skip to main content


Search for: All records

Creators/Authors contains: "Rankin, Stephen E."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Graphical abstract [Formula: see text] 
    more » « less
  2. Abstract

    Cellular uptake and expulsion mechanisms of engineered mesoporous silica nanoparticles (MSNPs) are important in their design for novel biomolecule isolation and delivery applications such as nanoharvesting, defined as using nanocarriers to transport and isolate valuable therapeutics (secondary metabolites) out of living plant organ cultures (e.g., hairy roots). Here, temperature‐dependent MSNP uptake and recovery processes in hairy roots are examined as a function of surface chemistry. MSNP uptake into hairy roots and time‐dependent expulsion are quantified using Ti content (present for biomolecule binding) and fluorescence spectroscopy of fluorescently tagged MSNPs, respectively. The results suggest that functionalization and surface charge (regulated by amine group attachment) play the biggest role in the effectiveness of uptake and recovery. Comparison of MSNP interactions with hairy roots at 4 and 23 °C shows that weakly charged MSNPs functionalized only with Ti are taken up and expelled by thermally activated mechanisms, while amine‐modified positively charged particles are taken up and expelled mainly by direct penetration of cell walls. Amine‐functionalized MSNPs move spontaneously in and out of plant cells by dynamic exchange with a residence time of 20 ± 5 min, suggesting promise as a biomolecule nanoharvesting platform for plant organ cultures.

     
    more » « less
  3. Abstract

    Redox probe transport through supported lipid bilayers and nanopore‐confined lipid assemblies on silica thin films is examined using electrochemical impedance spectroscopy (EIS). These supported lipid systems are emerging biomimetic separation and sensor platforms. The ability to quantify the accessibility of the pore structure of the mesoporous silica thin films is demonstrated, which is essential for the incorporation of carriers into the lipids for selective solute transport. Redox probe molecules with varying hydrophilicity are used to compare ion transport in supported lipid pore‐spanning bilayers (enveloped bilayers) and novel lipid filled pores of mesoporous silica thin films. The films feature orthogonally oriented 8–10 nm cylindrical nanopores formed by deposition of P123‐templated silica sols onto chemically modified fluorine‐doped tin oxide. Nanopore accessibility is confirmed by EIS with hydrophilic probe 1,1′‐ferrocenedimethanol (FDM). Filling the pores with lipid 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine results in a superior barrier (with roughly 1/9 the permeability) to transport of FDM compared to fragile enveloped lipid bilayers deposited by vesicle fusion. The pore‐confined lipids not only provide a better barrier to FDM, but also a better pathway for the transport across the films of a hydrophobic redox probe 1,1′‐dioctadecyl‐4,4′‐bipyridinium dibromide, with an ideal transport selectivity of 11 compared to FDM.

     
    more » « less
  4. Incorporation of lipid assemblies on the surface and within pores of mesoporous silica particles provides for biomimetic approaches to analyte sensing and separations using high surface area platforms. This work investigates the effect of pore confinement on the location and the diffusivity of lipid assemblies in mesoporous silica spherical particles (SBAS) as a function of nanopore diameters (nonporous, 3.0, 5.4, and 9.1 nm), which span the range of the thickness of the 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine lipid bilayer (≈4 nm). Large‐diameter SBAS are imaged with sufficient spatial resolution to distinguish lipids at the exterior surface and in the center of the particles. Lipids incorporated on the silica by evaporation deposition exist as exterior lipid bilayers on all particles and lipid assemblies in the pores of 5.4 and 9.1 nm pore diameter materials. Lipid diffusivity increases with pore size and decreases in the presence of bilayer tethering functional groups. Lipid diffusivity in the core of the particles is similar to the surface diffusivity, consistent with long‐range mobility in accessible, ordered (but randomly oriented) mesopores of SBAS materials. This work presents a framework for interpreting high density loading of lipid bilayers and their function within mesoporous materials.

     
    more » « less
  5. Abstract

    TiO2films of varying thicknesses (up to ≈1.0 µm) with vertically oriented, accessible 7–9 nm nanopores are synthesized using an evaporation‐induced self‐assembly layer‐by‐layer technique. The hypothesis behind the approach is that epitaxial alignment of hydrophobic blocks of surfactant templates induces a consistent, accessible mesophase orientation across a multilayer film, ultimately leading to continuous, vertically aligned pore channels. Characterization using grazing incidence X‐ray scattering, scanning electron microscopy, and impedance spectroscopy indicates that the pores are oriented vertically even in relatively thick films (up to 1 µm). These films contain a combination of amorphous and nanocrystalline anatase titania of value for electrochemical energy storage. When applied as negative electrodes in lithium‐ion batteries, a capacity of 254 mAh g−1is obtained after 200 cycles for a single‐layer TiO2film prepared on modified substrate, higher than on unmodified substrate or nonporous TiO2film, due to the high accessibility of the vertically oriented channels in the films. Thicker films on modified substrate have increased absolute capacity because of higher mass loading but a reduced specific capacity because of transport limitations. These results suggest that the multilayer epitaxial approach is a viable way to prepare high capacity TiO2films with vertically oriented continuous nanopores.

     
    more » « less