Design of Raman reporter-embedded magnetic/plasmonic hybrid nanostirrers for reliable microfluidic SERS biosensors.

Magnetic-based microfluidic SERS biosensors hold great potential in various biological analyses due to their integrated advantages including easy manipulation, miniaturization and ultrasensitivity. However, it remains challenging to collect reliable SERS nanoprobe signals for quantitative analysis due to the irregular aggregation of magnetic carriers in a microfluidic chamber. Here, magnetic/plasmonic hybrid nanostirrers embedded with a Raman reporter are developed as capture carriers to improve the reliability of microfluidic SERS biosensors. Experimental results revealed that SERS signals from magnetic hybrid nanostirrers could serve as microenvironment beacons of their irregular aggregation, and a signal filtering method was proposed through exploring the relationship between the intensity range of beacons and the signal reproducibility of SERS nanoprobes using interleukin 6 as a model target analyte. Using the signal filtering method, reliable SERS nanoprobe signals with high reproducibility could be picked out from similar microenvironments according to their beacon intensity, and then the influence of irregular aggregation of magnetic carriers on the SERS nanoprobe could be eliminated. The filtered SERS nanoprobe signals also exhibited excellent repeatability from independent tests, which lay a solid foundation for a reliable working curve and subsequent accurate bioassay. This study provides a simple but promising route for reliable microfluidic SERS biosensors, which will further promote their practical application in biological analysis.

Periodic Surface-Enhanced Raman Scattering-Encoded Magnetic Beads for Reliable Quantitative Surface-Enhanced Raman Scattering-Based Multiplex Bioassay.

Surface-enhanced Raman scattering (SERS)-based immunoassay on encoded beads is highly attractive with the advantages of ultrasensitivity, multiplex and high throughput. However, it was a great challenge to screen out in-focus signals of the immunoconjugated SERS nanoprobes on spherical bead conveniently. Here, periodic SERS-encoded magnetic beads (PSE-MBs) were developed through droplet optofluidic technique by using monodisperse SERS-encoded magnetic nanospheres as building blocks. The designed PSE-MBs not only exhibit huge coding capacity, but also provide the strongest and reproducible SERS coding signals as "in-focus beacons". When PSE-MBs are used as capture carriers in SERS-based immunoassay, both multiple target analytes and in-focus signals of SERS nanoprobes could be easily identified according to the collected SERS coding signals. Thus, reliable quantitative analysis of multiple target analytes could be conveniently achieved by such detection protocol. Additionally, the magnetic ingredient in PSE-MBs made the operation easily during the bioassay. The multiple advantages of PSE-MBs including large coding capacity, in-focus beacons and magnetic operation endorse them to be robust capture carriers in reliable quantitative SERS-based multiplex immunoassay.

Template-assisted synthesis of Ag/AgCl hollow microcubes and their composition-dependent photocatalytic activity for the degradation of phenol.

Plasmonic photocatalysts with hollow structures and tunable composition exhibit significant advantages due to their high efficiency in light collection and effective charge transfer across the tight contact heterojunction interface. Herein, hollow Ag/AgCl microcubes were developed by treating nanosheet-assembled hollow Ag microcubes with FeCl3, where a part of Ag at the interface could be in situ transformed and oxidized into AgCl. Equally, by adjusting the concentration of Fe3+ ions, Ag/AgCl hollow microcubes with different compositions could be easily achieved. Electron transfer was favored by a lot of tiny Ag/AgCl heterojunctions induced by the in situ oxidation of the multicrystalline Ag hollow microcube template containing a number of grain boundaries. The designed hollow Ag/AgCl microcubes exhibited strong visible-light adsorption owing to the surface plasmon resonance effect of Ag nanoparticles, in addition to the multiple light-reflections inside the hollow structure. The as-obtained products were then used as visible-light photocatalysts, where the results indicated that 91.6% of phenol was degraded within 150 min under visible light by the as-obtained sample with a Ag to AgCl ratio of 1 : 3. The superior visible-light photocatalytic activity resulted from the enhancement of the visible light-harvesting and the efficient charge separation at the Ag and AgCl contact interfaces.

Cu-Embedded SnSe2 with a High Figure of Merit at Ecofriendly Temperature.

There are many studies concentrated on high-temperature performance of SnSe2, but few studies were conducted on low-temperature properties of embedded SnSe2. In this work, a series of SnCu x Se2 (x = 0, 0.01, 0.02, and 0.05) layered structures have been successfully synthesized by a melt quenching, mechanical milling process, and spark plasma sintering (SPS) method. Meanwhile, the thermal and electrical transport properties of all synthesized samples are measured. These results suggest that the embedding of Cu into SnSe2 results in a high carrier concentration (1019/cm3). In addition, the enhancement of defect and interfacial phonon scattering caused by Cu embedding as well as the weak van der Waals force between layers makes a low thermal conductivity (0.81 W/mK) for the SnCu0.01Se2 at 300 K. Moreover, the maximum ZT is acquired up to 0.75 for the SnCu0.01Se2 sample at 300 K, which is about 2 orders of magnitude higher than the pristine sample (0.009). These features indicate that Cu-embedded SnSe2 can be a promising thermoelectric material at gentle temperature.

Controlled synthesis of homogeneous Ag nanosheet-assembled film for effective SERS substrate.

Homogeneous Ag nanosheet-assembled film was successfully fabricated by using Cu plate through a simple modified solution method, where weak reductive Cu2O layer and complexing agent citrate ions were both introduced into the reaction system to control the reaction process. Meanwhile, citrate ions were used as morphology-controlled reagent to lead Ag units to grow in the form of nanosheet. The growth process exhibited that Ag nanosheet-assembled film formed slowly with reaction proceeding. Additionally, the pack density of nanosheets in the final product was found to be adjusted by the concentrations of Ag(+) ions in precursor solution. Using Rhodamine 6G (R6G) as probing molecules, the surface-enhanced Raman scattering (SERS) experiments showed that the Ag film assembled by nanosheets with high pack density exhibited excellent detecting performance, which could be used as effective SERS substrate for ultrasensitive detecting. Besides, a novel quintuplet SERS substrate could be synthesized in one batch by our method, which showed good reproducibility and a linear dependence between analyte concentrations and intensities, revealing the advantage of this method for easily scale-up production.

Template-assisted synthesis of uniform nanosheet-assembled silver hollow microcubes.

Uniform silver hollow microcubes assembled by nanosheets have been synthesized by using Cu(2)O cubes as chemical template at room temperature. In the reaction system, the Ag(+) ions were reduced by Cu(+) ions released from Cu(2)O cubes, meanwhile the morphology of silver growth units were controlled by trisodium citrate in the form of nanosheets around the template during the reaction. It was found that the concentrations of acid, citrate ions and AgNO(3) were critical to the formation of perfect nanosheet-assembled hollow microcubes. According to the experiment results, an interface redox growth mechanism of nanosheet-assembled Ag hollow microcubes was proposed. Since the obtained Ag hollow cubes are composed of Ag nanosheets, the hierarchical shells are bestrewed with pores or gaps which created abundant active "hot spots" for highly sensitive surface enhanced Raman scattering (SERS) detection. The SERS experiments using rhodamine 6G (R6G) as probing molecules showed that the pack density and porous structure of the shell in the final products strongly affected the SERS signals. The product with higher porous shell structure exhibited stronger SERS signals than others, indicating the rough Ag hollow microcubes could act as excellent substrates for ultrasensitive detection.

Thiolate-assisted cation exchange reaction for the synthesis of near-infrared photoluminescent Hg(x)Cd(1-x)Te nanocrystals.

In this paper, we report the synthesis of dot- and branch-shaped Hg(x)Cd(1-x)Te nanocrystals (NCs) with good stability and a high quantum yield of about 30% through an elaborate cation exchange reaction at room temperature. The large red-shifts in both absorption spectra and photoluminescence (PL) spectra confirmed the substitution of mercury ions for cadmium ions and the formation of Hg(x)Cd(1-x)Te NCs. Interesting periodical XRD peaks observed in as-obtained Hg(x)Cd(1-x)Te NCs indicated the formation of layered metal thiolates, which not only played a key role in introducing mercury ions during the cation exchange process, but also acted as ligands to maintain the emission stability of newly formed Hg(x)Cd(1-x)Te NCs. The results indicate that the red-shift in PL emission has close-correlation with several parameters (such as the amounts of thiols and mercury ions, the sample store time, etc.).

Synthesis of high saturation magnetization superparamagnetic Fe3O4 hollow microspheres for swift chromium removal.

High saturation magnetization monodisperse Fe(3)O(4) hollow microspheres (109.48 emu/g) with superparamagnetic property at room temperature are promptly synthesized by a one-step solvothermal process with the presence of sodium dodecylbenzenesulfonate as an additive. The as-synthesized products possess superparamagnetism, large cavity, high water solubility, and saturation magnetization at room temperature. In particular, these hollow microspheres exhibit both of a rather short separation time from industry wastewater and a high adsorption capacity about 180 mg/g at high Cr(VI) concentrations, which is much better than those of reported magnetite solid nanoparticles. In addition, the X-ray photoelectron spectra (XPS) show that the uptake of Cr(VI) into the spheres was mainly governed by a physicochemical process. The micelle-assisted Ostwald ripening process was proposed to explain the rapid formation of hollow structures by a series of control experiments. The as-manufactured products with the two advantages mentioned above serve as ideal candidates for environmental remediation materials.

Structural, optical, and magnetic studies of manganese-doped zinc oxide hierarchical microspheres by self-assembly of nanoparticles.

In this study, a series of manganese [Mn]-doped zinc oxide [ZnO] hierarchical microspheres [HMSs] are prepared by hydrothermal method only using zinc acetate and manganese acetate as precursors and ethylene glycol as solvent. X-ray diffraction indicates that all of the as-obtained samples including the highest Mn (7 mol%) in the crystal lattice of ZnO have a pure phase (hexagonal wurtzite structure). A broad Raman spectrum from as-synthesized doping samples ranges from 500 to 600 cm-1, revealing the successful doping of paramagnetic Mn2+ ions in the host ZnO. Optical absorption analysis of the samples exhibits a blueshift in the absorption band edge with increasing dopant concentration, and corresponding photoluminescence spectra show that Mn doping suppresses both near-band edge UV emission and defect-related blue emission. In particular, magnetic measurements confirm robust room-temperature ferromagnetic behavior with a high Curie temperature exceeding 400 K, signifying that the as-formed Mn-doped ZnO HMSs will have immense potential in spintronic devices and spin-based electronic technologies.

Wet chemical synthesis and magnetic properties of single crystal Co nanochains with surface amorphous passivation Co layers.

: In this study, for the first time, high-yield chain-like one-dimensional (1D) Co nanostructures without any impurity have been produced by means of a solution dispersion approach under permanent-magnet. Size, morphology, component, and structure of the as-made samples have been confirmed by several techniques, and nanochains (NCs) with diameter of approximately 60 nm consisting of single-crystalline Co and amorphous Co-capped layer (about 3 nm) have been materialized. The as-synthesized Co samples do not include any other adulterants. The high-quality NC growth mechanism is proposed to be driven by magnetostatic interaction because NC can be reorganized under a weak magnetic field. Room-temperature-enhanced coercivity of NCs was observed, which is considered to have potential applications in spin filtering, high density magnetic recording, and nanosensors. PACS: 61.46.Df; 75.50; 81.07.Vb; 81.07.

Controlled synthesis of high quality type-II/type-I CdS/ZnSe/ZnS core/shell1/shell2 nanocrystals.

Using phosphine-free and "green" chalcogen precursors, controlled synthesis of high quality CdS/ZnSe/ZnS core/shell1/shell2 nanocrystals has been successfully carried out using different sized CdS nanocrystals as cores. The properties and structures of the synthesized nanocrystals were characterized by absorption spectroscopy, photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and inductively coupled plasma mass spectroscopy (ICP-MS). By changing CdS core sizes and/or ZnSe shell thicknesses, the PL range of CdS/ZnSe core/shell nanocrystals could be adjusted from 500 nm to 630 nm with type-II optical characteristics. The PL quantum yields (QYs) of these nanocrystals were 50-60% after the growth of thick ZnS shells, their full width at half maximum (FWHM) was kept below 50 nm during the entire growth process, and the total Cd content was reduced to about 1% in atomic ratio. TEM images showed narrow size distributions and XRD results demonstrated the zinc blende structure of CdS was retained following subsequent growth of ZnSe and ZnS shells. More than 2 g of high quality CdS/ZnSe/ZnS nanocrystals were successfully prepared in a large scale synthesis with the use of only low-cost, green, and environmentally friendly reagents.

Synthesis and assembly of monodisperse spherical Cu2S nanocrystals.

High-quality monodisperse Cu(2)S nanocrystals (sizes from 2 nm to 20 nm) have been successfully synthesized by the reaction of copper stearate (CuSt(2)) and dodecanethiol (DDT) in 1-octadecene (ODE). The nanocrystals were characterized using X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), and transmission electron microscopy (TEM). These as-prepared Cu(2)S nanocrystals with certain sizes have been found with good self-assembly behaviors, and they were easily to assemble into two-dimensional and three-dimensional superlattice structures. DDT served as both sulfur source and capping ligand, and was found a key factor to affect the growth and the self-assembly behaviors of the Cu(2)S nanocrystals.

Controlled synthesis of different types iron oxides nanocrystals in paraffin oil.

Monodisperse Fe3O4 and FeO nanocrystals (NCs) with different sizes (from 10 nm to 50 nm) and different shapes (cube, sphere, and ellipsoid) were synthesized by simply adjusting reaction temperature or molar ratio of Fe/oleic acid (OA) during the decomposition of FeO(OH) in noncoordinating solvent. The concentration of OA affected the nucleation and growth of NCs by improving the chemical reaction driving force during the syntheses of different types of iron oxide NCs. It has been found that the reaction temperature influenced the reaction activity between FeO(OH) and OA. The structure of Fe oleate complexes was studied using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) were used for structural and chemical characterization of as-prepared iron oxide NCs.

Room temperature synthesis of HgTe nanocrystals.

We report a new method to synthesize monodisperse zinc blende HgTe nanocrystals at room temperature in noncoordinating solvent-octadecene. Thiol was needed to control the reaction at a suitable nucleation and growth speed. In the early stage of the reaction, HgTe nanocrystals formed aggregates, and then the aggregates were dispersed and individual dot-shaped nanocrystals were formed with stronger photoluminescence emitting. UV-vis, photoluminescence, and TEM have been used to study the properties of as-prepared HgTe nanocrystals.