Scanning Probe-Directed Assembly and Rapid Chemical Writing Using Nanoscopic Flow of Phospholipids

Vytautas Navikas
AMER CHEMICAL SOC, 2019
Article

Résumé

Nanofluidic systems offer a huge potential for discovery of new molecular transport and chemical phenomena that can be employed for future technologies. Herein, we report on the transport behavior of surface-reactive compounds in a nanometer-scale flow of phospholipids from a scanning probe. We have investigated microscopic deposit formation on polycrystalline gold by lithographic printing and writing of 1,2-dioleoyl-sn-glycero-3-phosphocholine and eicosanethiol mixtures, with the latter compound being a model case for self-assembled monolayers (SAMs). By analyzing the ink transport rates, we found that the transfer of thiols was fully controlled by the fluid lipid matrix allowing to achieve a certain jetting regime, i.e., transport rates previously not reported in dip-pen nanolithography (DPN) studies on surface-reactive, SAM-forming molecules. Such a transport behavior deviated significantly from the so-called molecular diffusion models, and it was most obvious at the high writing speeds, close to 100 mu m s(-1). Moreover, the combined data from imaging ellipsometry, scanning electron microscopy, atomic force microscopy (AFM), and spectroscopy revealed a rapid and efficient ink phase separation occurring in the AFM tip-gold contact zone. The force curve analysis indicated formation of a mixed ink meniscus behaving as a self-organizing liquid. Based on our data, it has to be considered as one of the co-acting mechanisms driving the surface reactions and self-assembly under such highly nonequilibrium, crowded environment conditions. The results of the present study significantly extend the capabilities of DPN using standard AFM instrumentation: in the writing regime, the patterning speed was already comparable to that achievable by using electron beam systems. We demonstrate that lipid flow-controlled chemical patterning process is directly applicable for rapid prototyping of solid-state devices having mesoscopic features as well as for biomolecular architectures.

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https://infoscience.epfl.ch/record/269795?ln=fr

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Vytautas Navikas
AMER CHEMICAL SOC, 2019
Article

Résumé

Official source

https://infoscience.epfl.ch/record/269795?ln=fr

À propos de ce résultat

Concepts associés (28)

Concepts associés

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Publications associées (23)

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Introduction Recently, we introduced a new deposition method, based on Ion Plating Plasma Assisted technology, to coat titanium implants with a thin but hard nanostructured layer composed of titanium carbide and titanium oxides, clustered around graphitic carbon. The nanostructured layer has a double effect: protects the bulk titanium against the harsh conditions of biological tissues and in the same time has a stimulating action on osteoblasts. Results The aim of this work is to describe the biological effects of this layer on osteoblasts cultured in vitro. We demonstrate that the nanostructured layer causes an overexpression of many early genes correlated to proteins involved in bone turnover and an increase in the number of surface receptors for alpha 3 beta 1 integrin, talin, paxillin. Analyses at single-cell level, by scanning electron microscopy, atomic force microscopy, and single cell force spectroscopy, show how the proliferation, adhesion and spreading of cells cultured on coated titanium samples are higher than on uncoated titanium ones. Finally, the chemistry of the layer induces a better formation of blood clots and a higher number of adhered platelets, compared to the uncoated cases, and these are useful features to improve the speed of implant osseointegration. Conclusion In summary, the nanostructured TiC film, due to its physical and chemical properties, can be used to protect the implants and to improve their acceptance by the bone.

Public Library of Science2016

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The understanding of material self-assembling and self-organization mechanisms, at mesoscale, is crucial for nanotechnologies development. Such structures, hierarchically organized in superlattices or colloïdal crystals, are observed in inorganic or organo-metallic precipitates. The classical characterization, using electron microscopy and X-ray diffraction, of a synthesized powder is inadequate to describe the hierarchically organized polycrystalline structure of the final particles. Here, we have highlighted the successive steps that lead to the spontaneous formation of a cobalt oxalate dihydrate (COD) colloïdal crystals that precipitate in aqueous media. The characterization of the final particles, made by X-ray and electronic diffraction, has allowed us to determine the controversial crystalline phase of the precipitated COD. The β and γ COD phases has been discriminated by comparing experimental results with simulations of X-ray diffractogram and electron diffraction patterns for these both structures. The precipitated COD corresponds to the γ phase indicating that it comes from solid dehydration of cobalt oxalate tetrahydrate. The final powder characterization, performed by X-ray diffraction (XRD), atomic force microscopy (AFM), low voltage high resolution scanning electron microscopy (LVHRSEM) and transmission electron microscopy (TEM), gives some diverging results about monocrystalline or polycrystalline nature of the precipitates. XRD and AFM analysis show a polycrystalline structure of particles whereas LVHRSEM, TEM and electron diffraction observations indicate a monocrystalline structure. This apparent contradiction has led us to elaborate a new characterization method allowing to follow the growth and the structural evolution of the precipitate as a function of time. The cryo- preparation techniques are well adapted as they allow freezing and direct observation of solid state suspension by electron microscopy. The freeze/drying method has been modified and used for both SEM and TEM, and has allowed us to study the morphological and structural evolution of the COD precipitate from nanoscale to mesoscale. In addition, TEM analysis of samples prepared by classical techniques has been performed to complement cryo-electron microscopy observations. The combination of these two methods show that COD precipitation is a complex multi-step process leading to the formation of a core/shell heterostructure. The anisotropic core is porous and partially crystalline. It is formed by agglomeration of isolated primary particles and agregated ones (15-20 nm sized secondary particles). The crystalline shell corresponds to the final particles faces and is made up by the layer by layer self-assembling and alignment of 5-7 nm sized crystalline primary particles. These nanoparticles are aligned and perfectly ordered in strings of nanograins in the layer structure. The self-assembling occurs in the last step of growth where we have a lower ionic strength and supersaturation inducing slower kinetics of growth and aggregation. Moreover, the crystalline order in the primary and secondary particles increase with the time of reaction consistent with a continuous process of primary particle nucleation and growth. Our results show that self-assembling occurs layer by layer with terraces, kinks and steps that are present on the faces. This reminds the layer by layer crystalline growth models but in this case, the buiding blocks are colloïdal instead of atomic or molecular. Based on these different results, we propose an original model describing the COD precipitate growth. In addition, we have studied the poly(methacrylic acid-sodium salt) effect on the COD precipitation. This additive (PMMA) appeared to be a very good growth inhibitor. The PMMA effect on the final particles morphology is dramatic. Its concentration variation in solution slows down the nanoparticles aggregation rates along a [101] preferential direction. The crystal habit can then be controlled and we have synthesized platelets, cubes and rods with tailored length. The use of cryogenic electron microscopy has been shown to be a powerful tool for the understanding of time dependent aspects of particle growth. The use of such techniques for the study of other systems, where the final precipitate appearance may hide particle substructures, will help to elucidate growth mechanisms and allow finer control of nanostructured materials for many applications. The complex self-assembling and self-organization processes could then be highlighted and studied on a nanometer to micrometer scale.

EPFL2004

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This thesis further explores the possibilities of scanning near-field optical microscopy (SNOM) in both materials and life sciences. Two experimental SNOM setups were developed: one designed for infrared spectroscopy applications and the other for the imaging of fluorescently labeled samples. The results of the experiments that were conducted with both setups are presented and analyzed in this thesis. Diffraction limits the resolution of lens-based microscopes to a value close to that of the wavelength of the light that is used to illuminate the samples. SNOM instruments overcome this limit by probing the near-field light — the light that remains within close vicinity of the sample and decays exponentially away from it. The SNOM concept and instrumental design are described. A comparison of SNOM with other novel microscopies (electron, atomic force, and scanning tunneling microscopies) outlines the main advantages of SNOM — the sole optical microscopy technique with a nanometer resolution. Aperture-based infrared SNOM (IR-SNOM), performed in the spectroscopic mode using the Vanderbilt University free electron laser, recently started delivering spatially resolved information on the distribution of chemical species and on other laterally fluctuating properties. The IR-SNOM combines the IR spectroscopy's chemical specificity and the SNOM's high optical and topographical resolutions. The IR-SNOM experimental setup is described in detail and results from the study of cells, boron nitride and lithium fluoride thin films are presented and analyzed. They demonstrate the great potential of this new technique. An overview of the development of IR-SNOM, as well as a consideration of its future possibilities are presented. The newly built SNOM instrument at EPFL was used for experiments that are complementary to the aforementioned IR-SNOM experiments. Specifically, the new SNOM enabled the study of fluorescently marked samples. Images of fluorescently labeled cells and carbon nanotubes are presented and analyzed. The results further demonstrate the exciting possibilities of SNOM.

EPFL2005

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EPFL2004

EPFL2005