Rabah Boukherroub

Preparation of Superhydrophobic Coatings on Zinc as Effective Corrosion Barriers

Stable superhydrophobic films with a contact angle of 151 +/- 2 degrees were prepared on zinc substrates by a simple immersion technique into a methanol solution of hydrolyzed 1H,1H,2H,2H-perfluorooctyltrichlorosilane [CF3(CF2)5(CH2)2SiCl3, PFTS] for 5 days at room temperature followed by a short annealing at 130 degrees C in air for 1 h. The superhydrophobic film provides an effective corrosion-resistant coating for the zinc interface when immersed in an aqueous solution of sodium chloride (3% NaCl) for up to 29 days. The corrosion process was investigated by following the change of the water contact angle over time and by electrochemical means. The results are compared to those of unprotected zinc interfaces.

Sensing using localised surface plasmon resonance sensors

The bright colours of noble metal particles have attracted considerable interest since historical times, where they were used as decorative pigments in stained glass windows. More recently, the tuneable optical properties of metal nanoparticles and their addressability via spectroscopic techniques have brought them back into the forefront of fundamental and applied research fields. Much of the recent attention concerning metal nanoparticles such as gold and silver has been their use as small-volume, ultra-sensitive label-free optical sensors. Plasmonic nanoparticles act in this case as transducers that convert changes in the local refractive index into spectral shifts of the localized surface plasmon resonance (LSPR) band. This LSPR-shift assay is a general technique for measuring binding affinities and rates from any molecule that induces a change in the local refractive index around the metallic nanostructures. By attaching molecular recognition elements (chemical or biological ligands) on the nanostructures, specificity and selectivity to the analyte of interest are introduced into the nanosensor. In this review, we will discuss the different methods used to fabricate plasmonic nanosensors. A special emphasis will be given to techniques used to link plasmonic nanostructures to surfaces. While the difference between colorimetric and refractive index sensing approaches will be briefly described, the importance to distinguish between bulk refractive index (RI) sensing and molecular near-field refractive index sensing will be discussed. The recent progress made in the development of novel surface functionalization strategies together with the formation of optically and mechanically stable LSPR sensors will be highlighted.

The preparation of flat H–Si(111) surfaces in 40% NH4F revisited

Abstract The reasons why ideally flat H–Si(111) surface can be prepared by NH 4 F etching are investigated from correlation between AFM observations and experimental conditions used for etching. It is shown that pitting may be completely suppressed if a one side polished wafer is immersed in an oxygen free solution. An analytical electrochemical study of the (111) and rough face of the same n-Si wafer is presented to yield insight into observations.

Reduction and Functionalization of Graphene Oxide Sheets Using Biomimetic Dopamine Derivatives in One Step

An easy and environmentally friendly chemical method for the simultaneous reduction and noncovalent functionalization of graphene oxide (GO) using dopamine derivatives is described. The reaction takes place at room temperature under ultrasonication of an aqueous suspension of GO and a dopamine derivative. X-ray photoelectron spectroscopy, FT-IR spectroscopy, and cyclic voltammetry characterizations revealed that the resulting material consists of graphene functionalized with the dopamine derivative. This one-step protocol is applied for simultaneous reduction and functionalization of graphene oxide with a dopamine derivative bearing an azide function. The chemical reactivity of the azide function was demonstrated by a postfunctionalization with ethynylferrocene using the Cu(I) catalyzed 1,3-dipolar cyloaddition.

Lysozyme detection on aptamer functionalized graphene-coated SPR interfaces.

The paper reports on a surface plasmon resonance (SPR)-based approach for the sensitive and selective detection of lysozyme. The SPR sensor consists of a 50 nm gold film coated with a thin film of reduced graphene oxide (rGO) functionalized with anti-lysozyme DNA aptamer. The SPR chip coating with rGO matrix was achieved through electrophoretic deposition of graphene oxide (GO) at 150 V. Electrophoretic deposition resulted in partial reduction of GO to rGO with a thickness depending on the deposition time. For very short time pulses of 20 s, the resulting rGO film had a thickness of several nanometers and was appropriate for SPR sensing. The utility of the graphene-based SPR sensor for the selective and sensitive detection of proteins was demonstrated using lysozyme as model protein. Functionalization of rGO matrix with anti-lysozyme DNA aptamer through π-stacking interactions allowed selective SPR detection of lysozyme. The graphene-based SPR biosensor provides a means for the label-free, concentration-dependent and selective detection of lysozymes with a detection limit of 0.5 nM.

Recent advances in the development of graphene-based surface plasmon resonance (SPR) interfaces

Surface plasmon resonance (SPR) is a powerful technique for measurement of biomolecular interactions in real-time in a label-free environment. One of the most common techniques for plasmon excitation is the Kretschmann configuration, and numerous studies of ligand–analyte interactions have been performed on surfaces functionalized with a variety of biomolecules, for example DNA, RNA, glycans, proteins, and peptides. A significant limitation of SPR is that the substrate must be a thin metal film. Post-coating of the metal thin film with a thin dielectric top layer has been reported to enhance the performance of the SPR sensor, but is highly dependent on the thickness of the upper layer and its dielectric constant. Graphene is a single-atom thin planar sheet of sp2 carbon atoms perfectly arranged in a honeycomb lattice. Graphene and graphene oxide are good supports for biomolecules because of their large surface area and rich π conjugation structure, making them suitable dielectric top layers for SPR sensing. In this paper, we review some of the key issues in the development of graphene-based SPR chips. The actual challenges of using these interfaces for studying biomolecular interactions will be discussed and the first examples of the use of graphene-on-metal SPR interfaces for biological sensing will be presented.

The synthesis of citrate-modified silver nanoparticles in an aqueous suspension of graphene oxide nanosheets and their antibacterial activity

A composite material consisting of silver nanoparticles (Ag NPs) deposited on graphene oxide (GO) nanosheets is prepared by chemical reduction of Ag metal ions by sodium borohydride (NaBH4) in the presence of trisodium citrate acting as a stabilizing agent to prevent agglomeration of the nanoparticles. The synthesized GO/Ag NPs composite was characterized by UV/vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM analysis confirmed a high density of Ag NPs on the GO nanosheets with a particle size range of 2-25 nm. The activity of the GO/Ag NPs suspension as an antibacterial agent against Gram positive bacteria Staphylococcus aureus and Bacillus subtilis was investigated. The percentage of the killing bacterial colonies by Ag NPs (without GO) is found to be 96-97% while 100% of killing bacterial colonies is only obtained using GO/Ag NPs suspension. Moreover, it was also observed that leakage of sugars and proteins from the cell wall of both S. aureus and B. subtilis in interaction with GO/Ag NPs suspension is higher compared to Ag NPs (without GO) and GO nanosheets.

Stabilization of porous silicon electroluminescence by surface passivation with controlled covalent bonds

Stabilization of electroluminescence (EL) from nanocrystalline porous silicon (PS) diodes has been achieved by replacing silicon–hydrogen bonds terminating the surface of nanocrystalline silicon with more stable silicon–carbon (Si–C) and silicon–oxygen (Si–O–C) bonds without significant effects on the electrical properties. The surface modification is performed by a thermal treatment of partially and anodically oxidized PS sample at about 90 °C with organic molecules: 1-decene, ethyl undecylenate, or n-caprinaldehyde. The porous silicon device whose surface has been modified with stable covalent bonds shows no degradation in the EL efficiency and EL output intensity under dc operation for several hours. The improved stability can be attributed to the high chemical resistance of Si–C and Si–O–C bonds against current-induced surface oxidation associated with the generation of nonradiative defects.

Quantitative testing of robustness on superomniphobic surfaces by drop impact

The quality of a liquid-repellent surface is quantified by both the apparent contact angle θ(0) that a sessile drop adopts on it and the value of the liquid pressure threshold the surface can withstand without being impaled by the liquid, hence maintaining a low-friction condition. We designed surfaces covered with nanowires obtained by the vapor-liquid-solid (VLS) growth technique that are able to repel most of the existing nonpolar liquids including those with very low surface tension as well as many polar liquids with moderate to high surface tension. These superomniphobic surfaces exhibit apparent contact angles ranging from 125 to 160° depending on the liquid. We tested the robustness of the surfaces against impalement by carrying out drop impact experiments. Our results show how this robustness depends on Youngs contact angle θ(0) related to the surface tension of the liquid and that the orientational growth of nanowires is a favorable factor for robustness.

Direct Functionalization of Nanodiamond Particles Using Dopamine Derivatives

The article reports on the strong linking of dopamine derivatives as a simple and a versatile strategy for the surface functionalization of hydroxyl-terminated nanodiamond (ND-OH) particles. Azide- (ND-N(3)) or poly-N-isopropylacrylamide-terminated (ND-PNIPAM) particles were obtained from ND-OH particles through the reaction with the corresponding dopamine derivatives. The azide-terminated ND particles were further derivatized with a fluorescent probe, alkynyl-pyrene, via copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition. The modified ND particles were characterized using transmission Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, electrochemical measurements, thermogravimetric analysis (TGA), and particle size measurements. The surface loading of ND particles with dopamine was estimated from TGA and UV-vis spectroscopy and was found to be around 0.27 mmol g(-1). Because of its simple, gentle nature and versatility, the chemistry developed in this work can be used as an avenue for the preparation of functional nanodiamond particles for various applications.