30 research outputs found

    Materials Processing for Production of Nanostructured Thin Films

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    Thin films are important in many of the technologies used every day, impacting major markets for energy, medicine, and coatings. Scientists and engineers have been producing thin films on a wide range of surfaces for many decades but now have begun to explore giving these films new and controlled structures at the nanometer scale. These efforts are part of the new horizons opened by the field of nanoscience and impart novel structures and properties to these thin films. This book covers some of the methods for making these nanostructured thin films and their applications in areas impacting on health and energy usage

    Композити графена и наноструктурисаних оксида као компоненте биосензора глукозе и полифенола

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    Present doctoral dissertation describes the development of novel glucose and polyphenolic index biosensors, based on a combination of graphene nanomaterials and nano-structured metal oxides. An in-depth examination of how mentioned nanomaterials separately influence the electrochemical performances of developed biosensors, as well as their synergic effect, is provided within the scope of this dissertation. In order to obtain desired working electrodes, synthesized nanocomposites were applicated on the surface of screen printed carbon electrodes (SPCEs). Cyclic voltammetry and chronoamperometry were electrochemical methods utilized for testing electrochemical performances of synthetized nanocomposites as well as the final biosensors. Glucose biosensor was based on the modification of graphene nanoribbons (GNR) with Bi2O3 nanoparticles. The synthesized GNR@Bi2O3 nanocomposite was introduced to the surface of SPCE, in order to obtain the working electrode (SPCE/GNR@Bi2O3). Glucose biosensor was prepared by immobilization of glucose-oxidase (GOx), from Aspergillus niger, on the surface of SPCE/GNR@Bi2O3, and followed by coating of the enzyme with Nafion (Naf) solution. Developed SPCE/GNR@Bi2O3/GOx/Naf biosensor has been successfully applied for the quantification of glucose in a honey sample. Polyphenolic index biosensor was constructed by modification of graphene nanoplatelets (GNP) with MnO2 nanoparticles. In order to produce the working electrode (SPCE/GNP@MnO2), SPCE has been modified with GNP@MnO2 nanocomposite. The final polyphenolic index biosensor has been produced by immobilization of the laccase, from Trametes Versicolor (TvL), onto the SPCE/GNP@MnO2 surface, and followed by the application of Naf. Using the developed SPCE/GNP@MnO2/TvL/Naf biosensor, the polyphenolic index in wine was successfully determined.Представљена докторска дисертација описује развој нових биосензора за одређивање глукозе и полифенолног индекса који се заснивају на комбинацији графенских наноматеријала и наноструктурисаних металних оксида. Утицај поменутих наноматеријала на електрохемијске перформансе развијених биосензора, као и њихов синергијски ефекат, је детаљно проучен у оквиру ове дисертације. Синтетисани нанокомпозити су нанети на површину штампаних угљеничних електрода (SPCE) у циљу добијања радних електрода. Циклична волтаметрија и хроноамперометрија су електрохемисјке методе које су коришћене за испитивање електрохемијских перформанси синтетисаних нанокомпозита, као и финалних биосензора. Биосензор за одређивање глукозе се заснивао на модификацији графенских нанотрачица (GNR) са Bi2O3 наночестицама. Синтетисани GNR@Bi2O3 нанокомпозит је нанет на површину SPCE у циљу добијања радне електроде (SPCE/GNR@Bi2O3). Биосензор за одређивање глукозе је припремљен имобилизацијом глукоза-оксидазе (GOx) из Aspergillus niger на површину SPCE/GNR@Bi2O3, што је праћено превлачењем ензима са раствором нафиона (Naf). Развијени SPCE/GNR@Bi2O3/GOx/Naf биосензор је успешно примењен за квантификацију глукозе у узорку меда. Биосензор за одређивање полифенолног индекса се базирао на модификацији графенских наноплочица (GNP) са MnO2 наночестицама. SPCE је модификована са GNP@MnO2 нанокомпозитом у циљу конструкције радне електроде (SPCE/GNP@MnO2). Биосензор за одређивање полифенолног индекса је конструисан након имобилизације лаказе из Trametes Versicolor (TvL) на површину SPCE/GNP@MnO2, након чега је уследило наношење Naf раствора. Полифенолни индекс у узорцима вина је одређен користећи развијени SPCE/GNP@MnO2/TvL/Naf биосензор

    Present and Future of Surface-Enhanced Raman Scattering.

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    The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article

    Chemical Approaches for Nanofabrication Based on Colloidal Lithography with Organosilanes, Nanoparticles and Nickel Films: The Role of Water in Directing Surface Self-Assembly

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    The capabilities for accomplishing fundamental surface studies with molecular systems are demonstrated in this dissertation using measurement and imaging modes of scanning probe microscopy. Model systems were chosen for investigations of surface self-assembly mechanisms, with an emphasis on understanding the role of interfacial water in surface reactivity. A key strategy for molecular level studies was to prepare nanostructures using protocols with colloidal lithography and scanning probe-based lithography (SPL). Nanofabricated samples were characterized ex situ with contact and tapping-mode atomic force microscopy (AFM) after key reaction steps, providing direct views of changes in surface morphology at the nanoscale. Magnetic sample modulation (MSM) combined with contact mode AFM provided a route to detect the vibration of magnetic nanomaterials in response to an externally applied electromagnetic field. Nanoscale measurements of the size-scaling effects for physical properties such as conductance and nanomagnetism are contemporary topics in the field of nanoscience. Protocols of SPL were used for studies with organic thin films; nanoshaving and nanografting experiments provided a means to prepare ultra-small nanostructures. Nickel-coated nanostructures were constructed on amine-terminated nanorings of aminopropyltriethoxysilane (APTES) using colloidal lithography and chemical steps of electroless deposition (ELD), nickel was deposited by an autocatalytic redox reaction using palladium as a catalyst. Protocols were developed to investigate the role of water in the association and placement of silane molecules on surfaces as a strategy for indirectly tracking the location of water on surfaces. Visible light photocatalysis was used to prepare nanostructured films by immersing surface masks of monodisperse spheres in solutions of an aryl halide and then irradiating the solution with blue light. Films of aryl halide are linked to the surface by C-Au bonds to form robust films that resist the effects of oxidation. Nanostructured films of octaethylporphyrin (OEP) were prepared with immersion particle lithography by reaction with silicon tetrachloride. Porphyrins bound to the surface through covalent Si-O-surface linkages coordinated to the centers of the macrocycles in a kebob arrangement. The Si-O-Si “skewer” strategy was also successful for encapsulating Au nanoparticles with porphyrins to make core-shell nanoparticles. Fundamental studies targeted questions related to controlling surface assembly and interfacial chemistry details

    Towards bottom-up silicon nanowire-based biosensing:: Innovative concepts for fabricating lab-on-a-chip devices

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    The term "Lab-on-a-Chip" (LoC) describes highly miniaturized systems in which the functionalities of entire laboratories are scaled down to the size of transportable microchips. Particularly in the field of chemical and bio-analysis, such platforms are desired for a fast and highly sensitive sample analysis at the point of care. This work focuses on silicon nanowire (SiNW) based sensors. Innovative device fabrication concepts are developed from various directions, for a facile and reliable assembly of LoC analysis systems. Firstly, a multifunctional microfluidic set-up is developed which allows for a facile reversible sealing of channel structures on virtually any kind of substrate while maintaining the possibility of a rapid prototyping of versatile channel designs and the applicability of high working pressures of up to 600 kPa. Secondly, a 3-(triethoxysilyl)propylsuccinic anhydride (TESPSA) based surface modification strategy for the attachment of specific receptor molecules without additional binding site passivation is explored. Thirdly, bottom-up grown SiNWs are utilized for producing parallel arrays of Schottky barrier field-effect transistors (FETs) via contact printing. Using the initially developed microfluidic set-up, the concept of the TESPSA-based receptor immobilization is proved via fluorescence microscopy and by applying the SiNW FETs as biosensors. Using a receptor-analyte system based on a set of antibodies and a peptide from human influenza hemagglutinin, it is shown that antibodies immobilized with the developed method maintain the specificity for their antigens. The fourth major research field in this work is the microfluidics-based alignment of one-dimensional nanostructures and their deposition at predetermined trapping sites for reliably fabricating single NW-based FETs. Such devices are expected to provide superior sensitivity over sensors based on parallel arrays of FETs. Consequently, within this work, innovative LoC devices fabrication approaches over a broad range of length scales, from micrometer scale down to the molecular level, are investigated. The presented methods are considered a highly versatile and beneficial tool set not only for SiNW-based biosensors, but also for any other LoC application.Unter dem Begriff „Lab-on-a-Chip“ (LoC) fasst man stark miniaturisierte Systeme zusammen, die die Fähigkeiten eines ganzen Labors auf einen transportablem Mikrochip übertragen. Insbesondere im Bereich der Analyse chemischer und biologischer Proben werden solche Plattformen bevorzugt eingesetzt, da sie direkt am Ort der Probenentnahme schnelle, hoch sensible Messungen ermöglichen. Im Mittelpunkt dieser Doktorarbeit stehen Sensoren auf Basis von Siliziumnanodrähten (SiNWs). Auf verschiedenen Gebieten werden innovative Konzepte zur einfachen und zuverlässigen Herstellung von LoC Systemen entwickelt. Zu Beginn wird ein multifunktionaler Mikrofluidik-Aufbau vorgestellt, der ein einfaches reversibles Verschließen von Mikrofluidik-Kanälen auf nahezu allen möglichen Substraten erlaubt. Der Aufbau ermöglicht das schnelle Anfertigen und Testen verschiedener Kanalstrukturen sowie das Betreiben von Fluidik-Experimenten mit hohen Arbeitsdrücken von bis zu 600 kPa. Der zweite Schwerpunkt der Arbeit ist die Entwicklung einer Methode zur Funktionalisierung von Sensor-Oberflächen mittels 3-(Triethoxysilyl) Propyl Bernsteinsäure Anhydrid (TESPSA) für die Immobilisierung spezifischer Rezeptormoleküle. Bei dieser Methode entfällt die Notwendigkeit einer zusätzlichen Passivierung ungenutzter Anbindungsstellen. Des Weiteren erfolgt die Herstellung von Parallelschaltungen von Schottky-Barrieren-Feld-Effekt-Transistoren (SB-FETs) aus „bottom-up“ gewachsenen SiNWs durch mechanisches Abreiben der SiNWs vom Wachstumssubstrat auf ein Empfängersubstrat. Unter Verwendung des eingangs entwickelten Mikrofluidik-Aufbaus wird die prinzipielle Anwendbarkeit der TESPSA-basierten Rezeptor-Immobilisierung nachgewiesen, sowohl anhand von Fluoreszenzmikroskopie-Untersuchungen als auch mit Hilfe der SiNW FETs als Biosensoren. Mittels eines Rezeptor-Analyt-Systems, bestehend aus verschiedenen Antikörpern und einem Peptid des Influenzavirus A, wird gezeigt, dass Antikörper, die über TESPSA an Oberflächen gebunden werden, ihre Spezifizität für ihre Antigene beibehalten. Der vierte große Forschungsabschnitt dieser Arbeit widmet sich der mikrofluidischen Ausrichtung eindimensionaler Nanomaterialien und deren Ablage an vorgegebenen Fangstellen, wodurch eine zuverlässige Herstellung von FETs aus Einzelnanodrähten erreicht wird. Es wird davon ausgegangen, dass Einzelnanodraht-FETs gegenüber Parallelschaltungen von Nanodraht-FETs verbesserte Sensoreigenschaften aufweisen. Folglich beinhaltet diese Arbeit viele zukunftsweisende Ansätze für die Herstellung von LoC Systemen. Untersuchungen über eine Bandbreite von Längenskalen, von Mikrometer großen Strukturen bis hinab zur molekularen Ebene, werden präsentiert. Es wird davon ausgegangen, dass die vorgestellten Methoden als eine vielfältige Sammlung von Werkzeugen nicht nur bei der Herstellung von Biosensoren auf SiNW-Basis Einsatz finden, sondern ganz allgemein den Aufbau verschiedenster LoC Systeme vorantreiben

    Carbon Nanotubes for Electronics and Energy

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    Ever since their discovery, carbon nanotubes have been touted as a new material for the future and a correspondingly lengthy list of possible applications are often cited in the literature. This excitement for carbon nanotubes is a result of their richly varying physical, electronic and optical properties, where it is possible to have single, double and multiple carbon walls with each wall potentially being either semiconducting or metallic and possessing unique optical transitions covering the ultraviolet to infrared spectral range. However, to date the realization of many of the proposed applications has been hindered by exactly the characteristic that made carbon nanotubes so attractive in the first place, namely the inherent inhomogeneity and varying properties of as-prepared or grown material. In order to become a true advanced material of the future, methods to prepare carbon nanotubes with defined length, wall number, diameter, electronic and optical property are necessary. Additionally, such methods to sort carbon nanotubes must afford high purity levels, be amenable to large-scale preparation and be compatible with subsequent integration into device architectures. In this work these issues are addressed with the use of gel based sorting techniques, which with the use of an automated gel permeation system allows for the routine preparation of milligram quantities of metallic and semiconducting carbon nanotubes, chirality pure single walled carbon nanotubes and even double walled carbon nanotubes sorted by their outer-wall electronic type. Having developed techniques to prepare large quantities, methodologies to control the order and orientation of this 1 D nanomaterial on the macro scale are developed. Inks of carbon nanotubes with liquid crystal concentrations and aligned films thereof are developed and this newfound control over the electronic and structural property opened the door for energy related applications. For example the use of thin films as the transparent electrodes in silicon:carbon nanotube solar cells or as the light harvesting layer in combination with fullerenes with the goal of creating an all carbon solar cell. Likewise on the few nanotube level the unique optical transitions of different nanotube chiralities are used in the fabrication of nanoscale photosensitive elements

    Charge-Modulated Extended Gate Organic Field Effect Transistor for Biosensing Applications

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    The interest in organic field effect transistors (OFETs) employed as a biosensing platform has grown in recent years, driven largely by the potential to create inexpensive, sensitive analytical devices with a wide range of chemical and biological sensing applications. A particularly promising architecture for these type of devices is the Charge-Modulated Organic Field-Effect Transistor (CM-OFET). In the CM-OFET, a control gate electrode is capacitively coupled to a floating gate and used to bias the OFET, eliminating the need for an additional, often macroscale, reference electrode. In addition, charge accumulated in a designated sensing region of the floating gate modulates the output source drain current, ISD, of the transistor, providing sensing activity that is spatially separated from the organic semiconductor layer. Here, a CM-OFET based on solution processed Tips-pentacene as the organic semi-conductor that is both low cost and very simple to fabricate is reported. The CM-OFET biosensors fabricated here were predominantly based on the widely used Si/SiO2 substrates, where the degenerately doped Si acted as the gate electrode with a SiO2 dielectric layer. A limited number of Al/Al2O3 based CM-FETS are also presented. This thesis includes a detailed description of fabrication of these CM-OFET devices alongside a detailed discussion of the principle of operation, both as organic transistors and as analytical for monitoring pH and protein detection. The thesis focusses primarily on the characteristics of CM-OFET devices based on the Si/SiO2 substrate. The fabrication of Si/SiO2 CM-OFETs was very simple, requiring only a single lithography or shadow evaporation stage. Despite the simplicity, the CM-OFETs reliably displayed electrical characteristics typical of organic field effect transistors. The electrical characteristics were reproducible with over 90% yield. However, the responses of the devices when tested for pH sensing and protein detection, were inconsistent and with large error. Further analysis of the CM-OFET architecture revealed limitations associated with the geometrical layout of the Si/SiO2 CM-OFET device may have caused this deficiency in sensing response. A modified CM-OFET employing Al/Al2O3 as gate and gate dielectric layers was designed in which the geometry was optimized to maximise sensitivity to changes in charge within the sensing region. A process for the fabrication of the Al/Al2O3 CM-OFET was developed and the Al-based CM-OFETs were found to exhibit behaviour typical of an organic transistor, albeit with relatively lower source drain current compared to Si/SiO2 CM-OFET devices. Due to limited time, the sensitivity of the Al-based CM-OFET was not fully characterized. Further work regarding the enhancement of the device’s charge carrier mobility of the device and particularly, experimental investigation of the Al/Al2O3 CM-OFET for sensing applications is needed

    NANOSCALE PATTERNING AND 3D ASSEMBLY FOR BIOMEDICAL APPLICATIONS

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    Due to the inherent planarity of nanoscale patterning, there is a pressing need to develop novel approaches for parallel and cost-effective three dimensional (3D) patterning and assembly at the nanoscale. The 3D devices formed by such approaches are important for chem-bio sensing, nanoelectronics and photonics, nanorobotics, and nanobiotechnology. The body of work presented in this thesis is focused on developing scalable and manufacturable processes to create curved and foldable 3D nanostructures with precise surface patterns, in a highly parallel and cost-efficient method. Specifically, two new approaches were developed which include the spontaneous curving of nanostructures using grain reflow and creation of nanopatterned channels, wells, and semiconducting conical nanopores using metal assisted plasma etching process. During plasma etching of silicon with carbon tetraflouride and oxygen, it was discovered that certain metals present during the process undergo characteristic changes. In the grain reflow process, tin grains were found to undergo grain coalescence, resulting in the spontaneous curving of structures with tight radii of curvature of the order of a few nanometers. Another approach presented in the thesis for the large scale parallel patterning in the nanoscale involves using catalytic etching of silicon, assisted by lithographically patterned noble metal geometries. Using this method, three dimensional structures such as nanopore arrays and gold (Au) nanoparticles (NPs) coated micro or nano wells and channels can be fabricated in silicon in a highly parallel fashion. I also investigated the applications of the 3D nanostructures formed by the aforementioned processes. Conical nanopore arrays were used for voltage gated biomolecular sensing and separations. Ionic transport through these pores was investigated and it was found that the rectification ratios could be enhanced by a factor of 100 by voltage gating on the semiconducting substrate alone, and that these pores could function as ionic switches with high on-off ratios. Further, multifunctional 3D nanostructures were also combined with bacteria to create a nanoscale bionic system that can be remotely controlled using a laser. Overall, these results present important advancements in the development of nanoscale patterning and 3D assembly of curved and porous nanostructures with applications in biomedical sciences and microorganism robotics

    Light-addressable potentiometric sensors based on self-assembled organic monolayer modified silicon on sapphire substrates

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    PhDLight-addressable potentiometric sensors (LAPS) have become attractive in many chemical and biological sensor applications. This thesis introduces the use of self-assembled organic monolayers (SAMs) as the insulator in LAPS and scanning photo-induced impedance microscopy (SPIM) for the first time. Two types of monolayer assemblies with alkenes (1-octadecene or undecylenic acid) and alkynes (1, 8-nonadiyne) were immobilised on hydrogenated silicon on sapphire (SOS) or silicon through thermal hydrosilylation. Further derivations were performed on the 1, 8-nonadiyne monolayers via “click” reactions. The monolayers were characterised by water contact angle, ellipsometry and X-ray photoelectron spectroscopy (XPS). LAPS/SPIM measurements with SAM-modified SOS showed the same good spatial resolution that was previously obtained with a conventional SiO2 insulator on SOS, but also a significant improvement in the accuracy of LAPS and the sensitivity of SPIM. Surface potential imaging using LAPS insulated by SAMs was validated by studying micropatterns of poly(allylamine hydrochloride) (PAH), poly(styrene sulfonate) (PSS) and DNA on a PAH template. Two potential strategies for chemically patterning SAMs on oxide-free SOS or Si substrates were investigated and compared. Microcontact printing (μCP) followed by “click” chemistry is a mild and efficient means of modifying the surface, whereas the combination of photolithography and “click” chemistry is not. LAPS was also shown to be extremely sensitive to surface contamination. LAPS/SPIM insulated by SAMs can also generate impedance images with high resolution and high sensitivity. Microcapsules labelled with gold nanoparticles (AuNPs) integrated with a femtosecond laser were used for the validation. In contrast, capsules without AuNPs showed no SPIM response at all, indicating that the impregnation with AuNPs can significantly increase the impedance of microcapsules. Finally, new instrumentation to integrate two-photon fluorescence microscopy with LAPS/SPIM was proposed. Preliminary results have shown that the new technique is promising to produce two-dimensional electrochemical images and two-photon fluorescent images of the cell-attachment area with subcellular resolutionChina Scholarship Council Queen Mary University of London
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