High Uniform Size Research Articles

Ultrasensitive Characterization of Mechanical Oscillations and Plasmon Energy Shift in Gold Nanorods.

Mechanical vibrational resonances in metal nanoparticles are intensively studied because they provide insight into nanoscale elasticity and for their potential application to ultrasensitive mass detection. In this paper, we use broadband femtosecond pump-probe spectroscopy to study the longitudinal acoustic phonons of arrays of gold nanorods with different aspect ratios, fabricated by electron beam lithography with very high size uniformity. We follow in real time the impulsively excited extensional oscillations of the nanorods by measuring the transient shift of the localized surface plasmon band. Broadband and high-sensitivity detection of the time-dependent extinction spectra enables one to develop a model that quantitatively describes the periodic variation of the plasmon extinction coefficient starting from the steady-state spectrum with only one additional free parameter. This model allows us to retrieve the time-dependent elongation of the nanorods with an ultrahigh sensitivity and to measure oscillation amplitudes of just a few picometers and plasmon energy shifts on the order of 10(-2) meV.

Acid-free sol-gel fabrication of glass thin films embedded with II-VI colloidal quantum dots

II-VI colloidal quantum dots (QDs) are ideal for optical sensors thanks to their high fluorescent brightness and good size uniformity. However, embedding colloidal QDs into a glass matrix with the standard sol-gel process leads to the QDs being damaged by the acid catalyst. Here, we report an acid-free sol-gel technique, which proves to be both simple and effective in fabricating silica glass thin films embedded with commercial II-VI colloidal QDs. Octadecylamine ligands are used as a bifunctional aid to not only stabilize the QDs in solution, but also assist the formation of the SiO2 gel. We demonstrate that high-quality QD-embedded glass thin films can be developed with this technique, and our fluorescent tests indicate that, except for a small blueshift in the emission spectrum, the QDs are very well preserved through the sol-gel process. This method offers a fast and low-cost path towards thin-film QD sensors with good mechanical and thermal stabilities, which are desirable for applications involving highly focused laser beams, such as ultrafast nanophotonics.

Spontaneous phase separation during self-assembly in bi-dispersed spherical iron oxide nanoparticle monolayers

Recent developments in the synthesis of iron oxide nanoparticles have resulted in the ability to fabricate roughly spherical particles with extremely high size uniformity (low polydispersity). These particles can form self-assembled monolayer films at an air-water interface. When the polydispersity of the particles is low, these monolayers can be well-ordered over a length scale dozens of times the particle size. The van der Waals force between the particles is what drives this self-assembly. Through the use of Grazing Incidence X-Ray Diffraction we demonstrate that, when these films are formed at the liquid surface from bi-dispersed solutions containing 10 and 20 nm spherical particles suspended in chloroform, the particles phase separate into well-ordered patches during the self-assembly process. Furthermore, the domain sizes of these phase separated regions are at most 2–3 times smaller than that of a film comprising only mono-dispersed particles and their degree of disorder is comparable. This is shown for multiple solutions with differing ratios of 10 and 20 nm particles.

Electronic structures of GeSi nanoislands grown on pit-patterned Si(001) substrate

Patterning pit on Si(001) substrate prior to Ge deposition is an important approach to achieve GeSi nanoislands with high ordering and size uniformity. In present work, the electronic structures of realistic uncapped pyramid, dome, barn and cupola nanoislands grown in {105} pits are systematically investigated by solving Schrodinger equation for heavy-hole, which resorts to inhomogeneous strain distribution and nonlinear composition-dependent band parameters. Uniform, partitioned and equilibrium composition profile (CP) in nanoisland and inverted pyramid structure are simulated separately. We demonstrate the huge impact of composition profile on localization of heavy-hole: wave function of ground state is confined near pit facets for uniform CP, at bottom of nanoisland for partitioned CP and at top of nanoisland for equilibrium CP. Moreover, such localization is gradually compromised by the size effect as pit filling ratio or pit size decreases. The results pave the fundamental guideline of designing nanoislands on pit-patterned substrates for desired applications.

Biosynthesis of silver nanoparticles using Acacia leucophloea extract and their antibacterial activity.

The immense potential of nanobiotechnology makes it an intensely researched field in modern medicine. Green nanomaterial synthesis techniques for medicinal applications are desired because of their biocompatibility and lack of toxic byproducts. We report the toxic byproducts free phytosynthesis of stable silver nanoparticles (AgNPs) using the bark extract of the traditional medicinal plant Acacia leucophloea (Fabaceae). Visual observation, ultraviolet–visible spectroscopy, and transmission electron microscopy (TEM) were used to characterize the synthesized AgNPs. The visible yellow-brown color formation and surface plasmon resonance at 440 nm indicates the biosynthesis of AgNP. The TEM images show polydisperse, mostly spherical AgNP particles of 17–29 nm. Fourier transform infrared spectroscopy revealed that primary amines, aldehyde/ketone, aromatic, azo, and nitro compounds of the A. leucophloea extract may participate in the bioreduction and capping of the formed AgNPs. X-ray diffraction confirmed the crystallinity of the AgNPs. The in vitro agar well diffusion method confirmed the potential antibacterial activity of the plant extract and synthesized AgNPs against the common bacterial pathogens Staphylococcus aureus (MTCC 737), Bacillus cereus (MTCC 1272), Listeria monocytogenes (MTCC 657), and Shigella flexneri (MTCC 1475). This research combines the inherent antimicrobial activity of silver metals with the A. leucophloea extract, yielding antibacterial activity-enhanced AgNPs. This new biomimetic approach using traditional medicinal plant (A. leucophloea) barks to synthesize biocompatible antibacterial AgNPs could easily be scaled up for additional biomedical applications. These polydisperse AgNPs green-synthesized via A. leucophloea bark extract can readily be used in many applications not requiring high uniformity in particle size or shape.

PEGylated, NH2-Terminated PAMAM Dendrimers: A Microscopic View from Atomistic Computer Simulations

Poly(amido amine) (PAMAM) dendrimers are promising nanocarriers in a wide range of biomedical applications including gene and drug delivery and as imaging agents. They have unique structural properties and are characterized by high size uniformity, low polydispersity, and a large number of modifiable surface groups. Drug-dendrimer systems are usually further modified through the conjugation of ligands in order to confer the carriers' specific characteristics designed to enhance their efficacy. The chemistry and structure of the solvated ligand-conjugated dendrimer nanocarriers (DNCs) will dictate how they interact with the physiological environment and, therefore, their fate and function. Understanding the microstructures of ligand-conjugated DNCs is, therefore, of great relevance within the context of drug delivery applications. In this work, we investigate the effect of poly(ethylene glycol) (PEG) on the microstructure of solvated, NH2-terminated PAMAM DNCs using fully atomistic molecular dynamics simulations. Several variables including dendrimer generation (2-5), PEGylation density (0-50%), and PEG Mw (500 and 1000) were investigated. The results obtained showed a good match with available experimental results, including size as a function of dendrimer degeneration (G2NH2-G5NH2). No back-folding is observed for PAMAM dendrimers with generation lower than G5NH2. G2NH2 and G3NH2 showed a dense-packed, nonglobular structure, and G4NH2 and G5NH2 have a segmented, "open" structure. Our results help settle a long-standing debate with respect to "back-folding" as the microstructural information obtained here is reconciled with experimental results. PEGylation was found to influence the microstructure in a different way, including an expected increase in the overall size of the DNCs, while not affecting much the solvation of unmodified terminal (primary) amines. It also serves to expand the core of dendrimers, reduce the surface charge, and change solvation behavior of different generation branching amines. We show that the microstructure of a PEG layer with the same number of repeat units can be significantly altered by changing the grafting density and size of PEG. Potential consequences in the design of PEGylated dendrimers for drug delivery and targeting are discussed based on the obtained microstructural information.

An emulsion-based droplet hydrothermal synthesis method for the production of uniform sized zeolite nanocrystals

A droplet based new hydrothermal synthesis method for nano-zeolite synthesis in bulk amount with uniform size, shape and morphology is presented. The proposed process addresses the limitation and shortcomings of droplet based microfluidic reactors and conventional hydrothermal methods. The process has been designed on the concept of mixing two immiscible solutions at high speed which then produces nano/submicron size droplets. Confinement within the droplet provides uniform heat transfer, enhanced mass transfer to growing crystal, chaotic advection within droplet facilitate rapid mixing, prevent the contact between growing crystals etc. Fine-tuned nano-cubic LTA zeolite crystals of size ∼100nm with uniform morphology and size distribution were prepared. Just within 4h of reaction time (aging+crystallization) well shaped cubic crystals with high crystallinity and size uniformity can be synthesized by the proposed synthesis process. Diffraction and electron microscopic studies reveal the high phase purity and size uniformity of as-synthesized LTA zeolite particles.

Large-scale production of tungsten trioxide nanoparticles for electrochromic application

Large-scale, high yield production of tungsten trioxide (WO3) particles was successfully realized by using a facile, high-temperature, catalyst-free, solid evaporation route with ammonium paratungstate tetrahydrate as raw material. The crystalline structure, size, and morphology of the as-synthesized WO3 particles were systematically investigated by combined techniques of X-ray diffraction and electron microscopy, as a function of reaction temperature, deposition temperature, carrier gas flow rate, and size of the quartz tube. With low carrier gas flow rate (1–2 L min−1), the WO3 products collected from different deposition regions were found to exhibit a diversity of forms, such as thick rods, irregular, polyhedral, and octahedral particles, depending on the reaction temperature. At a reaction temperature of 1350 °C, increasing the carrier gas flow rate led to the formation of semi-spherical or quasi-spherical WO3 particles with decreased size and improved size distribution. A reaction temperature of 1350 °C and an Ar flow rate of 6 L min−1 yielded optimized quasi-spherical WO3 nanoparticles with high size uniformity, which have been found to exhibit stable electrochromic performance with high colour contrast and H+ insertion ability. The WO3 nanoparticles that can be effectively produced in high quantity are promising electrochromic candidates for potential applications in large-area smart windows.

Novel sulpiride-loaded solid lipid nanoparticles with enhanced intestinal permeability

BackgroundSolid lipid nanoparticles (SLN), novel drug delivery carriers, can be utilized in enhancing both intestinal permeability and dissolution of poorly absorbed drugs. The aim of this work was to enhance the intestinal permeability of sulpiride by loading into SLN.MethodsA unique ultrasonic melt-emulsification method with minimum stress conditions was used for the preparation of SLN. The mixture of the drug and the melted lipids was simply dispersed in an aqueous solution of a surfactant at a temperature that was 10°C higher than the melting points of the lipids using probe sonication, and was then simultaneously dispersed in cold water. Several formulation parameters were optimized, including the drug-to-lipid ratio, and the types of lipids and surfactants used. The produced SLN were evaluated for their particle size and shape, surface charge, entrapment efficiency, crystallinity of the drug and lipids, and the drug release profile. The rat everted sac intestine model was utilized to evaluate the change in intestinal permeability of sulpiride by loading into SLN.ResultsThe method adopted allowed successful preparation of SLN with a monodispersed particle size of 147.8–298.8 nm. Both scanning electron microscopic and atomic force microscopic images showed uniform spherical particles and confirmed the sizes determined by the light scattering technique. Combination of triglycerides with stearic acid resulted in a marked increase in zeta potential, entrapment efficiency, and drug loading; however, the particle size was increased. The type of surfactant used was critical for particle size, charge, drug loading, and entrapment efficiency. Generally, the in vitro release profile demonstrated by all formulations showed the common biphasic mode with a varying degree of burst release. The everted sac model showed markedly enhanced sulpiride permeability in the case of the SLN-loaded formulation. The in situ results showed a very good correlation with the in vitro release data.ConclusionIncorporation of sulpiride into SLN results in enhanced intestinal permeability of sulpiride, that may in turn increase overall oral absorption of the drug. The superior attributes of the prepared SLN, specifically the high particle size uniformity and drug loading capacity, is considered novel, especially given the simplicity and modest nature of the sonication method used.

Photoactive spherical colloids for opal photonic crystals

The synthesis and characterization of submicrometer‐sized polymer particles, functionalized by different techniques with fluorescent dyes and featuring tunable surface charges, are described. Dyes with a polymerizable moiety were incorporated during emulsifier‐free or seeded emulsion polymerization, whereas non‐polymerizable dyes were included into preformed nanoparticles by a swelling and deswelling process. The particle surface charge was controlled through the choice of suitable initiators. All the nanoparticles were successfully used to grow high optical quality opal photonic crystals by the vertical deposition technique. Optical characterization of such photonic crystals pointed out the presence of the optical stop band and the high‐energy van Hove‐like structures, both scaling with the particle diameter according to the scaling laws of photonic crystals and possessing the expected angular dispersion. These results are indicative of the high size uniformity and of the surface quality of the nanospheres independently on the synthetic method adopted. Preliminary data seem to suggest some effect of the opal photonic band structure on the dye fluorescence spectra. POLYM. COMPOS., 34:1443–1450, 2013. © 2013 Society of Plastics Engineers.

The effect of laser repetition rate on the LASiS synthesis of biocompatible silver nanoparticles in aqueous starch solution

Laser ablation-based nanoparticle synthesis in solution is rapidly becoming popular, particularly for potential biomedical and life science applications. This method promises one pot synthesis and concomitant bio-functionalization, is devoid of toxic chemicals, does not require complicated apparatus, can be combined with natural stabilizers, is directly biocompatible, and has high particle size uniformity. Size control and reduction is generally determined by the laser settings; that the size and size distribution scales with laser fluence is well described. Conversely, the effect of the laser repetition rate on the final nanoparticle product in laser ablation is less well-documented, especially in the presence of stabilizers. Here, the influence of the laser repetition rate during laser ablation synthesis of silver nanoparticles in the presence of starch as a stabilizer was investigated. The increment of the repetition rate does not negatively influence the ablation efficiency, but rather shows increased productivity, causes a red-shift in the plasmon resonance peak of the silver–starch nanoparticles, an increase in mean particle size and size distribution, and a distinct lack of agglomerate formation. Optimal results were achieved at 10 Hz repetition rate, with a mean particle size of ~10 nm and a bandwidth of ~6 nm ‘full width at half maximum’ (FWHM). Stability measurements showed no significant changes in mean particle size or agglomeration or even flocculation. However, zeta potential measurements showed that optimal double layer charge is achieved at 30 Hz. Consequently, Ag–NP synthesis via the laser ablation synthesis in solution (LASiS) method in starch solution seems to be a trade-off between small size and narrow size distributions and inherent and long-term stability.

Ultrasmall PEGylated MnxFe3−xO4 (x = 0–0.34) nanoparticles: effects of Mn(ii) doping on T1- and T2-weighted magnetic resonance imaging

We report a facile synthesis of water-soluble, ultrasmall, PEGylated MnxFe3−xO4 nanoparticles (MFNPs) (x = 0–0.34) and the Mn(II) doping effects on T1- and T2-weighted magnetic resonance imaging (MRI). By adjusting the reaction conditions, the ‘x’ value can be continuously tuned from 0 to 0.34. The produced MFNPs are of high crystallinity and size uniformity with an average diameter of ∼6 nm, which show excellent colloidal stability in H2O, PBS, and tolerate a high salt concentration (1 M NaCl) and a wide pH range from 7 to 11. The results of FTIR demonstrate that both HOOC–PEG–COOH and TEG were modified on the nanocrystal surfaces. The saturation magnetization of the MFNPs gradually increases with increasing Mn2+ concentration and reaches 75.5 emu g−1 for x = 0.34. Careful investigation of the Mn(II) doping effects on T1- and T2-weighted MRI reveals that T2 contrast effects are enhanced while T1 contrast effects are weakened with the increase of the ‘x’ value of the MFNPs. Furthermore, the T1 contrast effects of the MFNPs are concentration dependant. A concentration which is lower than 0.500 mM is needed for the MFNPs to act as T1 and T2 dual contrast agents at 3 T.

Photoinitiated RAFT Dispersion Polymerization: A Straightforward Approach toward Highly Monodisperse Functional Microspheres

A straightforward dispersion polymerization procedure for the synthesis of monodisperse functional polymeric microspheres is proposed in this article. This method overcomes the problems deriving from the highly sensitive nucleation stage by introducing both photoinitiation and a RAFT chain transfer agent to the reaction. The process of the formation and growth of particles in the procedure was investigated and found to be quite different from that in a traditional dispersion polymerization. Various kinds of PMMA-based functional microspheres with high size uniformity were synthesized in a single step by this strategy. The microspheres remained uniform in size, even at concentrations of cross-linker or functional comonomer up to 10 wt %.

Morphology-controlled synthesis, characterization, growth mechanism of SmOHCO3 with high uniform size and photoluminescence property of SmOHCO3:Eu3 +

Octahedral and spherical SmOHCO3 particles with uniform sizes had been successfully synthesized on a large scale by a simple hydrothermal method using (NH2)2CO as the precipitant without any complex agent. The SmOHCO3 crystal was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy and photoluminescence. The molar ratio of (NH2)2CO to Sm3+, reaction temperature and reaction time had crucial influences on the morphology and microstructure evolution of the SmOHCO3 crystal. The possible formation mechanisms for the octahedral and spherical SmOHCO3 were proposed. The synthesis and optical properties of SmOHCO3:Eu3+ microcrystals under ultraviolet light excitation were investigated. More importantly, the results showed that the SmOHCO3:Eu3+ samples obtained by using different dosages of (NH2)2CO exhibited interesting morphology-dependent optical properties. Furthermore, this general and facile method might be of much significance in the synthesis of many other lanthanide compounds with various morphology and new optical properties.

Novel optical f iber-based laser direct writing process for micromachining of metal

A laser micromachining technique for the fabrication of metallic microstructures is proposed. The fabrication of microstructures is done by laser-induced wet etching that adopts an optical fiber as a machining tool. The laser beam delivered through the multimode fiber directly irradiates on the workpiece while maintaining a proper gap to avoid fiber damage. The manufacture of microstructures with high surface quality and good size uniformity is realized. Microgrooves with aspect ratio over 10 and microholes with a nearly straight cross-section can be produced by the proposed technique. The overall etching results are examined closely with respect to process variables.

Synthesis and Upconversion Luminescence of Uniform β-NaYF4:Yb3+/Tm3+ Hexagonal Nanoplates

Yb3+ and Tm3+-codoped hexagonal-phase NaYF4 powders were prepared by a facile hydrothermal method. The results of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) showed that the as-prepared powders were well crystallized nanoplates with high size-uniformity. Under the excitation from a 980 nm laser diode, upconversion (UC) emissions centered at approximately 291 nm (1I6 --> 3H6), approximately 346 nm (1I6 --> 3F4), approximately 361 nm (1D2 --> 3H6), approximately 451 nm (1D2 --> 3F4), approximately 474 nm (1G4 --> 3H6), approximately 644 nm (1G4 --> 3F4), and approximately 799 nm (3H4 --> 3H6) were observed in the sample. Furthermore, the intensity dependence of UC emissions on excitation power was measured. The results indicated that populating the 1I6, 1D2, 1G4, and 3H4 states were five-photon, four-photon, three-photon, and two-photon UC processes, respectively.

One‐Step Emulsification of Multiple Concentric Shells with Capillary Microfluidic Devices

Emulsions have long been utilized to make materials for foods, drugs, cosmetics, and displays because of their efficient encapsulation properties. While they are most commonly made in bulk, recent advances in microfluidics have enabled the design and manipulation of emulsion drops with unprecedented control and flexibility, albeit only on a drop-bydrop basis. Multiple-phase emulsions of very high uniformity in size can be prepared using precise control of flow that can be achieved in tailored poly(dimethylsiloxane) (PDMS) or capillary devices. The monodisperse single and double emulsion drops produced by such microfluidic devices can be employed to make functional microparticles and microcapsules, respectively. For example, nonspherical and Janus microparticles with optical, electrical, and magnetic functionalities can be prepared from monodisperse single emulsion drops. Moreover, polymeric microcapsules, vesicles, and colloidosomes can be prepared from double emulsion drops. Double emulsion drops provide particularly effective encapsulation of active materials with high encapsulation efficiency; in addition, many routes to controlled release are feasible. Even greater structural and functional enhancement of the microcapsules can be achieved with multiple emulsion drops of yet higher order. For example, multiple emulsion drops of high order are useful in the production of complex microcapsules for encapsulation and sequential release of multi-component active materials while avoiding cross-contamination. However, production of such multiple emulsion drops remains a challenge. Most previous approaches utilize sequential emulsification using a series of single drop makers. Thus, the device fabrication entails complex procedures and delicate control of flow rates required to synchronize the frequencies of drop generations in all drop makers. Moreover, the dispersed phases are used as the continuous carrier fluid of the inner drops before the sequential emulsification, making it difficult to achieve full control of a diameter of each layer in the multiple emulsion drops. By contrast, single-step emulsification obviates the shortcomings of sequential emulsification and enhances the controllability and the stability of the generation of multiple emulsion drops using an even simpler device design. Although double emulsion drops have been prepared through single-step emulsification, coaxial introduction of four or more immiscible fluids into a single channel is challenging, making it difficult to produce higher-order multiple emulsion drops through single-step emulsification. Herein, we report a facile one-step emulsification approach to make monodisperse multiple emulsion drops of high order using stable biphasic flows in confining channels. Through controlled surface modification of glass capillary devices, immiscible multiphase streams flow through a single orifice, forming layered coaxial interfaces. Breakup of the interfaces is achieved in dripping or jetting modes, determined by the flow rates. In the dripping mode, breakup is triggered by inserting a drop in the core of the emulsion, facilitating the production of monodisperse triple or quadruple emulsion drops with an onionlike configuration. In addition, by using the jetting breakup mode, the number of drops in the core can be manipulated. The essential strategy of our approach relies on the stable flow of two fluids through a single channel without the formation of drops, which commonly occurs because of Rayleigh-Plateau instability. The flow of two immiscible fluids through a single capillary channel exhibits two distinct patterns consisting of either drops or a jet, depending on several control parameters. In either case, the fluid with the higher affinity to the wall forms the continuous phase while that with the lower affinity flows through the center, without contacting the wall, either as distinct drops or a jet. In most cases, this jet is unstable to formation of drops because of the Rayleigh-Plateau instability. However, the spatial confinement of the interface because of the geometry of capillary can, in fact, provide additional stability to the jet, suppressing the breakup into drops. This is the particularly effective when the width of the inner fluid is large, so that the interface between the two fluids is formed near the capillary wall; then strong confinement of the continuous fluid helps prevent the Rayleigh-Plateau instability and the subsequent breakup into drops. We exploit this feature to produce high-order multiple emulsions through a one-step emulsification process. The design of the device for producing triple emulsion drops of water-in-oil-in-water-in-oil (W1/O2/W3/O4) phases comprises two tapered cylindrical capillaries, one for injection and the other for collection. Each is inserted into a square capillary, the inner dimension of which is slightly larger than the outer diameter of the cylindrical capillary before they are tapered, as shown schematically in Figure 1a. The cylindrical capillaries are treated to make them hydrophobic; the outer square capillary is treated to make it hydrophilic. In addition, a small tapered capillary is inserted into the space between the collection and the square capillaries to simultaneously [*] Dr. S.-H. Kim, Prof. D. A. Weitz School of Engineering and Applied Sciences, Department of Physics Harvard University, Cambridge, MA 02138 (USA) E-mail: weitz@seas.harvard.edu Homepage: http://weitzlab.seas.harvard.edu/

Controlled synthesis, characterization, mechanism, and photoluminescence property of nanoerythrocyte-like HoVO 4 with high uniform size and morphology

Nanoerythrocyte-like, dodecahedron and nanoparticle HoVO 4 with high uniform size had been successfully synthesized on a large scale by a simple and facile complex agent assisted hydrothermal method. The nanoerythrocyte-like HoVO 4 was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and photoluminescence. The possible formation mechanism of the nanoerythrocyte-like HoVO 4 was proposed. The PL results showed the pure HoVO 4 products with different size and morphology displayed the same emission band with diverse relative intensity under the excitation of 455 nm and the red emission transition 5F 5→ 5I 8 was the most prominent group, whose peak situated at 659 nm. Furthermore, this general and facile method may be applied in the synthesis of other lanthanide compounds with nanoerythrocyte-like morphology.

Facile synthesis of ultrasmall PEGylated iron oxide nanoparticles for dual-contrastT1- andT2-weighted magnetic resonance imaging

The development of new types of high-performance nanoparticulate MR contrast agents with eitherpositive (T1) or dual-contrast (both positive and negative,T1 + T2) ability is of great importance. Here we report a facile synthesisof ultrasmall PEGylated iron oxide nanoparticles for dual-contrastT1- andT2-weighted MRI. The produced superparamagnetic iron oxide nanoparticles(SPIONs) are of high crystallinity and size uniformity with an average diameter of5.4 nm, and can be individually dispersed in the physiological buffer with highstability. The SPIONs reveal an impressive saturation magnetization of 94 emu g − 1 Fe3O4, the highestr1 of 19.7 mM − 1 s − 1 and thelowest r2/r1 ratio of 2.0 at 1.5 T reported so far for PEGylated iron oxide nanoparticles.T1- andT2-weightedMR images showed that the SPIONs could not only improve surrounding water proton signals in theT1-weighted image, but induce significant signal reduction in theT2-weighted image. The good contrast effect of the SPIONs asT1 + T2 dual-contrast agents might be due to its high magnetization, optimal nanoparticle size forT1 + T2 dual-contrast agents, high size monodispersity and excellent colloidal stability. In vitro cellexperiments showed that the SPIONs have little effect on HeLa cell viability.

Ripening of bimodally distributed AgCl nanoparticles

Ripening of AgCl nanoparticles with a bimodal size distribution has been carefully studied in ethylene glycol containing poly(vinyl pyrrolidone) (PVP) as capping molecules and at elevated temperatures (e.g., 160 °C). The resulting AgCl particles exhibit high uniformity in size and cube-tetrapod morphology that are significantly different from the original AgCl nanoparticles. In addition, enhanced reducing ability of ethylene glycol at high temperature partially reduces AgCl to form Ag nanocrystalline domains in the AgCl particles, leading the AgCl particles to be efficiently absorbing visible light and to serve as a class of visible-light-driven photocatalysts due to the strong surface plasmon resonance (SPR) associated with the Ag nanocrystallites.