Jean-Marc Krafft

Optimized immobilization of gold nanoparticles on planar surfaces through alkyldithiols and their use to build 3D biosensors.

This paper describes a controlled way to immobilize gold nanoparticles on planar gold surfaces and the use of the resulting 3D platform to build up a 3D biosensor. The surface was first functionalized by grafting hexanedithiol, this molecule has 2 thiol end groups, which enables its chemical grafting to planar gold while retaining a free thiol group to attach nanoparticles. This step was optimized by varying experimental parameters such as solvent, temperature and immersion time. The grafting was monitored by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). The high resolution XPS sulfur peak made clear the existence of two contributions, S bound to gold and free S, thus led us to determine the optimal conditions to graft hexanedithiol in an extended conformation. 15 nm spherical gold nanoparticles were then immobilized on the resulting surface and their presence was evidenced by surface enhanced Raman spectroscopy (SERS) and atomic force microscopy (AFM). The resulting gold layer was used to build up a 3D biosensor by grafting protein A (PrA), rabbit immunoglobulin (rIgG), and bovine serum albumin (BSA), respectively. Each step was characterized by PM-IRRAS then compared to the results on planar gold surface. Despite the small size of particles and their rather low density on the planar surface, the amount of immobilized proteins, starting from PrA, was almost doubled. The amount of rIgG fixed on the 3D layer was also significantly increased ( approximately 4 times higher than on planar surfaces), however accompanied by a slight decrease of their accessibility, checked by assaying the recognition of a secondary IgG. This work demonstrates the feasibility and interest of building arrays of nanoparticles to immobilize molecular receptors; it also shows that controlling the conditions of elaboration of the biosensor at each step is determining for optimizing the number of molecular receptors.

Optimizing the immobilization of gold nanoparticles on functionalized silicon surfaces: amine- vs thiol-terminated silane

Immobilization of gold nanoparticles on planar surfaces is of great interest to many scientific communities; chemists, physicists, biologists, and the various communities working at the interfaces between these disciplines. Controlling the immobilization step, especially nanoparticles dispersion and coverage, is an important issue for all of these communities. We studied the parameters that can influence this interaction, starting with the nature of the terminal chemical function. Thus, we have carefully grafted silanes terminated by either amine or thiol groups starting from aminopropyltriethoxysilane (APTES) or mercaptopropyltriethoxysilane. We also changed the chain length for thiol-terminated layers through covalent grafting of mercaptoundecanoic acid (MUA) on APTES-modified layers, and the protocol of nanoparticles deposition to evaluate whether other factors must be taken into consideration to rationalize this interaction. The formed layers were characterized by X-ray photoelectron spectroscopy and gold nanoparticles deposition was monitored by scanning electron microscopy and surface-enhanced Raman scattering. We observed significant differences in terms of nanoparticles dispersion and density depending on the nature of the chemical layer on silicon. The use of ultrasounds during the deposition process was very efficient to limit aggregates formation. The optimal deposition procedures were obtained through the use of APTES and APTES/MUA functionalization. They were compared in terms of coverage, dispersion, and densities of isolated nanoparticles. The APTES/MUA surfaces clearly showed better results that may arise from both the longer chain and the dilution of thiol end groups.

Characterization of zinc hydroxynitrates by diffuse reflectance infrared spectroscopy--structural modifications during thermal treatment.

Four zinc hydroxynitrates are known, but only the Infrared spectrum of Zn5(OH)8(NO3)2.2H2O is reported in the literature. Here, we report the IR spectra of the other three zinc hydroxynitrates, namely Zn(OH)(NO3).H2O, Zn3(OH)4(NO3)2 and Zn5(OH)8(NO3)2. The positions of the bands of the nitrate groups between 1000 and 1600 cm(-1) are discussed in relation to the structure of these compounds. The modifications of these IR spectra with temperature are consistent with previous studies on the thermal decomposition of these compounds.

Catalysts for aromatics hydrogenation in presence of sulfur: reactivities of nanoparticles of ruthenium metal and sulfide dispersed in acidic Y zeolites

Zeolite-supported ruthenium sulfide and ruthenium metal catalysts were prepared with various Si/Al ratios, with and without extra-framework Al species. They were characterized by means of NMR, HRTEM and FTIR. For the sulfided catalysts, the activity for the tetralin hydrogenation, carried out in presence of H2S was very high and roughly 10 times the activity (expressed per gram of catalyst) of an industrial hydrotreating catalyst, i.e. NiMo/Al2O3. The differences in activities within the series of zeolites were discussed in terms of dispersion of the active phase and acidity of the zeolitic support. The catalytic properties of the metal catalysts were much lower than those of the sulfided catalysts in similar testing conditions.

Selective Modification of the Acid–Base Properties of Ceria by Supported Au

Au supported on CeO(2) prepared by deposition-precipitation with urea leads to a basic catalyst. Au acts in two ways as surface modifier. First, Au selectively interacts with Ce(4+) cations by either blocking access to or reducing Ce(4+) to Ce(3+). Second, the resulting Au atoms (presumably as Au(+) ions) act as soft, weak Lewis acid sites stabilizing carbanion intermediates and enhancing hydride abstraction in the dehydrogenation of alcohols. In consequence, the thus-synthesized basic catalyst catalyzes the dehydrogenation of propan-2-ol to acetone with high efficiency and without notable deactivation. Additionally, the dehydration pathway of propan-2-ol is eliminated, as Au also quantitatively blocks access to strongly acidic Ce(4+) ions or reduces them to Ce(3+).

Study of Residual Oxygen Species over Molybdenum Carbide Prepared During In Situ DRIFTS Experiments

In situ diffuse reflectance infrared Fourier transform spectroscopy was applied to monitor the temperature-programmed carburization of molybdenum trioxide. This technique indicated the existence of surface residual oxygen species on Mo2C synthesized even up to 973 K, indicating incomplete carburization. The presence of residual oxygen species on the carbide was deduced from the IR band at 790 cm-1. It was observed that the Mo2C sample, prepared with a final temperature of 1023 K, presented a higher density of sites titrated by carbon monoxide and a higher activity in benzene hydrogenation than the samples prepared at 923 or 973 K. This higher density of sites and activity were interpreted in terms of improved degrees of carburization at the surface of the carbide. The temperature-programmed desorption of benzene over those three Mo2C samples showed that the higher the activity in benzene hydrogenation, the lower the maximum desorption temperature: the tendency also observed going from Mo to Ru. This desorption temperature evolution could be explained in terms of an increased degree of carburization, which conferred to Mo2C a reactivity toward benzene closer to that of Ru.

Biosensors elaborated on gold nanoparticles, a PM-IRRAS characterisation of the IgG binding efficiency

This work is focused on studying the grafting of gold nanoparticles (Np) on a cystamine self-assembled monolayer on gold, in order to build sensitive immunosensors. The synthesis and deposition of gold nanoparticles, 13 and 55 nm sizes, were characterised by combining Polarisation Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS), X-ray Photoelectron Spectroscopy (XPS) Surface Enhanced Raman Scattering (SERS), and Atomic Force Microscopy (AFM) which all indicated the formation of a dispersed layer of nanoparticles. This observation is explained by the compromise between the high reactivity of amine-terminated layers towards gold, and interparticle repulsions. Nps were then functionalised with antibody probes, and the recognition by an anti-rIgG was assayed both on planar and Np gold surfaces. The important result is that nanoparticles of 55 nm are preferable for the following reasons: they enable to build a denser and well dispersed layer and they increase both the number of receptors (IgGs) and their accessibility. Beside these geometric improvements, a net enhancement of the Raman signal was observed on the 55 nm nanoparticle layer, making this new platform promising for optical detection based biosensors.

High surface area supports with strong Brønsted acidity in an open porosity

Two routes for the preparation of high surface area silica-alumina materials with strong Bronsted acidity and open porosity are examined: one uses the organisation of β-zeolite seeds with surfactant micelles, and the other the delamination of Al-Magadiite, a naturally occurring sodium phyllosilicate. The textures, of these materials are characterised using N 2 -sorption and the localisation of most of the Al in tetrahedral substitution in the silica, framework is shown using 27 Al MAS NMR. These two materials show good activity for the cracking of cumene. Furthermore, the characterization of their acidity by FTIR of adsorbed CO reveals the presence of strong and medium Bronsted acid sites.

Dispersion and states of platinum ions in BEA-zeolite pores: effect of the framework basicity

Pt/Cs-BEA materials prepared by a classical ion-exchange procedure using two Cs-BEA supports with different Cs loadings, and a reference acidic Pt/H-BEA, have been studied to investigate the effect of the framework basicity (evaluated by FT-IR of adsorbed CO2) on the state of platinum species after the initial steps (introduction of Pt complex by ion-exchange and subsequent calcination) of the preparation procedure. DR-UV data revealed that the framework basicity affects the structure of the Pt2+ complexes introduced as countercations in the zeolite by ion exchange. FT-IR spectra of adsorbed CO indicated that zeolite basicity rules the fate of platinum species in the subsequent calcination. Hence, in Pt/H-BEA essentially well dispersed Ptδ+ (4≥δ≥1) are present, while PtOx particles progressively prevail as the basic character of the zeolite increases.

Probing the strength, concentration and environment of basic sites in zeolites by IR spectroscopy

Abstract Three protic probe molecules were used to characterize by FTIR spectroscopy the strength, concentration and environment of basic sites in series of faujasites (FAU structure) in which either the Al content (Y, X and LSX) or the nature of the framework charge compensating alkali cation (Na, K, Cs) was varied. The frequency shifts observed for adsorbed MBOH and adsorbed methylacetylene well account for variations in the basic strength of the zeolitic framework oxygen atoms. Interestingly, methylacetylene also informs on the environment of the basic sites. Lastly H 2 S dissociation brings quantitative information on the amount of basic sites. The results show the high potential and the complementarity of these protic probes to describe the strength, concentration and environment of basic sites.