Yuangang Zheng

Synthesis of Highly Fluorescent Metal (Ag, Au, Pt, and Cu) Nanoclusters by Electrostatically Induced Reversible Phase Transfer

This paper reports a simple and scalable method for the synthesis of highly fluorescent Ag, Au, Pt, and Cu nanoclusters (NCs) based on a mild etching environment made possible by phase transfer via electrostatic interactions. Using Ag as a model metal, a simple and fast (total synthesis time < 3 h) phase transfer cycle (aqueous → organic (2 h incubation) → aqueous) has been developed to process originally polydisperse, nonfluorescent, and unstable Ag NCs into monodisperse, highly fluorescent, and extremely stable Ag NCs in the same phase (aqueous) and protected by the same thiol ligand. The synthetic protocol was successfully extended to fabricate highly fluorescent Ag NCs protected by custom-designed peptides with desired functionalities (e.g., carboxyl, hydroxyl, and amine). The facile synthetic method developed in this study should largely contribute to the practical applications of this new class of fluorescence probes.

Protein Induces Layer-by-Layer Exfoliation of Transition Metal Dichalcogenides

Here, we report a general and facile method for effective layer-by-layer exfoliation of transition metal dichalcogenides (TMDs) and graphite in water by using protein, bovine serum albumin (BSA) to produce single-layer nanosheets, which cannot be achieved using other commonly used bio- and synthetic polymers. Besides serving as an effective exfoliating agent, BSA can also function as a strong stabilizing agent against reaggregation of single-layer nanosheets for greatly improving their biocompatibility in biomedical applications. With significantly increased surface area, single-layer MoS2 nanosheets also exhibit a much higher binding capacity to pesticides and a much larger specific capacitance. The protein exfoliation process is carefully investigated with various control experiments and density functional theory simulations. It is interesting to find that the nonpolar groups of protein can firmly bind to TMD layers or graphene to expose polar groups in water, facilitating the effective exfoliation of single-layer nanosheets in aqueous solution. The present work will enable to optimize the fabrication of various 2D materials at high yield and large scale, and bring more opportunities to investigate the unique properties of 2D materials and exploit their novel applications.

Three-photon absorption in water-soluble ZnS nanocrystals

We report on large three-photon absorption (3PA) in glutathione-capped ZnS semiconductor nanocrystals (NCs), determined by both Z-scan and transient transmission techniques with 120fs laser pulses. The monodispersed, water-soluble ZnS NCs are synthesized by a modified protocol with a mean diameter of 2.5nm. Their 3PA cross section is determined to be ∼2.7×10−78cm6s2photon−2 at an optimal wavelength of commercial Ti:sapphire femtosecond lasers. This value is nearly one order of magnitude greater than that of CdS NCs, and four to five orders of magnitude higher than those of the previously reported common UV fluorescent dyes.

Composite Metal–Oxide Nanocatalysts

To incorporate new functionalities, various oxide materials can be composited with metal nanoparticles to form metal–oxide nanostructures, which are very promising for a wide range of applications. In this review, we summarize the recent developments in advanced synthesis of structure‐diversified core–shell, yolk–shell, Janus, and their combined metal–oxide nanostructures. We also summarize their representative catalytic applications including organic reduction and oxidation, CO oxidation, CO2 conversion, water–gas shift reaction, and water splitting. We discuss recyclable metal–oxide nanocatalysts with mesoporous, hollow, or multilayered structures. We highlight perspectives for their challenges ahead and opportunities for their widely used applications in plasmon localization enhanced photocatalysis, artificial enzyme catalysis, and catalytic biomass conversion.

Convenient purification of gold clusters by co-precipitation for improved sensing of hydrogen peroxide, mercury ions and pesticides

An effective separation process is developed to remove free protein from the protein-protected gold clusters via co-precipitation with zinc hydroxide on their surface. After dialysis, the purified clusters exhibit an enhanced fluorescence for improved sensitive detection and selective visualization.

Multicomponent Fibers by Multi-interfacial Polyelectrolyte Complexation

In multi-interfacial polyelectrolyte complexation (MIPC), fusion of nascent fibers from multiple interfaces brings the interfaces to a point from which a composite fiber is drawn. MIPC applied to two, three, and four polyelectrolyte complex interfaces leads to various patterned multicomponent fibers. Cells encapsulated in these fibers exhibit migration, aggregation and spreading in relation to the initial cell or matrix pattern.

Controlled photostability of luminescent nanocrystalline ZnO solution for selective detection of aldehydes

Water-soluble, silane-functionalized ZnO nanocrystals were synthesized with improved colloidal stability, and their photostability was controlled for the selective detection of aldehydes.

Auger recombination and intraband absorption of two-photon-excited carriers in colloidal CdSe quantum dots

Auger recombination, quantized Auger rate, and intraband absorption of two-photon-excited carriers in colloidal CdSe quantum dots have been investigated systematically with femtosecond Z scans and transient absorption measurements. The Auger constant is revealed to be on the order of 10−30cm6s−1, while the intraband absorption cross sections are found to be in the range of 10−18–10−17cm2. The authors’ experimental evidence demonstrates that the Auger recombination or the intraband absorption takes place under the condition that the average electron-hole pair per quantum dot is in excess of the unity.

High efficiency and nearly cubic power dependence of below-band-edge photoluminescence in water-soluble, copper-doped ZnSe/ZnS quantum dots.

Three-photon absorption (3PA) and three-photon-excited photoluminescence (3PE-PL) of ZnSe/ZnS and copper-doped ZnSe/ZnS core-shell quantum dots (QDs) in aqueous solutions have been unambiguously determined by Z-scan and 3PE-PL measurements with 200-fs laser pulses at 1000 nm. The 3PA cross-section is as high as 3.5 x 10(-77) cm6 s2 photon(-2) for 4.1 nm-sized, copper-doped ZnSe/ZnS QDs, while their below-band-edge PL is found to be nearly cubic dependent on the excitation intensity, with efficiency enhanced by approximately 20 fold compared to the undoped ZnSe/ZnS QDs.

Effects of quantum dots on different renal proximal tubule cell models and on gel-free renal tubules generated in vitro

Abstract We investigated the interactions of different types of human and porcine renal proximal tubule-derived cells with core-shell CdSe@ZnS quantum dots (QDs) coated with polymerized histidine-formaldehyde (pHF). The results revealed that porcine and human proximal tubule cells showed a markedly different uptake behavior. This applied to flat epithelial monolayers, as well as to proximal tubules formed on two-dimensional (2D) surfaces in vitro. Primary human cells were most sensitive to the cytotoxic effects of QDs, but displayed inter-donor variability, which appeared to depend on the state of differentiation. The results suggested that human proximal tubule-derived cells were more appropriate than porcine cells for in vitro nanotoxicology. Primary human cells might be suitable when their state of differentiation and inter-donor variability were well-controlled. Furthermore, the results suggested that gel-free proximal tubules formed in vitro could be used as test system to address uptake and transport of nanometer-sized particles in human renal structures.