Alexandros A. Vradis

Nanoporous alumina enhanced surface plasmon resonance sensors

The signal enhancement of an easy to fabricate, nanoporous alumina assisted surface plasmon resonance (SPR) sensor is investigated. It is theoretically shown that the presence of a thin (under 200nm) porous alumina layer on top of an aluminum film supporting the surface plasmons, may significantly increase (over one order of magnitude) the sensitivity of the SPR method in the case where the adsorption of relatively small molecules is probed. The comparative experimental investigation of self-assembled monolayer formation on planar metal films and porous alumina layers verifies the theoretical predictions. Based on these results, we discuss the extended applicability of this setup in biosensor and other related applications.

Electrochemical synthesis of large diameter monocrystalline nickel nanowires in porous alumina membranes

In this work, the synthesis of long, single-crystal nickel nanowires (NWs) using dc electrodeposition is reported. Porous alumina membranes with 220 nm mean pore diameter were used as a template. This diameter is much larger than what is usually reported in single crystal NWs synthesis. The dependence of the NW crystal structure upon applied voltage as well as the change in crystal structure along the NWs length is also investigated. Finally, in order to get sufficient understanding of the present results, a model based on two competing growth mechanisms is proposed, revealing the dependence of crystal structure upon the voltage applied during the electrodeposition process.

A peptide corresponding to the C-terminal region of pleiotrophin inhibits angiogenesis in vivo and in vitro.

Pleiotrophin (PTN) is a heparin‐binding growth factor that plays a significant role in tumor growth and angiogenesis. We have previously shown that in order for PTN to induce migration of endothelial cells, binding to both ανβ3 integrin and its receptor protein tyrosine phosphatase beta/zeta (RPTPβ/ζ) is required. In the present study we show that a synthetic peptide corresponding to the last 25 amino acids of the C‐terminal region of PTN (PTN112–136) inhibited angiogenesis in the in vivo chicken embryo chorioallantoic membrane (CAM) assay and PTN‐induced migration and tube formation of human endothelial cells in vitro. PTN112–136 inhibited binding of PTN to ανβ3 integrin, and as shown by surface plasmon resonance (SPR) measurements, specifically interacted with the specificity loop of the extracellular domain of β3. Moreover, it abolished PTN‐induced FAK Y397 phosphorylation, similarly to the effect of a neutralizing ανβ3‐selective antibody. PTN112–136 did not affect binding of PTN to RPTPβ/ζ in endothelial cells and induced β3 Y773 phosphorylation and ERK1/2 activation to a similar extent with PTN. This effect was inhibited by down‐regulation of RPTPβ/ζ by siRNA or by c‐src inhibition, suggesting that PTN112–136 may interact with RPTPβ/ζ. NMR spectroscopy studies showed that PTN112–136 was characterized by conformational flexibility and absence of any element of secondary structure at room temperature, although the biologically active peptide segment 123–132 may adopt a defined structure at lower temperature. Collectively, our data suggest that although PTN112–136 induces some of the signaling pathways triggered by PTN, it inhibits PTN‐induced angiogenic activities through inhibition of PTN binding to ανβ3 integrin. J. Cell. Biochem. 112: 1532–1543, 2011.

Complexation of lysozyme with adsorbed PtBS-b-SCPI block polyelectrolyte micelles on silver surface.

We present a study of the interaction of the positively charged model protein lysozyme with the negatively charged amphiphilic diblock polyelectrolyte micelles of poly(tert-butylstyrene-b-sodium (sulfamate/carboxylate)isoprene) (PtBS-b-SCPI) on the silver/water interface. The adsorption kinetics are monitored by surface plasmon resonance, and the surface morphology is probed by atomic force microscopy. The micellar adsorption is described by stretched-exponential kinetics, and the micellar layer morphology shows that the micelles do not lose their integrity upon adsorption. The complexation of lysozyme with the adsorbed micellar layers depends on the micelles arrangement and density in the underlying layer, and lysozyme follows the local morphology of the underlying roughness. When the micellar adsorbed amount is small, the layers show low capacity in protein complexation and low resistance in loading. When the micellar adsorbed amount is high, the situation is reversed. The adsorbed layers both with or without added protein are found to be irreversibly adsorbed on the Ag surface.

Compton-profile measurements on (Bi1.6Pb0.4)Sr2Ca2Cu3O10+x superconductor

Abstract In this paper the measured Compton profiles (CPs) of the ceramic superconductor (Bi1.6Pb0.4)Sr2Ca2Cu3O10+x above and below Tc are presented. The observed difference in the CPs between the normal and superconducting state suggests a redistribution of the electron momentum during the superconducting transition.

Compton profile anisotropies in Bi1.6Pb0.4Sr2Ca2Cu3O10+x superconductor

Abstract We present Compton profile (CP) anisotropies measured on the high-Tc (HTc) superconductor Bi1.6Pb0.4Sr2Ca2Cu3O10+x. Our results, based on measurements of high statistical accuracy, reveal the existence of an excess charge of about 0.8 electrons in the basal planes, possessing a rather low component of momentum. This can be attributed to the strong metallic behavior of these planes. Furthermore, symmetric features on the directional CP difference indicate that Bi–O bands are not crossing the Fermi level, confirming previous experimental evidence that Bi–O bands are not of metallic character.

Fabrication of an aluminum-porous alumina sensor by in situ monitoring anodization of thin aluminum films

The aim of the present work is to optimize a well-known plasmon-based aluminum/porous anodic alumina sensor. This kind of sensors is produced by partial electrochemical anodization of an aluminum film, while the remaining, non-anodized metallic film is used for supporting the propagation of surface plasmons. The anodized porous alumina is preferable against a flat solid surface as it presents much larger sensing area and thus enhanced detecting efficiency. In this work, a novel method for controlling the remaining aluminum film thickness is reported, based on a simple optical reflectance measurement during the electrochemical anodization of the initial metallic film.