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Essential to the success of any surface-based carbohydrate biochip technology is that interactions of the particular interface with the target protein be reliable and reproducible and not susceptible to unwanted nonspecific adsorption events. This condition is particularly important when the technology is intended for the evaluation of low-affinity interactions such as those typically encountered between lectins and their monomeric glycan ligands. In this paper, we describe the fabrication of glycan (mannoside and lactoside) monolayers immobilized on hydrogenated crystalline silicon (111) surfaces. An efficient conjugation protocol featuring a key "click"-based coupling step has been developed which ensures the obtention of interfaces with controlled glycan density. The adsorption behavior of these newly developed interfaces with the lectins, Lens culinaris and Peanut agglutinin, has been probed using quantitative IR-ATR and the data interpreted using various isothermal models. The analysis reveals that protein physisorption to the interface is more prevalent than specific chemisorption for the majority of washing protocols investigated. Physisorption can be greatly suppressed through application of a strong surfactinated rinse. The coexistence of chemisorption and physisorption processes is further demonstrated by quantification of the amounts of adsorbed proteins distributed on the surface, in correlation with the results obtained by atomic force microscopy (AFM). Taken together, the data demonstrates that the nonspecific adsorption of proteins to these glycan-terminated surfaces can be effectively eliminated through the proper control of the chemical structure of the surface monolayer combined with the implementation of an appropriate surface-rinse protocol., (Copyright © 2015 Elsevier Inc. All rights reserved.)

A key challenge in the development of glycan arrays is that the sensing interface be fabricated reliably so as to ensure the sensitive and accurate analysis of the protein-carbohydrate interaction of interest, reproducibly. These goals are complicated in the case of glycan arrays as surface sugar density can influence dramatically the strength and mode of interaction of the sugar ligand at any interface with lectin partners. In this Article, we describe the preparation of carboxydecyl-terminated crystalline silicon (111) surfaces onto which are grafted either mannosyl moieties or a mixture of mannose and spacer alcohol molecules to provide "diluted" surfaces. The fabrication of the silicon surfaces was achieved efficiently through a strategy implicating a "click" coupling step. The interactions of these newly fabricated glycan interfaces with the lectin, Lens culinaris, have been characterized using quantitative infrared (IR) spectroscopy in the attenuated total geometry (ATR). The density of mannose probes and lectin targets was precisely determined for the first time by the aid of special IR calibration experiments, thus allowing for the interpretation of the distribution of mannose and its multivalent binding with lectins. These experimental findings were accounted for by numerical simulations of lectin adsorption.

Various poly(ethylene glycol) monomethyl ether moieties were grafted onto hydrogenated silicon surfaces in order to investigate the influence of the molecular design on the antifouling performance of such coatings. The grafted chains were either oligo(ethylene oxide) chains (EG)(n)OMe bound to silicon via Si-O-C covalent bonds, or hybrid alkyl/oligo(ethylene oxide) chains C(p)(EG)(n)OMe bound via Si-C covalent bonds (from home-synthesized precursors). Quantitative IR spectroscopy gave the molecular coverage of the grafted layers, and AFM imaging demonstrated that a proper surfactinated rinse yields C(p)(EG)(n)OMe layers free of unwanted residues. The protein-repellent character of these grafted layers (here, toward BSA) was studied by IR and AFM imaging. C(p)(EG)(n)OMe layers exhibit a lower surface concentration than (EG)(n)OMe layers, because of the presence of a solvent in the grafting solution; they however demonstrate high resistance against BSA adsorption for high values of the n/p ratio and a higher stability than (EG)(n)OMe. This behavior is consistently explained by the poor ordering capability of the alkyl part of the layer, contrary to what is observed for similar layers on Au, and the key role of an entangled arrangement of the ethylene oxide chains which forms when these chains are long enough.

The use of an amorphous silicon-carbon alloy overcoating on silver nanostructures in a localized surface plasmon resonance (LSPR) sensing platform allows for decreasing the detection limit by an order of magnitude as compared to sensors based on gold nanostructures deposited on glass. In addition, silver based multilayer structures show a distinct plasmonic behaviour as compared to gold based nanostructures, which provides the sensor with an increased short-range sensitivity and a decreased long-range sensitivity.

The paper reports on a novel surface plasmon resonance (SPR) substrate architecture based on the coating of a gold (Au) or silver (Ag) substrate with 5 nm thin amorphous silicon-carbon alloy films. Ag/a-Si(1-x)C(x):H and Au/a-Si(1-x)C(x):H multilayers are found to provide a significant advantage in terms of sensitivity over both Ag and Au for SPR refractive index sensing. The possibility for the subsequent linking of stable organic monolayers through Si-C bonds is demonstrated. In a proof-of-principle experiment that this structure can be used for real-time biosensing experiments, amine terminated biotin was covalently linked to the acid-terminated SPR surface and the specific streptavidin-biotin interaction recorded.

This paper describes a novel platform for preparing localized surface plasmon resonance (LSPR) sensing surfaces. It is based on the coating of gold nanostructures deposited on glass with an amorphous silicon-carbon alloy overcoating. The interest in coating the Au NSs with an amorphous silicon-carbon alloy resides in the possibility of incorporating carboxyl functions directly onto the surface via Si-C covalent bonds. This permits the use of hyrdosilylation reactions to modify the sensor surface. The use of this multilayer structure for the detection of hybridization events is discussed., (Copyright 2009 Elsevier B.V. All rights reserved.)

Silicon is considered as a promising anode material for Li-ion batteries because of its record capacity (about 4000 mAh g −1 ), more than ten times higher than that of graphite, which is used in commercial batteries. However, its use is severely limited, due to the important swelling of the material in the loaded (lithiated) state (more than 300%), and the instability of the solid-electrolyte interphase layer (SEI). The poor mechanical stability and chemical passivation properties make the cyclability of silicon electrodes far from being able to meet the requirements for battery systems and have motivated a wealth of studies and many proposals to circumvent these limitations. In this review, an outlook of the material research devoted to silicon electrodes for Li-ion batteries is presented, with special attention to material fundamental properties associated with various forms of silicon used in this context. The strategies associated with silicon nano-structuration and with the elaboration of composite materials, aimed at improving the electrode cyclability, are deliberately kept out of this scope. On the opposite, the interest of in situ techniques for the study of silicon electrodes is stressed, and the major results obtained using the latter techniques briefly reviewed. [ABSTRACT FROM AUTHOR]

The use of the hydrogenated surface of silicon is hampered by its chemical instability by surface oxidation. The researchers have attempted to modify this surface by direct grafting through the establishment of covalent silicon-carbon bonds from the reaction of chemical species on the surface. Different grafting methods can be implemented for the preparation of grafted surfaces. The choice of an electrochemical reaction allows fast grafting from the hydrogenated surface. We studied the formation of a phenyl layer by electrochemical reduction of aryl diazonium salts (BF4-,+N2-ph- OCH3) on a p-Si-H (111) electrode in an aqueous medium (0.05M H2SO4 + 0.05M HF). The grafting of an organic layer by reduction is confirmed by the observation of a cyclic voltammetry peak around -0.3V/SCE. In-situ infrared spectroscopy (IR) analysis allows to identify the chemical functions present on the grafted surface, allowing a direct monitoring of the grafting reaction. [ABSTRACT FROM AUTHOR]

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The formation of macropores in silicon during electrochemical etching processes has attracted much interest. Experimental evidences indicate that charge transport in silicon and in the electrolyte should realistically be taken into account in order to be able to describe the macropore morphology. However, up to now, none of the existing models has the requested degree of sophistication to reach such a goal. Therefore, we have undertaken the development of a mathematical model (phase-field model) to describe the motion and shape of the silicon/electrolyte interface during anodic dissolution. It is formulated in terms of the fundamental expression for the electrochemical potential and contains terms which describe the process of silicon dissolution during electrochemical attack in a hydrofluoric acid (HF) solution. It should allow us to explore the influence of the physical parameters on the etching process and to obtain the spatial profiles across the interface of various quantities of interest, such as the hole concentration, the current density, or the electrostatic potential. As a first step, we find that this model correctly describes the space charge region formed at the silicon side of the interface. [ABSTRACT FROM AUTHOR]

Controlled electrochemical formation of porous silica can be realized in dilute aqueous, neutral-pH, fluoride medium. Formation of a porous film is initiated by sweeping the potential applied to silicon to values higher than 20 V. Film formation, reaching a steady state, may be pursued in a wide range of potentials, including lower potentials. The origin of a threshold potential for porous film initiation has been explained quantitatively. All of the films appear mesoporous. Films grown at high potentials exhibit a variety of macrostructures superimposed on the mesoporosity. These macrostructures result from selective dissolution of silica induced by local pH lowering due to oxygen evolution. Films grown at potentials lower than 15 V appear uniform on the micrometer scale. However, all of the films also exhibit a stratified structure on the scale of a few tens of nanometres. This periodic structure can be traced back to the oscillatory behavior observed during the electrochemical dissolution of silicon in fluoride medium. It suggests that periodic breaking of the growing film may be responsible for this morphology. [ABSTRACT FROM AUTHOR]

Abstract: Si-based photocathodes have been investigated for use as counterelectrodes in oxide-based photoelectrochemical water purification cells. Bare p-type silicon (either crystalline silicon or amorphous hydrogenated silicon a-Si:H obtained by plasma deposition) is found to exhibit poor catalytic properties for the photoelectrochemical reduction of dioxygen. Improvement in photocathode performance has been sought through the deposition of small amounts of platinum on the Si surface, and improvement in electrode stability has been sought through the formation of a thin organic layer covalently anchored to the Si surface, or through the deposition of a thin conductive-oxide film. Combining both treatments allows to obtain photocathodes with performances just slightly better than those of a bare Pt cathode. Much larger improvements in photocathode performance (+0.9 V shift in the voltammetric curves) have been obtained by using a p+/i/n+ a-Si:H structure with similar coatings. The concept is readily scalable to large-area electrodes, which appears promising for practical sunlight powered water purification reactors. To cite this article: J.-N. Chazalviel et al., C. R. Chimie 9 (2006) . [Copyright &y& Elsevier]

Abstract: Direct grafting of organic monolayers on Si is of prime interest in order to give specific properties to a silicon surface. However, for microelectronics applications, this possibility is hampered by the limited stability of the grafted layers. It has been previously established that alkyl layers attached to Si surfaces through Si–C bonds become unstable at 250–300°C, by desorption of alkenes. Changing the nature of the bonding to the surface might allow one to circumvent this desorption pathway and increase the layer stability. In our work, decanol and decyl aldehyde are reacted with the Si(111)–H surface at ∼100°C during 20h in order to obtain alkoxy monolayers. FTIR measurements performed in ATR geometry show that the grafted molecule surface coverage is on the order of 33% after reaction with decanol and 50% after reaction with decyl aldehyde. Characterization by AFM essentially reveals that the morphology of the grafted surfaces is unaffected as compared to that of Si–H surfaces. However, the edges of the terraces at alcohol-grafted surfaces exhibit some pitting, probably due to the presence of water in the grafting liquid. Thermal stability studies show that alkoxy chains progressively disappear from the Si surface between 200 and 400°C. From the CH2/CH3 ratio in the CH region (2760–3070cm−1), it appears that the chains undergo progressive dissociation by C–C bond breaking before their complete disappearance from the surface. Therefore, the thermal behaviour of alkoxy monolayers appears quite distinct from that of alkyl monolayers that tend to leave the surface in a much narrower temperature range (250–350°C), essentially via breaking of the Si–C bonds. [Copyright &y& Elsevier]

Silicon electrodes represent a great potential on increasing the energy density of Li-ion batteries, but stabilization during cycling is an important issue to be solved for enabling a reliable application. Such stabilization has been sought for by surface grafting of hydrogenated amorphous silicon (a-Si:H) electrodes. Grafting a molecular monolayer of carboxydecyl moieties (acid grafting) or poly(oxoethylene) (PEG) chains decreases the irreversible capacity and stabilizes the solid-electrolyte interphase (SEI) on a-Si:H. FTIR spectroscopy confirms a breathing behavior of the SEI layer at each step of charge/discharge through in-situ experiments, but also shows that acid grafting reduces this behavior to a large extent. In this way, acid grafting decreases the amount of charge irreversibly consumed for the formation of a spontaneous SEI and stabilizes the SEI along the electrochemical cycles. [ABSTRACT FROM AUTHOR]