Laboratory for Sensors


Laboratory for Sensors

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Lehmann K.,Albert Ludwigs University of Freiburg | Lehmann K.,Laboratory for Sensors | Yurchenko O.,Albert Ludwigs University of Freiburg | Yurchenko O.,Laboratory for Sensors | And 9 more authors.
Carbon | Year: 2017

Hierarchical carbon nanowalls (CNW) are synthesized by plasma-enhanced chemical vapor deposition using p-xylene as a complex precursor. In contrast to ordinary CNW, synthesized with short-chained carbons, hierarchical CNW show a unique multi-scale pore structure, made up of micro- and mesopores connected by tubular macropores, offering higher surface area and surface accessibility. Their morphology, graphitic structure, surface area and accessibility are verified by transmission and scanning electron microscopy, gas sorption and impedance spectroscopy. Focused ion beam scanning electron microscopy tomography demonstrates the presence of macropores ensuring pore connectivity down to the substrate. Nitrogen/krypton physisorption confirms the micro- and mesoporous structure contributing extensively to the surface area. The impedance spectra are evaluated according to standard RC and transmission line models. The sample deposited for 60 min, with a structure height of 4.75 μm, features a volumetric capacitance of 2.6 F cm−3 and a response time of 25 ms. Hierarchical CNW exhibit a two to six times higher volumetric capacitance than CNW of similar proportions, reported in literature. Hierarchical CNW offer a promising way to realize high power and energy density requirements in electrochemical energy systems, like supercapacitors, due to their good conductivity, high surface area and open pore structure. © 2017 Elsevier Ltd

Weltin A.,Albert Ludwigs University of Freiburg | Weltin A.,Laboratory for Sensors | Slotwinksi K.,Albert Ludwigs University of Freiburg | Kieninger J.,Albert Ludwigs University of Freiburg | And 4 more authors.
17th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2013 | Year: 2013

A novel multiparametric microsensor system for online cell culture monitoring with human tumor cells is introduced. The system combines cell culture, microiluidics and biosensors on a single chip. It features pH, oxygen, glucose and lactate sensors on a transparent chip. The sensor performance was proven in cell culture environment. Cellular metabolism of T98G brain tumor cells was measured. Extracellular acidification and respiration can be quantified. Medium was efficiently transported to the biosensors by microiluidics. Glucose consumption and lactate production was measured in cycles with low analyte volumes (< 15 μl). Alteration of cellular metabolism by compounds could be monitored successfully.

Dincer C.,Albert Ludwigs University of Freiburg | Dincer C.,Laboratory for Sensors | Ktaich R.,Albert Ludwigs University of Freiburg | Ktaich R.,Laboratory for Sensors | And 7 more authors.
Electrochimica Acta | Year: 2015

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. © 2015 Elsevier Ltd.

Ledernez L.,Laboratory for Sensors | Ledernez L.,Albert Ludwigs University of Freiburg | Olcaytug F.,Laboratory for Sensors | Olcaytug F.,Albert Ludwigs University of Freiburg | And 2 more authors.
Contributions to Plasma Physics | Year: 2012

The deposition of dielectric nanofilms by magnetron AF plasma polymerization between two planar electrodes shows a number of advantages over the standard RF method without magnetron enhancement. Because it is powered at 15 kHz, it works as a DC discharge swapping side every half cycle. We investigated here the effect of the magnetron on the breakdown voltage in our system taking Paschen curves with a DC power source. Subsequently, we related the Paschen curves with the deposition rate of the coating, showing that the Paschen minimum corresponds to the maximum growth rate as far as the pressure and the inter-electrode distance are concerned. This result can be used to quickly determine the maximum growth rate in a given configuration via the measurement of a Paschen curve. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Meskath S.,Albert Ludwigs University of Freiburg | Urban G.,Laboratory for Sensors | Heinze J.,Albert Ludwigs University of Freiburg
Proceedings of IEEE Sensors | Year: 2010

We present a new optical polymer thin film sensor for high sensitivity and rapid response gas detection. Amphiphilic polymer co-networks (APCN) are used as sensor matrices for fast nitrogen dioxide detection. The sensor consists of an APCN in which the indicator has been embedded. The APCNs were synthesized by free radical induced photopolymerization and result in poly(2-(dimethylamino) ethyl acrylate)-l-polydimethylsiloxane (PDMAEA-l-PDMS). Thin and optical clear films of nanophase-separated co-networks are formed which are well suited for simple impregnation with indicators. Due to the high gas permeability of silicone containing APCNs, accurate gas detection at the sub-ppm level is feasible within seconds. As a result of nanophase separation, there is a spatial separation between areas in which the indicator reagent is well immobilized and areas that advantageously take care of the diffusive transport of the analyte. Thanks to the huge interface between the heterogeneous phases and therefore the good accessibility of the indicator, it is possible to design sensors with high sensitivity. Here, we describe the determination of nitrogen dioxide in the sub ppm-range, which occurs within seconds, using DPPD (N,N′-diphenyl-1,4- phenylendiamine) as indicator. The thin film response is reproducible and irreversible. With our kinetic-optical method response times within seconds were achieved. ©2010 IEEE.

Kiefer R.,Albert Ludwigs University of Freiburg | Kiefer R.,Laboratory for Sensors | Kiefer R.,University of Tartu | Weis D.G.,Albert Ludwigs University of Freiburg | And 4 more authors.
Synthetic Metals | Year: 2013

The nature of polypyrrole (PPy) is largely influenced by the potential used for its polymerization. To investigate this influence, PPy-bilayer actuators were created using different polymerization potentials in order to examine the effect of the polymerization potential on the involvement of anions and cations in the actuation process. Cyclic voltammetry and chronoamperometry methods were used to record the ion behaviour while simultaneous measurements were made of the PPy-bilayer deflection in order to characterize the PPy-bilayer actuation properties. A polymerization potential close to 0.85 V and 1.1 V produced a PPy-bilayer actuator which managed an optimum deflection in an electrolyte consisting of TBAPF6 (tetrabutyl ammonium hexaflourophosphate) in propylene carbonate (PC). Electrochemical quartz crystal microbalance (EQCM) measurements showed the degree to which solvated cations and anions are involved in the charging and discharging processes during actuation of the PPy-bilayers. The influence of anions and cations during actuation of the PPy-bilayer at reduction and oxidation is described by the model of reversible σ-dimerization. © 2013 Elsevier B.V. All rights reserved.

Dincer C.,Albert Ludwigs University of Freiburg | Dincer C.,Laboratory for Sensors | Laubender E.,Albert Ludwigs University of Freiburg | Hees J.,Fraunhofer Institute for Applied Solid State Physics | And 4 more authors.
Electrochemistry Communications | Year: 2012

Boron doped diamond (BDD) is a promising electrode material for electrochemical biosensor applications due to its low bio-fouling, chemical stability, and large potential window. For the first time, BDD nanoelectrode arrays (NEA) were studied using Scanning Electrochemical Microscopy (SECM) measurements. Using the phase-operated shear force technique and feedback mode, it was possible to scan a platinum (Pt) nanode with an active radius of 167 nm over a diamond array at a constant distance of 45 nm and to detect the electrochemical activity of single BDD nanodes in the 100 nm range. © 2012 Elsevier B.V.

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