Viscosity gradient as a novel mechanism for the centrifugation-based separation of nanoparticles

A nanoparticle-based molecular beacon for directly detecting attomolar small RNA from plasma without purification

Molecular beacons (MBs) are DNA-based probes that detect DNA or RNA fragments and hold promise for monitoring diseases and studying protein-nucleic acid interactions. MBs usually use fluorescent molecules as fluorophores for reporting the target detection event. However, the fluorescence of the traditional fluorescent molecules can bleach and even be interfered with the background autofluorescence, reducing the detection performance. Hence, we propose to develop a nanoparticle-based MB (NPMB) that uses upconversion nanoparticles (UCNPs) as a fluorophore, which can be excited by near-infrared light to avoid background autofluorescence and thus enables us to detect small RNA from complicated clinical samples such as plasma. Specifically, we employ a DNA hairpin structure, with one segment complementary to the target RNA, to position a quencher (gold nanoparticles, Au NPs) and the UCNP fluorophore in close proximity, leading to the quenching of the fluorescence of UCNPs in the absence of a target nucleic acid. Only when the hairpin structure is complementary with the detection target, will the hairpin structure be destroyed to separate Au NPs and UCNPs, resulting in the instant recovery of the fluorescence signal of UCNPs and the consequent ultrasensitive detection of the target concentrations. The NPMB has an ultra-low background signal because UCNPs can be excited with NIR light with a wavelength longer than the emitted visible light. We demonstrate that the NPMB can successfully detect a small (22-nt) RNA (using a microRNA cancer biomarker, miR-21, as an example) and a small single-stranded DNA (complementing the cDNA of miR-21) in aqueous solutions from 1 aM to 1 pM, with the linear detection range being 10 aM to 1 pM for the former and 1 aM to 100 fM for the latter. We further show that the NPMB can be used to detect unpurified small RNA (miR-21) in clinical samples such as plasma with the same detection region. Our work suggests that the NPMB is a promising label-free and purification-free method for detecting small nucleic acid biomarkers in clinical samples with a detection limit as low as the aM level.

A theoretical understanding of ionic current through a nanochannel driven by a viscosity gradient

HYPOTHESIS

Different thermodynamic forces owing to the gradient of temperature, electrical potential, or concentration can drive ionic current through charged membranes. It has been recently shown that a viscosity gradient can drive an electrical current through a negatively charged nanochannel (Wiener and Stein, arXiv: 1807.09106). A model description of this phenomenon, based on the Maxwell-Stefan equation will help unravel the dominating physical mechanisms in so-called visco-migration.

THEORY

To understand the physical mechanisms underlying this phenomenon, we employed the Maxwell-Stefan equation to develop a 1D model and obtain a relation between the flux of solvents and the driving forces. Viscosity gradients are known to drive transport, but the development of an electrical current has not been theoretically described prior to this work.

FINDINGS

Our 1D model shows that the ionic current depends on the ideality of the solvent, though both ideal and non-ideal scenarios demonstrated good agreement with experimental data. We employed the model to understand the impact of solution bulk ionic strength and pH on the drift of ionic species with same reservoirs solution properties. Our modeling results unveiled the significant impact of bulk solution properties on the drift of ions which is in agreement with the experiments. Moreover, we have shown that the diffusion gradient along the nanochannel contributes significantly into driving ionic species if we even apply a small ionic concentration gradient to both reservoirs. Our modeling results may pave the way for finding novel applications for drift of ions in a diffusion gradient, which can be induced by connecting reservoirs of different viscosity fluids.

A highly efficient three-solvent methodology for separating colloidal nanoparticles

This study has established a three-solvent methodology for separating nanomaterials, such as monometallic nanoparticles, miscible and immiscible nanoalloys. After systematically investigating the separation methods in two-solvent and three-solvent systems, a three-solvent theoretical model has been proposed to thoroughly reveal the centrifugation mechanism of colloidal particles. PVP plays an important role in the formation of emulsion droplets as the key factor for separation. Based on the three-solvent model, a novel solvent system has been discovered, with low-toxicity solvents and high separation efficiency. This study can open a new path for the separation of colloidal particles in both research and industrial fields and further promote the development of functional nanomaterials in greener pathways.

Novel pathway for the sonochemical synthesis of silver nanoparticles with near-spherical shape and high stability in aqueous media

The present study shows the development of a novel sonochemical synthesis pathway of sub-15 nm silver nanoparticles (AgNPs) with quasi-spherical shape and high stability in aqueous suspension. Different analytical techniques such as on-line UV-Vis spectroscopy, Atomic Force Microscopy (AFM), and Transmission Electron Microscopy (TEM) were complementarily used to characterize the evolution of the properties of AgNPs synthesized with this new route. Furthermore, different centrifugation conditions were studied to establish a practical, simple and straightforward purification method. Particle size was determined by TEM employing two different deposition methods, showing that purified AgNPs have a size of 8.1 nm ± 2.4 nm with a narrow dispersion of the size distribution (95% coverage interval from 3.4 to 13 nm). Critical information of the shape and crystalline structure of these sub-15 nm AgNPs, provided by shape descriptors (circularity and roundness) using TEM and high resolution (HR)-TEM measurements, confirmed the generation of AgNPs with quasi-spherical shapes with certain twin-fault particles promoted by the high energy of the ultrasonic treatment. Elemental analysis by TEM-EDS confirmed the high purity of the sub-15 nm AgNPs, consisting solely of Ag. At the optical level, these AgNPs showed a bandgap energy of (2.795 ± 0.002) eV. Finally, the evaluation of the effects of ultraviolet radiation (UVC: 254 nm and UVA: 365 nm) and storage temperature on the spectral stability revealed high stability of the optical properties and subsequently dimensional properties of sub-15 nm AgNPs in the short-term (600 min) and long-term (24 weeks).

Ultracentrifugation Techniques for the Ordering of Nanoparticles

A centrifugal field can provide an external force for the ordering of nanoparticles. Especially with the knowledge from in-situ characterization by analytical (ultra)centrifugation, nanoparticle ordering can be rationally realized in preparative (ultra)centrifugation. This review summarizes the work back to the 1990s, where intuitive use of centrifugation was achieved for the fabrication of colloidal crystals to the very recent work where analytical (ultra)centrifugation is employed to tailor-make concentration gradients for advanced materials. This review is divided into three main parts. In the introduction part, the history of ordering microbeads in gravity is discussed and with the size of particles reduced to nanometers, a centrifugal field is necessary. In the next part, the research on the ordering of nanoparticles in analytical and preparative centrifugation in recent decades is described. In the last part, the applications of the functional materials, fabricated from centrifugation-induced nanoparticle superstructures are briefly discussed.

Methods to Scale Down Graphene Oxide Size and Size Implication in Anti-cancer Applications

Despite considerable progress in the comprehension of the mechanisms involved in the origin and development of cancer, with improved diagnosis and treatment, this disease remains a major public health challenge with a considerable impact on the social and economic system, as well as on the individual. One way to improve effectiveness and reduce side effects is to consider responsive stimuli delivery systems that provide tailor-made release profiles with excellent spatial and temporal control. 2D nanomaterials possess special physicochemical properties (e.g., light, ultrasonic and magnetic responses) and biological behaviors such as endocytosis, biodistribution, biodegradation, and excretory pathways, which lead to their use in various biomedical applications. In particular, among 2D nanomaterials, graphene and its derivatives, namely graphene oxide (GO) nanomaterials, have attracted enormous attention in cancer diagnosis and therapy because they combine, in a unique material, extremely small size, NIR absorption, delocalized electrons, extremely high surface area, and versatile surface functionality. Taking into account the fundamental role played by GO size, in this review, we summarize the main methods employed to reduce and homogenize in nanometric scale the lateral dimensions of graphene oxide produced by chemical exfoliation of graphite, as well as post-synthesis separation techniques to uniform the size. We also discuss the implication of the small size in cancer treatment by exploiting GO nanocarriers as an effective theranostic tool.

The immuno-reactivity of polypseudorotaxane functionalized magnetic CDMNP-PEG-CD nanoparticles

pH‐magnetic dual‐responsive nanocomposites have been widely used in drug delivery and gene therapy. Recently, a polypseudorotaxane functionalized magnetic nanoparticle (MNP) was developed by synthesizing the magnetic nanoparticles with cyclodextrin (CD) molecules (CDMNP) via polyethylene glycol (PEG) (CDMNP‐PEG‐CD). The purpose of this study was to explore the antigenicity and immunogenicity of the nanoparticles in vivo prior to their further application explorations. Here, nanoparticles were assessed in vivo for retention, bio‐distribution and immuno‐reactivity. The results showed that, once administered intravenously, CDMNP‐PEG‐CD induced a temporary blood monocyte response and was cleared effectively from the body through the urine system in mice. The introduction of β‐CD and PEG/β‐CD polypseudorotaxane on SiO₂ magnetic nanoparticles (SOMNP) limited particle intramuscular dispersion after being injected into mouse gastrocnemius muscle (GN), which led to the prolonged local inflammation and muscle toxicity by CDMNP and CDMNP‐PEG‐CD. In addition, T cells were found to be more susceptible for β‐CD–modified CDMNP; however, polypseudorotaxane modification partially attenuated β‐CD–induced T cell response in the implanted muscle. Our results suggested that CDMNP‐PEG‐CD nanoparticles or the decomposition components have potential to prime antigen‐presenting cells and to break the muscle autoimmune tolerance.

Layering of bidisperse charged nanoparticles in sedimentation

Bidisperse mixtures of charged nanoparticles form separate layers upon centrifugation as a result of minimization of the system's free energy in sedimentation-diffusion equilibrium. Different factors were investigated experimentally for their effects on the layering, and are supported by theoretical calculations of the full sedimentation profiles. Surprisingly, lighter/smaller nanoparticles can even sink below heavier/larger ones when the particle surface charge is carefully tuned. This study provides deeper insights into the control of layering in polydisperse particle mixtures during sedimentation.

Optimization of a rapid one-step platelet-rich plasma preparation method using syringe centrifugation with and without carprofen

Background

Carprofen and platelet-rich plasma (PRP) are widely used in small animal clinical practice. Separation layers have been used during blood centrifugation to increase platelet yield. The objectives of this study were to (1) identify the optimal centrifugation force for the one-step PRP preparation, (2) determine whether there is an advantage to using carprofen in one-step PRP preparation, and (3) compare platelet morphology from one-step PRP preparation with and without carprofen. We hypothesized that injectable carprofen (emulsion formula) could be used successfully as the separation layer in PRP preparation.

Results

Samples from 14 healthy dogs were used to determine the optimal centrifugation force using one-step PRP preparation in a disposable syringe without carprofen, with forces set at 300, 500, 700, 900, 1100, 1300, and 1500 xg for 5 min. Optimum centrifugation force, plasma volume, and platelet concentrations of one-step PRP preparation were found and recovered at 900 xg, 1.9 ± 0.28 ml, and 260.50 ± 58.39 X 10³ cell/μl, respectively. Samples from 12 healthy dogs were used to determine the optimal force (with forces set at 300, 500, 700, and 900 xg) for 5 min using one-step PRP preparation with carprofen. Optimum centrifugation force, plasma volume, and platelet concentrations for one-step PRP preparation with carprofen were found and recovered at 500 xg, 0.62 ± 0.16 ml and 948.50 ± 261.40 X 10³ cell/μl, respectively. One-step PRP preparation with carprofen increased the platelet yield from baseline by 1.76 and 4.95 fold, respectively. Samples from 3 healthy dogs were used to observe platelet morphologies after centrifugation by scanning electron microscopy. Images of platelets on glass slides from both preparation methods revealed pseudopods emerging from the margins of the discoid platelets.

Conclusions

One-step PRP centrifugation both with and without carprofen increased the platelet yield, but using carprofen (emulsion formula) as a separation layer resulted in a higher platelet yield. The clinical usefulness of PRP products from these methods should be further investigated.

Multivalent Patchy Colloids for Quantitative 3D Self-Assembly Studies

We report methods to synthesize sub-micron- and micron-sized patchy silica particles with fluorescently labeled hemispherical titania protrusions, as well as routes to efficiently characterize these particles and self-assemble these particles into non-close-packed structures. The synthesis methods expand upon earlier work in the literature, in which silica particles packed in a colloidal crystal were surface-patterned with a silane coupling agent. Here, hemispherical amorphous titania protrusions were successfully labeled with fluorescent dyes, allowing for imaging by confocal microscopy and super-resolution techniques. Confocal microscopy was exploited to experimentally determine the numbers of protrusions per particle over large numbers of particles for good statistical significance, and these distributions were compared to simulations predicting the number of patches as a function of core particle polydispersity and maximum separation between the particle surfaces. We self-assembled these patchy particles into open percolating gel networks by exploiting solvophobic attractions between the protrusions.

Core-composite mediated separation of diverse nanoparticles to purity

A generalized method for sorting nanoparticles based on their cores does not exist; it is an immediate necessity, and an approach incorporating cost-effectiveness and biocompatibility is in demand. Therefore, an efficient method for the separation of various mixed core-compositions or dissimilar metallic nanoparticles to their pure forms at the nano-bio interface was developed. Various simple core-combinations of monodispersed nanoparticles with dual cores, including silver plus gold, iron oxide plus gold and platinum plus gold, to the complex three-set core-combinations of platinum plus gold plus silver and platinum plus iron plus gold were sorted using step-gradient centrifugation in a sucrose suspension. Viscosity mediated differential terminal velocities of the nanoparticles permitted diversified dragging at different gradients allowing separation. Stability, purity and properties of the nanoparticles during separation were evaluated based on visual confirmation and by employing advanced instrumentations. Moreover, theoretical studies validated our experimental observations, revealing the roles of various parameters, such as the viscosity of sucrose, the density of the particles and the velocity and duration of centrifugation, involved during the separation process. This remarkably rapid, cost-efficient and sustainable strategy can be adapted to separate other cores of nanoparticles for various biomedical research purposes, primarily to understand nanoparticle induced toxicity and particle fate and transformations in natural biotic environments.

Putting a New Spin on It: Gradient Centrifugation for Analytical and Preparative Applications

Gradient centrifugation is an important technique in chemistry, biology, materials science and engineering. It has big potential beyond the well-known centrifugation for separation of molecules and particles. Various possibilities for special analysis and separation of particles, but also preparative applications like the production of gradient materials and controlled polymerizations exist. In all examples, a gradient of physical and/or chemical properties is generated by centrifugation and used for the further application. In this Concept article, selected examples of gradient centrifugation are presented, to show important developments in the field and discuss their applications, potential, and limitations. It concludes by analysing future trends of gradient centrifugation that are relevant for academic and industrial usage.

Formation of high-density CuBi2O4 thin film photocathodes with polyvinylpyrrolidone-metal interaction

We present a polymer-assisted spin coating process used to fabricate high-density p-type CuBi₂O₄ (CBO) thin films. Polyvinylpyrrolidone (PVP) is introduced in the precursor solutions in order to promote uniform nucleation of CBO and prevent formation of the secondary phase, such as Bi₂O_3, by Bi³⁺ ion hydrolysis. Slow PVP molecule decomposition during the two-step annealing process, with a 1 M/0.5 M (Bi³⁺/Cu²⁺) metal ion concentration, enables optimum contact at the CBO/substrate interface by avoiding formation of voids. This resulted in the formation of non-porous, compact CBO thin films. The highest current density of the photoelectrochemical (PEC) oxygen reduction reaction is obtained with non-porous, compact CBO thin films due to unimpeded charge transport through the CBO bulk, as well as across the interface. When combined with silicon, the high-density CBO thin film investigated in this work is expected to provide new PEC tandem cell options to use for solar applications.

Polypseudorotaxane functionalized magnetic nanoparticles as a dual responsive carrier for roxithromycin delivery

A magnetic-pH dual responsive drug delivery system was prepared for antibacterial therapy to reduce the side effects on nonpathological cells or tissues. Iron oxide (Fe₃O₄) core was surface-functionalized with silane coupling agents to link β‑cyclodextrin (β-CD) (CDMNP), and a polypseudorotaxanes shell where polyethyleneglycol chains threaded much CD molecules was further prepared on the magnetic Fe₃O₄ core (CDMNP-PEG-CD) to enhance loading capacity of roxithromycin (ROX). CDMNP-PEG-CD with a hydrodynamic diameter of ~168 nm was cytocompatible, superparamagnetic, magnetic-responsive and stable for 180 min of storage. No significant interaction with serum albumin was shown for the nanocomposites. The in vitro release from ROX-loaded CDMNP-PEG-CD nanocomposites was about 76% of total drug within 30 min at pH 1.0, 1.6-fold of that at pH 7.4 and 2-fold of that at pH 8.0, presenting pH-responsive drug release behaviors. The nanocomposites showed positive antibacterial activity against both E. coli and S. aureus based on an agar diffusion method. The antibacterial activity of the nanocomposites was more sensitive against E. coli than S. aureus, and the inhibition halo against E. coli was 85% more than that of Fe₃O₄. CDMNP-PEG-CD nanocomposites allowed for the localization and fast concentration of hydrophobic drugs, providing a broad potential range of therapeutic applications.

Plasmonic nanomaterial structuring for SERS enhancement

Au island over nanospheres (AuIoN) structures featuring a three-dimensional (3D) nanostructure on a two-dimensional (2D) array of nanospheres with different adhesion layers were fabricated as surface-enhanced Raman scattering (SERS) substrates.

Separation-cooperated assembly of liquid photonic crystals from polydisperse particles

Easy and cost-effective production of high-quality photonic crystals (PCs) remains challenging but attractive, not just because they are a type of gemstone but more for their scientific applications (e.g., serving as lossless waveguides, visual sensors, novel pigments and novel separation media). Herein presented is a separation-cooperated assembly (SCA) strategy able to organize cheap polydisperse particles into PCs. Its feasibility was validated through sink-induced SCA of poorly disperse (size variation up to 56%) particles into iridescent liquid PCs in 3 days or more. Strikingly, with a sharp photonic band gap down to 10 nm (ca. 1/7 of the reported 66 nm), the liquid PCs are able to cyclically recover their iridescent color in ca 20 s after agitation, and keep their structural order after dryness, making them practicable to write and paint directly. Also significant is that SCA yielded uniform particles with size variation down to 0.7%. It is thus an easy way to isolate homogeneous particles from disperse ones.

Multiphasic effect of vinyl pyrrolidone polymers on amyloidogenesis, from macromolecular crowding to inhibition

Deposition of misfolded amyloid polypeptides, associated with cell death, is the hallmark of many degenerative diseases (e.g. type II diabetes mellitus and Alzheimer's disease). In vivo, cellular and extracellular spaces are occupied by a high volume fraction of macromolecules. The resulting macromolecular crowding energetically affects reactions. Amyloidogenesis can either be promoted by macromolecular crowding through the excluded volume effect or inhibited due to a viscosity increase reducing kinetics. Macromolecular crowding can be mimicked in vitro by the addition of non-specific polymers, e.g. Ficoll, dextran and polyvinyl pyrrolidone (PVP), the latter being rarely used to study amyloid systems. We investigated the effect of PVP on amyloidogenesis of full-length human islet amyloid polypeptide (involved in type II diabetes) using fibrillisation and surface activity assays, ELISA, immunoblot and microscale thermophoresis. We demonstrate that high molecular mass PVP360 promotes amyloidogenesis due to volume exclusion and increase in effective amyloidogenic monomer concentration, like other crowders, but without the confounding effects of viscosity and surface activity. Interestingly, we also show that low molecular mass PVP10 has unique inhibitory properties as inhibition of fibril elongation occurs mainly in the bulk solution and is due to PVP10 directly and strongly interacting with amyloid species rather than the increase in viscosity typically associated with macromolecular crowding. In vivo, amyloidogenesis might be affected by the properties and proximity of endogenous macromolecular crowders, which could contribute to changes in associated pathogenesis. More generally, the PVP10 molecular backbone could be used to design small compounds as potential inhibitors of toxic species formation.

Density Gradient Strategy for Preparation of Broken In2O3 Microtubes with Remarkably Selective Detection of Triethylamine Vapor

Tubule-like structured metal oxides, combined with macroscale pores onto their surfaces, can fast facilitate gas-accessible diffusion into the sensing channels, thus leading a promoted utilization ratio of sensing layers. However, it generally remains a challenge for developing a reliable approach to prepare them. Herein, this contribution describes a density gradient strategy for obtaining broken In₂O₃ microtubes from the In₂O₃ products prepared using a chemical conversion method. These In₂O₃ microtubes hold a diameter about 1.5 μm with many broken regions and massive ultrafine nanopores onto their surfaces. When employed as a sensing element for detection of triethylamine (TEA) vapor, these broken In₂O₃ microtubes exhibited a significant response toward TEA at 1-100 ppm and the lowest detected concentration can reach 0.1 ppm. In addition, an excellent selectivity of the sensor to TEA was also displayed, though upon exposure of other interfering vapors, including ammonia, methanol, ethanol, isopropanol, acetone, toluene, and hydrogen. Such promoted sensing performances toward TEA were ascribed to the broken configuration (superior gas permeability and high utilization ratio), one-dimensional configuration with less agglomerations, and low bond energy for C-N in a TEA molecule.

Density gradient ultracentrifugation for colloidal nanostructures separation and investigation

In this article, we review the advancement in nanoseparation and concomitant purification of nanoparticles (NPs) by using density gradient ultracentrifugation technique (DGUC) and demonstrated by taking several typical examples. Study emphasizes the conceptual advances in classification, mechanism of DGUC and synthesis-structure-property relationships of NPs to provide the significant clue for the further synthesis optimization. Separation, concentration, and purification of NPs by DGUC can be achieved at the same time by introducing the water/oil interfaces into the separation chamber. We can develop an efficient method "lab in a tube" by introducing a reaction zone or an assembly zone in the gradient to find the surface reaction and assembly mechanism of NPs since the reaction time can be precisely controlled and the chemical environment change can be extremely fast. Finally, to achieve the best separation parameters for the colloidal systems, we gave the mathematical descriptions and computational optimized models as a new direction for making practicable and predictable DGUC separation method. Thus, it can be helpful for an efficient separation as well as for the synthesis optimization, assembly and surface reactions as a potential cornerstone for the future development in the nanotechnology and this review can be served as a plethora of advanced notes on the DGUC separation method.

A Facile Method for Separating and Enriching Nano and Submicron Particles from Titanium Dioxide Found in Food and Pharmaceutical Products

Recent studies indicate the presence of nano-scale titanium dioxide (TiO2) as an additive in human foodstuffs, but a practical protocol to isolate and separate nano-fractions from soluble foodstuffs as a source of material remains elusive. As such, we developed a method for separating the nano and submicron fractions found in commercial-grade TiO2 (E171) and E171 extracted from soluble foodstuffs and pharmaceutical products (e.g., chewing gum, pain reliever, and allergy medicine). Primary particle analysis of commercial-grade E171 indicated that 54% of particles were nano-sized (i.e., < 100 nm). Isolation and primary particle analysis of five consumer goods intended to be ingested revealed differences in the percent of nano-sized particles from 32%‒58%. Separation and enrichment of nano- and submicron-sized particles from commercial-grade E171 and E171 isolated from foodstuffs and pharmaceuticals was accomplished using rate-zonal centrifugation. Commercial-grade E171 was separated into nano- and submicron-enriched fractions consisting of a nano:submicron fraction of approximately 0.45:1 and 3.2:1, respectively. E171 extracted from gum had nano:submicron fractions of 1.4:1 and 0.19:1 for nano- and submicron-enriched, respectively. We show a difference in particle adhesion to the cell surface, which was found to be dependent on particle size and epithelial orientation. Finally, we provide evidence that E171 particles are not immediately cytotoxic to the Caco-2 human intestinal epithelium model. These data suggest that this separation method is appropriate for studies interested in isolating the nano-sized particle fraction taken directly from consumer products, in order to study separately the effects of nano and submicron particles.

Soy protein-directed one-pot synthesis of gold nanomaterials and their functional conductive devices

Gold nanomaterials were synthesized via a facile and green method, using soy protein isolate as reductant, template, and capping agent.

Polymer/Nanoparticle Hybrid Materials of Precise Dimensions by Size-Exclusive Fishing of Metal Nanoparticles

Polymer cages prepared by etching of gold nanoparticles from polymer templates by the "grafting around" method are designed for selective separation of metal nanoparticles. The separation process is demonstrated as a fast biphasic ligand exchange reaction. The high separation efficiency and size selectivity of the polymer cage is verified by comparison with the linear block copolymer.

The key role of nanoparticle seeds during site-selective growth of silver to fabricate core-shell or asymmetric dumbbell heterostructures

Herein, a novel method to induce site-specific deposition of plasmonic silver domain on controlled sites of seeded AgBr nanoparticles is designed. Novel core-shell heterostructures and dumbbell heterostructures are fabricated by heterogeneous silver growth. A curved silver shell with thickness up to 5 nm is generated covering the AgBr core in the core-shell metal-semiconductor hybrids. However, in the dumbbell hybrids, a large silver domain is exclusively grown on a single side of the AgBr seed with a solid contact like relationship between the head and the tail. Photogenerated electrons are facilitated to transfer from the semiconductor head to the metal tail enhancing charge separations. The significant role of seed size during seeded silver growth has been demonstrated.

Synthetic routes to magnetic nanoparticles for MPI

Magnetic particle imaging (MPI) is a new imaging technique for visualizing the three-dimensional distribution of superparamagnetic iron oxide nanoparticles with specific properties (MPI tracers). Initial results obtained with MPI using superparamagnetic iron oxide as blood pool markers suggest that the method has great potential for cardiovascular imaging. Conversely, no clinically approved MPI tracers currently exist that could be used to exploit this potential of MPI. This article describes thermal decomposition and coprecipitation, two relevant methods for synthesizing and optimizing superparamagnetic iron oxide nanoparticles for MPI. Furthermore it summarizes the recent literature on MPI tracers and explores what can be learned from structural studies with Resovist(®) for novel synthesis approaches.

High quality gold nanorods and nanospheres for surface-enhanced Raman scattering detection of 2,4-dichlorophenoxyacetic acid

Nearly monodisperse Au nanorods (NRs) with different aspect ratios were separated from home-synthesized polydisperse samples using a gradient centrifugation method. The morphology, size and its distribution, and photo-absorption property were analyzed by transmission electron microscopy, atomic force microscopy and UV-visible spectroscopy. Subsequently, using colloidal Au NRs (36.2 nm ×10.7 nm) with 97.4% yield after centrifugation and Au nanospheres (NSs) (22.9 ± 1.0 nm in diameter) with 97.6% yield as Au substrates, surface-enhanced Raman scattering (SERS) spectra of 2,4-dichlorophenoxyacetic acid (2,4-D) were recorded using laser excitation at 632.8 nm. Results show that surface enhancement factors (EF) for Au NRs and NSs are 6.2 × 10(5) and 5.7 × 10(4) using 1.0 × 10(-6) M 2,4-D, respectively, illustrating that EF value is a factor of ~10 greater for Au NRs substrates than for Au NSs substrates. As a result, large EF are a mainly result of chemical enhancement mechanisms. Thus, it is expected that Au NPs can find a comprehensive SERS application in the trace detection of pesticide residues.

Separation of nanoparticles in aqueous multiphase systems through centrifugation

This paper demonstrates the use of aqueous multiphase systems (MuPSs) as media for rate-zonal centrifugation to separate nanoparticles of different shapes and sizes. The properties of MuPSs do not change with time or during centrifugation; this stability facilitates sample collection after separation. A three-phase system demonstrates the separation of the reaction products (nanorods, nanospheres, and large particles) of a synthesis of gold nanorods, and enriches the nanorods from 48 to 99% in less than ten minutes using a benchtop centrifuge.