This review focuses on the recent development and various strategies in the preparation, microstructure, and magnetic properties of bare and surface functionalized iron oxide nanoparticles (IONPs); their corresponding biological application was also discussed. In order to implement the practical in vivo or in vitro applications, the IONPs must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of IONPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The new functionalized strategies, problems and major challenges, along with the current directions for the synthesis, surface functionalization and bioapplication of IONPs, are considered. Finally, some future trends and the prospects in these research areas are also discussed.

No abstract

This paper describes a facile method for generating Au@Ag core-shell nanocubes with edge lengths controllable in the range of 13.4 to 50 nm. The synthesis involved the use of single-crystal, spherical Au nanocrystals of 11 nm in size as the seeds in an aqueous system, with ascorbic acid serving as the reductant and cetyltrimethylammonium chloride (CTAC) as the capping agent. The thickness of the Ag shells could be finely tuned from 1.2 to 20 nm by varying the ratio of AgNO 3 precursor to Au seeds. We also investigated the growth mechanism by examining the effects of seeds (capped by CTAC or CTAB) and capping agent (CTAC vs. CTAB) on both size and shape of the resultant core-shell nanocrystals. Our results clearly indicate that CTAC worked much better than CTAB as a capping agent in both the syntheses of Au seeds and Au@Ag core-shell nanocubes. We further studied the localized surface plasmon resonance properties of the Au@Ag nanocubes as a function of the Ag shell thickness. By comparing with the extinction spectra obtained from theoretical calculations, we derived a critical value around 3 nm for the shell thickness at which the plasmon excitation of the Au cores would be completely screened by the Ag shells. Moreover, these Au@Ag core-shell nanocubes could be converted into Au-based hollow nanostructures containing the original Au seeds in the interiors through a galvanic replacement reaction. KeywordsCore-shell nanocubes; seed-mediated growth; cetyltrimethylammonium chloride; surface plasmonic property Gold (Au) and silver (Ag) nanocrystals have received considerable attention for many years because of their fascinating optical properties known as localized surface plasmon resonance (LSPR),1 -4 and their widespread use in applications related to photonics, catalysis, information storage, chemical/biological sensing, and surface-enhanced Raman scattering (SERS).5 -10 In an effort to tailor their properties and thus improve their performance in * corresponding author: xia@biomed.wustl.edu. Supporting Information Available:TEM and high-resolution TEM images of CTAB-Au seeds, TEM images of the products prepared by CTAB-Au seeds, extinction spectra of Au@Ag nanospheres calculated using Mie theory, extinction spectra and TEM image of the products obtained by dissolving Au@Ag core-shell nanocubes with Fe(NO 3 ) 3 solution, definition of the thickness of Ag shells, and description of truncation in a model for Au@Ag nanocubes. This material is available free of charge via the Internet at http://pubs.acs.org. 11 -20 Parallel to these developments, people have also looked into the possibility to combine Au and Ag into one single system to provide a new handle for controlling the optical and catalytic properties. To this end, Au-Ag alloy and core-shell nanocrystals have been prepared and investigated in the context of catalysis, plasmonics, sensing, imaging, and biomedicine.21 -35 Particularly, by combining Au and Ag into a core-shell configuration, their LSPR properties can be potentially tailored and finely t...

The carboxy-terminal domain (CTD) of RNA polymerase (Pol) II is an intrinsically disordered low-complexity region that is critical for pre-mRNA transcription and processing. The CTD consists of hepta-amino acid repeats varying in number from 52 in humans to 26 in yeast. Here we report that human and yeast CTDs undergo cooperative liquid phase separation, with the shorter yeast CTD forming less-stable droplets. In human cells, truncation of the CTD to the length of the yeast CTD decreases Pol II clustering and chromatin association, whereas CTD extension has the opposite effect. CTD droplets can incorporate intact Pol II and are dissolved by CTD phosphorylation with the transcription initiation factor IIH kinase CDK7. Together with published data, our results suggest that Pol II forms clusters or hubs at active genes through interactions between CTDs and with activators and that CTD phosphorylation liberates Pol II enzymes from hubs for promoter escape and transcription elongation.

We report on the synthesis of semiconductor nanocrystals of PbS, ZnS, CdS, and MnS through a facile and inexpensive synthetic process. Metal-oleylamine complexes, which were obtained from the reaction of metal chloride and oleylamine, were mixed with sulfur. The reaction mixture was heated under appropriate experimental conditions to produce metal sulfide nanocrystals. Uniform cube-shaped PbS nanocrystals with particle sizes of 6, 8, 9, and 13 nm were synthesized. The particle size was controlled by changing the relative amount of PbCl(2) and sulfur. Uniform 11 nm sized spherical ZnS nanocrystals were synthesized from the reaction of zinc chloride and sulfur, followed by one cycle of size-selective precipitation. CdS nanocrystals that consist of rods, bipods, and tripods were synthesized from a reaction mixture containing a 1:6 molar ratio of cadmium to sulfur. Spherical CdS nanocrystals (5.1 nm sized) were obtained from a reaction mixture with a cadmium to sulfur molar ratio of 2:1. MnS nanocrystals with various sizes and shapes were synthesized from the reaction of MnCl(2) and sulfur in oleylamine. Rod-shaped MnS nanocrystals with an average size of 20 nm (thickness) x 37 nm (length) were synthesized from a 1:1 molar ratio of MnCl(2) and sulfur at 240 degrees C. Novel bullet-shaped MnS nanocrystals with an average size of 17 nm (thickness) x 44 nm (length) were synthesized from the reaction of 4 mmol of MnCl(2) and 2 mmol of sulfur at 280 degrees C for 2 h. Shorter bullet-shaped MnS nanocrystals were synthesized from a 3:1 molar ratio of MnCl(2) and sulfur. Hexagon-shaped MnS nanocrystals were also obtained. All of the synthesized nanocrystals were highly crystalline.