Silica‐Coated Metal Nanoparticles

The advanced high‐quality synthesis of dense and porous silica‐coated nanostructures is enjoying ever‐increasing research interests for their important properties and diverse applications, especially for catalytic, controlled release, colorimetric diagnostics, photothermal therapy, surface enhanced Raman scattering (SERS) detection, and so forth. In this timely Focus Review, we summarize the up‐to‐date synthesis strategies, improved properties, and emerging applications of silica‐coated metal nanoparticles. In particular, the large scale synthesis of silica‐coated metal nanoparticles and the recent development of hollowed‐out silica‐coated metal nanoparticles by silica dissolution are emphasized for new and practical applications.     

Surface Modifications and Optoelectronic Characterization of TiO2‐Nanoparticles: Design of New Photo‐Electronic Materials

TiO₂ nanoparticles are of great current interest for applications in photo‐electronic materials including light‐energy conversion, artificial photosynthetic systems as well as photocatalysis. The success of these applications relies on the exciton recombination dynamics and visible‐light sensitivity of the TiO₂ nanomaterials. Thus, in order to develop the highly efficient photo‐electronic materials absorbing visible light, different low dimensional TiO₂ nanostructures such as nanodiscs, nanofibers and nanochains were synthesized, and thereafter their surfaces were modified by incorporating with Sn‐porphyrins and heteropoly acid. The optoelectronic properties of the surface‐modified nanomaterials were investigated with regard to the optical properties and the surface exciton dynamics by using both steady‐state and ultrafast time‐resolved laser spectroscopic techniques including single nanoparticle photoluminescence technique. These results were correlated with the photo‐electronic properties including photocatalytic activities and solar cell efficiencies, indicating that the electron transfer mechanism in the modified nanostructures may be similar to the “Z‐scheme” of the plant photosynthetic system so that both photocatalytic activity and solar cell efficiencies were synergistically enhanced by using two color illumination.     

Titania‐Coated Metal Nanostructures

The synergistic effect between metal and TiO₂ nanoparticles brings about new, enhanced functionalities for a myriad of applications, ranging from labeling and sensing to catalysis and surface‐enhanced Raman scattering. Although extensive work has been done in the preparation of concentric TiO₂‐coated metal nanostructures, current methods for the synthesis of noncentrosymmetric morphologies are still very limited. This Focus review summarizes the various methods used to prepare TiO₂‐coated metal nanostructures, with a particular emphasis on noncentrosymmetric morphologies, their novel plasmonic properties, and their promising applications in the fields of catalysis and photocatalysis.     

Cu‐Based Nanoparticles as Emerging Environmental Catalysts

This account provides an overview of current research activities on nanoparticles containing the earth‐abundant and inexpensive element copper (Cu) and Cu‐based nanoparticles, especially in the field of environmental catalysis. The different synthetic strategies with possible modification of the chemical/ physical properties of these nanoparticles using such strategies and/or conditions to improve catalytic activity are presented. The design and development of support and/or bimetallic systems (e. g., alloys, intermetallic, etc.) are also included. Herein, we report synthetic approaches of Cu and Cu‐based nanoparticles (monometallic copper, bimetallic copper and copper (II) oxide nanoparticles/nanostructures) and impregnation of such nanoparticles onto support material (e. g., Co₃O₄ nanostructure), along with their applications as environmental catalyst for various oxidation and reduction reactions. Finally, this account provides necessary advances and perspectives of Cu‐based nanoparticles in the environmental catalysis.     

Plasmon‐Mediated Syntheses of Metallic Nanostructures

The ability to prepare noble metal nanostructures of a desired composition, size, and shape enables their resulting properties to be exquisitely tailored, which has led to the use of these structures in numerous applications, ranging from medicine to electronics. The prospect of using light to guide nanoparticle reactions is extremely attractive since one can, in principle, regulate particle growth based on the ability of the nanostructures to absorb a specific excitation wavelength. Therefore, using the nature of light, one can generate a homogenous population of product nanoparticles from a heterogeneous starting population. The best example of this is afforded by plasmon‐mediated syntheses of metal nanoparticles, which use visible light irradiation and plasmon excitation to drive the chemical reduction of Ag⁺ by citrate. Since the initial discovery that Ag triangular prisms could be prepared by the photo‐induced conversion of Ag spherical nanoparticles, plasmon‐mediated synthesis has become a highly controllable technique for preparing a number of different Ag particles with tight control over shape, as well as a wide variety of Au‐Ag bimetallic nanostructures. We discuss the underlying physical and chemical factors that drive structural selection and conclude by outlining some of the important design considerations for controlling particle shape as learned through studies of plasmon‐mediated reactions, but applicable to all methods of noble metal nanocrystal synthesis.     

Bioinspired and green synthesis of nanoparticles from plant extracts with antiviral and antimicrobial properties: A critical review

Currently green synthesis of nanoparticles has attained much interest because of their safe nature, environmentally benign, ease in manufacturing, and low production cost. It is a reliable process for developing a wide array of nanostructures such as metal salts from plants/fungal/bacterial extract and hybrid materials. Green synthesis of nanoparticles provided promising and sustainable alternative approach to conventional synthesis approaches. Recent studies demonstrated that nanoparticles are highly promising for antiviral and antimicrobial properties. Here in, the advancement in green synthesis of nanoparticles using natural compounds such as plant extracts, fruit juices and other relevant sources have been highlighted. A deep insight into antiviral and antimicrobial activities of these nanoparticles provided. These nanoparticles offer diverse opportunity to counter life threating viral and other antimicrobial infections. This review offers understanding of the recent data that provide the readers various strategies to design and develop advance nanomaterials via greener approach. Current challenges, critical overview and future outlook of the green synthesis of nanoparticles and possibilities of their effective and exotic exploration for antimicrobial and antiviral applications are summarized.     

Controlled syntheses of polythiophene nanoparticles with plain and hollow nanostructures templated from unimolecular micelles

Polythiophene nanoparticles (PTNs), as one of the typical conjugated polymer nanoparticles (CPNs) with novel optical and electronic properties have won extensive attentions, especially their applications in electronics and bioimaging. However, PTNs obtained with traditional methods are usually nonuniform or unstable. Herein, we developed a novel method to prepare uniform and stable PTNs templated from star‐like unimolecular micelles. Cyclodextrin‐cored unimolecular micelles with tailored components were prepared through atom transfer radical polymerization, and PTNs with plain or hollow nanostructures can be obtained via crosslinking the suspended thiophene units in designed domain of unimolecular micelles. The unimolecular micelles and PTNs were characterized via nuclear magnetic resonance, Fourier transform infrared, transmission electron microscopy, atomic force microscopy, dynamic light scattering, ultraviolet–visible, and photoluminescence, indicating that the PTNs exhibit uniform size, controllable surface chemistry, and well‐defined nanostructures. The obtained PTNs have potential applications in optics, electronics, and bioimaging. Also, this provides a new way to synthesize CPNs with tailored sizes, nanostructures, and surface chemistry. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1550–1555     

DNA‐Encoded Tuning of Geometric and Plasmonic Properties of Nanoparticles Growing from Gold Nanorod Seeds

Systematically controlling the morphology of nanoparticles, especially those growing from gold nanorod (AuNR) seeds, are underexplored; however, the AuNR and its related morphologies have shown promises in many applications. Herein we report the use of programmable DNA sequences to control AuNR overgrowth, resulting in gold nanoparticles varying from nanodumbbell to nanooctahedron, as well as shapes in between, with high yield and reproducibility. Kinetic studies revealed two representative pathways for the shape control evolving into distinct nanostructures. Furthermore, the geometric and plasmonic properties of the gold nanoparticles could be precisely controlled by adjusting the base compositions of DNA sequences or by introducing phosphorothioate modifications in the DNA. As a result, the surface plasmon resonance (SPR) peaks of the nanoparticles can be fine‐tuned in a wide range, from visible to second near‐infrared (NIR‐II) region beyond 1000 nm.     

Resorcinarene-Encapsulated Nanoparticles: Building Blocks for Self-Assembled Nanostructures

Calix[4]resorcinarene-derived surfactants are highly effectiveat stabilizing metal nanoparticles of different sizes, creating opportunities tofabricate well-defined nanostructures with size-tunable materials properties. Theresorcinarenes have a critical role in the dispersion of nanoparticles under varioussolvent conditions and in the robustness of the protective surfactant layer.Magnetic cobalt particles stabilized by resorcinarenes self-assemble intonanostructured ``bracelets' in toluene. Resorcinarene surfactants can also promote theself-organization of gold nanoparticles as large as 170 nm into two-dimensional arrays. Thesenanostructured films possess novel optoelectronic properties such as surface-enhancedRaman scattering (SERS), and are expected to have useful applications for chemical sensing.     

Nanorattles or Yolk–Shell Nanoparticles—What Are They,How Are They Made,and What Are They Good For?

The development of nanotechnology has led to the design of cutting‐edge nanomaterials with increasing levels of complexity. Although “traditional” solid, uniform nanoparticles are still the most frequently reported structures, new generations of nanoparticles have been constantly emerging over the last several decades. The outcome of this nano‐art extends beyond nanomaterials with alternative compositions and/or morphologies. The current state‐of‐the‐art allows for the design of nanostructures composed of different building blocks that exhibit diverse properties. Furthermore, those properties can be a reflection of either individual features, which are characteristic of a particular building block alone, and/or synergistic effects resulting from interactions between building blocks. Therefore, the unique structures as well as the outstanding properties of nanorattles have attracted increasing attention for possible biomedical and industrial applications. Although these nanoparticles resemble core–shell particles, they have a distinctive feature, which is a presence of a void that provides a homogenous environment for the encapsulated core. In this Review, we give a comprehensive insight into the fabrication of nanorattles. A special emphasis is put on the choice of building blocks as well as the choice of preparation method, because those two aspects further influence properties and thus possible future applications, which will also be discussed.     

Energy Transfer in Dye‐Coupled Lanthanide‐Doped Nanoparticles: From Design to Application

Surface modification with organic dye molecules is a useful strategy to manipulate the optical properties of lanthanide‐doped nanoparticles (LnNPs). It enables energy transfer between dyes and LnNPs, which provides unprecedented possibilities to gain new optical phenomena from the dye–LnNPs composite systems. This has led to a wide range of emerging applications, such as biosensing, drug delivery, gene targeting, information storage, and photon energy conversion. Herein, the mechanism of energy transfer and the structural‐dependent energy‐transfer properties in dye‐coupled LnNPs are reviewed. The design strategies for achieving effective dye–LnNP functionalization are presented. Recent advances in these composite nanomaterials in biomedicine and energy conversion applications are highlighted.     

Hydrothermal Synthesis of a rGO Nanosheet Enwrapped NiFe Nanoalloy for Superior Electrocatalytic Oxygen Evolution Reactions

Graphene‐based hybrid nanostructures possess many advantages in the field of electrochemical energy applications. In this work, a facile and efficient hydrothermal approach has been developed for the preparation of NiFe alloy nanoparticles/rGO hybrid nanostructures, in which the nanoparticles are well combined with rGO nanosheets and the size of the nanoparticles is about 100 nm. Moreover, the electrochemical oxygen evolution reaction (OER) tests confirmed that the obtained NiFe/rGO hybrid nanostructures possess notably higher activity than both the rGO‐free NiFe nanoparticles and pure Ni/rGO hybrids, and the optimal NiFe ratio is 2:1. The OER overpotential at 20 mA cm^?1?2 with Ni₂Fe/rGO is as low as 0.285 V, which is 96 mV lower than that of pure Ni/rGO hybrids. Meanwhile, the Ni₂Fe/rGO catalyst has excellent stability. Therefore, this work contributes a facile and efficient method to prepare a NiFe alloy nanoparticles/rGO hybrid structure for potential applications in the field of electrochemical energy devices, such as electrochemical water splitting cells, rechargeable metal/air batteries, etc.     

Nanosized Heterostructures of Au@Prussian Blue Analogues: Towards Multifunctionality at the Nanoscale

Access to multifunctionality at the nanoscale requires the development of hybrid nanostructures that combine materials of different natures. In this line of thought, current research on coordination polymers is not only focusing on their synthesis at the nanoscale, but also on combining these polymers with other materials. According to a novel and rational approach, single‐layer Au@Prussian blue analogue (PBA) and double‐layer Au@PBA@PBA′ core–shell nanoparticles (NPs) may be obtained through the growth of a cyano‐bridged coordination network on the gold surface. The nanosized heterostructures combine the plasmonic optical properties of the gold core and the magnetic properties of the PBA shell. Whereas the single‐layer nanoparticles are paramagnetic, the double‐layer nanostructures display ferromagnetism; therefore, the overall structural motif may be considered as multifunctional. The developed synthetic concept also includes an easy access to hollow PBA NPs.     

Bioconjugated Luminescent Nanoparticles for Biological Applications

Abstract

Inorganic nanostructures that interface with biological systems have recently attracted widespread interest in biology and medicine. Nanoparticles are thought to have potential as novel luminescent probes for both diagnostic (e.g., imaging) and therapeutic (e.g., drug delivery) purposes because of their size comparable to biomolecules and their novel optical, electronic, and magnetic properties. Critical issues for successful nanoparticle delivery include the ability to target specific tissues and cell types and escape from the biological particulate filter known as reticuloendothelial system. Three distinct types of luminescent nanoparticles have been identified which show promise in bioanalysis, namely dye‐doped nanoparticles, semiconductor and metal nanoparticles. In this article we examine the recent advances in the development of dye‐doped nanoparticles, metal and semiconductor nanoparticles, bioconjugation schemes to attach these nanoparticles to biomolecules and a few biological applications.     

Site‐Specific Chemical Surface Functionalization and Electronic Patterning of Graphene by Electrooxidative Lithography

The combination of different properties being manipulated on nanomaterials is one of the challenges in nanotechnology research. In particular, the possibility to tailor the electronic and chemical properties offers promising possibilities for the design of functional nanostructures. Herein, we report an approach that permits control of these properties on the basis of electrooxidative lithography to structure reduced graphene oxide functionalized with a self‐assembled monolayer of n‐octadecyltrichlorosilane. The electrochemical oxidation process first induces the formation of polar acid groups on the monolayer, which can be used to covalently bind nanoparticles and molecules and, secondly, also allows the reoxidation of the underlying reduced graphene oxide. As such, the chemical signature as well as the electronic properties of the substrate can be tailored on the micro‐ and nanometer scale. Details on the oxidation of the monolayer as well as thorough characterization of the electronic properties will be presented. Finally, the approach is used to demonstrate the fabrication of a sensitive glucose sensor device.     

Nanomaterial Application in DNA Binding Studies

Nanomaterials and nanotechnological devices will be certain to provide critically important applications in various fields of science and engineering due to the unique surface properties and special behavior of nanostructures typically with high ratios of surface area to volume. With a view to explore possibilities for the potential applications of some nanoscale particles, which show different behavior from that of ordinary materials, in the area of biomolecular recognition, we have tested the DNA binding properties of some ligands such as methylene green (MG), etc, in different buffer solutions of Au colloid.     

Palladium: a future key player in the nanomedical field?

Metal nanostructures offer invaluable possibilities for targeted drug delivery, detection/diagnosis and imaging. Whereas iron, gold, silver and platinum nanoarchitectures have largely dominated this field to date, several hurdles impede the widespread application of those nanopharmaceuticals in a clinical context. Therefore, technologies based on alternative metals are now being evaluated for their potential in medical applications. Palladium nanostructures are characterized by remarkable catalytic and optical properties. However, until recently, very few studies have taken advantage of these unique characteristics for applications in the biomedical field. Very recently, palladium nanostructures have been reported as prodrug activator, as photothermal agents and for anti-cancer/anti-microbial therapy. With only a handful of reports available, the pharmaceutical applications of palladium nanostructures reviewed here are in their infancy. Yet their interesting performance and toxicity profiles may qualify them as future key players in the nanomedical field.     

Silica-void-gold nanoparticles: temporally stable surface-enhanced Raman scattering substrates

Reproducible detection of a target molecule is demonstrated using temporally stable solution-phase silica-void-gold nanoparticles and surface-enhanced Raman scattering (SERS). These composite nanostructures are homogeneous (diameter = 45 +/- 4 nm) and entrap single 13 nm gold nanoparticle cores inside porous silica membranes which prevent electromagnetic coupling and aggregation between adjacent nanoparticles. The optical properties of the gold nanoparticle cores and structural changes of the composite nanostructures are characterized using extinction spectroscopy and transmission electron microscopy, respectively, and both techniques are used to monitor the formation of the silica membrane. The resulting nanostructures exhibit temporally stable optical properties in the presence of salt and 2-naphthalenethiol. Similar SERS spectral features are observed when 2-naphthalenethiol is incubated with both bare and membrane-encapsulated gold nanoparticles. Disappearance of the S-H Raman vibrational band centered at 2566 cm(-1) with the composite nanoparticles indicates that the target molecule is binding directly to the metal surface. Furthermore, these nanostructures exhibit reproducible SERS signals for at least a 2 h period. This first demonstration of utilizing solution-phase silica-void-gold nanoparticles as reproducible SERS substrates will allow for future fundamental studies in understanding the mechanisms of SERS using solution-phase nanostructures as well as for applications that involve the direct and reproducible detection of biological and environmental molecules.     

Controllable Synthesis and Optical Properties of Connected Zinc Oxide Nanoparticles

Connected zinc oxide (ZnO) nanoparticles are successfully synthesized by a simple solution‐based chemical route that uses evaporation and concentration technology. The influences of processing parameters, especially the evaporation and concentration time on the size and morphology of the nanoparticles, have been investigated by transmission electron microscopy (TEM) and high‐resolution TEM (HRTEM). The structure and optical properties are systematically characterized by X‐ray diffraction (XRD), UV/Vis spectrophotometery, and fluorescence spectroscopy (FL). It is found that the average diameter and morphology are strongly affected by the evaporation and concentration time. Additionally, the formation mechanism of the nanoparticles is also discussed. The studies revealed that the evaporation and concentration are important aggregation or nucleation processes for ZnO growth, which leads to the macro‐differences in morphology. These results provide some insight into the growth mechanism of ZnO nanostructures. The synthetic strategy developed in this study may also be extended to the preparation of other nanomaterials and promising applications in various fields of nanotechnology.