3,389 research outputs found

    Nanofabrication techniques in large-area molecular electronic devices

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    The societal impact of the electronics industry is enormous-not to mention how this industry impinges on the global economy. The foreseen limits of the current technology-technical, economic, and sustainability issues-open the door to the search for successor technologies. In this context, molecular electronics has emerged as a promising candidate that, at least in the short-term, will not likely replace our silicon-based electronics, but improve its performance through a nascent hybrid technology. Such technology will take advantage of both the small dimensions of the molecules and new functionalities resulting from the quantum effects that govern the properties at the molecular scale. An optimization of interface engineering and integration of molecules to form densely integrated individually addressable arrays of molecules are two crucial aspects in the molecular electronics field. These challenges should be met to establish the bridge between organic functional materials and hard electronics required for the incorporation of such hybrid technology in the market. In this review, the most advanced methods for fabricating large-area molecular electronic devices are presented, highlighting their advantages and limitations. Special emphasis is focused on bottom-up methodologies for the fabrication of well-ordered and tightly-packed monolayers onto the bottom electrode, followed by a description of the top-contact deposition methods so far used

    Functionalized Silicon Electrodes in Electrochemistry

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    Avoiding the growth of SiOx has been an enduring task for the use of silicon as an electrode material in dynamic electrochemistry. This is because electrochemical assays become unstable when the SiOx levels change during measurements. Moreover, the silicon electrode can be completely passivated for electron transfer if a thick layer of insulating SiOx grows on the surface. As such, the field of silicon electrochemistry was mainly developed by electron-transfer studies in nonaqueous electrolytes and by applications employing SiOx-passivated silicon-electrodes where no DC currents are required to cross the electrode/electrolyte interface. A solution to this challenge began by functionalizing Si-H electrodes with monolayers based on Si-O-Si linkages. These monolayers have proven very efficient to avoid SiOx formation but are not stable for a long-term operation in aqueous electrolytes due to hydrolysis. It was only with the development of self-assembled monolayers based on Si-C linkages that a reliable protection against SiOx formation was achieved, particularly with monolayers based on α,ω-dialkynes. This review discusses in detail how this surface chemistry achieves such protection, the electron-transfer behavior of these monolayer-modified silicon surfaces, and the new opportunities for electrochemical applications in aqueous solution

    Fully Integrated Biochip Platforms for Advanced Healthcare

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    Recent advances in microelectronics and biosensors are enabling developments of innovative biochips for advanced healthcare by providing fully integrated platforms for continuous monitoring of a large set of human disease biomarkers. Continuous monitoring of several human metabolites can be addressed by using fully integrated and minimally invasive devices located in the sub-cutis, typically in the peritoneal region. This extends the techniques of continuous monitoring of glucose currently being pursued with diabetic patients. However, several issues have to be considered in order to succeed in developing fully integrated and minimally invasive implantable devices. These innovative devices require a high-degree of integration, minimal invasive surgery, long-term biocompatibility, security and privacy in data transmission, high reliability, high reproducibility, high specificity, low detection limit and high sensitivity. Recent advances in the field have already proposed possible solutions for several of these issues. The aim of the present paper is to present a broad spectrum of recent results and to propose future directions of development in order to obtain fully implantable systems for the continuous monitoring of the human metabolism in advanced healthcare applications

    Engineering tunable bio-inspired polymeric coatings for amphiphobic fibrous materials

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    Chemical grafting has been widely used to modify the surface properties of materials, especially surface energy for controlled wetting, because of the resilience of such coatings/modifications. Reagents with multiple reactive sites have been used with the expectation that a monolayer will form. The step-growth polymerization mechanism, however, suggests the possibility of gel formation for hydrolysable moieties in the presence of physisorbed water. In the following chapters, we demonstrate that using alkyltrichlorosilanes (trivalent [3 reactive sites]) in the surface modification of a cellulosic material (paper) does not yield a monolayer but rather gives surface-bound polymeric particles. We infer that the presence of physisorbed (surface-bound) water allows for polymerization (or oligomerization) of the silane, prior to its attachment on the surface. Surface energy mismatch between the hydrophobic tails of the growing polymer and any unreacted bound water leads to the assembly of the polymerizing material into spherical particles to minimize surface tension. By varying paper grammage (16.2-201.4 g/m2), we varied the accessible surface area and thus the amount of surface-adsorbed water, allowing us to control the ratio of the silane to the bound water. Using this approach, polymeric particles were formed on the surface of cellulose fibers ranging from ~70 nm to a film. The hydrophobicity of the surface, as determined by water contact angles, correlates with particle sizes (p \u3c 0.001, Student t-test), and, hence, the hydrophobicity can be tuned (contact angle between 94Ëš and 149Ëš). Using a model structure of a house, we demonstrated that as a result of this modification, cardboard houses can be rendered self-cleaning or tolerant to surface running water. Each of the chapters below supports the mechanism via a series of applications, material characterization, and/or, smart engineering

    Nanobiotechnologie: Werkzeuge fĂĽr die Proteomik : molekulare Organisation und Manipulation von Proteinen und Proteinkomplexen in Nanodimensionen

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    First milestone of this Ph.D. thesis was the successful extension of conventional NTA/His-tag technique to self-assembling, multivalent chelator thiols for high-affinity recognition as well as stable and uniform immobilization of His-tagged proteins on chip surfaces. Bis-NTA was linked via an oligoethylene glycol to alkyl thiols by an efficient modular synthesis strategy yielding a novel, multivalent compound for formation of mixed SAMs with anti-adsorptive matrix thiols on gold. Multivalent chelator chips allow a specific, high-affinity, reversible, long-term immobilization of His-tagged proteins. In AFM studies reversibility of the specific protein immobilization process was visualized at single molecule level. The entire control over the orientation of the immobilized protein promotes this chip surface to an optimal platform for studies focusing on research targets at single molecule level and nanobiotechnology. Based on the constructed protein chip platform above and a novel AFM mode (contact oscillation mode, COM) – developed during the current Ph.D. work – protein nanolithography under physiological conditions enabling fabrication of active biomolecular patterns in countless variety has been established. Reversible COM-mediated nanostructuring is exceptionally suitable for multiplexed patterning of protein assemblies in situ. The first selfassembled protein layer acts as a biocompatible and ductile patterning material. Immobilized proteins can be replaced by the AFM tip applying COM, and the generated structures can be erased and refilled with different proteins, which are immobilized in a uniform and functional manner. Multi-protein arrays can be systematically fabricated by iterative erase-and-write processes, and employed for protein-protein interaction analysis. Fabrication of two-dimensionally arranged nanocatalytic centres with biological activity will establish a versatile tool for nanobiotechnology. As an alternative chip fabrication approach, the combined application of methodologies from surface chemistry, semiconductor technology, and chemical biology demonstrated successfully how pre-patterned templates for micro- and nanoarrays for protein chips are fabricated. The surface physical, as well the biophysical experiments, proved the functionality of this technology. The promises of such process technology are fast and economic fabrication of ready-to-use nanostructured biochips at industrial scale. Membrane proteins are complicated in handling and hence require sophisticated solutions for chip technological application. A silicon-on-insulator (SOI) chip substrate with microcavities and nanopores was employed for first technological investigation to construct a protein chip suitable for membrane proteins. The formation of an artificial lipid bilayer using vesicle fusion on oxidized SOI cavity substrates was verified by CLSM. Future AFM experiments will give further insights into the chip architecture and topography. This will provide last evidence of the sealing of the cavity by the lipid bilayer. Transmembrane proteins will be employed for reconstitution experiments on this membrane protein chip platform. Highly integrated microdevices will find application in basic biomedical and pharmaceutical research, whereas robust and portable point-of-care devices will be used in clinical settings.Erster Meilenstein der vorliegenden Arbeit war die erfolgreiche Erweiterung des konventionellen NTA/His-tag-Konzepts auf selbst-assemblierende, multivalente Chelatorthiole für die hochaffine Erkennung und stabile, einheitliche Immobilisierung His-getaggter Proteine auf Chipoberflächen. Mittels einer effizienten, modularen Synthesestrategie wurden Bis-NTA-Module über Oligoethylenglykoleinheiten an Alkylthiole angebunden. Diese Chelatorthiole wurden zusammen mit antiadsorptiven Matrixthiolen zur Ausbildung gemischter selbst-assemblierender Monolagen (SAMs) auf Goldoberflächen eingesetzt. Die multivalenten Chelatorchips erlauben eine spezifische, hochaffine, umkehrbare und langfristige Immobilisierung His-getaggter Proteine. Die Umkehrbarkeit der spezifischen Proteinimmobilisierung wurde in rasterkraftmikroskopischen (AFM) Studien bis zur Einzel-Molekül-Ebene visualisiert. Die vollständige Kontrolle über die Orientierung immobilisierter Proteine qualifiziert diese entwickelte Chipoberfläche zu einer optimalen Plattform für Anwendungsbereiche der Einzelmolekülbiochemie und Nanobiotechnologie. Basierend auf dieser Plattform für Proteinchips und einem – im Rahmen dieser Arbeit – neuentwickelten AFM-Modus (Kontaktoszillationsmodus, COM) wurde die „Protein-Nanolithographie“ etabliert, welche die Fabrikation von aktiven, biomolekularen Strukturen in unzähliger Vielfalt ermöglicht. Die umkehrbare COM-vermittelte Nanolithographie ist insbesondere für die multiplexe Anordnung von Proteinverbänden in situ geeignet. Die erste Schicht immobilisierter Proteine fungiert als ein biokompatibles und verformbares Strukturierungsmaterial. Diese immobilisierten Proteine können nun im Kontaktoszillationsmodus mit der AFM-Spitze lokal entfernt („Löschen“) und gegen andere Proteine – die an die freigelegte Chipoberfläche ebenfalls spezifisch und funktional immobilisieren – ausgetauscht werden („Schreiben“). Arrays, bestehend aus mehreren unterschiedlichen Proteinen können nun systematisch in iterativen Lösch-und-Schreib-Vorgängen fabriziert und für Proteininteraktionsanalysen eingesetzt werden. Die Fabrikation von zwei-dimensional arrangierten nanokatalytischen Zentren mit biologischer Aktivität wird von großem Nutzen für die Nanobiotechnologie sein. Eine alternative Herstellungsmethode aus einer Kombination von Oberflächenchemie, Halbleitertechnologie und chemischer Biologie wurde für die Fabrikation von vorstrukturierten Templaten für Mikro- und Nanoarrays entwickelt. Die Funktionalität dieser Chipplattform wurde anhand oberflächen- und biophysikalischer Experimente erfolgreich gezeigt. Zukünftiges Ziel ist die Anfertigung vorstrukturierter Template in der Dimension weniger Nanometer zur Ausbildung von Bio-Arrays mit einzelnen Molekülen. Ein weiteres Ziel besteht in der kompletten Verlagerung des Herstellungsprozesses in die Gasphase. Eine Produktion in der Gasphase verspricht eine schnelle und wirtschaftliche Erzeugung sofort einsatzbereiter nanostrukturierter Biochips im industriellen Maßstab. Der Umgang mit Membranproteinen verlangt besondere Vorkehrungen im experimentellen Milieu, ebenso speziell sind die Bedürfnisse in den entsprechenden Chip-Anwendungen. Ein Chip mit Mikrokavitäten und Nanoporen, basierend auf der „Silicon-on-Insulator“ (SOI)-Technologie, wurde für erste technologische Studien zum Entwurf eines Proteinchips für Membranproteine eingesetzt. Künstliche Lipidmembranen wurden auf der SOI-Oberfläche mittels Vesikelfusion ausgebildet und mit konfokaler Laser-Scanning-Mikroskopie gezeigt. Zukünftige AFM-Experimente werden weitere Einsichten in die Chiparchitektur und Topographie ermöglichen. Transmembranproteine werden in Rekonstitutionsexperimenten für funktionale Studien der Membranproteinchips eingesetzt. Anwendungsbereiche solcher hochintegrierten Mikrosysteme sind sowohl in der biologischen Grundlagenforschung als auch in mobilen Diagnostikgeräten im klinischen Einsatz zu finden

    Nano-chemistry and scanning probe nanolithographies

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    The development of nanometer-scale lithographies is the focus of an intense research activity because progress on nanotechnology depends on the capability to fabricate, position and interconnect nanometer-scale structures. The unique imaging and manipulation properties of atomic force microscopes have prompted the emergence of several scanning probe-based nanolithographies. In this tutorial review we present the most promising probe-based nanolithographies that are based on the spatial confinement of a chemical reaction within a nanometer-size region of the sample surface. The potential of local chemical nanolithography in nanometer-scale science and technology is illustrated by describing a range of applications such as the fabrication of conjugated molecular wires, optical microlenses, complex quantum devices or tailored chemical surfaces for controlling biorecognition processes.The authors would like to thank Fabio Biscarini for providing the much needed input to write the manuscript and Marta Tello for her valuable suggestions. This work was financially supported by the MCyT (Spain) (MAT2003-02655) and the European Commission (NAIMO, IP NMP4-CT-2004-500355).Peer reviewe

    Self-assembled monolayers: a journey from fundamental tools for understanding interfaces to commercial sensing technologies

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    Self-assembled monolayers were first described in the 1980s and have now become ubiquitous in many interfacial technologies. In this account, we discuss different self-assembled monolayer systems, outlining their positives and negatives. We then overview other researchers’ work and our own group’s journey in using self-assembled monolayers to develop new concepts in sensing and addressing general challenges faced by many types of sensors. Finally, we reflect on some of the challenges monolayer chemistry needs to address to facilitate further use of this powerful surface chemistry in commercial devices

    Application of Soft Lithography for Nano Functional Devices

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    Advances in nanomaterials integration in CMOS-based electrochemical sensors: a review

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    The monolithic integration of electrochemical sensors with instrumentation electronics on semiconductor technology is a promising approach to achieve sensor scalability, miniaturization and increased signal to noise ratio. Such an integration requires post-process modification of microchips (or wafers) fabricated in standard semiconductor technology (e.g. CMOS) to develop sensitive and selective sensing electrodes. This review focuses on the post-process fabrication techniques for addition of nanomaterials to the electrode surface, a key component in the construction of electrochemical sensors that has been widely used to achieve surface reactivity and sensitivity. Several CMOS-compatible techniques are summarized and discussed in this review for the deposition of nanomaterials such as gold, platinum, carbon nanotubes, polymers and metal oxide/nitride nanoparticles. These techniques include electroless deposition, electro-chemical deposition, lift-off, micro-spotting, dip-pen lithography, physical adsorption, self-assembly and hydrothermal methods. Finally, the review is concluded and summarized by stating the advantages and disadvantages of these deposition methods
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