenting carbohydrate ligands with almost a 3000‐fold increase in binding compared with a monovalent reference probe in free solution. The most effective GNP exhibited a dissociation constant (K_d) of 50 nM per monosaccharide, the most effective ligand of PA‐IL measured to date; another demonstration of the potential of glyco‐nanotechnology towards multivalent tools and potent anti‐adhesives for the prevention of pathogen invasion. The influence of ligand presentation density on their recognition by protein receptors is also demonstrated.     

非对称性Janus粒子的制备与可控组装

古罗马的双面神(Janus)常被用来描述具有两种不同化学结构或性质的不对称粒子, Janus粒子由于自身的特殊性能在药物载体、电子器件和乳液稳定等方面表现出良好的发展势头, 其应用前景日益受到人们的重视. 目前, Janus 粒子作为基本的组装基元受到越来越多的关注, 相关组装方法也被广泛地研究, 包括本体组装、界面组装和外界驱动力调控等, 特别是Janus 粒子的双亲修饰与功能化. 本文综述了现今Janus 粒子制备方法及对其进行修饰组装的最新研究进展, 详细讨论比较了一步合成法、聚合物自组装法和晶种直接生长等方法的特点及差异, 并对一些新型功能Janus粒子的设计及潜在的应用前景进行了展望.     

Recent advances on noncovalent molecular imprints for affinity separations

Molecularly imprinted polymers (MIPs) are tailor-made synthetic materials capable of selectively rebinding a target analyte, or a group of structurally related compounds based on a combination of recognition mechanisms including size, shape, and functionality. Among the advantageous properties of MIPs are the achievable specific affinity, the relative ease of preparation, and their mechanical and chemical robustness, which renders them ideal materials for applications as stationary phase (e. g., affinity chromatography or SPE), or as antibody mimics (e. g., biomimetic assays). Here, we review recent advancements on the application of MIPs in affinity separations and biomimetic assays, which have focused on the synthesis of size- and shape-uniform particles facilitating reproducibility, improved binding site accessibility, and enhanced affinity. While MIPs certainly offer promising potential as selective separation phase in a variety of applications, deeper understanding of the fundamental interactions governing imprinting, and rational understanding of the imprinting mechanism has yet to be achieved for providing rational guidelines in deliberately designing next-generation MIP materials.     

Importance of sample preparation on reliable surface characterisation of nano‐objects: ISO standard 20579‐4

The international ISO Standard 20579‐4, dealing with the history and preparation of nano‐objects for surface analysis, has been developed to help address some of the replication and reproducibility issues caused by the fundamental nature of nano‐objects. Although all types of samples requiring surface analysis need thoughtful preparation, nano‐objects, for which many properties are controlled by their surfaces, present additional challenges in order to avoid variations and artefacts due to the handling and preparation of materials prior to analysis. This international standard is part of a series of standards related to preparation of samples for surface chemical analysis. Parts 1 and 2 of ISO Standard series 20579 address general issues that apply to many samples. Part 3, which is still in development, will focus on biomaterials. Part 4 specifically considers issues that arise due to the inherent nature of nano‐objects. Because of sensitivity to their environment, the standard indicates the minimum information that needs to be reported about the handling and preparation of nano‐objects prior to surface analysis. This information should become part of sample provenance information that helps assure the reliability and usefulness of data obtained from surface‐analysis in the context of the synthesis, processing, and analysis history of a batch of material. Application of this standard can help address reproducibility and traceability issues associated with synthesis, processing, and characterization of nano‐objects in research and commercial applications.