The association of a mycotoxinochratoxin A (OTA)with a high-affinity DNA aptamer (anti-OTA) immobilized on a functionalized surface has been investigated at the molecular level. Anti-OTA aptamers ...are coupled by aminolysis in several steps on an acid-terminated alkyl monolayer grafted on a silicon substrate, and Fourier transform infrared spectroscopy in attenuated total reflection geometry is used to assess the immobilization of anti-OTA (in its unfolded single-strand form) and determine its areal density (ca. 1.4/nm2). IR spectra further demonstrate that the OTA/anti-OTA association is efficient and selective and that several association/dissociation cycles may be conducted on the same surface. The areal density of OTA measured after association on the surface (IR spectroscopy) and after dissociation from the surface (UV–vis spectroscopy) falls in the range 0.16–0.3/nm2 which is close to the areal density of a closed-packed monolayer of anti-OTA aptamers folded to form their G-quadruplex structure. The interactions between OTA and its aptamer at the surface are discussed with the help of density functional theory calculationsto identify the complex IR vibrational modes of OTA in solutionand UV–vis spectroscopyto determine the protonation state of the adsorbing species (i.e., OTA dissolved in the buffer solution).
Silicon nitride is used for many technological applications, but a quantitative knowledge of its surface chemistry is still lacking. Native oxynitride at the surface is generally removed using ...fluorinated etchants, but the chemical composition of surfaces still needs to be determined. In this work, the thinning (etching efficiency) of the layers after treatments in HF and NH4F solutions has been followed by using spectroscopic ellipsometry. A quantitative estimation of the chemical bonds found on the surface is obtained by a combination of infrared absorption spectroscopy in ATR mode, X-ray photoelectron spectroscopy, and colorimetry. Si–F bonds are the majority species present at the surface after silicon nitride etching; some Si–OH and a few Si–NH x bonds are also present. No Si–H bonds are present, an unfavorable feature for surface functionalization in view of the interest of such mildly reactive groups for achieving stable covalent grafting. Mechanisms are described to support the experimental results, and two methods are proposed for generating surface SiH species: enriching the material in silicon, or submitting the etched surface to a H2 plasma treatment.
Carbohydrate arrays are potentially one of the most attractive tools to study carbohydrate-based interactions. This paper describes a new analytical platform that exploits metal-enhanced fluorescence ...for the sensitive and selective screening of carbohydrate-lectin interactions. The chip consists of a glass slide covered with gold nanostructures, postcoated with a thin layer of amorphous silicon–carbon alloy (a-Si0.8C0.2:H). An immobilization strategy based on the formation of a covalent bond between propargyl-terminated glycans and surface-linked azide groups was used to attach various glycans at varying surface densities onto the interface and to fabricate a carbohydrate array via efficient local “click” chemistry strategy. The specific association of the new interface with fluorescently labeled lectins was assessed by fluorescence imaging and an excellent selectivity to specific proteins was achieved. Optimization of the surface architecture and the plasmonic transducer resulted in an enhancement of the fluorescence intensity by 1 order of magnitude, when compared to the corresponding substrate devoid of gold nanostructures. The limit of detection (LOD) of such microarrays is in the picomolar range, making it a promising system for development in pharmaceutical or biomedical applications.
Surface-enhanced Raman scattering (SERS), based on the enhancement of the Raman signal of molecules positioned within a few nanometres from a structured metal surface, is ideally suited to provide ...bacterial-specific molecular fingerprints which can be used for analytical purposes. However, for some complex structures such as bacteria, the generation of reproducible SERS spectra is still a challenging task. Among the various factors influencing the SERS variability (such as the nature of SERS-active substrate, Raman parameters and bacterial specificity), we demonstrate in this study that the environment of Gram-positive and Gram-negative bacteria deposited on ultra-thin silver films also impacts the origin of the SERS spectra. In the case of densely packed bacteria, the obtained SERS signatures were either characteristic of the secretion of adenosine triphosphate for
Staphylococcus aureus
(
S. aureus
) or the cell wall and the pili/flagella for
Escherichia coli
(
E. coli
), allowing for an easy discrimination between the various strains. In the case of isolated bacteria, SERS mapping together with principal component analysis revealed some variabilities of the spectra as a function of the bacteria environment and the bactericidal effect of the silver. However, the variability does not preclude the SERS signatures of various
E. coli
strains to be discriminated.
Graphical abstract
The structure of mixed acid/decyl monolayers (MLs) grafted on oxide-free Si(111) surfaces by photochemical hydrosilylation in a mixture of neat undecylenic acid and 1-decene is studied in detail. ...After appropriate surface cleaning of the as-grafted surfaces, atomic force microscopy (AFM) (topography and phase imaging) and calibrated FTIR analysis demonstrate that a mixed monolayer is formed, free of residue. When the acid-molecule fraction (ΓSOL) is >0.1, mixed MLs are homogeneous on the scale of observations and they are only slightly enriched in acid chains with respect to the solution. Conversely, when ΓSOL < 0.1, the acid chain fraction within the ML becomes quasi-independent of the solution composition and may become much larger than ΓSOL. In addition, dark domains are observed in AFM phase images. Correlations between the characteristic parameters of νCO IR bands and AFM phase images suggest a strong phase separation of acid and alkyl chains at various length scales. A model involving a structuration of the grafting solution is proposed to explain observations.
Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This ...contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate (MEMA), used as a spacer, for the ATRP synthesis of copolymers, and then post-functionalized with a propargyl chromium salen complex. The controlled homopolymerization of MEMA by ATRP was firstly described and proved to be more controlled in molar mass than that of AZMA for conversions up to 63%. The ATRP copolymerization of both monomers made it possible to control the molar masses and the composition, with nevertheless a slight increase in the dispersity (from 1.05 to 1.3) when the incorporation ratio of AZMA increased from 10 to 50 mol%. These copolymers were post-functionalized with chromium salen units by click chemistry and their activity was evaluated in the asymmetric ring opening of cyclohexene oxide with trimethylsilyl azide. At an equal catalytic ratio, a significant increase in enantioselectivity was obtained by using the copolymer containing the largest part of salen units, probably allowing, in this case, the more favorable bimetallic activation of both the engaged nucleophile and electrophile. Moreover, the catalytic polymer was recovered by simple filtration and re-engaged in subsequent catalytic runs, up to seven times, without loss of activity or selectivity.
Silicon as anode material for Li-ion batteries Ozanam, François; Rosso, Michel
Materials science & engineering. B, Solid-state materials for advanced technology,
11/2016, Letnik:
213
Journal Article
Recenzirano
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.
In the context of energy transition, irradiation is a powerful tool to mimic quickly the modification of electrode materials upon charge/discharge cycles in lithium-ion batteries. In this study, the ...evolution of the surface of silicon nanoparticles upon irradiation in two electrolytes, containing or not fluoroethylene carbonate (FEC), was studied. In the presence of FEC, irradiation leads to the formation of a homogeneous layer of a few nanometers thick, covering the whole surface of the nanoparticles. The formation of an artificial solid electrolyte interphase (SEI) layer through radiolysis is thus achieved. Without FEC, only patches of degradation products are formed on the nanoparticle surfaces for the same irradiation dose. In the absence of FEC, Li x PF y O z salts are formed. In the presence of FEC, Li x PO y , LiF, and Si–F bonds are generated. In both cases, the interphase contains Li2CO3 and a polymer containing ethylene carbonate units. Slightly different polymers are formed at the surface of nanoparticles in the presence or absence of FEC, i.e., more cross-linked in the former case. The elastomeric properties of the polymer formed in the presence of FEC are thought to be responsible for the formation of the homogeneous layer on the Si surfaces, leading to the generation of an artificial solid SEI through the radiolysis process. This SEI, however, prevents the efficient transfer of Li+ ions, and more work is required to optimize its intrinsic (electro)chemical properties.
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