Aqueous Synthesis, Doping, and Processing of n-Type Ag2Se for High Thermoelectric Performance at Near-Room-Temperature.

Herein, we have successfully synthesized binary Ag2Se, composite Ag0:Ag2Se, and ternary Cu+:Ag2Se through an ambient aqueous-solution-based approach in a one-pot reaction at room temperature and atmospheric pressure without involving high-temperature heating, multiple-processes treatment, and organic solvents/surfactants. Effective controllability over phases and compositions/components are demonstrated with feasibility for large-scale production through an exquisite alteration in reaction parameters especially pH for enhancing and understanding thermoelectric properties. Thermoelectric ZT reaches 0.8-1.1 at near-room-temperature for n-type Ag2Se and Cu+ doping further improves to 0.9-1.2 over a temperature range of 300-393 K, which is the largest compared to that reported by wet chemistry methods. This improvement is related to the enhanced electrical conductivity and the suppressed thermal conductivity due to the incorporation of Cu+ into the lattice of Ag2Se at very low concentrations (x%Cu+:Ag2Se, x = 1.0, 1.5, and 2.0).

Membrane-Penetrating Carbon Quantum Dots for Imaging Nucleic Acid Structures in Live Organisms.

The dynamics of DNA and RNA structures in live cells are important for understanding cell behaviors, such as transcription activity, protein expression, cell apoptosis, and hereditary disease, but are challenging to monitor in live organisms in real time. The difficulty is largely due to the lack of photostable imaging probes that can distinguish between DNA and RNA, and more importantly, are capable of crossing multiple membrane barriers ranging from the cell/organelle to the tissue/organ level. We report the discovery of a cationic carbon quantum dot (cQD) probe that emits spectrally distinguishable fluorescence upon binding with double-stranded DNA and single-stranded RNA in live cells, thereby enabling real-time monitoring of DNA and RNA localization and motion. A surprising finding is that the probe can penetrate through various types of biological barriers in vitro and in vivo. Combined with standard and super-resolution microscopy, photostable cQDs allow time-lapse imaging of chromatin and nucleoli during cell division and Caenorhabditis elegans (C. elegans) growth.

Morphological Growth and Theoretical Understanding of Gold and Other Noble Metal Nanoplates.

For the last decades, the chemical reduction of Au3+ to Au0 has been widely employed to produce various gold nanostructures. In comparison with the fast reduction, the slow reduction is systematically investigated in this research to provide more insights to reveal intermediary process and further disclose the underlying mechanism for growing gold nanostructures by using a series of simple ligands with aldehyde groups as weak reducing agents. The different binding energies of ligands to Aun+ (n=3, 1 and 0) exhibit variable binding affinities in starting, intermediate, and final gold species. For example, formic acid has much stronger binding affinity to Au+ than Au3+ , and thus Au+ intermediate is able to be stabilized/captured during slow reduction of Au3+ . Upon the disproportionation of Au+ to Au0 and Au3+ , formic acid has much stronger binding affinity to the newly formed Au0 than other ligands for the controlled formation of gold nanostructures. Meanwhile, the adsorption of ligands causes substantially decreased surface energies on different gold planes. There are much higher energies on {110} planes compared to the other two {111} and {100} planes with certain ratios in these energies, leading to morphological growth of gold nanosheets. In this paper, we experimentally demonstrate anisotropic growth of gold nanosheets by using various ligands with weak reducing and appropriate coordination capabilities, and further provide insights to understand their morphological growth mechanism behind. This synthetic strategy is successfully extended to prepare silver, palladium, and platinum nanoplates.

Phase Engineering of Hydrophobic Meso-Environments in Silica Particles for Technical Performance Enrichment.

Hexadecyltrimethylammonium bromide (CTAB) was utilized to template the growth of mesoporous silica particles via ammonia-catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS) in the reaction solutions with varied volume fractions of ethanol ( fR). The use of 9,10-bis(phenylethynyl) anthracene (BPEA) as a fluorescence probe unraveled a clear difference in interior structure between the CTAB micelles confined at different fR. At fR of 0.3, the confined CTAB micelles consisting of regularly and densely packed alkane chains, which created crystalline interiors, in which the doped BPEA molecules were effectively isolated in the monomeric form and well protected against aggressive attack from the surrounding environment. At fR of 0.4 or 0.5, the confined CTAB micelles consisting of less regularly but densely packed alkane chains created glassy interiors, which enabled reversible aggregation of the doped BPEA in response to the surrounding environmental change, for instance, the ethanol content in the particle dispersion. At fR of 0.6 or 0.7, the confined CTAB micelles consisting of loosely packed alkane chains created amorphous interiors, which offered sufficiently large free spaces to facilitate the material exchange with the surrounding environment, as evidenced by noticeable intake of the Pyronin Y molecules present in the particle dispersion. The revealed phase modulation of the interiors of surfactant micelles, confined in the pores of mesoporous particles, from crystalline to glassy and amorphous structures, which were scarcely reported in literature, will inspire rational design of mesoporous silica particles with desired technical performance according to the purposes of the practical application.

Dynamic mapping of spontaneously produced H2S in the entire cell space and in live animals using a rationally designed molecular switch.

Hydrogen sulfide (H2S) is a key signaling molecule in the cytoprotection, vascular mediation and neurotransmission of living organisms. In-depth understanding of its production, trafficking, and transformation in cells is very important in the way H2S mediates cellular signal transductions and organism functions; it also motivates the development of H2S probes and imaging technologies. A fundamental challenge, however, is how to engineer probes with sensitivity and cellular penetrability that allow detection of spontaneous production of H2S in the entire cell space and live animals. Here, we report a rationally designed molecular switch capable of accessing all intracellular compartments, including the nucleus, lysosomes and mitochondria, for H2S detection. Our probe comprised three functional domains (H2S sensing, fluorescence, and biomembrane penetration), could enter almost all cell types readily, and exhibit a rapid and ultrasensitive response to H2S (≤120-fold fluorescence enhancement) for the dynamic mapping of spontaneously produced H2S as well as its distribution in the whole cell. In particular, the probe traversed blood/tissue/cell barriers to achieve mapping of endogenous H2S in metabolic organs of a live Danio rerio (zebrafish). These results open-up exciting opportunities to investigate H2S physiology and H2S-related diseases.

Near-Infrared-Activated Upconversion Nanoprobes for Sensitive Endogenous Zn2+ Detection and Selective On-Demand Photodynamic Therapy.

As a light-activated noninvasive cancer treatment paradigm, photodynamic therapy (PDT) has attracted extensive attention because of its high treatment efficacy and low side effects. Especially, spatiotemporal control of singlet oxygen (1O2) release is highly desirable for realizing on-demand PDT, which, however, still remains a huge challenge. To address this issue, a novel switchable near-infrared (NIR)-responsive upconversion nanoprobe has been designed and successfully applied for controlled PDT that can be optically activated by tumor-associated disruption of labile Zn2+ (denoted as Zn2+ hereafter) homeostasis stimuli. Upon NIR irradiation, this theranostic probe can not only quantitatively detect the intracellular endogenous Zn2+ in situ but also selectively generate a great deal of cytotoxic reactive oxygen species (ROS) for efficiently killing breast cancer cells under the activation of excessive endogenous Zn2+, so as to maximally avoid adverse damage to normal cells. This study aims to propose a new tumor-specific PDT paradigm and, more importantly, provide a new avenue of thought for efficient cancer theranostics based on our designed highly sensitive upconversion nanoprobes.

Multinary I-III-VI2 and I2-II-IV-VI4 Semiconductor Nanostructures for Photocatalytic Applications.

Semiconductor nanostructures that can effectively serve as light-responsive photocatalysts have been of considerable interest over the past decade. This is because their use in light-induced photocatalysis can potentially address some of the most serious environmental and energy-related concerns facing the world today. One important application is photocatalytic hydrogen production from water under solar radiation. It is regarded as a clean and sustainable approach to hydrogen fuel generation because it makes use of renewable resources (i.e., sunlight and water), does not involve fossil fuel consumption, and does not result in environmental pollution or greenhouse gas emission. Another notable application is the photocatalytic degradation of nonbiodegradable dyes, which offers an effective way of ridding industrial wastewater of toxic organic pollutants prior to its release into the environment. Metal oxide semiconductors (e.g., TiO2) are the most widely studied class of semiconductor photocatalysts. Their nanostructured forms have been reported to efficiently generate hydrogen from water and effectively degrade organic dyes under ultraviolet-light irradiation. However, the wide band gap characteristic of most metal oxides precludes absorption of light in the visible region, which makes up a considerable portion of the solar radiation spectrum. Meanwhile, nanostructures of cadmium chalcogenide semiconductors (e.g., CdS), with their relatively narrow band gap that can be easily adjusted through size control and alloying, have displayed immense potential as visible-light-responsive photocatalysts, but the intrinsic toxicity of cadmium poses potential risks to human health and the environment. In developing new nanostructured semiconductors for light-driven photocatalysis, it is important to choose a semiconducting material that has a high absorption coefficient over a wide spectral range and is safe for use in real-world settings. Among the most promising candidates are the multinary chalcogenide semiconductors (MCSs), which include the ternary I-III-VI2 semiconductors (e.g., AgGaS2, CuInS2, and CuInSe2) and the quaternary I2-II-IV-VI4 semiconductors (e.g., Cu2ZnGeS4, Cu2ZnSnS4, and Ag2ZnSnS4). These inorganic compounds consist of environmentally benign elemental components, exhibit excellent light-harvesting properties, and possess band gap energies that are well-suited for solar photon absorption. Moreover, the band structures of these materials can be conveniently modified through alloying to boost their ability to harvest visible photons. In this Account, we provide a summary of recent research on the use of ternary I-III-VI2 and quaternary I2-II-IV-VI4 semiconductor nanostructures for light-induced photocatalytic applications, with focus on hydrogen production and organic dye degradation. We include a review of the solution-based methods that have been employed to prepare multinary chalcogenide semiconductor nanostructures of varying compositions, sizes, shapes, and crystal structures, which are factors that are known to have significant influence on the photocatalytic activity of semiconductor photocatalysts. The enhancement of photocatalytic performance through creation of hybrid nanoscale architectures is also presented. Lastly, views on the current challenges and future directions are discussed in the concluding section.

Unraveling the Growth Mechanism of Silica Particles in the Stöber Method: In Situ Seeded Growth Model.

In this work, we investigated the kinetic balance between ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) and subsequent condensation over the growth of silica particles in the Stöber method. Our results reveal that, at the initial stage, the reaction is dictated by TEOS hydrolysis to form silanol monomers, which is denoted as pathway I and is responsible for nucleation and growth of small silica particles via condensation of neighboring silanol monomers and siloxane network clusters derived thereafter. Afterward, the reaction is dictated by condensation of newly formed silanol monomers onto the earlier formed silica particles, which is denoted as pathway II and is responsible for the enlargement in size of silica particles. When TEOS hydrolysis is significantly promoted, either at high ammonia concentration (≥0.95 M) or at low ammonia concentration in the presence of LiOH as secondary catalyst, temporal separation of pathways I and II makes the Stöber method reminiscent of in situ seeded growth. This knowledge advance enables us not only to reconcile the most prevailing aggregation-only and monomer-addition models in literature into one consistent framework to interpret the Stöber process but also to grow monodisperse silica particles with sizes in the range 15-230 nm simply but precisely regulated by the ammonia concentration with the aid of LiOH.

Real-Time Discrimination and Versatile Profiling of Spontaneous Reactive Oxygen Species in Living Organisms with a Single Fluorescent Probe.

Fluorescent probes are powerful tools for the investigations of reactive oxygen species (ROS) in living organisms by visualization and imaging. However, the multiparallel assays of several ROS with multiple probes are often limited by the available number of spectrally nonoverlapping chromophores together with large invasive effects and discrepant biological locations. Meanwhile, the spontaneous ROS profilings in various living organs/tissues are also limited by the penetration capability of probes across different biological barriers and the stability in reactive in vivo environments. Here, we report a single fluorescent probe to achieve the effective discrimination and profiling of hydroxyl radicals (•OH) and hypochlorous acid (HClO) in living organisms. The probe is constructed by chemically grafting an additional five-membered heterocyclic ring and a lateral triethylene glycol chain to a fluorescein mother, which does not only turn off the fluorescence of fluorescein, but also create the dual reactive sites to ROS and the penetration capability in passing through various biological barriers. The reactions of probe with •OH and HClO simultaneously result in cyan and green emissions, respectively, providing the real-time discrimination and quantitative analysis of the two ROS in cellular mitochondria. Surprisingly, the accumulation of probes in the intestine and liver of a normal-state zebrafish and the transfer pathway from intestine-to-blood-to-organ/tissue-to-kidney-to-excretion clearly present the profiling of spontaneous •OH and HClO in these metabolic organs. In particular, the stress generation of •OH at the fresh wound of zebrafish is successfully visualized for the first time, in spite of its extremely short lifetime.

Color-Multiplexing-Based Fluorescent Test Paper: Dosage-Sensitive Visualization of Arsenic(III) with Discernable Scale as Low as 5 ppb.

Fluorescent colorimetry test papers are promising for the assays of environments, medicines, and foods by the observation of the naked eye on the variations of fluorescence brightness and color. Unlike dye-absorption-based pH test paper, however, the fluorescent test papers with wide color-emissive variations with target dosages for accurate quantification remain unsuccessful even if the multicolorful fluorescent probes are used. Here, we report the dosage-sensitive fluorescent colorimetry test paper with a very wide/consecutive "from red to cyan" response to the presence and amount of arsenic ions, As(III). Red quantum dots (QDs) were modified with glutathione and dithiothreitol to obtain the supersensitivity to As(III) by the quenching of red fluorescence through the formation of dispersive QDs aggregates. A small amount of cyan carbon dots (CDs) with spectral blue-green components as the photostable internal standard were mixed into the QDs solution to produce a composited red fluorescence. Upon the addition of As(III) into the sensory solution, the fluorescence color could gradually be reversed from red to cyan with a detection limit of 1.7 ppb As(III). When the sensory solution was printed onto a piece of filter paper, surprisingly a serial of color evolution from peach to pink to orange to khaki to yellowish to yellow-green to final cyan with the addition of As(III) was displayed and clearly discerned the dosage scale as low as 5 ppb. The methodology reported here opens a novel pathway toward the real applications of fluorescent test papers.

High-Level Incorporation of Silver in Gold Nanoclusters: Fluorescence Redshift upon Interaction with Hydrogen Peroxide and Fluorescence Enhancement with Herbicide.

High-level incorporation of Ag in Au nanoclusters (NCs) is conveniently achieved by controlling the concentration of Ag(+) in the synthesis of bovine serum albumin (BSA)-protected Au NCs, and the resulting structure is determined to be bimetallic Ag28 Au10-BSA NCs through a series of characterizations including energy-dispersive X-ray spectroscopy, mass spectroscopy, and X-ray photoelectron spectroscopy, together with density functional theory simulations. Interestingly, the Ag28 Au10 NCs exhibit a significant fluorescence redshift rather than quenching upon interaction with hydrogen peroxide, providing a new approach to the detection of hydrogen peroxide through direct comparison of their fluorescence peaks. Furthermore, the Ag28 Au10 NCs are also used for the sensitive and selective detection of herbicide through fluorescence enhancement. The detection limit for herbicide (0.1 nm) is far below the health value established by the U.S. Environmental Protection Agency; such sensitive detection was not achieved by using AuAg NCs with low-level incorporation of Ag or by using the individual metal NCs.

Preparation, Functionality, and Application of Metal Oxide-coated Noble Metal Nanoparticles.

With their remarkable properties and wide-ranging applications, nanostructures of noble metals and metal oxides have been receiving significantly increased attention in recent years. The desire to combine the properties of these two functional materials for specific applications has naturally prompted research in the design and synthesis of novel nanocomposites, consisting of both noble metal and metal-oxide components. In this review, particular attention is given to core-shell type metal oxide-coated noble metal nanostructures (i.e., metal@oxide), which display potential utility in applications, including photothermal therapy, catalytic conversions, photocatalysis, molecular sensing, and photovoltaics. Emerging research directions and areas are envisioned at the end to solicit more attention and work in this regard.

Anisotropically branched metal nanostructures.

Metal nanostructures display a multitude of technologically useful properties that can be tailored through fine-tuning of certain parameters, such as size, shape and composition. In many cases, the shape or morphology of metal nanostructures plays the most crucial role in the determination of their properties and their suitability in specific applications. In this tutorial review, we provide a summary of recent research that centers on metal nanostructures having anisotropically branched morphologies. The branched structural features that are exhibited by these materials endow them with unique properties that can be utilized in many important applications. The formation of branched architectures can be achieved in solution through a variety of synthetic strategies, four of which are highlighted in this review and these are: (1) seedless growth, (2) seeded growth, (3) templated growth, and (4) chemical etching. The usefulness of these anisotropically branched metal nanostructures in the areas of plasmonics, catalysis and biomedicine is also presented.

Protein Induces Layer-by-Layer Exfoliation of Transition Metal Dichalcogenides.

Here, we report a general and facile method for effective layer-by-layer exfoliation of transition metal dichalcogenides (TMDs) and graphite in water by using protein, bovine serum albumin (BSA) to produce single-layer nanosheets, which cannot be achieved using other commonly used bio- and synthetic polymers. Besides serving as an effective exfoliating agent, BSA can also function as a strong stabilizing agent against reaggregation of single-layer nanosheets for greatly improving their biocompatibility in biomedical applications. With significantly increased surface area, single-layer MoS2 nanosheets also exhibit a much higher binding capacity to pesticides and a much larger specific capacitance. The protein exfoliation process is carefully investigated with various control experiments and density functional theory simulations. It is interesting to find that the nonpolar groups of protein can firmly bind to TMD layers or graphene to expose polar groups in water, facilitating the effective exfoliation of single-layer nanosheets in aqueous solution. The present work will enable to optimize the fabrication of various 2D materials at high yield and large scale, and bring more opportunities to investigate the unique properties of 2D materials and exploit their novel applications.

Evaluation of polymeric nanoparticle formulations by effective imaging and quantitation of cellular uptake for controlled delivery of doxorubicin.

Various polymeric nanoparticles have been extensively engineered for applications in controlled drug release delivery in the last decades. Currently, there is a great demand to develop a strategy to qualitatively and quantitatively evaluate these polymeric nanoparticle formulations for producing innovative delivery systems. In this work, a screening platform is developed using luminescent quantum dots as drug model and imaging label to evaluate nanoparticle formulations incorporating either hydrophilic or hydrophobic drugs and imaging agents. It is validated that there is no influence of the incorporated entities on the cellular uptake profile. The use of quantum dots enables efficient detection and precise quantitation of cellular uptake of particles which occupy 25% of the cell volume. The correlation of quantum dot- and doxorubicin-incorporated nanoparticles is useful to develop an evaluation platform for nanoparticle formulations through imaging and quantitation. This platform is also used to observe the surface properties effect of other polymers such as chitosan and poly(ethylene) glycol on the cellular interaction and uptake. Moreover, quantum dots can be used to study microparticle theranostic delivery formulations by deliberately incorporating as visible ring surrounding the microparticles for their easy identifying and tracing in diagnostic and chemotherapeutic applications.

Alloyed ZnS-CuInS2 Semiconductor Nanorods and Their Nanoscale Heterostructures for Visible-Light-Driven Photocatalytic Hydrogen Generation.

A promising photocatalytic system in the form of heterostructured nanocrystals (HNCs) is presented wherein alloyed ZnS-CuInS2 (ZCIS) semiconductor nanorods are decorated with Pt and Pd4 S nanoparticles. This is apparently the first report on the colloidal preparation and photocatalytic behavior of ZCIS-Pt and ZCIS-Pd4 S nanoscale heterostructures. Incorporation of Pt and Pd4 S cocatalysts leads to considerable enhancement of the photocatalytic activity of ZCIS for visible-light-driven hydrogen production.

Amorphous ruthenium nanoparticles for enhanced electrochemical water splitting.

This paper demonstrates an optimized fabrication of amorphous Ru nanoparticles through annealing at various temperatures ranging from 150 to 700 °C, which are used as water oxidation catalyst for effective electrochemical water splitting under a low overpotential of less than 300 mV. The amorphous Ru nanoparticles with short-range ordered structure exhibit an optimal and stable electrocatalytic activity after annealing at 250 °C. Interestingly, a small quantity of such Ru nanoparticles in a thin film on fluorine-doped tin oxide glass is also effectively driven by a conventional crystalline silicon solar cell that has excellent capability for harvesting visible light. Remarkably, it achieves an overall solar-to-hydrogen efficiency of 11.3% in acidic electrolyte.

Self-assembly of colloidal one-dimensional nanocrystals.

The ability of nanoscopic materials to self-organize into large-scale assembly structures that exhibit unique collective properties has opened up new and exciting opportunities in the field of nanotechnology. Although earlier work on nanoscale self-assembly has focused on colloidal spherical nanocrystals as building blocks, there has been significant interest in recent years in the self-assembly of colloidal nanocrystals having well-defined facets or anisotropic shapes. In this review, particular attention is drawn to anisotropic one-dimensional (1D) nanocrystals, notably nanorods and nanowires, which can be arranged into a multitude of higher-order assembly structures. Different strategies have been developed to realize self-assembly of colloidal 1D nanocrystals and these are highlighted in the first part of this review. Self-assembly can take place (1) on substrates through evaporation control, external field facilitation and template use; (2) at interfaces, such as the liquid-liquid and the gas-liquid interface; and (3) in solutions via chemical bonding, depletion attraction forces and linker-mediated interactions. The choice of a self-assembly approach is pivotal to achieving the desired assembly configuration with properties that can be exploited for functional device applications. In the subsequent sections, the various assembly structures that have been created through 1D nanocrystal self-assembly are presented. These organized structures are broadly categorized into non-close-packed and close-packed configurations, and are further classified based on the different types of 1D nanocrystal alignment (side-by-side and end-to-end), orientation (horizontal and vertical) and ordering (nematic and smectic), and depending on the dimensionality of the structure (2D and 3D). The conditions under which different types of arrangements are achieved are also discussed.

White-Light Emission from an Integrated Upconversion Nanostructure: Toward Multicolor Displays Modulated by Laser Power.

The white backlight in displays is generated by optimizing the proportions of individual emitters with different wavelengths by variations in materials composition, phase, and structure. Color pixels usually result from the separation of white light or the excitation with multiwavelength or multipulse sources. However, it is a challenge to develop a material that comprises a single structure and emits over the full visible spectrum, but where the emission wavelengths can be controlled by a simple excitation source. Herein, we report an upconversion nanostructure that incorporates several lanthanide ions in the same core@shell@shell structure. The combination of multiple narrow spectral bands results in the emission of white light. The emission colors can be tuned by changing the excitation power density, which manipulates the photon transfer pathways. Applications such as flat-panel displays and imaging have been demonstrated.