Ruthy Sfez

Electrically conductive 2D-PAN-containing surfaces as a culturing substrate for neurons

In the present contribution we report on a novel route to synthesize 2D-polyaniline (2DPAN) on sulfonated-poly(styrene) (SPS) templates by allowing first monomer assembly followed by chemical oxidation to achieve polymerization. We show that Aplysia neurons grown on 2D-PAN exhibit an unusual growth pattern and adhesion to this conducting substrate that is manifested by the formation of giant lamellipodia. The lamellipodial domains are characterized by small gap between the plasma membrane and the 2D-PAN substrate (ca. 30 nm) and actin rich skeleton resembling the skeleton of growth cones. This behavior is characteristic to uniform substrates containing only 2DPAN. However, in patterned substrates containing additionally poly(L-lysine) Aplysia neurons prefer to extend new neurites on the poly(L-lysine) domains.

Polyaniline-coated single-walled carbon nanotubes: synthesis, characterization and impact on primary immune cells

Functionalized carbon nanotubes are increasingly exploited as innovative components for the development of advanced biomedical devices. In this study we report a novel synthetic route for the formation of single-walled carbon nanotube (SWCNT)–polyaniline (PANI) hybrids by in situ chemical polymerization. The surfactant sodium dodecylsulfate (SDS) is used as a template for monomer assembly and polymerization. The resulting composite preserves the surfactant and is characterized by a tight binding between SWCNTs and PANI. Having the idea of integrating these new types of SWCNT conjugates into advanced biomedical tools (i.e. implantable multi-electrode arrays), we explored their potential impact on the viability and function of cells from the immune system. We have compared the cytotoxic effects of SWCNT-COOH, SWCNT/SDS and SWCNT/SDS/PANI on mouse spleen cells and macrophages. The results indicate that biocompatibility of the different SWCNT conjugates is dependent both on the doses used and the type of cells.

Impaired Replication Stress Response in Cells from Immunodeficiency Patients Carrying Cernunnos/XLF Mutations

Non-Homologous End Joining (NHEJ) is one of the two major pathways of DNA Double Strand Breaks (DSBs) repair. Mutations in human NHEJ genes can lead to immunodeficiency due to its role in V(D)J recombination in the immune system. In addition, most patients carrying mutations in NHEJ genes display developmental anomalies which are likely the result of a general defect in repair of endogenously induced DSBs such as those arising during normal DNA replication. Cernunnos/XLF is a recently identified NHEJ gene which is mutated in immunodeficiency with microcephaly patients. Here we aimed to investigate whether Cernunnos/XLF mutations disrupt the ability of patient cells to respond to replication stress conditions. Our results demonstrate that Cernunnos/XLF mutated cells and cells downregulated for Cernunnos/XLF have increased sensitivity to conditions which perturb DNA replication. In addition, under replication stress, these cells exhibit impaired DSB repair and increased accumulation of cells in G2/M. Moreover Cernunnos/XLF mutated and down regulated cells display greater chromosomal instability, particularly at fragile sites, under replication stress conditions. These results provide evidence for the role of Cernunnos/XLF in repair of DSBs and maintenance of genomic stability under replication stress conditions. This is the first study of a NHEJ syndrome showing association with impaired cellular response to replication stress conditions. These findings may be related to the clinical features in these patients which are not due to the V(D)J recombination defect. Additionally, in light of the emerging important role of replication stress in the early stages of cancer development, our findings may provide a mechanism for the role of NHEJ in preventing tumorigenesis.

In situ SFM study of 2D-polyaniline surface-confined enzymatic polymerization

In this contribution we report on an in situ enzymatic self-assembly of a polyaniline (PAN) monolayer on modified hydroxyl-terminated surfaces. The consecutive assembly steps consist of a chemical deposition of 3-aminopropyltrimethoxysilane (APT) as a coupling agent with a positively-charged amine end group. The next step involved an electrostatic adhesion of sulfonated polystyrene (SPS) followed by electrostatic adhesion of anilinium. In situ enzymatic polymerization of the anilinium monolayer took place using horseradish peroxidase (HRP) enzyme and its substrate H2O2. The assembly steps were characterized by variable angle spectroscopic ellipsometry (VASE), UV-Vis-NIR spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy (XPS), contact potential difference (CPD) and scanning force microscopy (SFM). The SFM measurements were divided between ex situ analysis in which morphology of the obtained layers was determined, and in situ analysis which provided information on the dynamic process of the enzymatic polymerization.

Electrostatically self-assembled poly(4-vinylpyridine-co-vinylpyridinium-chloride)-based LED

We demonstrate the fabrication and characterization of an organic light-emitting diode (OLED) device based on self-assembled poly(4-vinyl-pyridine) (P4VPy) with poly(N-vinyl-carbazole) (PVK) and 2-(4-biphenylyl)-5-(4-tert-butyphenyl)-1,3,4-oxidiazole (PBD) as transport layers. The self-assembly is based on the electrostatic attraction of oppositely-charged polymers. We have shown here that we can use this self-assembled methodology to fabricate alternating multilayers, not only by the poly(phenyl-vinylene) (PPV) and derivatives, but also by partial protonation of P4VPy, by which the charge on P4VPy is generated by the protonation process. The multilayered structures are characterized by specular X-ray reflectivity (XRR), UV absorption, photoluminescence (PL) and electroluminescence (EL).

Led device based on self assembled poly(4-vinylpyridine) with pvk and pbd as transport layer

Abstract We demonstrate the fabrication and characterization of LED device based on self-assembled films of (PVPy/SPS) where PVPy stands for Poly(4-vinyl pyridine) with additional transport layers such as poly-vinyl-carbazole (PVK) and 2-(4-biphenylyl)-5-(4-tertbutyphenyl) -1,3,4-oxidiazole (PBD). The self-assembly is based on the electrostatic interaction; the charge on PVPy is generated by the protonation process. The EL properties of the device ITO/PVK/(PVPy/SPS)/Al and ITO/(PVPy/SPS)/PBD/Al are measured and discussed.

Continuous thermal control of hydrophilicity/hydrophobicity changes of hybrid films and of their directionality: Kinetics and substrate effects

A successful methodology for obtaining hybrid films which allow thermal triggering and continuous, irreversible, control of their hydrophilicity/hydrophobicity nature was developed. Two types of poly(dimethylsiloxane)-silica (PDMS@SiO2) films were prepared for that purpose: A hydrophilic film in which the thermal treatment causes an irreversible gradual increase of hydrophobicity; and a hydrophobic film that turns more hydrophilic upon thermal treatment. The opposite directionality of the change is dictated by the film substrate, on which the same hybrid is deposited. In both cases the thermal treatment induced a phase separation which caused the change in hydrophobicity. The magnitude of change in hydrophilicity/hydrophobicity is continuously controllable in both types of films by either the temperature or heating time. The films were characterized before and after heating by a variety of methods, including contact angle (CA) measurements with the sessile drop and the tilting plate methods, and by X-ray photoelectron spectroscopy (XPS) analysis. A thorough kinetic study was carried out, following the progress of the changes in the wettability property of the surfaces. The kinetics analyses proved that the changes in the wettability in all cases are due to phase separation processes, the directionality of which is determined by the treatment of the substrate on which the films are deposited. By monitoring the change of wettability (ΔCA) at various temperatures, an Arrhenius plot was obtained from which the activation energy and Arrhenius pre-exponential factor for the phase separation were derived, corroborating the proposed mechanism. To the best of our knowledge, this is the first use of phase separation behavior of a hybrid film in order to apply irreversible, thermally controllable change of surface wettability, tailored to proceed in opposite directions, and the first kinetic study of such a process.

Molecular and Ionic Dipole Effects on the Electronic Properties of Si/SiO2 Grafted Alkylamine Monolayers

In this work, we demonstrate the tunability of electronic properties of Si/SiO2 substrates by molecular and ionic surface modifications. The changes in the electronic properties such as the work function (WF) and electron affinity were experimentally measured by the contact potential difference technique and theoretically supported by density functional theory calculations. We attribute these molecular electronic effects mainly to the variations of molecular and surface dipoles of the ionic and neutral species. We have previously shown that for the alkylhalide monolayers, changing the tail group from Cl to I decreased the WF of the substrate. Here, we report on the opposite trend of WF changes, that is, the increase of the WF, obtained by using the anions of these halides from Cl- to I-. This trend was observed on self-assembled alkylammonium halide (-NH3+ X-, where X- = Cl-, Br-, or I-) monolayer-modified substrates. The monolayers formation was supported by ellipsometry measurements, X-ray photoelectron spectroscopy, and atomic force microscopy. Comparison of the theoretical and experimental data suggests that the ionic surface dipole depends mainly on the polarizability and the position of the counter halide anion along with the organization and packaging of the layer. The described ionic modification can be easily used for facile tailoring and design of the electronic properties Si/SiO2 substrates for various device applications.