Nanoparticle Vesicles with Controllable Surface Topographies through Block Copolymer-Mediated Self-Assembly of Silica Nanospheres

Silica nanoparticle vesicles (NPVs) with encapsulating capability and surface permeability are highly attractive in nanocatalysis, biosensing, and drug delivery systems. Herein, we report the facile fabrication of silica NPVs composed of a monolayer of silica nanospheres (SNSs, ca. 15 nm in diameter) through the block copolymer-mediated self-assembly of SNSs. The silica NPVs gain different surface topographies, such as raspberry- and brain coral-like topographies, under controlled heat treatment conditions. The vesicular assembly of SNSs is successful with a series of poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) block copolymers, and the size of NPVs can be tuned by changing their molecular weight. The polymer is easily extracted from the NPVs with their colloidal dispersibility and structural integrity intact. The polymer-free silica NPVs further serve as a reaction vessel and host for functional materials such as tin oxide nanoparticles.

Dendritic silica nanoparticles synthesized by a block copolymer-directed seed-regrowth approach

A facile seed regrowth method is presented for the preparation of a new type of colloidal dendritic silica nanoparticles (DSNPs) with unique Konpeito-like morphology and high surface area (∼400 m(2) g(-1)). Growth of silica nanoprotrusions on the surfaces of colloidal silica nanoparticles proceeds by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in the presence of a PEO-PPO-PEO-type block copolymer (Pluronic F127) under controlled pH conditions. The polymers adsorbed on the seed surface play a crucial role in the formation of DSNPs. DSNPs with controllable size (28-85 nm) and narrow size distributions can be obtained by using monodisperse silica nanoparticles with various sizes as seeds. The surface morphology of DSNPs is tunable by changing the concentration of TEOS. Additionally, novel dendritic silica nanochains are prepared using one-dimensionally assembled silica nanoparticles as the seeds.

Template-free ordered mesoporous silicas by binary nanoparticle assembly

Evaporation-induced convective binary assembly of large (A) and small (B) silica nanoparticles is demonstrated as a template-free route to three-dimensionally ordered mesoporous silicas (OMSs), the pore topology of which derives from the interconnected interstices of the resulting ordered nanoparticulate structures. Even without explicit solvent index matching or stabilization (e.g., charge or steric) beyond intrinsic properties of the amino acid nanoparticle synthesis solution, assembly of binary mixtures of silica nanoparticles of ca. 10-50 nm in diameter primarily obeys hard-sphere phase behavior despite differences in electrostatic character of the particles. Specifically, the particle size ratio, γ, governs symmetry of the assemblies among AB2 and AB13 phases and enables access of the AB phase. Small-angle X-ray scattering (SAXS) reveals the high yield of ordered binary assemblies and confirms, in combination with transmission electron microscopy, the AlB2, NaZn13, and NaCl crystalline isostructures. Interstitial solid solutions result for the smallest γ considered (γ ≤ 0.3), wherein cubic crystallization of the large particles is templated by interstitially mobile small particles. New mechanistic insight into factors influencing the yield of ordered binary structures includes the degree to which the smaller particles (ca. 15-24 nm) within the mixture undergo unary crystallization, as influenced by lysine or other basic amino acids used in the nanoparticle synthesis, as well as matching of the time scales for convective nanoparticle assembly and crystallization. Ultimately, the demonstrated robustness of the binary nanoparticle assembly and the control over silica particle size translate to a facile, template-free approach to OMSs with independently tunable pore topology and pore size.

Maintenance of ischemic β cell viability through delivery of lipids and ATP by targeted liposomes

Islet transplantation is a promising treatment for type 1 diabetes, but despite the successes, existing challenges prevent widespread application. Ischemia, occurring during pancreas preservation and isolation, as well as after islet transplantation, decreases islet viability and function. We hypothesized that the liposomal delivery of adenosine triphosphate (ATP) could prevent the loss of cell viability during an ischemic insult. In this work we use a model β cell line, INS-1 to probe the liposome/cell interactions and examined the ability of liposomes functionalized with the fibronectin-mimetic peptide PR_b to facilitate the delivery of ATP to ischemic β cells. We demonstrate that PR_b increases the binding and internalization of liposomes to the β cells. Unexpectedly, when comparing the ability of PR_b liposomes with and without ATP to protect INS-1 cells from ischemia we found that both formulations increased cell survival. By probing the functional activity of ischemic cells treated with PR_b functionalized liposomes with and without ATP we find that both lipids and ATP play a role in maintaining cell metabolic activity after an ischemic insult and preventing cell necrosis. This approach may be beneficial for preventing ischemia related damage to islet cells, especially in the organ preservation stage.

A targeted and FRET-based ratiometric fluorescent nanoprobe for imaging mitochondrial hydrogen peroxide in living cells

Hydrogen peroxide (H2 O2 ) is a prominent member of the reactive oxygen species family and plays crucial roles in living organisms, thus detecting H2 O2 and elucidating its biological functions has become an important area of biological and biomedical research. Herein, a multifunctional fluorescent nanoprobe is demonstrated for detecting mitochondrial H2 O2 . The nanoprobe is prepared by covalently linking a mitochondria-targeting ligand (triphenylphosphonium, TPP) and a H2 O2 recognition element (PFl) onto carbon dots (CDs). For this nanoprobe, the CD serves as the carrier and the FRET donor. In the presence of H2 O2 , the PFl moieties on a CD undergo structural and spectral conversion, affording the nanoplatform a FRET-based ratiometric probe for H2 O2 . The nanoprobe displays excellent water dispersibility, high sensitivity and selectivity, satisfactory cell permeability, and very low cytotoxicity. Following the living cell uptake, this nanoprobe can specifically target and stain the mitochondria; and it can detect the exogenous H2 O2 in L929 cells, as well as the endogenously produced mitochondrial H2 O2 in Raw 264.7 cells upon stimulation by PMA. This study shows that CDs can serve as promising nano-carriers for fabricating practical multifunctional fluorescent nanosensors.

Two-phase synthesis of monodisperse silica nanospheres with amines or ammonia catalyst and their controlled self-assembly

A significant progress has recently been made in the synthesis of monodisperse silica nanoparticles less than 30 nm in diameter by using basic amino acids (e.g., lysine) as a base catalyst for hydrolysis of silicon alkoxide. Alternatively, a more versatile and economical amino acid-free method has been developed to synthesize uniform silica nanospheres (SNSs) with low polydispersity (<12%) in liquid-liquid biphasic systems containing tetraethoxysilane (TEOS), water, and primary amine (or ammonia) under precisely controlled pH conditions (pH 10.8-11.4). The diameter of the SNSs determined from scanning electron microscopy (SEM) can be tuned from ∼12 to ∼36 nm by simply changing the initial pH of the aqueous phase in the reaction mixtures. Furthermore, the as-synthesized sol was taken as the starting material for studying the influences of the type of base catalysts on the solvent evaporation-induced three-dimensional (3D) self-assembly of SNSs. X-ray diffraction (XRD) and nitrogen adsorption-desorption are used to characterize the degree of packing of the resulting 3D arrays. The assembled SNSs with large interparticle mesopores with the diameter of ca. 8.1 nm and low packing fraction of ca. 66.1% are observed upon solvent evaporation of as-synthesized sol in the presence of primary amine. This indicates that SNSs are loosely packed, compared with the packing fraction of 74% for a face-centered cubic array of ideal hard spheres. In contrast, with the aid of an organic buffer or lysine as additives, the assembly of SNSs having smaller mesopores (ca. 3.9 nm) and higher packing fraction of 70.5-71.5% are achieved. It is suggested that the chemical additives with the ability to maintain relatively strong repulsive interaction until the final stage of evaporation play a vital role in the fabrication of well-ordered SNSs arrays.