Fabrication of size-tunable gold nanoparticles array with nanosphere lithography, reactive ion etching, and thermal annealing

Two-dimensional ordered arrays of gold (Au) nanoparticles were fabricated using two different variants of the nanosphere lithography technique. First, ordered arrays of polystyrene nanospheres on Si substrate were used as deposition masks through which gold films were deposited by electron beam evaporation. After the removal of the nanospheres, an array of triangular Au nanodisks was left on the Si substrate. After thermal annealing at increasing temperature, systematic shape transition of the nanostructures from original triangular Au nanodisks to rounded nanoparticles was observed. This approach allows us to systematically vary the size and morphology of the particles. In the second and novel technique, we made use of reactive ion etching to simultaneously reduce the dimension of the masking nanospheres and create arrays of nanopores on the substrate prior to the deposition of the Au films. These samples were subsequently annealed, which resulted in size-tunable and ordered Au nanoparticle arrays with the nanoparticles nested in the nanopores of the templated substrate. With the nanoparticles anchored in the nanopores, the substrate could be useful as a template for growth of other nanomaterials.     

Wettability transition induced transformation and entrapment of polymer nanostructures in cylindrical nanopores

We apply the concept of wettability transition to manipulate the morphology and entrapment of polymer nanostructures inside cylindrical nanopores of anodic aluminum oxide (AAO) membranes. When AAO/polystyrene (PS) hybrids, i.e., AAO/PS nanorods or AAO/PS nanotubes, are immersed into a polyethylene glycol (PEG) reservoir above the glass transition temperature of PS, a wettability transition from wetting to nonwetting of PS can be triggered due to the invasion of the more wettable PEG melt. The wettability transition enables us to develop a nondestructive method to entrap hemispherically capped nanorods inside nanopores. Moreover, we can obtain single nanorods with the desired aspect ratio by further dissolving the AAO template, in contrast to the drawbacks of nonuniformity or destructiveness from the conventional ultrasonication method. In the case of AAO/PS nanotubes, the wettability transition induced dewetting of PS nanotube walls results in the disconnection and entrapment of nonwetting PS domains (i.e., nanospheres, nanocapsules, or capped nanorods). Moreover, PEG is then washed to recover the pristine wettability of PS on the alumina surface; further annealing of the PS nanospheres inside AAO nanopores under vacuum can generate some unique nanostructures, particularly semicylindrical nanorods.     

Effect of Nonsolvent on the Formation of Polymer Nanomaterials in the Nanopores of Anodic Aluminum Oxide Templates

We study the effect of nonsolvent on the formation of polymer nanomaterials in the nanopores of porous templates. Water (nonsolvent) is added into a poly (methyl methacrylate) (PMMA) solution in dimethylformamide (DMF) confined in the nanopores of an anodic aluminum oxide (AAO) template. Water forms a wetting layer on the pore wall and causes the PMMA solution to be isolated in the center of the nanopore, resulting in the formation of PMMA nanospheres or nanorods after the solvent is evaporated. The formation of the polymer nanomaterials induced by nonsolvent is found to be driven by the Rayleigh‐instability‐type transformation. Without adding the nonsolvent, PMMA chains precipitate on the walls of the nanopores after the solvent is evaporated, and PMMA nanotubes are obtained.     

Synthesis and morphology of triangular pyramid-shaped puerarin microparticle with nanostructure

<正>A type of triangular pyramid-shaped microparticles of puerarin was synthesized by using oil-in-oil microemulsion approach which is simple and economical under the action of copper substrate.The pyramid-shaped microparticles would be made up of deposit of nanospheres or nanorods and have two significant characters.One is its complex surface morphology like coral reef.The other is a lot of nanopores in existence in the microparticle body.Two possible formation routes were speculated.     

Polymer brushes in nanopores surrounded by silicon-supported tris(trimethylsiloxy)silyl monolayers

A chemically grafted tris(trimethylsiloxy)silyl (tris(TMS)) monolayer on a silicon oxide substrate was used as a template for creating nanoclusters of polymer brushes. Polymer brushes were synthesized by surface-initiated polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and tert-butyl methacrylate (t-BMA) via atom transfer radical polymerization (ATRP) from alpha-bromoester groups tethered to the residual silanol groups on the silicon surface after generating a range of tris(TMS) coverage. CuBr/bpy and CuBr/PMDETA were used as the catalytic system for PMPC and Pt-BMA synthesis, respectively. The percentage of tris(TMS) coverage significantly influenced the thickness and morphology of the polymer brushes. Protrusions representing self-aggregation of PMPC brushes in nanopores as visualized by AFM analysis evidently suggested that PMPC brushes were distributed nanoscopically on the surface. The protrusion size and surface roughness corresponded quite well with the graft density of PMPC brushes. The fact that Pt-BMA brushes grown from nanopores were almost featureless implies that self-aggregation of PMPC brushes is truly a consequence of phase incompatibility between hydrophilic PMPC brushes and hydrophobic tris(TMS). The anti-fouling characteristic of PMPC brushes, inferred from plasma protein adsorption, was subsequently varied by controlling the surface coverage ratio between PMPC brushes and tris(TMS).     

DNA origami gatekeepers for solid-state nanopores

DNA has it covered: DNA origami gatekeeper nanoplates convert nanopores in solid-state membranes into versatile devices for label-free macromolecular sensing applications. The custom apertures in the nanoplates can be chemically addressed for sequence-specific detection of DNA.     

Novel Sensitive Fluorometric Determination of Exonuclease I Using Polydopamine Nanospheres

A novel fluorescence sensing platform based on polydopamine nanospheres and 6′-carboxyfluorescein labeled single-stranded DNA has been developed for monitoring the concentration of exonuclease I. Due to the interaction between single-stranded DNA and polydopamine nanospheres, the single-stranded DNA may be adsorbed on the surface of polydopamine nanospheres. The fluorescence of 6′-carboxyfluorescein was subsequently quenched by the polydopamine nanospheres through energy transfer or electron transfer. However, the 6′-carboxyfluorescein-labeled single-stranded DNA was specifically degraded by exonuclease I, producing mono or oligonucleotide fragments, which were not adsorbed by the polydopamine nanospheres, and thus the fluorescence signal was retained. The retained fluorescence of the sensing platform was found to be linear with the concentration of exonuclease I in the range of 0.15–10?U?mL^?1 with a detection limit of 0.05?U?mL^?1. In addition, the sensing platform was highly selective toward exonuclease I. Benefiting from the high efficiency and the simple design process, satisfactory performance has been successfully demonstrated for the determination of exonuclease I in complex samples.     

A Single‐Crystalline Mesoporous Quartz Superlattice

There has been significant interest in the crystallization of nanostructured silica into α‐quartz because of its physicochemical properties. We demonstrate a single‐crystalline mesoporous quartz superlattice, a silica polymorph with unprecedentedly ordered hierarchical structures on both the several tens of nanometers scale and the atomic one. The mesoporous quartz superlattice consists of periodically arranged α‐quartz nanospheres whose crystalline axes are mostly oriented in an assembly. The superlattice is prepared by thermal crystallization of amorphous silica nanospheres constituting a colloidal crystal. We found that the deposition of a strong flux of Li⁺ only on the surface of silica nanospheres is effective for crystallization.     

Gene transfection using biodegradable nanospheres: results in tissue culture and a rat osteotomy model

In this paper, we have investigated sustained release biodegradable nanospheres for the delivery of plasmid DNA. The nanospheres were formulated using a proprietary co-polymer emulsion technique to encapsulate plasmid DNA. Gene transfection with nanospheres containing reporter genes (human placental alkaline phosphatase (AP) or Luciferase) was demonstrated in tissue culture (293T and COS-7 cells), and also in vivo in a nonunion femoral fracture (osteotomy) rat model. The bone gap was filled with nanospheres and gene expression in the implantation site was measured five weeks after the initial surgery. The nanospheres had a mean diameter of 230 nm, with a DNA loading of 0.7%w/w. These nanospheres demonstrated sustained release of the encapsulated DNA under in vitro physiologic conditions with an 82% cumulative DNA release over 17 days. The transfection efficiency of the nanospheres in tissue culture was two to five orders of magnitude greater than the gene expression with the same amount of plasmid DNA in solution. In the rat studies, the mean AP activity in the tissue retrieved from the osteotomy site in the experimental group was 291.8±52.5 cpm Versus 54.1±26.5 cpm (mean±S.E.M., P=0.03) in the sham control group. In conclusion, plasmid DNA nanospheres could be used as an effective nonviral method of gene delivery. In the future, nanospheres containing therapeutic genes, such as those encoding parathyroid hormone peptide, 1–34 amino acids (PTH-34) or Bone Morphogenic Protein-4 (BMP-4), could be used for the healing of nonunion bone fracture sites.     

Partitioning and assembly of metal particles and their bioconjugates in aqueous two-phase systems

The behavior of metal nanospheres and nanowires and their bioconjugates in aqueous two-phase systems (ATPS) is described. The ATPS used in this work comprised poly(ethylene glycol) (PEG), dextran, and water or aqueous buffer. Au and Ag nanospheres less than 100 nm in diameter partition between the PEG-rich and dextran-rich phases on the basis of their surface chemistry and can be separated on this basis. Larger Au nanospheres and wires accumulate at the interface between the two aqueous phases. The influence of polymer molecular weight and concentration on interfacial assembly of Au wires is described. DNA-derivatized nanowires at the aqueous/aqueous interface retain the ability to selectively bind to fluorescent complementary DNA. In addition, Au nanoparticles have been bound to Au wires via selective DNA hybridization at the ATPS interface. Transmission electron microscopy and thermal denaturation experiments confirm that DNA-driven assembly is responsible for the formation of the nanosphere/wire assemblies. These results demonstrate the biocompatibility of the two-phase interface and point to future use as scaffolding in biorecognition-driven assembly.     

Surface-modified protein nanospheres as potential antiviral agents

A novel application of surface-modified protein nanospheres as potential antiviral agents is illustrated. By using a single-step sonochemical process, bovine serum albumin nanospheres were generated, whose surface was covalently conjugated with mercaptoethane sulfonate to chemically and electrostatically mimic cellular heparan sulfate. The nanospheres effectively inhibited HSV-1 infection.     

Surface-charge induced ion depletion and sample stacking near single nanopores in microfluidic devices

We report integrated nanopore/microchannel devices in which single nanopores are isolated between two microfluidic channels. The devices were formed by sandwiching track-etched conical nanopores in a poly(ethylene terephthalate) membrane between two poly(dimethylsiloxane) microchannels. Integration of the nanopores into microfluidic devices improves mass transport to the nanopore and allows easy coupling of applied potentials. Electrical and optical characterization of these individual nanopores suggests double layer overlap is not required to form an ion depletion region adjacent to the nanopore in the microchannel; rather, excess surface charge in the nanopore contributes to the formation of this ion depletion region. We used fluorescent probes to optically map the ion depletion region and the stacking of fluorescein near the nanopore/microchannel junction, and current measurements confirmed formation of the ion depletion region.     

Pushing the size limits in the replication of nanopores in anodized aluminum oxide via the layer-by-layer deposition of polyelectrolytes

We report on the successful replication of the smallest pores in anodized aluminum oxide (AAO) via the layer-by-layer (LBL) deposition of polyelectrolytes to date to yield free-standing, open nanotubes with inner and outer diameters (±2σ) down to 37 ± 4 and 52 ± 19 nm, respectively. This work is based on the fabrication of defined arrays of highly regular nanopores by anodic oxidation of aluminum. Pores with pore diameters between 53 ± 9 and 356 ± 14 nm and interpore distances between 110 ± 3 and 500 ± 17 nm were obtained using an optimized two-step anodization procedure. 3-(Ethoxydimethylsilyl)propylamine-coated pores were replicated by alternating LBL deposition of poly(styrenesulfonate) and poly(allylamine). The detrimental adsorption of polyelectrolyte on the top surface of the template that typically results in partial pore blocking was eliminated by controlling the surface energy of the top surface via deposition of an ultrathin gold layer. The thickness of the deposited LBL multilayer assembly at the pore orifice agreed to within the experimental error with the thicknesses measured by variable angle spectroscopic ellipsometry and atomic force microscopy (AFM) for layers assembled on flat substrates. The selective dissolution of the alumina template afforded free-standing, open polymer nanotubes that were stable without any cross-linking procedure. The nanotubes thus obtained possessed mean outer diameters as small as 52 nm, limited by the size of the AAO template.     

Electrochemical Quantitative Evaluation of the Surface Charge of a Poly(1-Vinylimidazole) Multilayer Film and Application to Nanopore pH Sensor

Nanopore pH sensing is based on the interaction between the surface charge of the nanopore and ions passing through the nanopore. The nanopore surface charge can be derived from the acid-base dissociation equilibrium of the modified polyelectrolyte. Various polyelectrolytes have been selected based on the acid dissociation constant of the monomer units, and various techniques have been applied to modify nanopores. However, they have been developed without clear guidelines for characterizing the surface modification status or surface charge. One reason has been the difficulty in accurately estimating the surface charge of nanopores in solution. Thus, in this study, the dissociation constant (pKa_app) of the surface charge of a modified polyelectrolyte nanopore was quantitatively estimated via electrochemical measurements. Previously, the modification status of nanopores has been evaluated using the ion current response. In addition, we monitored in real-time the polyelectrolyte modification status using a quartz crystal microbalance (QCM). Some polyelectrolytes were difficult to immobilize directly on the nanopore surface, and those polymers could be effectively modified by the layer-by-layer (LbL) technique. Therefore, we produced a guideline for the fabrication of a nanopore sensor for pH measurements under physiological conditions by quantitative evaluation of the pKa_app via electrochemical methods, the monitoring of the modification status by QCM, and the development of an effective modification method via the LbL technique.     

Nanopore formation by self-assembly of the model genetically engineered elastin-like polymer [(VPGVG)2(VPGEG)(VPGVG)2]15

The self-assembly characteristics of the model genetically engineered elastin-like polymer [(VPGVG)2(VPGEG)(VPGVG)2]15 have been studied in this work. An AFM study of the topology of polymer films deposited from acid and basic solutions on a hydrophobic silicon substrate has been carried out. Under acidic conditions, polymer deposition results in a flat surface with no particular topological features. However, from basic solutions, polymer deposition clearly shows an aperiodic pattern of nanopores ( approximately 70 nm width and separated about 150 nm). This dramatic dependence of film topology on pH is explained in terms of the different polarity of the free gamma-carboxyl group of the glutamic acid. In the carboxylate form, this moiety shows a markedly higher polarity than the rest of the polymer domains and the substrate itself. Under these conditions, the charged carboxylates impede hydrophobic contact with their surroundings, which is the predominant assembly pathway for this type of polymer. The charged domains, along with their hydration sphere, are then segregated from the hydrophobic surroundings giving rise to nanopores.     

Rapid Synthesis of Hollow Ag–Au Nanodendrites in 15 Seconds by Combining Galvanic Replacement and Precursor Reduction Reactions

Metallic nanomaterials displaying hollow interiors as well as sharp tips/branches at their surface (such as hollow nanodendrites) are attractive, because these features enable higher surface‐to‐volume ratios than their solid and/or rounded counterparts. This paper describes a simple strategy for the synthesis of Ag–Au nanodendrites in 15 s using Ag nanospheres prepared in a previous synthetic step as seeds. Our approach was based on the utilization of Ag nanospheres as seeds for Au deposition by a combination of galvanic replacement reaction between Ag and AuCl₄^?(aq) and AuCl₄^?(aq) reduction using hydroquinone in the presence of polyvinylpyrrolidone (PVP) as a stabilizer and water as the solvent. The produced Ag–Au nanodendrites presented monodisperse sizes, and their surface morphologies could be tuned as a function of growth time. Owing to their hollow interiors and sharp tips, the Ag–Au nanodendrites performed as effective substrates for surface‐enhanced Raman scattering (SERS) detection of 4‐MPy (4‐mercaptopyridine) and R6G (rhodamine 6G) as probe molecules. We believe that the approach described herein can serve as a protocol for the fast and one‐step synthesis of Ag–Au hollow nanondendrites with a wide range of sizes, compositions, and surface morphologies for applications in SERS and catalysis.     

Fabrication of nanocables by electrochemical deposition inside metal nanotubes

We report a novel route for fabricating Au-Te nanocables. Using nanoporous polycarbonate tract-etching (PCTE) membrane as the template, Au nanotubes were fabricated by electroless Au deposition inside the nanopores of the PCTE membrane. Using the Au nanotube membrane as a second template, Te was deposited on the surfaces of the Au nanotubes by slow electrochemical deposition, taking advantage of underpotential deposition (UPD). The deposition rate was sufficiently slow to radially grow Te nanotubes coaxially within the Au nanotubes to form nanocables.     

包覆铕配合物Eu(DBM)3phen的硅胶纳米荧光检测材料的制备

以十六烷基三甲基溴化铵(CTAB)和一种短链氟碳阴离子表面活性剂(Capstone FS-66)作为双模板,通过四乙氧基硅烷(TEOS)和含氯官能团的硅烷偶联剂制备了含氯官能团的大孔径树枝状介孔二氧化硅纳米球(MSNs);利用EuCl3·6H2O、1,10-邻菲啰啉盐酸盐和二苯甲酰甲烷合成铕的配合物Eu(DBM)3phen,然后以MSNs为基质填充Eu(DBM)3phen。为了更好地将Eu(DBM)3phen嵌入到纳米球孔道内,对所制备的介孔纳米球的孔道表面进行聚乙烯亚胺(PEI)修饰;同时为了解决荧光配合物从孔道泄露的问题,在纳米球表面层层自组装吸附多层聚合物,然后包覆一层二氧化硅膜形成核-壳结构。最后将所制备的荧光纳米球与3-氨丙基三乙氧基硅烷反应,使其表面带有氨基,用来嫁接生物分子如抗体等。通过透射电子显微镜(TEM)、荧光光度计和傅里叶红外光谱仪(FTIR)等多种方法对最终合成的纳米球的结构和性能进行了表征。结果表明:本制备的荧光纳米球粒径约为230μm、荧光强度约为2800a.u,1543cm^-1处出现了氨基的弯曲振动峰。     

Perforated, freely suspended layer-by-layer nanoscale membranes

Ultrathin, perforated, and freely suspended membranes with uniform nanopores in the range of tens of nanometers have been fabricated using a fast, simple method of spin-assisted layer-by-layer assembly on hydrophobic substrates. Membranes with thicknesses down to 20 nm were robust enough to be released from the sacrificial substrates, transferred onto various surfaces, and suspended over microscopic openings. The nanopore size can be controlled by tuning the number of polyelectrolyte bilayers, spinning speed, and a proper selection of hydrophobic substrates. We demonstrate that the formation of nanopores is caused by the partial dewetting of polyelectrolyte layers in the course of their deposition on the underlying hydrophobic surfaces. The nanoscale thickness of perforated membranes with relatively uniform size and a high concentration of nanopores provides perspectives for higher rates of transport through freely suspended LbL membranes. The highly perforated LbL membranes introduced here can serve as a novel platform for ultrafine separation considering an intriguing combination of nanopores, nanoscale membrane thickness, and easy functionalization.     

Water-dispersible, uniform nanospheres by heating-enabled micellization of amphiphilic block copolymers in polar solvents

Uniform nanospheres with tunable size down to 30 nm were prepared simply by heating amphiphilic block copolymers in polar solvents. Unlike reverse micelles prepared in nonpolar, oily solvents, these nanospheres have a hydrophilic surface, giving them good dispersibility in water. Furthermore, they are present as individual, separated, rigid particles upon casting from the solution other than continuous thin films of merged micelles cast from micellar solution in nonpolar solvents. These nanospheres were generated by a heating-enabled micellization process in which the affinity between the solvent and the polymer chains as well as the segmental mobility of both hydrophilic and hydrophobic blocks was enhanced, triggering the micellization of the glassy copolymers in polar solvents. This heating-enabled micellization produces purely well-defined nanospheres without interference of other morphologies. The micelle sizes and corona thickness are tunable mainly by changing the lengths of the hydrophobic and hydrophilic blocks, respectively. The heating-enabled micellization route for the preparation of polymeric nanospheres is extremely simple, and is particularly advantageous in producing rigid, micellar nanospheres from block copolymers with long glassy, hydrophobic blocks which are otherwise difficult to prepare with high efficiency and purity. Furthermore, encapsulation of hydrophobic molecules (e.g., dyes) into micelle cores could be integrated into the heating-enabled micellization, leading to a simple and effective process for dye-labeled nanoparticles and drug carriers.