@article{KrylovAdamzigWalteretal.2006, author = {Krylov, Andrey. V. and Adamzig, H. and Walter, A. D. and Loechel, B. and Kurth, E. and Pulz, O. and Szeponik, Jan and Wegerich, Franziska and Lisdat, Fred}, title = {Parallel generation and detection of superoxide and hydrogen peroxide in a fluidic chip}, series = {Sensors and actuators : B, Chemical}, volume = {119}, journal = {Sensors and actuators : B, Chemical}, number = {1}, publisher = {Elsevier}, address = {Lausanne}, issn = {0925-4005}, doi = {10.1016/j.snb.2005.11.062}, pages = {118 -- 126}, year = {2006}, abstract = {A fluidic chip system was developed, which combines a stable generation of superoxide radicals and hydrogen peroxide with their sensorial detection. The generation of both reactive oxygen species was achieved by immobilization of xanthine oxidase on controlled pore glass in a reaction chamber. Antioxidants can be introduced into the fluidic chip system by means of mixing chamber. The detection of both species is based on the amperometric principle using a biosensor chip with two working electrodes. As sensing protein for both electrodes cytochrome c was used. The novel system was designed for the quantification of the antioxidant efficiency of different potential scavengers of the respective reactive species in an aqueous medium. Several model antioxidants such as ascorbic acid or catalase have been tested under flow conditions.}, language = {en} } @article{BadalyanDierichStibaetal.2014, author = {Badalyan, Artavazd and Dierich, Marlen and Stiba, Konstanze and Schwuchow, Viola and Leimk{\"u}hler, Silke and Wollenberger, Ulla}, title = {Electrical wiring of the aldehyde oxidoreductase PaoABC with a polymer containing osmium redox centers}, series = {Biosensors}, volume = {4}, journal = {Biosensors}, number = {4}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/bios4040403}, pages = {403 -- 421}, year = {2014}, abstract = {Biosensors for the detection of benzaldehyde and g-aminobutyric acid (GABA) are reported using aldehyde oxidoreductase PaoABC from Escherichia coli immobilized in a polymer containing bound low potential osmium redox complexes. The electrically connected enzyme already electrooxidizes benzaldehyde at potentials below -0.15 V (vs. Ag|AgCl, 1 M KCl). The pH-dependence of benzaldehyde oxidation can be strongly influenced by the ionic strength. The effect is similar with the soluble osmium redox complex and therefore indicates a clear electrostatic effect on the bioelectrocatalytic efficiency of PaoABC in the osmium containing redox polymer. At lower ionic strength, the pH-optimum is high and can be switched to low pH-values at high ionic strength. This offers biosensing at high and low pH-values. A "reagentless" biosensor has been formed with enzyme wired onto a screen-printed electrode in a flow cell device. The response time to addition of benzaldehyde is 30 s, and the measuring range is between 10-150 µM and the detection limit of 5 µM (signal to noise ratio 3:1) of benzaldehyde. The relative standard deviation in a series (n = 13) for 200 µM benzaldehyde is 1.9\%. For the biosensor, a response to succinic semialdehyde was also identified. Based on this response and the ability to work at high pH a biosensor for GABA is proposed by coimmobilizing GABA-aminotransferase (GABA-T) and PaoABC in the osmium containing redox polymer.}, language = {en} } @article{CywinskiHammannHuehnetal.2014, author = {Cywinski, Piotr J. and Hammann, Tommy and Huehn, Dominik and Parak, Wolfgang J. and Hildebrandt, Niko and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Europium-quantum dot nanobioconjugates as luminescent probes for time-gated biosensing}, series = {Journal of biomedical optics}, volume = {19}, journal = {Journal of biomedical optics}, number = {10}, publisher = {SPIE}, address = {Bellingham}, issn = {1083-3668}, doi = {10.1117/1.JBO.19.10.101506}, pages = {8}, year = {2014}, abstract = {Nanobioconjugates have been synthesized using cadmium selenide quantum dots (QDs), europium complexes (EuCs), and biotin. In those conjugates, long-lived photoluminescence (PL) is provided by the europium complexes, which efficiently transfer energy via Forster resonance energy transfer (FRET) to the QDs in close spatial proximity. As a result, the conjugates have a PL emission spectrum characteristic for QDs combined with the long PL decay time characteristic for EuCs. The nanobioconjugates synthesis strategy and photo-physical properties are described as well as their performance in a time-resolved streptavidin-biotin PL assay. In order to prepare the QD-EuC-biotin conjugates, first an amphiphilic polymer has been functionalized with the EuC and biotin. Then, the polymer has been brought onto the surface of the QDs (either QD655 or QD705) to provide functionality and to make the QDs water dispersible. Due to a short distance between EuC and QD, an efficient FRET can be observed. Additionally, the QD-EuC-biotin conjugates' functionality has been demonstrated in a PL assay yielding good signal discrimination, both from autofluorescence and directly excited QDs. These newly designed QD-EuC-biotin conjugates expand the class of highly sensitive tools for bioanalytical optical detection methods for diagnostic and imaging applications. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)}, language = {en} } @article{HovestaedtMemczakPleineretal.2014, author = {Hovestaedt, Marc and Memczak, Henry and Pleiner, Dennis and Zhang, Xin and Rappich, Joerg and Bier, Frank Fabian and St{\"o}cklein, Walter F. M.}, title = {Characterization of a new maleimido functionalization of gold for surface plasmon resonance spectroscopy}, series = {Journal of molecular recognition : an international journal devoted to research on specific molecular recognition in chemistry, biology, biotechnology and medicine}, volume = {27}, journal = {Journal of molecular recognition : an international journal devoted to research on specific molecular recognition in chemistry, biology, biotechnology and medicine}, number = {12}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0952-3499}, doi = {10.1002/jmr.2396}, pages = {707 -- 713}, year = {2014}, abstract = {Para-maleimidophenyl (p-MP) modified gold surfaces have been prepared by one-step electrochemical deposition and used in surface plasmon resonance (SPR) studies. Therefore, a FITC mimotope peptide (MP1, 12 aa), a human mucin 1 epitope peptide (MUC, 9 aa) and a protein with their specific antibodies were used as model systems. The peptides were modified with an N-terminal cysteine for covalent and directed coupling to the maleimido functionalized surface by means of Michael addition. The coupling yield of the peptide, the binding characteristics of antibody and the unspecific adsorption of the analytes were investigated. The results expand the spectrum of biosensors usable with p-MP by widely used SPR and support its potential to be versatile for several electrochemical and optical biosensors. This allows the combination of an electrochemical and optical read-out for a broad variety of biomolecular interactions on the same chip. Copyright (c) 2014 John Wiley \& Sons, Ltd.}, language = {en} } @article{DongmoLeykDoscheetal.2016, author = {Dongmo, Saustin and Leyk, Janina and Dosche, Carsten and Richter-Landsberg, Christiane and Wollenberger, Ursula and Wittstock, Gunther}, title = {Electrogeneration of O-2(center dot-) and H2O2 Using Polymer-modified Microelectrodes in the Environment of Living Cells}, series = {Electroanalysis : an international journal devoted to fundamental and practical aspects of electroanalysis}, volume = {28}, journal = {Electroanalysis : an international journal devoted to fundamental and practical aspects of electroanalysis}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1040-0397}, doi = {10.1002/elan.201600267}, pages = {2400 -- 2407}, year = {2016}, abstract = {Microelectrodes modified with electropolymerized plumbagin (PLG) were used for the generation of superoxide radical (O-2(center dot-)) and hydrogen peroxide (H2O2) during oxygen reduction reaction (ORR) in an aqueous medium, specifically in serum-free cell culture media. This is enabled by the specific design of a polymer film on the microelectrode. The generation and diffusion of O-2(center dot-) during electrocatalytic ORR at a positionable PLG polymer-modified microelectrode was followed by fluorescence microscopy with the selective dye 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) and by amperometric detection using a cytochrome c-modified electrode at + 0.13 V. H2O2 production, either by direct oxygen reduction or as product of O-2(center dot-) disproportionation, was monitored by the reaction with Amplex UltraRed. The PLG polymer-modified microelectrodes were used to expose mammalian B6-RPE07 retinal cells to defined local fluxes of reactive oxygen species (ROS), and cellular responses and morphological alterations were observed. The use of a controllable source of ROS opens many possibilities to study how living cells respond to the presence of a certain flux of specific ROS.}, language = {en} } @article{OthmanWollenberger2020, author = {Othman, Abdelmageed M. and Wollenberger, Ulla}, title = {Amperometric biosensor based on coupling aminated laccase to functionalized carbon nanotubes for phenolics detection}, series = {International journal of biological macromolecules}, volume = {153}, journal = {International journal of biological macromolecules}, publisher = {Elsevier}, address = {New York, NY [u.a.]}, issn = {0141-8130}, doi = {10.1016/j.ijbiomac.2020.03.049}, pages = {855 -- 864}, year = {2020}, abstract = {A biosensor for phenolic compounds based on a chemically modified laccase from Coriolus hirsula immobilized on functionalized screen-printed carbon electrodes (SPCEs) was achieved. Different enzyme modifications and immobilization strategies were analyzed. The electrochemical response of the immobilized laccase on SPCEs modified with carboxyl functionalized multi-walled carbon nanotubes (COOH-MWCNT) was the highest when laccase was aminated prior to the adsorption onto the working electrode. The developed lactase biosensor sensitivity toward different phenolic compounds was assessed to determine the biosensor response with several phenolic compounds. The highest response was obtained for ABTS with a saturation value of I-max = 27.94 mu A. The electrocatalytic efficiency (I-max/K-m(app)) was the highest for ABTS (5588 mu A mu M-1) followed by syringaldazine (3014 mu A.mu M-1). The sensors were considerably stable, whereby 99.5, 82 and 77\% of the catalytic response using catechol as substrate was retained after 4, 8 and 10 successive cycles of reuse respectively, with response time average of 5 s for 12 cycles. No loss of activity was observed after 20 days of storage.}, language = {en} } @article{TadjoungWaffoMitrovaTiedemannetal.2021, author = {Tadjoung Waffo, Armel Franklin and Mitrova, Biljana and Tiedemann, Kim and Iobbi-Nivol, Chantal and Leimk{\"u}hler, Silke and Wollenberger, Ulla}, title = {Electrochemical trimethylamine n-oxide biosensor with enzyme-based oxygen-scavenging membrane for long-term operation under ambient air}, series = {Biosensors : open access journal}, volume = {11}, journal = {Biosensors : open access journal}, number = {4}, publisher = {MDPI}, address = {Basel}, issn = {2079-6374}, doi = {10.3390/bios11040098}, pages = {17}, year = {2021}, abstract = {An amperometric trimethylamine N-oxide (TMAO) biosensor is reported, where TMAO reductase (TorA) and glucose oxidase (GOD) and catalase (Cat) were immobilized on the electrode surface, enabling measurements of mediated enzymatic TMAO reduction at low potential under ambient air conditions. The oxygen anti-interference membrane composed of GOD, Cat and polyvinyl alcohol (PVA) hydrogel, together with glucose concentration, was optimized until the O-2 reduction current of a Clark-type electrode was completely suppressed for at least 3 h. For the preparation of the TMAO biosensor, Escherichia coli TorA was purified under anaerobic conditions and immobilized on the surface of a carbon electrode and covered by the optimized O-2 scavenging membrane. The TMAO sensor operates at a potential of -0.8 V vs. Ag/AgCl (1 M KCl), where the reduction of methylviologen (MV) is recorded. The sensor signal depends linearly on TMAO concentrations between 2 mu M and 15 mM, with a sensitivity of 2.75 +/- 1.7 mu A/mM. The developed biosensor is characterized by a response time of about 33 s and an operational stability over 3 weeks. Furthermore, measurements of TMAO concentration were performed in 10\% human serum, where the lowest detectable concentration is of 10 mu M TMAO.}, language = {en} }