Solution processability of nanocrystals coated with a stable monolayer of organic ligands (nanocrystal-ligands complexes) is the starting point for their applications, which is commonly measured by their solubility in media. A model described in the other report (10.1021/acs.nanolett.6b00737) reveals that instead of offering steric barrier between inorganic cores, it is the rotation/bending entropy of the C-C σ bonds within typical organic ligands that exponentially enhances solubility of the complexes in solution. Dramatic ligand chain-length effects on the solubility of CdSe-n-alkanoates complexes shall further reveal the power of the model. Subsequently, "entropic ligands" are introduced to maximize the intramolecular entropic effects, which increases solubility of various nanocrystals by 10(2)-10(6). Entropic ligands can further offer means to greatly improve performance of nanocrystals-based electronic and optoelectronic devices.

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Though Ag nanocrystals are predicted to be the best material for localized surface plasmon resonances (LSPR) in the visible light region, realization of their ideal LSPR properties is hindered by the stringent requirements: i.e., simultaneous control of their size, shape, crystallinity, and surface structure. To achieve this goal, a synthetic scheme in non-polar solvent coupled with mild oxidative etching by H + ions has been established. With a trace amount of Cl − ions as catalysts, H + ions (in the form of carboxylic acids) become active for selectively etching the nuclei (and small nanocrystals) with imperfect crystal structure, which results in a new growth mechanism for formation of monodisperse nanocrystals, namely "self-focusing of size/crystallinity distribution". H + ions, ligands, and other reagents in the scheme are confirmed to possess negligible effects on the surface dielectric properties of Ag nanocrystals. To eliminate radiative damping of LSPR, single-crystalline and monodisperse spherical Ag nanocrystals in the size range between 7 and 20 nm are synthesized using this one-pot scheme. With excellent control of all related structural parameters, the full width at half-maximum of LSPR spectra of single-crystalline Ag nanocrystals match theoretical predictions in the entire size range, and the maximum quality factor (∼20) of LSPR predicted by theory is realized. The Raman enhancement factor of the single-crystalline Ag nanocrystals for crystal violet (excitation at 514 nm) is 5 times higher than that of the typical multi-twinned nanocrystals with the same size.

Different mechanisms are proposed to account formation of monodisperse nanocrystals in literature, each of which is usually proposed to explain one set of experimental observations. Here, a general model based on mass conservation is developed to fully describe all possible channels including free growth by direct incorporation of the monomers converted from the precursors, growth by dissolution of a portion of the regular nanocrystals in solution, and growth by dissolution of the clusters in solution. The new model provides convenient yet quantitative methods to determine the channel ratios at a given time. Experimentally, an automated microreactor system is developed and applied for synthesis of monodisperse CdS nanocrystals, which is coupled with liquid-phase Fourier transform infrared and UV-vis measurements to, respectively, determine precursor conversion and size/concentration of nanocrystals with high reproducibility (<1%) and proper time resolution (<1 s). Different from the most-accepted model for formation of monodisperse nanocrystals, a burst of nucleation followed by growth of all nuclei by direct incorporation of the monomers converted from the precursors (or "focusing of size distribution"), all three basic channels are found to coexist during growth of monodisperse CdS nanocrystals. While the new theory and experimental methods are applied to study growth of monodisperse nanocrystals, they can be extended to offer a full kinetic picture for formation of colloidal nanocrystals.

A low-loss hollow core terahertz waveguide based on Kagome photonic crystal structure has been designed and fabricated by 3D printing. The 3D printed waveguide has been characterized by using THz time-domain spectroscopy. The results demonstrate that the obtained waveguide features average power propagation loss of 0.02 cm^-1 for 0.2-1.0 THz (the minimum is about 0.002 cm^-1 at 0.75 THz). More interesting, it could be simply mechanically spliced without any additional alignment, while maintaining the excellent performance. The 3D printing technique will be a promising solution to fabricate Kagome THz waveguide with well controllable characteristics and low cost.

BackgroundAs a promising candidate for artificial enzymes, catalytically active nanomaterials show several advantages over natural enzymes, such as controlled synthesis at low cost, tunability of catalytic activities, and high stability under stringent conditions. Rod-shaped Au–Pt core/shell nanoparticles (Au@Pt NRs), prepared by Au nanorod-mediated growth, exhibit peroxidase-like activities and could serve as an inexpensive replacement for horseradish peroxidase, with potential applications in various bio-detections. The determination of measles virus is accomplished by a capture-enzyme-linked immunosorbent assay (ELISA) using Au@Pt NR-antigen conjugates.ResultsBased on the enhanced catalytic properties of this nanozyme probe, a linear response was observed up to 10 ng/mL measles IgM antibodies in human serum, which is 1000 times more sensitive than commercial ELISA.ConclusionsHence, these findings provide positive proof of concept for the potential of Au@Pt NR-antigen conjugates in the development of colorimetric biosensors that are simple, robust, and cost-effective.Electronic supplementary materialThe online version of this article (10.1186/s12951-018-0371-0) contains supplementary material, which is available to authorized users.

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We investigated terahertz (THz) magneto-optical properties of a ferrofluid and a ferrofluid-filled photonic crystal (FFPC) by using the THz time-domain spectroscopy. A magnetoplasmon resonance splitting and an induced THz transparency phenomenon were demonstrated in the FFPC. The further investigation reveals that the induced transparency originates from the interference between magnetoplasmon modes in the hybrid magneto-optical system of FFPC, and the THz modulation with a 40% intensity modulation depth can be realized in this induced transparency frequency band. This device structure and its tunabilty scheme will have great potential applications in THz filtering, modulation and sensing.