A zinc oxide ͑ZnO͒ nanowire photodetector was fabricated by a simple method of growing ZnO nanowires bridging the gap of two patterned zinc electrodes. The nanowire growth is self-catalytic, involving the direct heating of patterned Zn electrodes at 700°C in an O 2 / Ar gas flow of 20 SCCM ͑standard cubic centimeter per minute at STP͒/80 SCCM, respectively, at atmospheric pressure for 3 h. The fabricated photodetector demonstrated fast response of shorter than 0.4 ms to UV illumination in air, which could be attributed to the adsorption, desorption, and diffusion of water molecules in the air onto the nanowire significantly influencing the photoresponse.

Integrin-mediated adhesions are critical for stem cell differentiation, cancer metastasis, and the immune response [Hynes RO (2009) Science 326:1216-1219. However, the mechanisms of early adhesion formation remain unclear, especially the effects of lateral clustering of integrins and the role of the Src family kinases. Using mobile Arg-Gly-Asp (RGD) peptide ligands on lipid bilayers with nano-fabricated physical barriers [Salaita K, et al. (2010) Science 327:1380-1385], we observe surprising long-range lateral movements of ligated integrins during the process of cell spreading. Initially, RGD-activated integrin clusters stimulate actin polymerization that radiates from the clusters. Myosin II contraction of actin from adjacent clusters produces contractile pairs that move toward each other against barriers. Force generated by myosin II stimulates a Src kinase-dependent lamellipodial extension and outward movement of clusters. Subsequent retraction by myosin II causes inward movement of clusters. The final cell spread area increases with the density of periodic barriers. Early integrin clustering recruits adhesion proteins, talin, paxillin, and FAK, irrespective of force generation. However, recruitment of vinculin is only observed upon contraction. Thus, we suggest that integrin activation and early clustering are independent of lateral forces. Clustering activates Src-dependent actin polymerization from clusters. Myosin contraction of clusters to lines stimulates active spreading with outward forces from actin polymerization followed by a second wave of contraction. Many of these early mechanical steps are not evident in cells spreading on immobilized matrices perhaps because of the low forces involved. These observations can provide new targets to control integrin-dependent adhesion and motility.cell adhesion | integrin reorganization | supported membranes T he integrins, a heterodimeric transmembrane receptor family, regulate many cellular processes including growth, differentiation, and death (1-3). Both chemical recognition and mechanical sensing are important factors in the outside-in integrin signaling pathway (4-6). Chemically, ligation of integrin receptors, such as fibronectin binding to α5β1 and αvβ3, results in conformational changes of the external domains and cytoplasmic tails causing the recruitment of various signaling molecules and adaptor proteins during focal adhesion formation (7,8). Mechanically, matrix rigidity and local matrix density regulate cell spreading, growth, and differentiation. Rigidity sensing depends upon local contractile force generation by the actin cytoskeleton on ligated integrin receptors (9-11). The spacing of Arg-Gly-Asp (RGD) peptide matrix ligands on 5 nm gold dots needs to be 60 nm or less for cell spreading (12). Recent findings with a constant overall density of RGD ligands, show that local clusters of four or more RGD ligands spaced by 60 nm are needed for sustained spreading, defining a minimal adhesion unit of four ligated integrins (13,14). Nevertheless, becau...

During development and tissue repair, progenitor cells are guided by both biochemical and biophysical cues of their microenvironment, including topographical signals. The topographical cues have been shown to play an important role in controlling the fate of cells. Systematic investigation of topographical structures with different geometries and sizes under the identical experimental conditions on the same chip will enhance the understanding of the role of shape and size in cell-topography interactions. A simple customizable multi-architecture chip (MARC) array is therefore developed to incorporate, on a single chip, distinct topographies of various architectural complexities, including both isotropic and anisotropic features, in nano- to micrometer dimensions, with different aspect ratios and hierarchical structures. Polydimethylsiloxane (PDMS) replicas of MARC are used to investigate the influence of different geometries and sizes in neural differentiation of primary murine neural progenitor cells (mNPCs). Anisotropic gratings (2 μm gratings, 250 nm gratings) and isotropic 1 μm pillars significantly promote differentiation of mNPCs into neurons, as indicated by expression of β-III-tubulin (59%, 58%, and 58%, respectively, compared to 30% on the control). In contrast, glial differentiation is enhanced on isotropic 2 μm holes and 1 μm pillars. These results illustrate that anisotropic topographies enhance neuronal differentiation while isotropic topographies enhance glial differentiation on the same chip under the same conditions. MARC enables simultaneous cost-effective investigation of multiple topographies, allowing efficient optimization of topographical and biochemical cues to modulate cell differentiation.