Showing papers by "Gerald Urban published in 2017"

Platinum nanowires anchored on graphene-supported platinum nanoparticles as a highly active electrocatalyst towards glucose oxidation for fuel cell applications.

Abstract: The limited performance of platinum-based electrocatalysts for glucose electrooxidation is a major concern for glucose fuel cells, since glucose electrooxidation is characterized by slow reaction kinetics and low diffusion coefficient. Here, the presented graphene-supported platinum-based hierarchical nanostructures attain highly enhanced electrocatalytic activity towards glucose oxidation. Platinum nanoparticles electrodeposited on graphene support retain mechanical stability and act as junctions allowing a reliable, smooth and dense growth of platinum nanowires with extremely small diameters (>10 nm) on graphene. The electrode's surface roughness was increased by factors up to 4000 to the geometrical surface area enabling maximized exploitation of the electrocatalytic activity of platinum and efficient electron transfer between nanowires and the substrate. The unique three-dimensional geometry of these hierarchical nanostructures has a significant impact on their catalytic performance offering short diffusional paths for slow glucose species, thus, mass transport limitations are optimized leading to lower polarization losses. This was examined by galvanostatic measurements of the operation as anodes in glucose half-cells under conditions corresponding to implantable glucose fuel cells. The presented hierarchical nanostructures show remarkably enhanced catalytic performance for glucose electrooxidation, i.e. a negatively shifted open circuit potential of −580 mV vs. Ag/AgCl, hence, representing appropriate electrocatalysts for use as anodes in glucose fuel cells. In combination with a non-metal N-doped graphene cathode, a cell potential of 0.65 V was achieved at a galvanostatic load of 17.5 μA cm−2 which noticeably surpasses the performance of state of the art catalysts for the aforementioned operation conditions.

Investigation of low temperature effects on work function based CO2 gas sensing of nanoparticulate CuO films

Abstract: The gas sensing behavior of semiconducting nanoparticulate copper oxide (CuO‐NPs) towards CO 2 with respect to different conditions affecting the signal response is investigated with the help of adsorption induced work function changes. Work function measurements have been carried out with the help of Kelvin probe. The analysis of cross‐sensitivities to humidity is conducted in the low temperature range between 25 °C and 110 °C and it is shown that for CuO‐NPs, optimization of work function based CO 2 sensing is possible by using a combined effect of humidity and temperature. Furthermore, the temperature induced effects during CO 2 sensing are explained using considerations of kinetics and thermodynamics of the process. We show that moderate temperatures of about 65 °C exert a positive influence on the kinetics of chemical processes occurring on the CuO‐NPs surface in the presence of water and CO 2 as well as counterbalance the negative impact of high humidity dependence on CO 2 gas sensing. However starting from 65 °C, CO 2 response decreases owing to a negative effect of temperature on the thermodynamics of the sensing reaction. Compared to other metal oxide based materials for CO 2 sensing, CuO‐NPs show promising results and enables the prospect towards the development of new CO 2 gas sensor operable at low temperatures.

Clinical on-site monitoring of ß-lactam antibiotics for a personalized antibiotherapy.

Abstract: An appropriate antibiotherapy is crucial for the safety and recovery of patients. Depending on the clinical conditions of patients, the required dose to effectively eradicate an infection may vary. An inadequate dosing not only reduces the efficacy of the antibiotic, but also promotes the emergence of antimicrobial resistances. Therefore, a personalized therapy is of great interest for improved patients’ outcome and will reduce in long-term the prevalence of multidrug-resistances. In this context, on-site monitoring of the antibiotic blood concentration is fundamental to facilitate an individual adjustment of the antibiotherapy. Herein, we present a bioinspired approach for the bedside monitoring of free accessible s-lactam antibiotics, including penicillins (piperacillin) and cephalosporins (cefuroxime and cefazolin) in untreated plasma samples. The introduced system combines a disposable microfluidic chip with a naturally occurring penicillin-binding protein, resulting in a high-performance platform, capable of gauging very low antibiotic concentrations (less than 6 ng ml−1) from only 1 µl of serum. The system’s applicability to a personalized antibiotherapy was successfully demonstrated by monitoring the pharmacokinetics of patients, treated with s-lactam antibiotics, undergoing surgery.

Low-Volume Label-Free Detection of Molecule-Protein Interactions on Microarrays by Imaging Reflectometric Interferometry.

Abstract: This system allows the high-throughput protein interaction analysis on microarrays. We apply the interference technology 1λ–imaging reflectometric interferometry (iRIf) as a label-free detection method and create microfluidic flow cells in microscope slide format for low reagent consumption and lab work compatibility. By now, most prominent for imaging label-free interaction analyses on microarrays are imaging surface plasmon resonance (SPR) methods, quartz crystal microbalance, or biolayer interferometry. SPR is sensitive against temperature drifts and suffers from plasmon crosstalk, and all systems lack array size (maximum 96 spots). Our detection system is robust against temperature drifts. Microarrays are analyzed with a spatial resolution of 7 µm and time resolution of ≤50 fps. System sensitivity is competitive, with random noise of <5 × 10−5 and baseline drift of <3 × 10−6. Currently available spotting technologies limit array sizes to ~4 spots/mm2 (1080 spots/array); our detection system would allo...

Flow rate independent sensing of thermal conductivity in a gas stream by a thermal MEMS-sensor – Simulation and experiments

Abstract: A thermal system for measuring thermal conductivity in a streaming gas is presented. The system features a heating element and a downstream temperature sensor on a membrane area surrounded by a substrate serving as heat sink. Simulations predict a flow independent region by use of the FEM heat transfer model in all directions in a laminar flow profile. Both simulation and experimental results show that the temperature of the downstream element is sensitive toward the gas type but insensitive toward the gas flow over a wide range. Furthermore, the findings show that the temperature of the downstream element in the flow independent region only depends on the gas’ thermal conductivity. The distance between the heater and the downstream temperature sensor is found to be a design parameter in order to shift the flow independent region according to the requirements of the application. The experimental results correspond very well to the theoretical predictions.

Dry film photoresist-based electrochemical microfluidic biosensor platform: Device fabrication, on-chip assay preparation, and system operation

Abstract: In recent years, biomarker diagnostics became an indispensable tool for the diagnosis of human disease, especially for the point-of-care diagnostics. An easy-to-use and low-cost sensor platform is highly desired to measure various types of analytes (e.g., biomarkers, hormones, and drugs) quantitatively and specifically. For this reason, dry film photoresist technology - enabling cheap, facile, and high-throughput fabrication - was used to manufacture the microfluidic biosensor presented here. Depending on the bioassay used afterwards, the versatile platform is capable of detecting various types of biomolecules. For the fabrication of the device, platinum electrodes are structured on a flexible polyimide (PI) foil in the only clean-room process step. The PI foil serves as a substrate for the electrodes, which are insulated with an epoxy-based photoresist. The microfluidic channel is subsequently generated by the development and lamination of dry film photoresist (DFR) foils onto the PI wafer. By using a hydrophobic stopping barrier in the channel, the channel is separated into two specific areas: an immobilization section for the enzyme-linked assay and an electrochemical measurement cell for the amperometric signal readout. The on-chip bioassay immobilization is performed by the adsorption of the biomolecules to the channel surface. The glucose oxidase enzyme is used as a transducer for electrochemical signal generation. In the presence of the substrate, glucose, hydrogen peroxide is produced, which is detected at the platinum working electrode. The stop-flow technique is applied to obtain signal amplification along with rapid detection. Different biomolecules can quantitatively be measured by means of the introduced microfluidic system, giving an indication of different types of diseases, or, in regard to therapeutic drug monitoring, facilitating a personalized therapy.

MgO-Doped (Zr,Sr)TiO3 Perovskite Humidity Sensors: Microstructural Effects on Water Permeation

Abstract: Porous (Zr0.5,Sr0.5)TiO3 and MgO (1, 3, 5 mol%) doped ZST nanocomposites have been developed and investigated as humidity sensing elements. The surface area analyser and FESEM data have indicated that the MgO doped perovskites are contained of the macropores and grain size of about 77 to 87 nm. EFTEM proved the reduction of particle size by addition of MgO dopant concentration. While pure ZST shows BET surface area of about 58 m2/g, MgO doped samples exhibit about 12 m2/g. Sensor contained of ZST doped with 3 mol% MgO shows highest sensitivity with about four orders of magnitude change in impedance within the range of 20% to 95% RH.

Biosensors and personalized drug therapy: what does the future hold?

Abstract: In recent years, personalized medicine (PM), targeting at a tailored drug therapy or preventive care as individualized as the disease itself, is getting increasingly important in human medicine, ph...

Rational Design of Morphological Characteristics to Determine the Optimal Hierarchical Nanostructures in Heterogeneous Catalysis

Abstract: This work draws attention to the optimal hierarchical nanostructure morphology and the morphological characteristics that lead to a rational design of heterogeneous nanocatalysts, especially for reactions that exhibit sluggish kinetics. A simplified methanol oxidation on two types of hierarchical nanostructures, external and internal, is reported. A complex system of asymmetric geometries was simplified by mapping 3 D geometries into 2 D models by using a mass transport approach. The macropore size was the most comprehensive characteristic to evaluate the specific activity and current density of hierarchical nanostructures. The optimal current densities for both types of nanostructures were achieved in macropore size ranges of 3.2–4.5 and 1.9–3.2 μm, respectively. The optimal mass activity of the internal nanostructures was achieved in the porosity range of 40–50 %, whereas that of the external hierarchical nanostructures was achieved at high porosity values. In comparison to internal hierarchical nanostructures, external hierarchical nanostructures tend to be cost-effective catalysts that have a high catalytic activity.

Highly Sensitive Electrochemical Glutamate Microsensors for Food Analysis

Abstract: Electrochemical microsensors are ideal to measure substances with low concentration in complex environments. The primary excitatory neurotransmitter l-glutamate is present in many foods as a distinctive flavour (enhancer) with a wide concentration range. In comparison to other methods, electrochemical sensors allow the rapid, precise, cost-effective, online measurement without any sample treatment. We developed a disposable electrochemical microsensor platform with multiple integrated, highly sensitive (detection limit <150 nM) and selective enzyme-based glutamate biosensors. We showed both the precise determination of glutamate levels in processed foods with high glutamate content (15–40 mM), e.g., broth, and in foods with low natural concentrations such as different types of cow’s milk (~250 μM). Hereby, we successfully demonstrated the capabilities of electrochemical biosensors in food monitoring, analysis and quality control.

Measurement of Young’s modulus and residual stress of atomic layer deposited Al2O3 and Pt thin films

Abstract: The accurate measurement of mechanical properties of thin films is required for the design of reliable nano/micro-electromechanical devices but is increasingly challenging for thicknesses approaching a few nanometers. We apply a combination of resonant and static mechanical test structures to measure elastic constants and residual stresses of 8–27 nm thick Al2O3 and Pt layers which have been fabricated through atomic layer deposition. Young's modulus of poly-crystalline Pt films was found to be reduced by less than 15% compared to the bulk value, whereas for amorphous Al2O3 it was reduced to about half of its bulk value. We observed no discernible dependence of the elastic constant on thickness or deposition method for Pt, but the use of plasma-enhanced atomic layer deposition was found to increase Young's modulus of Al2O3 by 10% compared to a thermal atomic layer deposition. As deposited, the Al2O3 layers had an average tensile residual stress of 131 MPa. The stress was found to be higher for thinner layers and layers deposited without the help of a remote plasma. No residual stress values could be extracted for Pt due to insufficient adhesion of the film without an underlying layer to promote nucleation.

Multi-parameter monitoring of binary gas mixtures: Concentration and flow rate by DC excitation of thermal sensor arrays

Abstract: This contribution presents a thermal sensor, which is capable of simultaneously determining gas concentrations of a binary gas mixture under flow conditions and its flow rate. The sensor design corresponds to the calorimetric principle. The multi-parameter detection is achieved by the use of two time independent excitation modes (power and temperature). Due to the developed sensor design, a flow independent, but gas sensitive region is obtained in power mode. In this flow range, the thermal conductivity is measured by analyzing the temperature of the downstream element. Gas concentration of the binary gas mixture is derived from the theoretical relationship to thermal conductivity. Afterwards, the flow rate is detected by evaluating the temperature difference between the down- and upstream temperature sensors in temperature excitation mode. This measurement technique has been successfully proven under laboratory conditions, where a flowing mixture of e.g. methane and carbon dioxide has been analyzed. The carried out measurements show an accuracy of ±5% in gas concentration and of ±3.3% in flow rate. This measuring method seems to be sufficient to analyze biogas in anaerobic distinctions. However, further investigation is needed to open this technique for this application.

(Invited) Electrochemical Characterization of Nanogap Interdigitated Electrode Arrays for Lab-on-a-Chip Applications

Abstract: In this work we present recent results on electrochemical characterization of the fabricated nanogap interdigitated electrode arrays (nIDAs) for Lab-on-a-Chip applications. The advantages of the presented nIDAs and their potential for application in bioelectrochemistry were studied using different electrochemical methods. Chronoamperometry is applied to achieve reversible redox processes which lead to an amplification of the measured current compared to a single electrode configuration and as a result,an increase in signal-to-noise ratio. For the electrochemical characterization of the created nIDAs ferrocenemethanol (FcMeOH) and p-aminophenol (pAP) were selected as redox couples. An amplification factor above 160 was obtained with FcMeOH for the nIDAs with 100 nm gap. An inverse correlation between gap size and amplification was proven. In addition, the formation of a polymer film during redox cycling could be verified to cause the lower amplification factor observed in pAP measurements. Furthermore, different electrode cleaning procedures were demonstrated by combination of O2 plasma and cyclic voltammetry. The nIDAs presented here offer many advantages including low-cost fabrication, high amplification and collection factors and thus are highly suitable for biosensor applications.

Zero consumption clark-type oxygen microsensor for cell culture monitoring

Abstract: This paper reports on fabrication and characterization of a true Clark-type microsensor to monitor oxygen locally in cell culture. We were able to implement the Ross principle to achieve zero analyte consumption, as verified by reading the counter electrode potential. Chronoamperometric protocols were applied for the first time in miniaturized Clark-type arrangements resulting in superior sensor stabil­ity. The sensor was applied for oxygen measurements in tumor cell culture.

Electrochemical Multisensor System for Monitoring the Hydrogen Peroxide Direct Synthesis in Microreactors

Abstract: We present an electrochemical sensor system for the detection of hydrogen peroxide inside a direct synthesis microreactor. The setup allows the online, in situ measurement of high reactant concentrations by amperometric detection across the micro channel width and length. The robust integration of the electrochemical cell in the microreactor was demonstrated. Hydrogen peroxide was detected under reaction conditions (pH 3–4, presence of bromide) showing linear behaviour up to 2 mM with high sensitivity and excellent stability. The linear range was increased up to 10 mM by applying a diffusion limiting pHEMA layer to the electrode surface.

A dished diaphragm for the miniature encapsulation of a pressure sensor for in-vivo applications

Abstract: This paper reports a miniaturized fluid-filled encapsulation of a pressure sensor which is, for the first time, based on a dished circular diaphragm. With this method a volume change is mainly compensated by diaphragm bending and leads to merely low pressure changes. The behavior of a titanium diaphragm was simulated and experimentally investigated. Finally a pressure sensor module was encapsulated. It performed well including small signal behavior, pressure transmission and hysteresis effects. Due to its size and titanium housing the sensor might be applicable as medical implant.

In-Situ Electrophoretic Mobility Determination by Particle Image Velocimetry for Efficient Microfluidic Enrichment of Bacteria

Abstract: We present a novel approach for the efficiency enhancement of microfluidic bacteria enrichment systems based on free-flow electrophoresis (FFE). FFE efficiency is highly dependent on the electrophoretic mobility μ of the bacteria. As μ varies strongly with the suspension medium, fast and accurate determination of μ is needed to achieve optimal enrichment performance from different suspension media. For the first time, μ is determined in-situ for multiple media during on-chip FFE by Particle Image Velocimetry (PIV) of fluorescent bacteria, obviating the need for separate measurement equipment or chemical staining of the bacteria.

Pericellular Oxygen Monitoring during Low-Level Light Therapy in Cell Culture Using a Microsensor System

Abstract: An electrochemical microsensor system to monitor the pericellular oxygen concentration of fibroblasts during low-level light therapy in vitro was developed. The system provides in-sight into the metabolism of the cells during and in consequence of illumination with visible red light. This approach is a unique method for real-time investigations of cellular respiration during light therapy. The presented sensor system features direct amperometric measurements by using chronoamperometric protocols for long-term stability. The oxygen measurements do not show a disturbance by light.