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Large arrays of femtoliter-sized chambers are important tools for single molecule research as well as bioanalytical applications. We have optimized the design and fabrication of two array types consisting of 250 × 250 (62 500) femtoliter chambers either by surface etching of fused silica slides or by polydimethylsiloxane (PDMS) molding. Highly diluted solutions of β-galactosidase were enclosed in such arrays to monitor the fluorogenic reactions of hundreds of individual enzyme molecules in parallel by wide-field fluorescence microscopy. An efficient mechanical sealing procedure was developed to prevent diffusion of the fluorescent reaction product out of the chambers. Different approaches for minimizing non-specific surface adsorption were explored. The signal acquisition was optimized to grant both a large field of view and an efficient signal acquisition from each femtoliter chamber. The optimized femtoliter array has enabled a three-in-one enzyme assay system: First, the concentration of active enzyme can be determined in a digital way by counting fluorescent chambers in the array. Second, the activity of the enzyme bulk solution is given by averaging many individual substrate turnover rates without the need for knowing the exact enzyme concentration. Third-unlike conventional enzyme assays-the distribution of individual substrate turnover rates yields insight into the conformational heterogeneity in an enzyme population. The substrate turnover rates of single β-galactosidase molecules were found to be broadly distributed and independent of the type of femtoliter array. In general, both types of femtoliter arrays are highly sensitive platforms for enzyme analysis at the single molecule level and yield consistent results.
Die übermäßige Verwendung von stickstoffbasierten Düngemitteln in der Landwirtschaft stellt eine Gefährdung für die Umwelt und Lebewesen dar. So ist die Analyse von Boden- und Grundwasser zu einem wesentlichen Bestandteil der Nachhaltigkeit und der ökologischen Erhaltung geworden. Dafür bietet der Multilyzer eine passende Lösung. Der Multilyzer ist ein mikrofluidisches Analysesystem zur Bestimmung niedrigster Konzentrationen von Nitrat, Nitrit und Ammonium, die alle wesentliche Bestandteile des Stickstoffkreislaufs sind. Welche bei Übermäßiger Aufnahme im Körper krebserregend wirken und den Sauerstofftransport im Blutkreislauf stören. Der Aufbau ist eine Kombination aus Absorptions- und Fluoreszenzspektroskopie. Der Betrieb mit einer 12 Volt Batterie ermöglicht die Verwendung des Multilyzer-Systems zur Online-Messung im Feld. Somit können sehr kurze Analysezeiten realisiert und der Einfluss von Umwandlungs- bzw. Abbauprozessen vermieden werden. Das gesamte Messsystem wird im Kompetenzzentrum Nanochem an der OTH Regensburg entwickelt, inklusive Fertigungstechnologien, Software- und Hardwaresteuerung.
In high-tech processing even smallest concentrations of metal ions in process media are of the utmost significance because they cause expensive production failures. Currently, cost-intensive equipment, special trained staff and time consuming analyses are necessary to detect these contaminations in order to avoid failures. The Centers of Excellence Nanochem and Sensorics at the University of Applied Sciences Regensburg (owner of patent PCT/EP2010/064833) and their industrial partner Micro-Epsilon GmbH are developing a new miniaturized measurement device which allows cost-effective real-time analysis of fluidic media for the first time. The system is fully automated and can be directly connected to wet-etch benches. Hence it allows continuous real-time surveillance of metal contaminations in the ppb-range through absorption spectroscopy in process media. For this purpose a very small sample amount of the process medium and a specific complexing agent are mixed together. This leads to an increase in the molar extinction coefficients and though even smallest contaminations become visible. The main parts of our development are the simulation of the different system components, their production and chemical analyses with the evaluation model.
Online trace analysis based on UV/Vis spectroscopy requires long detection paths. Therefore an isotropic wet etch process in silicon is developed to fabricate a 300 µm deep channel with low channel wall roughness for desired light guidance application. Four etchant compositions were compared in terms of etching rate, surface roughness and selectivity in a beaker process. The best fitting mixture was selected. To further increase the surface quality (bubble issue) a spin etcher tool is used for producing the channels. The dependence of homogeneity and defect density on media flux, and rotation velocity was investigated. Results show that high rotation velocity and high media flux lead to great defects in the channel wall. Through rotation of the wafer during etching, the etching rate of silicon rises compared to the beaker process due to the rapid removal of etch products and simultaneous supply of fresh etchant. After 38 min of etching, 300 µm deep semi-circular channels with high optical quality (Rq=10 nm±2 nm) over 3 m were produced.
The high surface to volume ratio of nanoparticles allows a detailed experimental study of the surface phenomena associated with solid bridging. Besides bulk analyses, the local view on the structure and composition via HRTEM is particularly essential. 50 nm core shell particles consisting of a silicon (Si) core and a SiO2 shell were used as model system to understand surface phenomena appearing for Si-based nanostructures. Evaporative drying from de-ionized water shows the most significant bridging effect based on SiO2. There is only a localized deposition of oxides between the particles during the drying process and no overall oxidation. For the deposition material, silicates are the most likely candidates.
Enhanced particle removal processes in wet cleaning as well as drying processes of semiconductor wafers can cause significant lateral forces on surface structures. These forces, however, must not exceed the mechanical stability of structures on the wafer. Thus, a mechanical fracture test was used to assess the lateral mechanical stability of polysilicon line structures in relevant process liquids. The mechanical test was based on nanomanipulation with an atomic force microscope. Compared to fracture tests in air, data acquired in liquid isopropanol revealed a stabilizing effect. The differences in fracture forces can be attributed to a stress corrosion process on the surface. The size of the generated damage was influenced by the viscosity of the surrounding media.
The mechanical stability of nanostructures depends on the surrounding medium. Their stability was probed by lateral force microscopy in liquid media. Previously reported data on water and isopropanol showed an increase in the fracture strength for the latter. Further tests with other alcohols (ethanol, 1-butanol) also showed an increasing strength. The interface between the liquid and the surface is the decisive factor for the influence of the media. When altering the interface with a cationic surfactant or a self-assembled monolayer, an increase of the fracture force by 100 % compared to de-ionized water could be measured.
In this work, a simple two-step method to create tunable self-assembled three-dimensional nanostructure array-like nanoantennas directly on the tip of an optical quartz glass fiber is described. The structures are prepared by using dry etching of the fiber tip. For the etching process, gold nanoparticles fabricated by thermal dewetting technique were used as template. The structures are applied as sensors for label-free analysis of organic substances in ppb range, such as drug residues in liquid solutions. The measurements are carried out by a portable Raman device with an exchangeable sensor head utilizing the SERS-effect. This method allows in situ applications. In order to characterize the SERS cells, para-thiocresol and diclofenac sodium are used as model substances. For optimization of the substrate performance, different thicknesses of the dewetting-layer (6, 9, 12 nm), different etching times for formation of the pillars (6, 8, 10 and 12 min), and different thicknesses of SERS-metallization (25, 50, 75 nm) of gold and silver are compared. In order to show the applicability of the structure on the tip of a fiber, measurements from the upper side and from the underside of the substrate on quartz plates are compared. Reproducible SERS enhancement factors up to 10 7 {10^{7}} were achieved.
In this work, a simple cost effective method to create tunable self-assembled three-dimensional nanostructure array-like nanoantennas on a tip of an optical quartz glass fiber is described. The structures are prepared using lithography-less dry etching. Gold nanoparticles are used as an etching mask using a thin metal-film thermal dewetting technique. The structures are applied as sensor for label-free analysis of organic substances in ppb range, such as drug residues in groundwater. The measurements are carried out by means of a Surface-enhanced Raman scattering (SERS) effect, an exchangeable sensor head, and a portable Raman device. This method allows in situ applications. Parathiocresol is used as a model substance to characterize the SERS cells. For metallization, gold and silver are compared. Reproducible SERS enhancement factors up to 10 7 are evaluated.