Synthesis of surface-modified quantum dots

The review discusses the main methods used to obtain surface-modified quantum dots, specifically silicon, heavy metal chalcogenide and pnictide semiconductor nanoparticles. Examples of transformation processes of the grafted layer are considered. The importance of surface modification of A^IIB^VI- and A^IIIB^V-type semiconductor nanoparticles for the practical application of quantum dots is shown. It was determined that the most promising areas of their practical application are biology, medicine, and pharmacology. Special attention is paid to the hydrophilization of quantum dots, because only these materials can be used in biomedical applications. Modification of the quantum dot surface with amino acids is considered.

     

石墨烯量子点负载银纳米粒子制备及氧还原电催化活性

银基氧还原电催化剂具有较高的电催化活性且价格相对低廉,因而受到广泛关注. 本文采用简单、预先合成的石墨烯量子点作为载体和还原剂,制得了负载于石墨烯量子点、且无保护剂和表面活性剂的表面洁净银纳米粒子（Ag NPs/GQDs）. 电化学研究表明,Ag NPs/GQDs复合电催化剂的氧还原有较高的电催化活性,氧在碱性溶液中可经4电子途径还原为水. 与商业铂碳电极（Pt/C）相比,AgNPs/GQDs电极具有高催化电流密度、良好稳定性和极佳抗甲醇性能. 该银纳米粒子对开发高性能和低成本的非铂氧还原电催化剂有潜在的应用前景.     

Surface-Active Fluorinated Quantum Dots for Enhanced Cellular Uptake

Fluorescent nanoparticles, such as quantum dots, hold great potential for biomedical applications, mainly sensing and bioimaging. However, the inefficient cell uptake of some nanoparticles hampers their application in clinical practice. Here, the effect of the modification of the quantum dot surface with fluorinated ligands to increase their surface activity and, thus, enhance their cellular uptake was explored.     

Promising avenues of research in nanoscience: chemistry of semiconductor nanoparticles

The state-of-the-art in the field of research on semiconductor nanoparticles is analyzed; cadmium chalcogenide nanoparticles are considered in most detail. Emphasis is placed on the methods of synthesis and on control of the size, composition, and structure of semiconductor nanoparticles — “quantum dots”. The state of the surface plays a significant role in determining the properties of nanoparticles. Organized nanostructures comprised of quantum dots are considered. The properties of semiconductor nanoparticles are described. Prospects for applications of semiconductor nanomaterials are discussed. Dedicated to Academician V. I. Minkin on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 811–836, April, 2005.     

Excited State Relaxation and Stabilization of Hydrogen Terminated Silicon Quantum Dots

Silicon is the leading semiconductor material in microelectronic industry. Owing to the large surface to volume ratio, low-dimensional Si nanostructures, for instance, silicon quantum dots exhibit diverse electronic and optical properties. Passivating the surface of Si nanostructures by a suitable species is thereby required to stabilize and engineer the dot properties in different environment. Recent theoretical advances in the investigation of the excited state properties of silicon quantum dots (QDs) are reviewed in this article. The theoretical calculations reveal that the excited state relaxation is prevalent in hydrogenated silicon nanoparticles. Stokes shift due to structure relaxation in the excited state varies with the particle size. It is therefore desirable to minimize Stokes shift for the purpose of maximizing its quantum yield or efficiency in photoluminescence applications. Consequently, surface functionalization by a suitable species turns out to be the most effective avenue. Determination of proper passivating agent is of outmost importance to satisfy the practical necessity. All these intermingled factors are briefly addressed in this article.     

Supramolecular nanostructures based on bacterial reaction center proteins and quantum dots

Design of the nanostructures based on membrane proteins (the key functional elements of biomembranes) and colloid nanoparticles is a fascinating field at the interface of biochemistry and colloids, nanotechnology and biomedicine. The review discusses the main achievements in the field of ultrathin films prepared from bacterial reaction center proteins and light-harvesting complexes, as well as these complexes tagged with quantum dots. The principles of preparation of these thin films and their structure and properties at different interfaces are described; as well as their characteristics estimated using a combination of the modern interfacial techniques (absorption and fluorescence spectroscopy, atomic force and Brewster angle microscopy, etc.) are discussed. Further approaches to develop the nanostructures based on the membrane proteins and quantum dots are suggested. These supramolecular nanostructures are promising prototypes of the materials for photovoltaic, optoelectronic and biosensing applications.     

The fabrication strategies and enhanced performances of metal-organic frameworks and carbon dots composites: State of the art review

Metal-organic frameworks (MOFs) with large specific surface area, considerable pore volume, controllable structure, and high concentration of active metal sites have been applied widely in researches like catalysis and sensing. However, potential applications of MOFs in both photocatalysis and luminescence sensors are facing major challenges arising from their severe charge recombination, low utilization of solar energy, low quantum yield, limited charge transfer between the metal ions/clusters and the ligand. Recent studies revealed that rational introduction of carbon dots (CDs) with excellent optical properties, unique quantum confinement and high conductivity can greatly enhance the functions of MOFs. In this paper, typical synthesis methods of these CD-MOF composites as well as their potential applications in photocatalysis and sensing are reviewed with emphasis. Representative examples of these CD-MOF composites are discussed, and key features and advantages of CD-MOF composites that will facilitate future applications are highlighted.     

Luminescent rare earth nanomaterials for bioprobe applications

Inorganic fluorescent nanoparticles (NPs) have initiated an extensive upsurge in biological application research. Just as quantum dots are regarded as a vigorous reinforcement of the organic dye family, rare earth (RE) fluorescent NPs, as another phosphors branch, also possess unique optical characteristics. The advantages of RE NPs in photostability and colorimetric purity make them suitable for bioprobe applications. Since the preparation technologies have been well developed, it is favourable to prompt the research in the interdisciplinary field of biology and material sciences. Herein, we summarize the synthesis and performance, together with bioprobe applications of RE oxide, sulfoxide, vanadate, phosphate, fluoride, and sodium RE fluoride nanomaterials. The prospects of these promising materials as applied in the biological field is described to draw readers' attention and to attract more research interest.     

Carbon quantum dots from natural resource: A review

Carbon quantum dots (CQDs) are a new class of fluorescence small carbon nanoparticles with a particle size of less than 10 nm and have vast applications in the field of bioimaging, biosensing and disease-detection. These are promising materials for nano-biotechnology since it has smaller particle size, excellent biocompatibility and excitation wavelength dependent photoluminescence (PL) behavior, photo induced electron transfer, chemical inertness and low toxicity. These materials have excellent fluorescent properties such as broad excitation spectra, narrow and tunable emission spectra, and high photostability against photo bleaching and blinking than other fluorescent semiconductor quantum dots. This review article demonstrate the recent progress in the synthesis, functionalization and technical applications of carbon quantum dots using electrochemical oxidation, combustion/thermal, chemical change, microwave heating, arc-discharge, and laser ablation methods from various natural resources. Natural carbon sources are used for the preparation of CQDs due to its low cost, environmental friendly and widely available.     

Highly Fluorescent Semiconducting Polymer Dots for Biology and Medicine

In recent years, semiconducting polymer nanoparticles have attracted considerable attention because of their outstanding characteristics as fluorescent probes. These nanoparticles, which primarily consist of π‐conjugated polymers and are called polymer dots (Pdots) when they exhibit small particle size and high brightness, have demonstrated utility in a wide range of applications such as fluorescence imaging and biosensing. In this review, we summarize recent findings of the photophysical properties of Pdots which speak to the merits of these entities as fluorescent labels. This review also highlights the surface functionalization and biomolecular conjugation of Pdots, and their applications in cellular labeling, in vivo imaging, single‐particle tracking, biosensing, and drug delivery. We discuss the relationship between the physical properties and performance, and evaluate the merits and limitations of the Pdot probes for certain imaging tasks and fluorescence assays. We also tackle the current challenges of Pdots and share our perspective on the future directions of the field.     

Light microscopy with doughnut modes: a concept to detect, characterize, and manipulate individual nanoobjects

Higher order laser modes, mainly called doughnut modes (DMs) have use in many different branches of research, such as, bio-imaging, material science, single-molecule microscopy, and spectroscopy. The main reason of their increasing importance is that recently, the techniques to generate well-defined DMs have been refined or rediscovered. Although their potential is still not fully utilized, their specifically polarized field distribution gives rise to a wide field of applications. They are contributing to complete our fundamental knowledge of the optical properties of single emitting species, such as molecules, nanoparticles, or quantum dots, offering insight into the three-dimensional dipole or particle orientation in space. The perfect zero intensity in the focus center qualifies some DMs for stimulated emission depletion (STED) microscopy. For the same reason, they have been suggested for trapping and tweezing applications.     

Ultrasensitive detection and molecular imaging with magnetic nanoparticles

Recent advances in nanotechnology have produced a variety of nanoparticles ranging from semiconductor quantum dots (QDs), magnetic nanoparticles (MNPs), metallic nanoparticles, to polymeric nanoparticles. Their unique electronic, magnetic, and optical properties have enabled a broad spectrum of biomedical applications such as ultrasensitive detection, medical imaging, and specific therapeutics. MNPs made from iron oxide, in particular, have attracted extensive interest and have already been used in clinical studies owing to their capability of deep-tissue imaging, non-immunogenesis, and low toxicity. In this Research Highlight article, we attempt to highlight the recent breakthroughs in MNP synthesis based on a non-hydrolytic approach, nanoparticle (NP) surface engineering, their unique structural and magnetic properties, and current applications in ultrasensitive detection and imaging with a special focus on innovative bioassays. We will also discuss our perspectives on future research directions.     

Polymer Dots as Effective Phototheranostic Agents

Conjugated polymer dots (Pdots, also named polymer nanoparticles, PNPs), which consist of π‐conjugated organic polymers, are novel organic nanomaterials with size in the range of 1–100 nm. Compared with traditional organic small molecules, semiconductor quantum dots and inorganic nanomaterials, the Pdots exhibit significant potential applications in biological imaging, sensing and detection, drug delivery and theranostics, due to their advantages of special optical properties, diverse structure, easy surface modification and good biocompatibility. In this short review, we present a brief summary of the current development in Pdots as phototheranostic agents, including fluorescence imaging, photoacoustic imaging, photodynamic therapy and photothermal therapy. Current challenges in Pdot research and future directions in the field are proposed.     

Influence of cobalt concentration on structural and optical properties of ZnS quantum dots

ZnS and Co-doped ZnS nanoparticles have been prepared by simple chemical precipitation method. Zinc acetate, sodium sulfide, and cobalt nitrate have been used as precursors for the preparation of Co-doped ZnS quantum dots. The X-ray diffraction results revealed that the undoped and Co-doped ZnS quantum dots exhibit hexagonal structure. The average grain size of quantum dot was found to lie in the range of 2.6–3.8 nm. The surface morphology has been studied using scanning electron microscope. The compositional analysis results confirm the presence of Co, Zn and S in the sample. The optical properties of undoped and Co-doped ZnS quantum dots have been studied using absorption spectra. TEM results show that undoped and Co-doped ZnS nanoparticles exhibit a uniform size distribution with average size of 2.5–3.4 nm.     

Nanoparticles as fluorescent labels for optical imaging and sensing in genomics and proteomics

Optical labelling reagents (dyes and fluorophores) are an essential component of probe-based biomolecule detection, an approach widely employed in a variety of areas including environmental analysis, disease diagnostics, pharmaceutical screening, and proteomic and genomic studies. Recently, functional nanomaterials, as a new generation of high-value optical labels, have been applied to molecular detection. The great potential of such recent optical labels has paved the way for the development of new biomolecule assays with unprecedented analytical performance characteristics, related to sensitivity, multiplexing capability, sample throughput, cost-effectiveness and ease of use. This review aims to provide an overview of recent advances using different nanoparticles (such as quantum dots, rare earth doped nanoparticles or gold nanoparticles) for analytical genomics and proteomics, with particular emphasis on the outlook for different strategies of using nanoparticles for bioimaging and quantitative bioanalytical applications, as well as possibilities and limitations of nanoparticles in such a growing field.     

Biocompatible organic dots with aggregation-induced emission for in vitro and in vivo fluorescence imaging

Fluorescent probes play a key role in modern biomedical research. As compared to inorganic quantum dots (QDs) composed with heavy metal elements, organic dye-based fluorescent nanoparticles have higher biocompatibility and are richer in variety. However, traditional organic fluorophores tend to quench fluorescence upon aggregation, which is known as aggregation-caused quenching (ACQ) effect that hinders the fabrication of highly emissive fluorescent nanoparticles. In this work, we demonstrate the synthesis of organic fluorescent dots with aggregation-induced emission (AIE) in far-red/near-infrared (FA/NIR) region. A conventional ACQ-characteristic fluorescent dye, 3,4:9,10-tetracarboxylic perylene bisimide (PBI), is converted into an AIE fluorogen through attaching two tetraphenylethylene (TPE) moieties. The fluorescent dots with surface folic acid groups are fabricated from PBI derivative (DTPEPBI), showing specific targeting effect to folate receptor-overexpressed cancer cells. In vivo studies also suggest that the folic acid-functionalized AIE dots preferentially accumulate in the tumor site through enhanced permeability and retention (EPR) effect and folate receptor-mediated active targeting effect. The low cyto-toxicity, good FR/NIR contrast and excellent targeting ability in in vitro/in vivo imaging indicate that the AIE dots have great potentials in advanced bioimaging applications.     

pH-sensitive ligand for luminescent quantum dots

We developed a strategy to switch the luminescence of semiconductor quantum dots with chemical stimulations. It is based on the photoinduced transfer of either energy from CdSe-ZnS core-shell quantum dots to [1,3]oxazine ligands or electrons from the organic to the inorganic components. The organic ligands incorporate a dithiolane anchoring group, an electron-rich indole, and a 4-nitrophenylazophenoxy chromophore in their molecular skeleton. Their adsorption on the surface of the quantum dots results in partial luminescence quenching. Electron transfer from the indole fragment to the nanoparticles is mainly responsible for the decrease in luminescence intensity. Upon addition of base, the [1,3]oxazine ring of the ligands opens to generate a 4-nitrophenylazophenolate chromophore, which absorbs in the range of wavelengths where the quantum dots emit. This transformation activates an energy-transfer pathway from the excited nanoparticles to the ligands. In addition, the oxidation potential of the ligand shifts in the negative direction, improving the efficiency of electron transfer. The overall result is a decrease in the luminescence quantum yield of 83%. Addition of acid also opens the [1,3]oxazine ring of the ligands. However, the resulting 4-nitrophenylazophenol does not absorb in the visible region and cannot accept energy from the excited nanoparticles. Furthermore, the oxidation potential shifts in the positive direction, lowering the electron-transfer efficiency. In fact, the luminescence quantum yield increases by 33% as a result of this transformation. These changes are fully reversible and can be exploited to probe the pH of aqueous solutions from 3 to 11. Indeed, our sensitive quantum dots adjust their luminescence in response to variations in pH within this particular range of values. Thus, our general design strategy can eventually lead to the development of pH-sensitive luminescent probes for biomedical applications based on the unique photophysical properties of semiconductor quantum dots.     

纳米碳点的制备与应用研究进展

纳米碳点是碳纳米材料家族的新成员,近年来在国内外受到广泛关注。与传统的荧光染料和半导体量子点发光材料相比,碳点不仅具有优异的光学性能及尺寸效应,且具有制备成本低廉、生物相容性好、易于官能化、能带结构可调等优势。本文在理清有关碳点概念的基础之上,介绍了碳点结构特征和制备策略,着重综述了纳米碳点在生物成像与诊疗、传感器件、催化、光电器件和能量存储领域的最新研究进展,探讨了碳点研究目前存在的问题及未来的发展方向。     

量子点在生物检测中的应用

过去十几年里,量子点从材料科学到生命科学、从基础研究到实际应用都开展了广泛的研究。 量子点在生物成像、光治疗、药物/基因转运、太阳能电池等领域均具有广泛的应用。 通过调节量子点的表面性质,实现量子点与细胞相互作用的可控性是一个关键的问题。 伴随着量子点潜在毒性问题的产生,纳米毒性成为纳米材料安全性评估的重要指标,并且受到科学家们的高度关注。 本文综述了量子点的特性、细胞生物学应用及在生物医药领域相关的细胞毒性研究,并展望了量子点的未来发展趋势。     

Luminescent chemosensors based on semiconductor quantum dots

Semiconductor quantum dots are inorganic nanoparticles with unique photophysical properties. In particular, their huge one- and two-photon absorption cross sections, tunable emission bands and excellent photobleaching resistances are stimulating the development of luminescent probes for biomedical imaging and sensing applications. Indeed, electron and energy transfer processes can be designed to switch the luminescence of semiconductor quantum dots in response to molecular recognition events. On the basis of these operating principles, the presence of target analytes can be transduced into detectable luminescence signals. In fact, luminescent chemosensors based on semiconductor quantum dots are starting to be developed to detect small molecules, monitor DNA hybridization, assess protein-ligand complementarities, test enzymatic activity and probe pH distributions. Although fundamental research is still very much needed to understand further the fundamental factors regulating the behavior of these systems and refine their performance, it is becoming apparent that sensitive probes based on semiconductor quantum dots will become invaluable analytical tools for a diversity of applications in biomedical research.