Application of thin metal film elements in bioanalysis

Advanced metal deposition and microfabrication techniques enable preparation of metal surfaces with high precision and excellent control over their size and shape with subnanometer resolution. Thin metal films of different types and functions can be found in many analytical instruments. Surfaces with high optical quality serve as mirrors, beam splitters, antireflective coatings etc. Smooth metal coating is crucial in electron microscopy. Unique properties of the thin metal films are widely used in optical systems, as tools for sample manipulation but also for chemical sensing and detection. While some of the applications are widespread and belong to the basic curriculum in analytical chemistry, the newer or less common uses of thin metal films are well known only to the experts in the field. The purpose of this critical review is to highlight the role of thin metal films in bioanalysis and summarize some of their main applications in current bioanalytical instrumentation.     

Water-Dispersible Gold Nanoclusters: Synthesis Strategies,Optical Properties,and Biological Applications

Atomically precise gold nanoclusters (AuNCs) are an emerging class of quantum-sized nanomaterials. Intrinsic discrete electronic energy levels have endowed them with fascinating electronic and optical properties. They have been widely applied in the fields of optoelectronics, photovoltaics, catalysis, biochemical sensing, bio-imaging, and therapeutics. Nevertheless, most AuNCs are synthesized in organic solvents and do not disperse in aqueous solutions; this restricts their biological applications. In this review, we focus on the recent progress in the preparation of water-dispersible AuNCs and their biological applications. We first review different methods of synthesis, including direct synthesis from hydrophilic templates and indirect phase transfer of hydrophobic AuNCs. We then discuss their photophysical properties, such as emission enhancement and fluorescence lifetimes. Next, we summarize their latest applications in the fields of biosensing, biolabeling, and bioimaging. Finally, we outline the challenges and potential for the future development of these AuNCs.     

Sub-nanometre sized metal clusters: from synthetic challenges to the unique property discoveries

Sub-nanometre sized metal clusters, with dimensions between metal atoms and nanoparticles, have attracted more and more attention due to their unique electronic structures and the subsequent unusual physical and chemical properties. However, the tiny size of the metal clusters brings the difficulty of their synthesis compared to the easier preparation of large nanoparticles. Up to now various synthetic techniques and routes have been successfully applied to the preparation of sub-nanometre clusters. Among the metals, gold clusters, especially the alkanethiolate monolayer protected clusters (MPCs), have been extensively investigated during the past decades. In recent years, silver and copper nanoclusters have also attracted enormous interest mainly due to their excellent photoluminescent properties. Meanwhile, more structural characteristics, particular optical, catalytic, electronic and magnetic properties and the related technical applications of the metal nanoclusters have been discovered in recent years. In this critical review, recent advances in sub-nanometre sized metal clusters (Au, Ag, Cu, etc.) including the synthetic techniques, structural characterizations, novel physical, chemical and optical properties and their potential applications are discussed in detail. We finally give a brief outlook on the future development of metal nanoclusters from the viewpoint of controlled synthesis and their potential applications.     

Synthesis, structure and properties of metal nanoclusters

Metal nanoclusters have physical properties differing significantly from their bulk counterparts. Metallic properties such as delocalization of electrons in bulk metals which imbue them with high electrical and thermal conductivity, light reflectivity and mechanical ductility may be wholly or partially absent in metal nanoclusters, while new properties develop. We review modern synthetic methods used to form metal nanoclusters. The focus of this critical review is solution based chemical synthesis methods which produce fully dispersed clusters. Control of cluster size and surface chemistry using inverse micelles is emphasized. Two classes of metals are discussed, transition metals such as Au and Pt, and base metals such as Co, Fe and Ni. The optical and catalytic properties of the former are discussed and the magnetic properties of the latter are given as examples of unexpected new size-dependent properties of nanoclusters. We show how classical surface science methods of characterization augmented by chemical analysis methods such as liquid chromatography can be used to provide feedback for improvements in synthetic protocols. Characterization of metal clusters by their optical, catalytic, or magnetic behavior also provides insights leading to improvements in synthetic methods. The collective physical properties of closely interacting clusters are reviewed followed by speculation on future technical applications of clusters. (125 references).     

Nanomaterials in fluorescence-based biosensing

Fluorescence-based detection is the most common method utilized in biosensing because of its high sensitivity, simplicity, and diversity. In the era of nanotechnology, nanomaterials are starting to replace traditional organic dyes as detection labels because they offer superior optical properties, such as brighter fluorescence, wider selections of excitation and emission wavelengths, higher photostability, etc. Their size- or shape-controllable optical characteristics also facilitate the selection of diverse probes for higher assay throughput. Furthermore, the nanostructure can provide a solid support for sensing assays with multiple probe molecules attached to each nanostructure, simplifying assay design and increasing the labeling ratio for higher sensitivity. The current review summarizes the applications of nanomaterials—including quantum dots, metal nanoparticles, and silica nanoparticles—in biosensing using detection techniques such as fluorescence, fluorescence resonance energy transfer (FRET), fluorescence lifetime measurement, and multiphoton microscopy. The advantages nanomaterials bring to the field of biosensing are discussed. The review also points out the importance of analytical separations in the preparation of nanomaterials with fine optical and physical properties for biosensing. In conclusion, nanotechnology provides a great opportunity to analytical chemists to develop better sensing strategies, but also relies on modern analytical techniques to pave its way to practical applications.

Significance of nanomaterials in electrochemical sensors for nitrate detection: A review

Nanomaterial-enabled electrochemical sensors are designed as an economical, efficient, and user-friendly analytical tool for on-site and routine nitrate analysis over a wide range of environmental samples. The remarkable advances and tunable attributes of nanomaterials have greatly improved the analytical performance of electrochemical nitrate sensors. In this review, a comprehensive elucidation of the recent advances in nanomaterial-based electrochemical nitrate sensors is presented. The review firstly provides a general introduction, followed by typical electrochemical sensing methods. The next two sections detail various nanomaterials, including graphene derivatives, carbon nanotubes/fibers, metal/bimetal/metal oxide nanoparticles, and conducting polymers for modifying electrodes in enzymatic and non-enzymatic electrochemical nitrate sensors. Finally, the perspectives and current challenges in achieving real-world applications of nanomaterial-based electrochemical nitrate sensors are outlined.     

Ligand Engineering in Metal Nanoclusters: from Structural Control to Functional Modulation

Ligand-protected metal nanoclusters have drawn increasing research interest because of their unique physicochemical properties and practical applications. Great efforts have been made in pursuing rational synthesis of metal nanoclusters and establishing the structure-property relationships. As an indispensable part of ligand-protected metal nanoclusters, ligands play multiple roles in determining their structures and properties. In this perspective, we demonstrate the importance of ligand engineering in terms of the control of structures, optical and catalytic properties of metal nanoclusters. Furthermore, we will show that ligand engineering is prospective in structural design and preorganization of surface metal sites.     

Recent progress in applications of ligand-stabilized metal nanoclusters

Due to a nanotechnology boom in science and technology, the metal nanoclusters or nanoparticles stabilized by polymers and organic ligands have achieved much attention recently all over the world. We have studied on the preparation of polymer-stabilized metal nanoclusters by chemical methods, and applied them mainly to catalyses. Here the recent progresses in our group are presented in the structure control of bimetallic and trimetallic nanoclusters and in the applications of metal nanoclusters not only to the catalyses but also to the sensing responsive to pH and molecular recognition, and to the electro-optic properties of liquid-crystalline display rapidly responsive to frequency modulation. Preparation of trimetallic nanoclusters with a triple core/shell structure is especially emphasized to serve as a very active catalyst at a special atomic ratio of three elements.     

Fluorescent nanoparticles for intracellular sensing: A review

Fluorescent nanoparticles (NPs), including semiconductor NPs (Quantum Dots), metal NPs, silica NPs, polymer NPs, etc., have been a major focus of research and development during the past decade. The fluorescent nanoparticles show unique chemical and optical properties, such as brighter fluorescence, higher photostability and higher biocompatibility, compared to classical fluorescent organic dyes. Moreover, the nanoparticles can also act as multivalent scaffolds for the realization of supramolecular assemblies, since their high surface to volume ratio allow distinct spatial domains to be functionalized, which can provide a versatile synthetic platform for the implementation of different sensing schemes. Their excellent properties make them one of the most useful tools that chemistry has supplied to biomedical research, enabling the intracellular monitoring of many different species for medical and biological purposes. In this review, we focus on the developments and analytical applications of fluorescent nanoparticles in chemical and biological sensing within the intracellular environment. The review also points out the great potential of fluorescent NPs for fluorescence lifetime imaging microscopy (FLIM). Finally, we also give an overview of the current methods for delivering of fluorescent NPs into cells, where critically examine the benefits and liabilities of each strategy.     

基于金属纳米簇的荧光传感平台的最新研究进展

荧光纳米生物传感平台由于具有灵敏度高、选择性好、操作简单、成本低、实时监测等特点,吸引了广泛的关注。近年来,随着纳米技术的飞速发展,具有纳米结构的材料(纳米材料)在生物传感领域显示出独特的优势。与传统材料相比,纳米材料显示出独特的物化性质,如光学、电学、机械、催化和磁性等。金属(如Au、Ag、Cu及其合金)纳米簇(MNCs)是纳米科学和纳米技术领域中一种新颖的多功能纳米材料,其通常由几个到几十个金属原子组成,其核的尺寸通常小于2 nm。由于其发光能力强、易于合成和进行表面功能化、生物相容性好、尺寸超小、毒性低等优点,金属纳米簇在能源催化、医学诊断、电子器件、生物传感等领域得到了广泛的应用。此外,金属纳米簇的荧光性能极佳(如大的斯托克斯位移、可调节的荧光、高的光学稳定性和荧光量子产率等),因此被作为荧光纳米探针广泛应用于生物传感领域。该综述介绍了近年来基于不同构建机制的金属纳米簇基的传感平台的研究进展,及其在检测离子、生物分子、pH和温度传感等方面的应用。相信该综述能为从不同传感机理构建更具前景的生物传感器提供一些新见解和理论指导。     

铜纳米簇的制备、聚集诱导荧光增强性能及应用研究进展

铜纳米簇不仅具有金属纳米簇的特异性,还有前驱体价格便宜等优点,因此有广泛的应用前景。从配体辅助法、模板法、微波法、电化学法和刻蚀法等综述了铜纳米簇的制备方法。从离子诱导聚集、pH诱导聚集、组装诱导聚集和溶剂诱导聚集增强发射等方面综述了铜纳米簇聚集诱导荧光发射增强性能。从离子检测、小分子检测、酶活性检测、生物大分子检测和生物成像等方面综述了铜纳米簇的应用,并对铜纳米簇的制备、性能优化和应用等方面作了展望。     

Progress on the development of DNA-mediated metal nanomaterials for environmental and biological analysis

This review summarized the recent progress on the synthesis, morphologies and properties of DNA-mediated metal nanomaterials including nanoparticles and nanoclusters. Moreover, their applications to environmental and biological analysis were introduced with the developing prospect in analytical chemistry.     

面向食品安全分析的核酸适配体传感技术

食品中危害因子的检测一直是国内外食品安全领域致力解决的重要问题。核酸适配体是一类通过体外筛选技术得到的单链DNA或RNA,具有特异性强、稳定性好和靶分子广等特点,因而被广泛用于食品安全检测领域。近年来,随着纳米传感技术的快速发展,互补结合适配体和纳米材料的特殊性质,可实现对靶标物质的超灵敏、高选择性及快速检测。本文总结了近年来筛选的食品危害因子适配体,综述了面向食品安全检测的基于适配体传感和纳米材料修饰的分析检测技术的进展,主要包括比色法、荧光法、电化学法以及表面等离子体共振技术,并探讨了适配体传感检测所存在的问题和未来的发展趋势。     

Developing Graphene‐Based Nanohybrids for Electrochemical Sensing

Graphene‐based nanohybrid is considered to be the most promising nanomaterial for electrochemical sensing applications due to the defects created on the graphene oxide layers. These defects provide graphene oxide unique properties, such as excellent conductivity, large specific surface area, and electrocatalytic activity. These unique properties encourage scientists to develop novel graphene‐based nanohybrids and improve the sensing efficiency. This review, therefore, addresses this topic by comprehensively discussing the strategies to fabricate novel graphene based nanohybrids with high sensitivity. The combinations of graphene with various nanomaterials, such as metal nanoclusters, metal compound nanoparticles, carbon materials, polymers and peptides, in the direction of electrochemical sensing, were systematically analyzed. Meanwhile, the challenges in the functional design and application of graphene‐based nanohybrids were described and the reasonable solutions were proposed.     

Ordered mesoporous metal oxides: synthesis and applications

Great progress has been made in the preparation and application of ordered mesoporous metal oxides during the past decade. However, the applications of these novel and interesting materials have not been reviewed comprehensively in the literature. In the current review we first describe different methods for the preparation of ordered mesoporous metal oxides; we then review their applications in energy conversion and storage, catalysis, sensing, adsorption and separation. The correlations between the textural properties of ordered mesoporous metal oxides and their specific performance are highlighted in different examples, including the rate of Li intercalation, sensing, and the magnetic properties. These results demonstrate that the mesoporosity has a direct impact on the properties and potential applications of such materials. Although the scope of the current review is limited to ordered mesoporous metal oxides, we believe that the information may be useful for those working in a number of fields.     

Insight of the photoluminescence of atomically precise bimetallic nanoclusters with free electrons

Noble-metal nanoclusters with emission properties are promising candidtes for cell imaging, biosensing, photo-therapy applications due to their ultra-small size, good photostability, and high biocompatibility. It is of great importance to realize the atomic precision of such metal nanoclusters (NCs) because they allow us to investigate the origin of fluorescence at the atomic level. However, compared to quantum dots (QDs) and organic dyes, noble metal nanoclusters usually suffered from low quantum yield, which significantly limited their applications. Doping with other metal atoms is an effective strategy to enhance the fluorescent properties of metal NCs. Therefore, bimetallic nanoclusters possess enhanced emission properties relative to their monometallic counterparts. Although a couple of reviews have existed for bimetallic nanocluster, few of them concern their emissive properties. In this context, the emissive properties of atomically precise bimetallic nanoclusters are summarized in this minireview. Synergistic effect, state of aggregation, assembly, and isomerism on the fluorescence of bimetallic clusters and structure-photoluminescence property correlations are also discussed.     

DNA‐Templated Copper Nanoprobes: Overview,Feature, Application,and Current Development in Detection Technologies

Metal nanoprobes have recently attracted board research interestinr their application in establishing sensing systems due to their unique optical, electrical, physical, and chemical properties. In comparison to gold and silver nanoprobes, analytical platform based on copper nanoprobes (Cu‐NPs) is still in the early stages of development. In this review, we focus on single‐stranded, and double‐stranded DNA capped Cu‐NPs sensing systems which have been designed for various analytes, including metal ions, anions, small molecules, biomolecules (DNA, RNA, and protein, etc.). In addition, the application of Cu‐NPs in biological labeling or bio‐imaging platforms has also been introduced and summarized.     

多彩金纳米簇:从结构到生物传感和成像

金纳米簇是一种具有发光性能的“类分子”新兴纳米材料.通过调控金原子数目和配体组成性质,金纳米簇可以实现同激发光下不同波段发射,从而展现出“五彩缤纷”的发光特性,这使其被广泛应用于光催化、光学器件、传感和成像等多个领域.因此,开发和优化具有优异发光性能的金纳米簇一直是化学、材料和生物学科的研究热点.本文立足于金纳米簇的发...     

Responsive polymers for analytical applications: A review

Stimuli-responsive polymers are capable of translating changes in their local environment to changes in their chemical and/or physical properties. This ability allows stimuli-responsive polymers to be used for a wide range of applications. In this review, we highlight the analytical applications of stimuli-responsive polymers that have been published over the past few years with a focus on their applications in sensing/biosensing and separations. From this review, we hope to make clear that while the history of using stimuli-responsive polymers for analytical applications is rich, there are still a number of directions to explore and exciting advancements to be made in this flourishing field of research.     

Synthesis and applications of mesoporous nanocomposites containing metal nanoparticles

Metal nanoparticles (NP) and mesoporous (MP) oxides are complementary materials, since the size scale of pores in MP oxides matches that of NP and both systems have potential applications in similar fields. Besides, nanocomposites obtained through their combination possess not only the intrinsic properties of each component, but also new features derived from the synergy between them, mainly due to the high interfacial area between the metal and the oxide. Thus, new optical, catalytic and sensing properties can be achieved that are not easily available from the individual components. In this review, we focus our attention on such NP@MP composites, not only from the point of view of the most common synthesis pathways but also briefly describing their applications in fields as diverse as (photo)catalysis, sensing, photochromism and other optical properties, as well as patterning.