Chung-Yuan Mou

Size Effect on Cell Uptake in Well‐Suspended, Uniform Mesoporous Silica Nanoparticles

because itdetermines the mechanism and rate of cell uptake of ananoparticle and its ability to permeate through tissue. Theinvestigation of particle size effects will impact on allapplications of nanoparticles in biomedicine. It has beenfoundthatparticlesizecanaffecttheefficiencyandpathwayofcellularuptakebyinfluencingtheadhesionoftheparticlesandtheir interaction with cells.

Synthesis of mesoporous silica nanoparticles

Good control of the morphology, particle size, uniformity and dispersity of mesoporous silica nanoparticles (MSNs) is of increasing importance to their use in catalyst, adsorption, polymer filler, optical devices, bio-imaging, drug delivery, and biomedical applications. This review discusses different synthesis methodologies to prepare well-dispersed MSNs and hollow silica nanoparticles (HSNs) with tunable dimensions ranging from a few to hundreds of nanometers of different mesostructures. The methods include fast self-assembly, soft and hard templating, a modified Stöber method, dissolving-reconstruction and modified aerogel approaches. In practical applications, the MSNs prepared by these methods demonstrate good potential for use in high-performance catalysis, antireflection coating, transparent polymer-MSNs nanocomposites, drug-release and theranostic systems.

Pressure dependence of fragile-to-strong transition and a possible second critical point in supercooled confined water

By confining water in nanopores of silica glass, we can bypass the crystallization and study the pressure effect on the dynamical behavior in deeply supercooled state using neutron scattering. We observe a clear evidence of a cusplike fragile-to-strong (FS) dynamic transition. Here we show that the transition temperature decreases steadily with an increasing pressure, until it intersects the homogenous nucleation temperature line of bulk water at a pressure of 1600 bar. Above this pressure, it is no longer possible to discern the characteristic feature of the FS transition. Identification of this end point with the possible second critical point is discussed.

Tubules-Within-a-Tubule Hierarchical Order of Mesoporous Molecular Sieves in MCM-41

The recently discovered mesoporous aluminosilicate MCM-41 consists of hexagonal arrays of nanometer-sized cylindrical pores. It is shown that this material can be synthesized by cooperative condensation of silicate and cylindrical cationic micelles. Careful control of the surfactant-water content and the rate of condensation of silica at high alkalinity resulted in hollow tubules 0.3 to 3 micrometers in diameter. The wall of the tubules consisted of coaxial cylindrical pores, nanometers in size, that are characteristic of those of MCM-41. The formation of this higher order structure may take place through a liquid crystal phase transformation mechanism involving an anisotropic membrane-to-tubule phase change. The hierarchical organization of this “tubules-within-a-tubule” particle texture is similar to that of the frustules of marine diatoms.

Highly efficient cellular labeling of mesoporous nanoparticles in human mesenchymal stem cells: implication for stem cell tracking

Tracking the distribution of stem cells is crucial to their therapeutic use. However, the usage of current vectors in cellular labeling is restricted by their low internalizing efficiency. Here, we reported a cellular labeling approach with a novel vector composed of mesoporous silica nanoparticles (MSNs) conjugated with fluorescein isothiocyanate in human bone marrow mesenchymal stem cells and 3T3‐L1 cells, and the mechanism about fluorescein isothiocyanate‐conjugated MSNs (FITC‐MSNs) internalization was studied. FITC‐MSNs were efficiently internalized into mesenchymal stem cells and 3T3‐L1 cells even in short‐term incubation. The process displayed a time‐ and concentration‐dependent manner and was dependent on clathrin‐mediated endocytosis. In addition, clathrin‐dependent endocytosis seemed to play a decisive role on more internalization and longer stay of FITC‐MSNs in mesenchymal stem cells than in 3T3‐L1 cells. The internalization of FITC‐MSNs did not affect the cell viability, proliferation, immunophenotype, and differentiation potential of mesenchymal stem cells, and 3T3‐L1 cells. Finally, FITC‐MSNs could escape from endolysosomal vesicles and were retained the architectonic integrity after internalization. We conclude that the advantages of biocompatibility, durability, and higher efficiency in internalization suit MSNs to be a better vector for stem cell tracking than others currently used.

Strong metal-support interactions between gold nanoparticles and ZnO nanorods in CO oxidation.

The catalytic performances of supported gold nanoparticles depend critically on the nature of support. Here, we report the first evidence of strong metal-support interactions (SMSI) between gold nanoparticles and ZnO nanorods based on results of structural and spectroscopic characterization. The catalyst shows encapsulation of gold nanoparticles by ZnO and the electron transfer between gold and the support. Detailed characterizations of the interaction between Au nanoparticles and ZnO were done with transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and FTIR study of adsorbed CO. The significance of the SMSI effect is further investigated by probing the efficiency of CO oxidation over the Au/ZnO-nanorod. In contrast to the classical reductive SMSI in the TiO(2) supported group VIII metals which appears after high temperature reduction in H(2) with electron transfer from the support to metals, the oxidative SMSI in Au/ZnO-nanorod system gives oxygen-induced burial and electron transfer from gold to support. In CO oxidation, we found that the oxidative SMSI state is associated with positively charged gold nanoparticles with strong effect on its catalytic activity before and after encapsulation. The oxidative SMSI can be reversed by hydrogen treatment to induce AuZn alloy formation, de-encapsulation, and electron transfer from support to Au. Our discovery of the SMSI effects in Au/ZnO nanorods gives new understandings of the interaction between gold and support and provides new way to control the interaction between gold and the support as well as catalytic activity.

Probing bright and dark surface-plasmon modes in individual and coupled noble metal nanoparticles using an electron beam.

The rich structure of bright and dark surface-plasmon modes localized in individual and coupled gold nanoparticles is unveiled by electron-energy-loss spectroscopy performed in a scanning transmission electron microscope. Spatially resolved maps of surface-plasmon modes in the approximately 1.5-2.5 eV range (wavelengths approximately 500-800 nm), collected for individual nanorods, coupled nanorod dimers, and touching nanosphere dimers, are in excellent agreement with theory. Surface-plasmon maps constructed from the spatially and spectrally resolved energy-loss signals are shown to mimic rather well the near fields calculated for external illumination in the case of bright surface-plasmon modes (i.e., those coupling to external light). Dark surface-plasmon modes that cannot be excited by optical means are also found, and our electron probing technique provides further insight into their corresponding spatial distribution and symmetry, which are not accessible to any other existing techniques. Our results initiate the study of a whole set of new dark surface-plasmon modes that should become a source of new applications in sensing and microscopy but have escaped experimental scrutiny so far.

Mesoporous silica nanoparticles as nanocarriers

Modern nanomedicine aims at delivering drugs or cells specifically to defective cells; therefore, this calls for developing multifunctional nanocarriers for drug delivery and cell-tracking. Mesoporous silica nanoparticles (MSNs) are well suited for this task. In this feature article, we highlight the strategies in the synthesis and functionalization of small, uniform and colloidal stable MSNs. We then discuss cell uptake of MSNs and tracking cells, as both aspects are closely related to the efficacy of drug delivery and theranostics. Some examples of stimulated drug delivery are described. For application considerations, toxicity and pharmacokinetics are critical issues and in vivo studies are summarized.

The structure of the liquid–vapor interface

A formal derivation is presented for the equilibrium relation between the singlet density in a fluid and the direct correlation function and for the equivalent relation involving the pair number density. It is shown that this relation is equivalent to the macroscopic condition for hydrostatic equilibrium when the singlet density varies sufficiently slowly to permit the introduction of local thermodynamics. Some aspects of the usage of this in the determination of the singlet density in the liquid–vapor transition region are discussed.

Surface charge-mediated rapid hepatobiliary excretion of mesoporous silica nanoparticles.

Nanoparticle-assisted drug delivery has been emerging as an active research area in recent years. The in vivo biodistribution of nanoparticle and its following mechanisms of biodegradation and/or excretion determine the feasibility and applicability of such a nano-delivery platform in the practical clinical translation. In this work we report the synthesis of the highly positive charge, near-infrared fluorescent mesoporous silica nanoparticles (MSNs) that demonstrate rapid hepatobiliary excretion, for use as traceable drug delivery platforms of high capacity. MSNs were incorporated with near-infrared fluorescent dye indocyanine green (ICG) via covalent or ionic bonding, to derive comparable constructs of significantly different net surface charge. In vivo fluorescence imaging and subsequent inductively coupled plasma-mass spectroscopy of harvested tissues, urine, and feces revealed markedly different uptake and elimination behaviors between the two conjugations; with more highly charged moieties (+34.4 mV at pH 7.4) being quickly excreted from the liver into the gastrointestinal tract, while less charged moieties (-17.6 mV at pH 7.4) remained sequestered within the liver. Taken together, these findings suggest that charge-dependent adsorption of serum proteins greatly facilitates the hepatobiliary excretion of silica nanoparticles, and that nanoparticle residence time in vivo can be regulated by manipulation of surface charge.