Gerald Urban | Albert-Ludwigs-Universität Freiburg (original) (raw)

Papers by Gerald Urban

2017 IEEE SENSORS, 2017

This paper reports a miniaturized fluid-filled encapsulation of a pressure sensor which is, for t... more 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.

Fresenius Journal of Analytical Chemistry, 1990

Thin Solid Films, 2020

The influence of high temperature annealing up to 800 ∘ C on electrical resistivity and temperatu... more The influence of high temperature annealing up to 800 ∘ C on electrical resistivity and temperature coefficient of resistance of magnetron sputtered platinum films were investigated experimentally and theoretically. Highly adherent platinum films were manufactured on silicon oxide interfaces without using additional adhesion layers like titanium or tantalum. Such platinum films can be extremely useful for the fabrication of microelectromechanical sensors. X-ray diffraction studies exhibit grain sizes in the range of 39 nm for the as-deposited case to 162 nm after annealing at 800 ∘ C. Thereby film resistivity values decrease from 16.8 ± 0.4 µΩ cm to 12.7 ± 0.2 µΩ cm and temperature coefficient of resistance values increase from 2180 ppm/K to 2810 ppm/K. A good accordance to the model of Mayadas and Shatzkes for resistivity as well as Tellier and Tosser for temperature coefficient of resistance could be found. The reflection coefficient for electrons at grain boundaries is extracted for both models.

Nanotechnology, 2016

The lack of performance of graphene-based electrocatalysts for oxygen reduction (ORR) is a major ... more The lack of performance of graphene-based electrocatalysts for oxygen reduction (ORR) is a major concern for fuel cells which can be mastered using nanocomposites. This work is highlighted by the optimization of nitrogen(N)-doped graphene/carbon nanotubes (CNTs) nanocomposite's ORR performance examined by galvanostatic measurements in realistically approached glucose half-cells. Obtained results mark an essential step for the development of nanocarbon-based cathodes, as we specifically evaluate the electrode performance under real fuel cell conditions. The 2D simulations exclusively represent an important approach for understanding the catalytic efficiency of the nanocomposite with unique structure. The kinetics features extracted from simulations are consistent with the experimentally determined kinetics. The morphology analysis reveals a 3D porous structure. The results demonstrate that the incorporation of CNTs implements mesoscale channels for improved mass transport and leads to efficient 4-electron transfer and enhanced overall catalytic activity in pH-neutral media. The nanocomposite shows increased specific surface area of 142 m 2 g −1 , positively shifted ORR onset potential of 67 mV and higher open circuit potential of 268 mV versus Ag/AgCl compared to N-graphene (11 m 2 g −1 , −17, 220 mV). The findings are supported by 2D simulations giving qualitative evidence to the significant role of CNTs for achieving better accessibility of pores, i.e. enabling improved transfer of oxygen and OH − , and providing more reaction sites in the nanocomposite. The nanocomposite demonstrates better ORR performance than constituent components regarding potential application in miniaturized single-compartment glucose-based fuel cells.

Journal of The Electrochemical Society, 2016

Efficiency, selectivity and sensitivity are important issues in catalytic applications, such as f... more Efficiency, selectivity and sensitivity are important issues in catalytic applications, such as fuel cells and electrochemical sensors. This paper discusses the catalytic activity of porous layers in heterogeneous reactions based on the impact of pore morphology on pore accessibility in liquids. We present three-dimensional simulations to discuss some critical geometrical characteristics that influence the overall catalytic activity of porous catalyst. Sensitivity is proportional to the overall catalytic activity of the surface area. However, selectivity depends on pore accessibility. Simulation results demonstrate that at constant k 0 , porous layers with small pores and large numbers of pores are selective to the species with high diffusion coefficient because of high pore accessibility. In contrast, porous electrodes with low number of large pores and a large top surface area are selective to the species with low diffusion coefficient because of low pore accessibility. Additionally, pore accessibility influences the diffusional resistance, which has an impact on the local pH-value. High diffusional resistance in the porous layer leads to an accumulation of reaction products and a modification in the concentration of buffer molecules, which change local pH-value and therefore the catalytic behavior. Several porous surfaces in various forms were investigated as heterogeneous catalysts in order to increase the catalytic activity, especially the electrocatalytic activity of electrodes. Catalytic activity is proportional to the reaction rate, which is defined by the number of molecules catalyzed per second. 1-3 Thus, catalytic activity depends on the rate of turnover on the active sites and on the number of active sites. Many research groups tried to adjust the catalytic activity through variation of electrode material composition. The mono-metal, 4 bimetal 12 Current density is one of measurable quantities that is influenced by the catalytic surface area. 15 Enhancement of the current density by increasing the surface roughness factor was observed for the oxidation of methanol, 16 ethanol 9 and glucose. 18,23,24 Park et al. 23,24 The high surface Rf of mesoporous electrode influences the faradaic z E-mail: olena.yurchenko@fmf.uni-freiburg.de current of kinetic controlled reactions, as in case of glucose oxidation, more than the faradaic current of diffusion-controlled reactions, as in case of L-ascorbic acid and 4-acetomidophenol oxidation. The high Rf enhances the faradaic current of reactions with sluggish electron transfer because of highly enlarged nanoscopic area. Roughness factor was often used in literature as the experimental characterizing parameter to optimize the electrode catalytic activity in liquid mediums. However, it is critical to use Rf as a characterizing parameter apart from other morphological characteristics and regardless the catalytic properties as well as the diffusion coefficient of active species. The investigations revealed that the electrode selectivity and activity have complex dependency on electrode morphology, i.e., the pore-size, distance among pores and the film thickness. For example, the Pt-nanotube arrays electrode with low roughness factor (Rf = 286) and the directly deposited Pt electrode with comparable rough surface (Rf = 183) exhibited different sensitivity toward glucose, ascorbic acid, uric acid and acetamidophenol. 18 Furthermore, the observation of the reaction current, based on the mesoporous surface area, proves that the surface morphology influences the surface catalytic activity. It was observed by Koehler et al. 25 that the fabrication process of mesoporous electrode influenced the oxidation efficiency at the electrode surface. They presented a fabrication process by which Rf was increased by 111%, while the current density of glucose oxidation increased by 250%. Catalytic activity is not only influenced by Rf and the number of catalytic sites, but also by pore accessibility. The mechanism of mass transport of active species and electrode film roughness are key aspects of determining the catalytic activity. One main limitation of mass transport in pores is the pore morphology, i.e., pore-size and the pore connectivity.

Electrochimica Acta, 2015

Abstract In this paper we present nanocrystalline boron-doped diamond nanoelectrode arrays (BDD-N... more Abstract In this paper we present nanocrystalline boron-doped diamond nanoelectrode arrays (BDD-NEAs) for the low-level detection of biogenic substances such as dopamine (DA) without the need for a selective membrane. We achieved a sensitive and reproducible detection of dopamine in the presence of ascorbic acid (AA) with oxygen (O-) terminated BDD-NEAs. To improve the peak separation between dopamine and ascorbic acid, differential pulse voltammetry (DPV) was employed. Therewith, it was possible to measure dopamine with a sensitivity of 57.9 nA μM −1 cm −2 . The detection limit was less than 100 nM with a linear behavior up to a concentration of 20 μM. The choice of the appropriate termination, the combination of the advantages of nanoelectrode arrays together with the outstanding electrochemical properties of boron-doped diamond and the right measurement method allowed successful measurement of dopamine in physiological concentrations in the presence of ascorbic acid.

Procedia Engineering, 2015

We present an electrochemical metabolic monitoring system, which is combined with a spheroid 3D t... more We present an electrochemical metabolic monitoring system, which is combined with a spheroid 3D tumor cell culture environment. It allows the continuous and precise monitoring of lactate production rates of single human hepatocyte spheroids online over days. Lactate concentration was measured using an electrochemical microsensor enabling the real-time monitoring of metabolic rates in combination with drug exposure. This setup can be used for drug testing as a powerful tool for fundamental research in general biology and toxicology.

Stem Cell Engineering, 2010

Stem cells are characterized by their ability to self-renew and to generate a diverse range of ph... more Stem cells are characterized by their ability to self-renew and to generate a diverse range of physiological cell types (Singec et al., Annu Rev Med. 2007; 58:313–328). In mammals, stem cells found in the mature organism (somatic stem cells) generate progeny of a specific cell lineage or tissue type (multipotency). For example, a hematopoietic stem cell gives rise to the cell lineages found in bone marrow and blood, while a central nervous system (CNS) neural stem cell generates neurons, oligodendrocytes, and astroglia (Murry and Keller, Cell. 2008; 132:661–680). At an earlier developmental stage, embryonic stem (ES) cells obtained from the inner cell mass of blastocyst-stage embryos exhibit limitless capacity to self-renew and can give rise to any cell type of the organism, thereby defining pluripotency (Murry and Keller, Cell. 2008; 132:661–680; Singec et al. Annu Rev Med. 2007; 58:313–328). The term “totipotent” is reserved for cells that can also give rise to the trophoblast and extraembryonic tissue in vivo, such as the fertilized egg (zygote). These designations exemplify how differentiation toward a specific mature cell phenotype is accompanied by an increasingly limited spectrum of potential descendant cell types and by a diminished proliferative capacity (Yeo et al., Hum Reprod. 2008; 23:67–73) (Fig. 1 ). In addition, recent advances in reprogramming of adult somatic cell types into pluripotent cells (Takahashi et al., Cell. 2007; 131:861–872) are aimed at controlling the regulatory mechanisms that govern stemness and pluripotency, which may soon enable even more refined modulation of cell fate (Yeo et al., Hum Reprod. 2008; 23:67–73; Pruszak and Isacson, Development and engineering of dopamine neurons. Austin, TX: Landis Bioscience; 2008; Jaenisch and Young, Cell. 2008; 132:567–582). To achieve translation of stem cell biology into clinical applications, somatic, embryonic, and reprogrammed stem cell sources alike are presently being investigated. Despite the fast-paced progress of stem cell research as a field, many aspects of cell development in the dish are still not fully understood. To ensure appropriate patterning, signaling parameters for cell lineage specification need to be identified, and generating the phenotype of interest requires close monitoring and controlled modulation of the microenvironmental conditions in the dish.

Thin Solid Films, 1986

Abstract Carbon films of high conductivity and very low hydrocarbon content were prepared by the ... more Abstract Carbon films of high conductivity and very low hydrocarbon content were prepared by the decomposition of acetylene using a parallel plate glow discharge apparatus. The electrical conductivity of the carbon films was determined mainly by the non-self-biased electrode, the r.f. power, the electrode temperature and the ratio of acetylene to argon partial pressures. The substrates were placed on the non-biased, r.f.-excited electrode. The electrode temperature was measured immediately before and after each deposition process. Argon, containing 4–30 vol.% acetylene at total pressures between 10 and 100 mTorr and power densities of 1–2W cm-2 at 7MHz were used. The electrode temperature was kept stable within 10 K. IR absorption studies as well as secondary ion mass spectrometric analysis indicated a very low hydrocarbon content of the films. Their room temperature conductivity of 10-2-10-5Ω-1cm-1 depended strongly on the electrode temperature and the applied discharge power. Optical gaps of about 0.75 eV were typical for these samples. The films were glassy in appearance, hard and stable. Pattern generation by reactive ion etching in an oxygen plasma using photoresist masks was carried out.

Sensors and Actuators A: Physical, 2006

Bacterial tests such as growth inhibition tests are the only convenient investigation method to d... more Bacterial tests such as growth inhibition tests are the only convenient investigation method to detect the impacts of water soluble drugs, e.g. antibiotics, on bacteria. These are cumbersome methods for determining the inhibiting effect of toxic components. The principle of these inhibition tests is the detection of cell numbers by measuring the optical density. With this time-consuming and complicate method only endpoint detection and no monitoring of cell growth is possible, which is obviously a drawback. Furthermore, coloured and turbid components cannot be tested. 1536 sinale well CS suspension CI current injection CE electrolyte ' 1.53mm

2014 44th European Solid State Device Research Conference (ESSDERC), 2014

We present gas sensor devices based on ultrathin SnO2 films, which are integrated on CMOS fabrica... more We present gas sensor devices based on ultrathin SnO2 films, which are integrated on CMOS fabricated micro-hotplate (μhp) chips. Bimetallic nanoparticles (NPs) such as PdAu, PtAu, and PdPt have been synthesized for optimizing the sensing performance of these sensors. We demonstrate that functionalization of nanocrystalline SnO2 gas sensing films with PdAu-NPs leads to a strongly improved sensitivity to the toxic gas carbon monoxide (CO) while the cross sensitivity to humidity is almost completely suppressed. We conclude that specific functionalization of CMOS integrated SnO2 thin film gas sensors with different types of NPs is a powerful strategy towards sensor arrays capable for distinguishing several target gases. Such CMOS integrated arrays are highly promising candidates for realizing smart multi-parameter sensing devices for the consumer market.

In diesem Kapitel wurde nachträglich eine Danksagung eingefügt, inhaltlich wurde das Kapitel nich... more In diesem Kapitel wurde nachträglich eine Danksagung eingefügt, inhaltlich wurde das Kapitel nicht verändert.

Biomedical Engineering / Biomedizinische Technik, 2017

The most common complication after implantation of foreign material is infection, leading to impl... more The most common complication after implantation of foreign material is infection, leading to implant failure and severe patient discomfort. Smoldering-infections proceed inapparently and might not get verified by radiological diagnostics. Early identification of this type of infection might significantly reduce the rate of complications. Therefore, we manufactured a microsensor strip in a hybrid of thin-film and laminate technology in a wafer-level process. It comprises electrochemical, amperometric microsensors for glucose, oxygen and lactate as well as an integrated reference electrode. Microsensors have been implanted in the mouse dorsal skin fold chamber, which got inoculated with a human-pathogen bacterial strain. A selective signal could be measured for all parameters and time points. The infection led to measurable changes of the wound environment as given by a decrease of the oxygen- as well as the glucose-concentration while the lactate concentration increased markedly over...

EXS, 1997

Integrated and miniaturized biosensor arrays were developed exhibiting outstanding performance. B... more Integrated and miniaturized biosensor arrays were developed exhibiting outstanding performance. Biosensors with negligible sensitivity to interferences and high long-term stability were produced by modifying electrochemical transducers and utilizing photopatternable enzyme membranes. The use of appropriate miniaturization technology leads to mass producible devices for in vivo and ex vivo applications.

Encyclopedia of Analytical Chemistry, Sep 15, 2006

This paper presents the use of biosensor devices for bioanalytical purposes. In contrast to commo... more This paper presents the use of biosensor devices for bioanalytical purposes. In contrast to common analytical tools using sophisticated and bulky devices, biosensors should be able to perform measurements in untreated samples in a simple and inexpensive manner. As a model creating biosensors serves nature which produces a variety of selective molecules during evolution that can be used in technical sensor devices. Combining such natural molecules with methods from microelectronics, mass fabrication of laboratories on chip seems feasible. Emerging markets for such tools can be seen in medicine, drug screening and biotechnology. After explaining the principles of biosensors different transducing methods are explained showing advantages and disadvantages for creating biosensors. The greatest emphasis is laid on electrochemical and optical principles which exhibit an overwhelming experience and the largest impact on future developments. Despite such developments, acoustic and calorimetric transducers are also explained. As biological sensing agents enzymes, antibodies and DNA are described with appropriate immobilizing procedures. Additionally, new aspects for creating a laboratory-on-chip using microanalytical systems (μTAS) including microfluidics and actuator modules are given for creating sensing systems for metabolic parameters and also cell-based and affinity-based systems for screening purposes. The purpose of this section is to give an overview and to explain the present possibilities for creating biosensor systems and ends up with an outlook in the near analytical future for new sophisticated and miniaturized analytical systems.

The 13th International Conference on Solid-State Sensors, Actuators and Microsystems, 2005. Digest of Technical Papers. TRANSDUCERS '05.

At the Institute of Microsystem Technology of the Albert-Ludwigs-Universitat, Freiburg, a foil-fi... more At the Institute of Microsystem Technology of the Albert-Ludwigs-Universitat, Freiburg, a foil-fingerprint sensor (FFPS) was developed for application in the broad biometric field. The sensor principle is patented and contains new know-how, which is based on knowledge of microsystem technology (Patent WO03/098535). It possesses, in this form, a world-wide unique position. These new flexible and foil-based sensors are primarily conceived for installation on smartcards. The flexible fingerprint sensor has crucial advantages compared to sensors at present on the market. It can replace today's expensive silicon fingerprint sensors and amend the possible application area.

Sensors and Actuators B: Chemical, 2003

A novel miniaturized amperometric carbon dioxide sensor with fabrication compatibility to most mo... more A novel miniaturized amperometric carbon dioxide sensor with fabrication compatibility to most modern MEMS production techniques and with a miniaturization potential down to 100μm has been developed. The electrochemical detection concept is based on a pH-dependent dissociation of copper complexes. The pH change of an electrolyte solution occurring due a variation of the pCO2 results in a variation of the