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1.  Direct-write polymer nanolithography in ultra-high vacuum 
Polymer nanostructures were directly written onto substrates in ultra-high vacuum. The polymer ink was coated onto atomic force microscope (AFM) probes that could be heated to control the ink viscosity. Then, the ink-coated probes were placed into an ultra-high vacuum (UHV) AFM and used to write polymer nanostructures on surfaces, including surfaces cleaned in UHV. Controlling the writing speed of the tip enabled the control over the number of monolayers of the polymer ink deposited on the surface from a single to tens of monolayers, with higher writing speeds generating thinner polymer nanostructures. Deposition onto silicon oxide-terminated substrates led to polymer chains standing upright on the surface, whereas deposition onto vacuum reconstructed silicon yielded polymer chains aligned along the surface.
PMCID: PMC3304329  PMID: 22428096
additive lithography; polymer; scanning probe lithography; ultra high vacuum
2.  Control of Nanoscale Environment to Improve Stability of Immobilized Proteins on Diamond Surfaces 
Advanced functional materials  2011;21(6):1040-1050.
Immunoassays for detection of bacterial pathogens rely on the selectivity and stability of bio-recognition elements such as antibodies tethered to sensor surfaces. The search for novel surfaces that improve the stability of biomolecules and assay performance has been pursued for a long time. However, the anticipated improvements in stability have not been realized in practice under physiological conditions because the surface functionalization layers on commonly used substrates, silica and gold, are themselves unstable on time scales of days. In this paper, we show that covalent linking of antibodies to diamond surfaces leads to substantial improvements in biological activity of proteins as measured by the ability to selectively capture cells of the pathogenic bacterium Escherichia coli O157:H7 even after exposure to buffer solutions at 37 °C for extended periods of time, approaching 2 weeks. Our results from ELISA, XPS, fluorescence microscopy, and MD simulations suggest that by using highly stable surface chemistry and controlling the nanoscale organization of the antibodies on the surface, it is possible to achieve significant improvements in biological activity and stability. Our findings can be easily extended to functionalization of micro and nanodimensional sensors and structures of biomedical diagnostic and therapeutic interest.
PMCID: PMC3177702  PMID: 21949497
3.  Cadherin-Mediated Cell–Cell Contact Regulates Keratinocyte Differentiation 
Cell–extracellular matrix (ECM) and cell–cell interactions regulate keratinocyte cell fate and differentiation. In the present analysis, we examined the differentiation of primary human keratinocytes cultured on micropatterned substrates that varied the extent of cell–cell contact while maintaining constant cell–ECM areas. Bowtie-shaped micropatterned areas (75–1600 µm2) were engineered to either permit or prevent cell–cell contact for pairs of adherent keratinocytes. Cell pairs with direct cell–cell contact exhibited enhanced expression of the differentiation markers involucrin and keratin 10 compared to cells with no cell–cell contact. In contrast, available cell-spreading area, as regulated by pattern size, did not alter keratinocyte involucrin expression. Disruption of E-cadherin binding by either antibody blocking or expression of a dominant-negative receptor diminished the ability of micropattern-regulated cell–cell contact to modulate involucrin expression. These results demonstrate that cadherin-mediated cell–cell contact regulates early keratinocyte differentiation independently from changes in cell shape.
PMCID: PMC2693873  PMID: 18754040

Results 1-3 (3)