Visible‐Light‐Induced Electron Transport from Small to Large Nanoparticles in Bimodal Gold Nanoparticle‐Loaded Titanium(IV) Oxide

A key to realizing the sustainable society is to develop highly active photocatalysts for selective organic synthesis effectively using sunlight as the energy source. Recently, metal‐oxide‐supported gold nanoparticles (NPs) have emerged as a new type of visible‐light photocatalysts driven by the excitation of localized surface plasmon resonance of Au NPs. Here we show that visible‐light irradiation (λ>430 nm) of TiO₂‐supported Au NPs with a bimodal size distribution (BM‐Au/TiO₂) gives rise to the long‐range (>40 nm) electron transport from about 14 small (ca. 2 nm) Au NPs to one large (ca. 9 nm) Au NP through the conduction band of TiO₂. As a result of the enhancement of charge separation, BM‐Au/TiO₂ exhibits a high level of visible‐light activity for the one‐step synthesis of azobenzenes from nitrobenzenes at 25 °C with a yield greater than 95 % and a selectivity greater than 99 %, whereas unimodal Au/TiO₂ (UM‐Au/TiO₂) is photocatalytically inactive.     

Close‐Packed Two‐Dimensional Silver Nanoparticle Arrays: Quadrupolar and Dipolar Surface Plasmon Resonance Coupling

Silver nanoparticles (NPs) ranging in size from 40 to 100 nm were prepared in high yield by using an improved seed‐mediated method. The homogeneous Ag NPs were used as building blocks for 2D assembled Ag NP arrays by using an oil/water interface. A close‐packed 2D array of Ag NPs was fabricated by using packing molecules (3‐mercaptopropyltrimethoxysilane) to control the interparticle spacing. The homogeneous 2D Ag NP array exhibited a strong quadrupolar cooperative plasmon mode resonance and a dipolar red‐shift relative to individual Ag NPs suspended in solution. A well‐arranged 2D Ag NP array was embedded in polydimethylsiloxane film and, with biaxial stretching to control the interparticle distance, concomitant variations of the quadrupolar and dipolar couplings were observed. As the interparticle distance increased, the intensity of the quadrupolar cooperative plasmon mode resonance decreased and dipolar coupling completely disappeared. The local electric field of the 2D Ag NP array was calculated by using finite difference time domain simulation and qualitatively showed agreement with the experimental measurements.     

Engineering of UV‐absorbing polypropylene films containing poly(2‐(2′‐hydroxy‐5′‐methacryloxyethylphenyl)‐2H‐benzotriazole) nanoparticles

Ultraviolet‐absorbing nanoparticles (NPs) were prepared by emulsion co‐polymerization of the vinylic monomer 2‐(2′‐hydroxy‐5′‐methacryloxyethylphenyl)‐2H‐benzotriazole (Norbloc?, NB) with the crosslinking monomer divinylbenzene. The effect of total monomer, surfactant, crosslinker, and initiator concentrations on the size and size distribution of the formed NPs was elucidated. The NB monomer and the formed polyNB (PNB) NPs of 19 ± 2 nm were then incorporated into polypropylene (PP) films by melt‐compounding technique by using cast film extrusion. Increasing the PNB NP concentrations integrated within the PP films decreased their UV transmittance. Migration of the UV absorbing PNB NPs from the PP films was not observed during 3 years of storage at room temperature or while exposure to extreme conditions. Under the same conditions, a significant migration was observed for the NB monomer‐containing films. Overall, the PNB NP‐containing films are clear and transparent, although the haze was affected by the addition of NB and PNB NPs. Moreover, the films have good mechanical properties and UV‐blocking quality. Copyright © 2017 John Wiley & Sons, Ltd.     

Precise Size‐Selective Sieving of Nanoparticles Using a Highly Oriented Two‐Dimensional Supramolecular Polymer

The development of size‐selective membranes with well‐defined nanopores towards the precise separation of nanometer‐sized substances is a challenging task to achieve. Here a supramolecular membrane is presented that comprises a highly oriented, honeycomb‐like, 2D supramolecular polymer on a polycarbonate filter support. It enables precise size‐selective sieving of colloidal nanoparticles (NPs). Owing to the uniform parallel‐aligned nanocavities within the 2D supramolecular polymers, the composite membrane shows a high size‐selectivity with a sub‐nanometer accuracy in the cutoff size of about 4.0 nm. In principle, the species of size‐separable particles are unlimited, as demonstrated by quantum dots, noble metal, and metal oxide NPs. This supramolecular membrane combined with filtration advances the potential of NPs in terms of their monochromatic emission and size monodispersity, and also enables rapid removal of small magnetic NP adsorbents that are otherwise difficult to capture.     

A Surfactant‐Encapsulating Polyoxometalate Nanowire Assembly as a New Carrier for Nanoscale Noble‐Metal Catalysts

The loading of noble‐metal nanoparticles (NMNPs) onto various carriers to obtain stable and highly efficient catalysts is currently an important strategy in the development of noble metal (NM)‐based catalytic reactions and their applications. We herein report a nanowire supramolecular assembly constructed from the surfactant‐encapsulating polyoxometalates (SEPs) CTAB‐PW₁₂, which can act as new carriers for NMNPs. In this case, the Ag NPs are loaded onto the SEP nanowire assembly with a narrow size distribution from 5 to 20 nm in diameter; the average size is approximately 10 nm. The Ag NPs on the nanowire assemblies are well stabilized and the over agglomeration of Ag NPs is avoided owing to the existence of well‐arranged polyoxometalate (POM) units in the SEP assembly and the hydrophobic surfactant on the surface of the nanowire assembly. Furthermore, the loading amount of the Ag NPs can be adjusted by controlling the concentration of the AgNO₃ aqueous solution. The resultant Ag/CTAB‐PW₁₂ composite materials exhibit high activity and good stability for the catalytic reduction of 4‐nitrophenol (4‐NP) with NaBH₄ in isopropanol/H₂O solution. The NMNPs‐loaded SEP nanoassembly may represent a new composite catalyst system for application in NM‐based catalysis.     

In Situ Synthesis of Self‐Assembled Gold Nanoparticles on Glass or Silicon Substrates through Reactive Inkjet Printing

A facile and low cost method for the synthesis of self‐assembled nanoparticles (NPs) with minimal size variation and chemical waste by using reactive inkjet printing was developed. Gold NPs with diameters as small as (8±2) nm can be made at low temperature (120 °C). The size of the resulting NPs can be readily controlled through the concentration of the gold precursor and oleylamine ink. The pure gold composition of the synthesized NPs was confirmed by energy‐dispersive X‐ray spectroscopy (EDXS) analysis. High‐resolution SEM (HRSEM) and TEM (HRTEM), and X‐ray diffraction revealed their size and face‐centered cubic (fcc) crystal structure, respectively. Owing to the high density of the NP film, UV/Vis spectroscopy showed a red shift in the intrinsic plasmonic resonance peak. We envision the extension of this approach to the synthesis of other nanomaterials and the production of tailored functional nanomaterials and devices.     

Plasmon-Enhanced Electrochemiluminescence at the Single-Nanoparticle Level

Plasmon-enhanced electrochemiluminescence (ECL) at the single-nanoparticle (NP) level was investigated by ECL microscopy. The Au NPs were assembled into an ordered array, providing a high-throughput platform that can easily locate each NP in sequential characterizations. A strong dependence of ECL intensity on Au NP configurations was observed. We demonstrate for the first time that at the single-particle level, the ECL of Ru(bpy)₃²⁺-TPrA was majorly quenched by small Au NPs (<40 nm), while enhanced by large Au ones (>80 nm) due to the localized surface plasmon resonance (LSPR). Notably, the ECL intensity was further increased by the coupling effect of neighboring Au NPs. Finite Difference Time Domain (FDTD) simulations conformed well with the experimental results. This plasmon enhanced ECL microscopy for arrayed single NPs provides a reliable tool for screening electrocatalytic activity at a single particle.     

Highly selective immobilization of Au nanoparticles onto isolated and dense nanopatterns of poly(2-vinyl pyridine) brushes down to single-particle resolution

Chemical patterns consisting of poly(2-vinyl pyridine) (P2VP) brushes in a background of a cross-linked polystyrene (PS) mat enabled the highly selective placement of citrate-stabilized Au nanoparticles (NPs) in arrays on surfaces. The cross-linked PS mat prevented the nonspecific binding of Au NPs, and the regions functionalized with P2VP brushes allowed the immobilization of the particles. Isolated chemical patterns of feature sizes from hundreds to tens of nanometers were prepared by standard lithographic techniques. The number of 13 nm Au NPs bound per feature increased linearly with increasing area of the patterns. This behavior is similar to previous reports using 40 nm particles or larger. Arrays of single NPs were obtained by reducing the dimensions of patterned P2VP brushes to below ~20 nm. To generate dense (center-to-center distance = 80 nm) linear chemical patterns for the placement of rows of single NPs, a block-copolymer (BCP)-assisted lithographic process was used. BCPs healed defects associated with the standard lithographic patterning of small dimensions at high densities and led to highly registered, linear, single NP arrays.     

Ultrahighly Sensitive Homogeneous Detection of DNA and MicroRNA by Using Single‐Silver‐Nanoparticle Counting

DNA and RNA analysis is of high importance for clinical diagnoses, forensic analysis, and basic studies in the biological and biomedical fields. In this paper, we report the ultrahighly sensitive homogeneous detection of DNA and microRNA by using a novel single‐silver‐nanoparticle counting (SSNPC) technique. The principle of SSNPC is based on the photon‐burst counting of single silver nanoparticles (Ag NPs) in a highly focused laser beam (about 0.5 fL detection volume) due to Brownian motion and the strong resonance Rayleigh scattering of single Ag NPs. We first investigated the performance of the SSNPC system and then developed an ultrasensitive homogeneous detection method for DNA and microRNA based on this single‐nanoparticle technique. Sandwich nucleic acid hybridization models were utilized in the assays. In the hybridization process, when two Ag‐NP–oligonucleotide conjugates were mixed in a sample containing DNA (or microRNA) targets, the binding of the targets caused the Ag NPs to form dimers (or oligomers), which led to a reduction in the photon‐burst counts. The SSNPC method was used to measure the change in the photon‐burst counts. The relationship between the change of the photon‐burst counts and the target concentration showed a good linearity. This method was used for the assay of sequence‐specific DNA fragments and microRNAs. The detection limits were at about the 1 fM level, which is 2–5 orders of magnitude more sensitive than current homogeneous methods.     

Protein‐Sized Bright Fluorogenic Nanoparticles Based on Cross‐Linked Calixarene Micelles with Cyanine Corona

The key challenge in the field of fluorescent nanoparticles (NPs) for biological applications is to achieve superior brightness for sizes equivalent to single proteins (3–7 nm). We propose a concept of shell‐cross‐linked fluorescent micelles, in which PEGylated cyanine 3 and 5 bis‐azides form a covalently attached corona on micelles of amphiphilic calixarene bearing four alkyne groups. The fluorescence quantum yield of the obtained monodisperse NPs, with a size of 7 nm, is a function of viscosity and reached up to 15 % in glycerol. In the on‐state they are circa 2‐fold brighter than quantum dots (QD‐585), which makes them the smallest PEGylated organic NPs of this high brightness. FRET between cyanine 3 and 5 cross‐linkers at the surface of NPs suggests their integrity in physiological media, organic solvents, and living cells, in which the NPs rapidly internalize, showing excellent imaging contrast. Calixarene micelles with a cyanine corona constitute a new platform for the development of protein‐sized ultrabright fluorescent NPs.     

Probing nanocolumnar silver nanoparticle/zinc oxide hierarchical assemblies with advanced surface plasmon resonance and their enhanced photocatalytic performance for formaldehyde removal

Recent advances in photocatalysis focus on the development of materials with hierarchical structure and on the surface plasmon resonance (SPR) phenomenon exhibited by metal nanoparticles (NPs). In this work, both are combined in a material where size‐controllable Ag‐NPs are uniformly loaded onto the hierarchical microporous and mesoporous and nanocolumnar structures of ZnO, resulting in Ag‐NP/ZnO nanocomposites. The embedded Ag‐NPs slightly decrease the hydrophobicity of fibrous ZnO, improve its wettability, and increase the absorption of formaldehyde (H₂CO) onto the photocatalyst, all of this resulting in excellent photodegradation of formaldehyde in aqueous solution. Besides, we found that Ag‐NPs with optimal size not only accelerate the charge transfer to the surface of ZnO, but also strengthen the SPR effect in the intercolumnar channels of fibrous ZnO particles combining with high concentration of photo‐generated radical species. The micro‐to‐mesoporous ZnO is like a nanoarray packed Ag‐NPs. With Ag‐NPs of diameter 2.5 < ? < 6.5 nm, ZnO exhibits the most superior photodegradation rate constant value of 0.0239 min^?1 with total formaldehyde removal of 97%. This work presents a new feasible approach involving highly sophisticated Ag‐NP/ZnO architecture combining the SPR effect and hierarchically ordered structures, which results in high photocatalytic activity for formaldehyde photodegradation.     

Ultra‐pH‐Responsive and Tumor‐Penetrating Nanoplatform for Targeted siRNA Delivery with Robust Anti‐Cancer Efficacy

RNA interference (RNAi) gene silencing technologies have shown significant potential for treating various diseases, including cancer. However, clinical success in cancer therapy remains elusive, mainly owing to suboptimal in vivo delivery of RNAi therapeutics such as small interference RNA (siRNA) to tumors. Herein, we developed a library of polymers that respond to a narrow pH change (ultra‐pH‐responsive), and demonstrated the utility of these materials in targeted and deep tumor‐penetrating nanoparticle (NP) for in vivo RNAi. The new NP platform is mainly composed of the following key components: i) internalizing RGD (iRGD) to enhance tumor targeting and tissue penetration; ii) polyethylene glycol (PEG) chains to prolong blood circulation; and iii) sharp pH‐responsive hydrophobic polymer to improve endosome escape. Through systematic studies of structure–function relationship, the optimized RNAi NPs (<70 nm) showed efficient gene silencing and significant inhibition of tumor growth with negligible toxicities in vivo.     

Synthesis of α‐MoC1−x Nanoparticles with a Surface‐Modified SBA‐15 Hard Template: Determination of Structure–Function Relationships in Acetic Acid Deoxygenation

Surface modification of mesoporous SBA‐15 silica generated a hydrophobic environment for a molybdenum diamine (Mo‐diamine) precursor solution, enabling direct growth of isolated 1.9±0.4 nm α‐MoC_1?x nanoparticles (NPs) inside the pores of the support. The resulting NP catalysts are bifunctional, and compared to bulk α‐MoC_1?x and β‐Mo₂C, the NPs exhibit a greater acid‐site:H‐site ratio and a fraction of stronger acid sites. The greater acid‐site:H‐site ratio results in higher decarbonylation (DCO) selectivity during acetic acid hydrodeoxygenation (HDO) reactions, and the stronger acid sites lead to higher activity and ketonization (KET) selectivity at high temperatures. The hard‐templating synthetic method could be a versatile route toward carbide NPs of varying size, composition, and phase, on a range of mesoporous oxide supports.     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.     

Self-Assembly of Nanoparticles into Two-Dimensional Arrays for Catalytic Applications

Self-assembly of nanoparticles (NPs) is at the heart of nanotechnology, and has shown many potential applications in fabricating nanodevices with highly controlled functionality. Two-dimensional (2D) arrays of NPs can provide a thin and uniform NP array with each NP being exposed on the surface to maximize NP catalysis. This minireview summarizes the recent progress on the fabrication and application of 2D NP arrays. It conveys the important message to readers that creation of libraries of NP arrays with varying catalytic strengths is an exciting direction in catalysis. This approach can be used to solve complicated catalytic problems in which multiple chemical reactions need to be catalyzed in a single reaction vessel.     

Viologen‐Templated Arrays of Cucurbit[7]uril‐Modified Iron‐Oxide Nanoparticles

Magnetic and fluorescent assemblies of iron‐oxide nanoparticles (NPs) were constructed by threading a viologen‐based ditopic ligand, DPV²⁺, into the cavity of cucurbituril (CB[7]) macrocycles adsorbed on the surface of the NPs. Evidence for the formation of 1:2 inclusion complexes that involve DPV²⁺ and two CB[7] macrocycles was first obtained in solution by ¹H NMR and emission spectroscopy. DPV²⁺ was found to induce self‐assembly of nanoparticle arrays (DPV²⁺?CB[7]NPs) by bridging CB[7] molecules on different NPs. The resulting viologen‐crosslinked iron‐oxide nanoparticles exhibited increased saturation magnetization and emission properties. This facile supramolecular approach to NP self‐assembly provides a platform for the synthesis of smart and innovative materials that can achieve a high degree of functionality and complexity and that are needed for a wide range of applications.     

Rare‐Earth Nanoparticles with Enhanced Upconversion Emission and Suppressed Rare‐Earth‐Ion Leakage

Upconversion emissions from rare‐earth nanoparticles have attracted much interest as potential biolabels, for which small particle size and high emission intensity are both desired. Herein we report a facile way to achieve NaYF₄:Yb,Er@CaF₂ nanoparticles (NPs) with a small size (10–13 nm) and highly enhanced (ca. 300 times) upconversion emission compared with the pristine NPs. The CaF₂ shell protects the rare‐earth ions from leaking, when the nanoparticles are exposed to buffer solution, and ensures biological safety for the potential bioprobe applications. With the upconversion emission from NaYF₄:Yb,Er@CaF₂ NPs, HeLa cells were imaged with low background interference.     

Designed Synthesis of Well‐Defined Pd@Pt Core–Shell Nanoparticles with Controlled Shell Thickness as Efficient Oxygen Reduction Electrocatalysts

Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs.     

In Situ Synthesis of Silver Nanoparticles for Ag‐NP/Cotton Nanocomposite and Its Bactericidal Effect

For years, nanotechnology has been considered as an important field that has opened new opportunities for extensive research. In biomedical applications, of all the metal nanoparticles, silver nanoparticles (Ag‐NPs) have played an important role because of their antibacterial properties. Ag‐NPs have been demonstrated to possess antibacterial properties in many applications. However, the minimum number of NPs required on the surface to prevent bacterial growth is yet to be determined. It is worthwhile studying the decrease of bacterial growth rate or the level of inhibition as a function of the size or density of NPs. Therefore, in this paper we discuss the size of the NPs that can stimulate the bactericidal property. It should also be noted that NPs larger than 100 nm might not be effective against bacteria. Moreover, this study employs polyvinyl pyrrolidone (PVP) and cellulose as reductants to form strong covalent bonds under UV light, which can help synthesize Ag‐NP/cotton nanocomposites. This type of nanocomposite displays high cell viability and improved antimicrobial activity. A fairly simple application involves the use of UV light to increase particle distribution and impart bactericidal property.     

C‐S cross‐coupling reaction using novel and green synthesized CuO nanoparticles assisted by Euphorbia maculata extract

In the present study, biosynthesis of CuO nanoparticles using a rapid, eco‐friendly, cost‐effective and efficient method has been reported employing aqueous Euphorbia maculata extract as mild, renewable and non‐toxic reducing and capping agents without adding any surfactants. The biogenic and green method has some benefits compared to conventional physical and chemical methods. It is simple, cheap and environmentally friendly. The biosynthesized CuO NP displayed a color change pattern (from sky blue to black) on preparation and presented its respective broad peak at 365 nm, which was analyzed by UV–Vis spectroscopy. Using the FT‐IR analysis, biomolecules in E. maculata extract which are responsible for bioreduction activity and synthesize of CuO NP, were identified. The XRD, EDX and FESEM results confirmed the successful synthesis of CuO nanoparticles of 18 nm sizes, with spherical and sponge crystal structure. The catalytic activity of biosynthesized CuO NPs was studied in C‐S cross‐coupling reaction. This method has the advantages of high yields, easy work‐up, and simple reusability. The recovered CuO NP can be reused four times without any considerable loss of its catalytic activity.