@article{MolinnusBaeckerSiegertetal.2015, author = {Molinnus, Denise and B{\"a}cker, Matthias and Siegert, Petra and Willenberg, H. and Poghossian, Arshak and Keusgen, M. and Sch{\"o}ning, Michael Josef}, title = {Detection of Adrenaline Based on Substrate Recycling Amplification}, series = {Procedia Engineering}, volume = {120}, journal = {Procedia Engineering}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1877-7058}, doi = {10.1016/j.proeng.2015.08.708}, pages = {540 -- 543}, year = {2015}, abstract = {An amperometric enzyme biosensor has been applied for the detection of adrenaline. The adrenaline biosensor has been prepared by modification of an oxygen electrode with the enzyme laccase that operates at a broad pH range between pH 3.5 to pH 8. The enzyme molecules were immobilized via cross-linking with glutaraldehyde. The sensitivity of the developed adrenaline biosensor in different pH buffer solutions has been studied.}, language = {en} } @article{PoghossianGeisslerSchoening2019, author = {Poghossian, Arshak and Geissler, Hanno and Sch{\"o}ning, Michael Josef}, title = {Rapid methods and sensors for milk quality monitoring and spoilage detection}, series = {Biosensors and Bioelectronics}, volume = {140}, journal = {Biosensors and Bioelectronics}, number = {Article 111272}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0956-5663}, doi = {10.1016/j.bios.2019.04.040}, year = {2019}, language = {en} } @article{PoghossianIngebrandtOffenhaeusseretal.2009, author = {Poghossian, Arshak and Ingebrandt, S. and Offenh{\"a}usser, A. and Sch{\"o}ning, Michael Josef}, title = {Field-effect devices for detecting cellular signals}, series = {Seminars in Cell \& Developmental Biology. 20 (2009), H. 1}, journal = {Seminars in Cell \& Developmental Biology. 20 (2009), H. 1}, publisher = {Elsevier}, address = {Amsterdam}, isbn = {1096-3634}, pages = {41 -- 48}, year = {2009}, language = {en} } @article{BaeckerRakowskiPoghossianetal.2013, author = {B{\"a}cker, Matthias and Rakowski, D. and Poghossian, Arshak and Biselli, Manfred and Wagner, Patrick and Sch{\"o}ning, Michael Josef}, title = {Chip-based amperometric enzyme sensor system for monitoring of bioprocesses by flow-injection analysis}, series = {Journal of Biotechnology}, volume = {163}, journal = {Journal of Biotechnology}, number = {4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0168-1656}, doi = {10.1016/j.jbiotec.2012.03.014}, pages = {371 -- 376}, year = {2013}, abstract = {A microfluidic chip integrating amperometric enzyme sensors for the detection of glucose, glutamate and glutamine in cell-culture fermentation processes has been developed. The enzymes glucose oxidase, glutamate oxidase and glutaminase were immobilized by means of cross-linking with glutaraldehyde on platinum thin-film electrodes integrated within a microfluidic channel. The biosensor chip was coupled to a flow-injection analysis system for electrochemical characterization of the sensors. The sensors have been characterized in terms of sensitivity, linear working range and detection limit. The sensitivity evaluated from the respective peak areas was 1.47, 3.68 and 0.28 μAs/mM for the glucose, glutamate and glutamine sensor, respectively. The calibration curves were linear up to a concentration of 20 mM glucose and glutamine and up to 10 mM for glutamate. The lower detection limit amounted to be 0.05 mM for the glucose and glutamate sensor, respectively, and 0.1 mM for the glutamine sensor. Experiments in cell-culture medium have demonstrated a good correlation between the glutamate, glutamine and glucose concentrations measured with the chip-based biosensors in a differential-mode and the commercially available instrumentation. The obtained results demonstrate the feasibility of the realized microfluidic biosensor chip for monitoring of bioprocesses.}, language = {en} } @article{HuckPoghossianWagneretal.2012, author = {Huck, Christina and Poghossian, Arshak and Wagner, Patrick and Sch{\"o}ning, Michael Josef}, title = {Combined amperometric/field-effect sensor for the detection of dissolved hydrogen}, series = {Sensors and actuators B: Chemical}, volume = {187}, journal = {Sensors and actuators B: Chemical}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0925-4005}, doi = {10.1016/j.snb.2012.10.050}, pages = {168 -- 173}, year = {2012}, abstract = {Real-time and reliable monitoring of the biogas process is crucial for a stable and efficient operation of biogas production in order to avoid digester breakdowns. The concentration of dissolved hydrogen (H₂) represents one of the key parameters for biogas process control. In this work, a one-chip integrated combined amperometric/field-effect sensor for monitoring the dissolved H₂ concentration has been developed for biogas applications. The combination of two different transducer principles might allow a more accurate and reliable measurement of dissolved H₂ as an early warning indicator of digester failures. The feasibility of the approach has been demonstrated by simultaneous amperometric/field-effect measurements of dissolved H₂ concentrations in electrolyte solutions. Both, the amperometric and the field-effect transducer show a linear response behaviour in the H₂ concentration range from 0.1 to 3\% (v/v) with a slope of 198.4 ± 13.7 nA/\% (v/v) and 14.9 ± 0.5 mV/\% (v/v), respectively.}, language = {en} } @article{HuckPoghossianBaeckeretal.2014, author = {Huck, Christina and Poghossian, Arshak and B{\"a}cker, Matthias and Chaudhuri, S. and Zander, W. and Schubert, J. and Begoyan, V. K. and Buniatyan, V. V. and Wagner, P. and Sch{\"o}ning, Michael Josef}, title = {Capacitively coupled electrolyte-conductivity sensor based on high-k material of barium strontium titanate}, series = {Sensors and actuators. B: Chemical}, journal = {Sensors and actuators. B: Chemical}, number = {198}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1873-3077 (E-Journal); 0925-4005 (Print)}, doi = {10.1016/j.snb.2014.02.103}, pages = {102 -- 109}, year = {2014}, language = {en} } @article{SchusserMenzelBaeckeretal.2013, author = {Schusser, Sebastian and Menzel, S. and B{\"a}cker, Matthias and Leinhos, Marcel and Poghossian, Arshak and Wagner, P. and Sch{\"o}ning, Michael Josef}, title = {Degradation of thin poly(lactic acid) films: characterization by capacitance-voltage, atomic force microscopy, scanning electron microscopy and contact-angle measurements}, series = {Electrochimica Acta}, volume = {Vol. 113}, journal = {Electrochimica Acta}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1873-3859 (E-Journal); 0013-4686 (Print)}, pages = {779 -- 784}, year = {2013}, language = {en} } @article{BaeckerKochEibenetal.2017, author = {B{\"a}cker, Matthias and Koch, Claudia and Eiben, Sabine and Geiger, Fania and Eber, Fabian and Gliemann, Hartmut and Poghossian, Arshak and Wege, Christina and Sch{\"o}ning, Michael Josef}, title = {Tobacco mosaic virus as enzyme nanocarrier for electrochemical biosensors}, series = {Sensors and Actuators B: Chemical}, volume = {238}, journal = {Sensors and Actuators B: Chemical}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0925-4005}, doi = {10.1016/j.snb.2016.07.096}, pages = {716 -- 722}, year = {2017}, abstract = {The conjunction of (bio-)chemical recognition elements with nanoscale biological building blocks such as virus particles is considered as a very promising strategy for the creation of biohybrids opening novel opportunities for label-free biosensing. This work presents a new approach for the development of biosensors using tobacco mosaic virus (TMV) nanotubes or coat proteins (CPs) as enzyme nanocarriers. Sensor chips combining an array of Pt electrodes loaded with glucose oxidase (GOD)-modified TMV nanotubes or CP aggregates were used for amperometric detection of glucose as a model system for the first time. The presence of TMV nanotubes or CPs on the sensor surface allows binding of a high amount of precisely positioned enzymes without substantial loss of their activity, and may also ensure accessibility of their active centers for analyte molecules. Specific and efficient immobilization of streptavidin-conjugated GOD ([SA]-GOD) complexes on biotinylated TMV nanotubes or CPs was achieved via bioaffinity binding. These layouts were tested in parallel with glucose sensors with adsorptively immobilized [SA]-GOD, as well as [SA]-GOD crosslinked with glutardialdehyde, and came out to exhibit superior sensor performance. The achieved results underline a great potential of an integration of virus/biomolecule hybrids with electronic transducers for future applications in biosensorics and biochips.}, language = {en} } @article{PoghossianWeilBaeckeretal.2012, author = {Poghossian, Arshak and Weil, M. H. and B{\"a}cker, Matthias and Mayer, D. and Sch{\"o}ning, Michael Josef}, title = {Field-effect Devices Functionalised with Gold-Nanoparticle/Macromolecule Hybrids: New Opportunities for a Label-Free Biosensing}, series = {Procedia Engineering}, journal = {Procedia Engineering}, number = {47}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1877-7058}, doi = {10.1016/j.proeng.2012.09.136}, pages = {273 -- 276}, year = {2012}, abstract = {Field-effect capacitive electrolyte-insulator-semiconductor (EIS) sensors functionalised with citrate-capped gold nanoparticles (AuNP) have been used for the electrostatic detection of macromolecules by their intrinsic molecular charge. The EIS sensor detects the charge changes in the AuNP/macromolecule hybrids induced by the adsorption or binding events. A feasibility of the proposed detection scheme has been exemplary demonstrated by realising EIS sensors for the detection of poly-D-lysine molecules.}, language = {en} } @article{BronderPoghossianJessingetal.2019, author = {Bronder, Thomas and Poghossian, Arshak and Jessing, Max P. and Keusgen, Michael and Sch{\"o}ning, Michael Josef}, title = {Surface regeneration and reusability of label-free DNA biosensors based on weak polyelectrolyte-modified capacitive field-effect structures}, series = {Biosensors and Bioelectronics}, volume = {126}, journal = {Biosensors and Bioelectronics}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0956-5663}, doi = {10.1016/j.bios.2018.11.019}, pages = {510 -- 517}, year = {2019}, language = {en} } @article{PoghossianMalzahnAbouzaretal.2011, author = {Poghossian, Arshak and Malzahn, K. and Abouzar, Maryam H. and Mehndiratta, P. and Katz, E. and Sch{\"o}ning, Michael Josef}, title = {Integration of biomolecular logic gates with field-effect transducers}, series = {Electrochimica Acta. 56 (2011), H. 26}, journal = {Electrochimica Acta. 56 (2011), H. 26}, publisher = {Elsevier}, address = {Amsterdam}, isbn = {0013-4686}, pages = {9661 -- 9665}, year = {2011}, language = {en} } @article{SchusserPoghossianBaeckeretal.2015, author = {Schusser, Sebastian and Poghossian, Arshak and B{\"a}cker, Matthias and Krischer, M. and Leinhos, Marcel and Wagner, P. and Sch{\"o}ning, Michael Josef}, title = {An application of field-effect sensors for in-situ monitoring of degradation of biopolymers}, series = {Sensors and actuators B: Chemical}, volume = {207, Part B}, journal = {Sensors and actuators B: Chemical}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1873-3077 (E-Journal); 0925-4005 (Print)}, doi = {10.1016/j.snb.2014.10.058}, pages = {954 -- 959}, year = {2015}, abstract = {The characterization of the degradation kinetics of biodegradable polymers is mandatory with regard to their proper application. In the present work, polymer-modified electrolyte-insulator-semiconductor (PMEIS) field-effect sensors have been applied for in-situ monitoring of the pH-dependent degradation kinetics of the commercially available biopolymer poly(d,l-lactic acid) (PDLLA) in buffer solutions from pH 3 to pH 13. PDLLA films of 500 nm thickness were deposited on the surface of an Al-p-Si-SiO2-Ta2O5 structure from a polymer solution by means of spin-coating method. The PMEIS sensor is, in principle, capable to detect any changes in bulk, surface and interface properties of the polymer induced by degradation processes. A faster degradation has been observed for PDLLA films exposed to alkaline solutions (pH 9, pH 11 and pH 13).}, language = {en} } @article{SchusserPoghossianBaeckeretal.2012, author = {Schusser, Sebastian and Poghossian, Arshak and B{\"a}cker, Matthias and Leinhos, Marcel and Wagner, Patrick and Sch{\"o}ning, Michael Josef}, title = {Characterization of biodegradable polymers with capacitive field-effect sensors}, series = {Sensors and actuators B: Chemical}, volume = {187}, journal = {Sensors and actuators B: Chemical}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0925-4005}, doi = {10.1016/j.snb.2012.07.099}, pages = {2 -- 7}, year = {2012}, abstract = {In vitro studies of the degradation kinetic of biopolymers are essential for the design and optimization of implantable biomedical devices. In the presented work, a field-effect capacitive sensor has been applied for the real-time and in situ monitoring of degradation processes of biopolymers for the first time. The polymer-covered field-effect sensor is, in principle, capable to detect any changes in bulk, surface and interface properties of the polymer induced by degradation processes. The feasibility of this approach has been experimentally proven by using the commercially available biomedical polymer poly(D,L-lactic acid) (PDLLA) as a model system. PDLLA films of different thicknesses were deposited on the Ta₂O₅-gate surface of the field-effect structure from a polymer solution by means of spin-coating method. The polymer-modified field-effect sensors have been characterized by means of capacitance-voltage and impedance-spectroscopy method. The degradation of the PDLLA was accelerated by changing the degradation medium from neutral (pH 7.2) to alkaline (pH 9) condition, resulting in drastic changes in the capacitance and impedance spectra of the polymer-modified field-effect sensor.}, language = {en} } @article{SchusserKrischerMolinetal.2015, author = {Schusser, Sebastian and Krischer, M. and Molin, D. G. M. and Akker, N. M. S. van den and B{\"a}cker, Matthias and Poghossian, Arshak and Sch{\"o}ning, Michael Josef}, title = {Sensor System for in-situ and Real-time Monitoring of Polymer (bio) degradation}, series = {Procedia Engineering}, volume = {120}, journal = {Procedia Engineering}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1877-7058}, doi = {10.1016/j.proeng.2015.08.815}, pages = {948 -- 951}, year = {2015}, abstract = {A sensor system for investigating (bio)degradationprocesses of polymers is presented. The system utilizes semiconductor field-effect sensors and is capable of monitoring the degradation process in-situ and in real-time. The degradation of the polymer poly(d,l-lactic acid) is exemplarily monitored in solutions with different pH value, pH-buffer solution containing the model enzyme lipase from Rhizomucormiehei and cell-culture medium containing supernatants from stimulated and non-stimulated THP-1-derived macrophages mimicking activation of the immune system.}, language = {en} } @article{MolinnusHardtKaeveretal.2018, author = {Molinnus, Denise and Hardt, G. and K{\"a}ver, L. and Willenberg, H.S. and Kr{\"o}ger, J.-C. and Poghossian, Arshak and Keusgen, Michael and Sch{\"o}ning, Michael Josef}, title = {Chip-based biosensor for the detection of low adrenaline concentrations to support adrenal venous sampling}, series = {Sensor and Actuators B: Chemical}, volume = {272}, journal = {Sensor and Actuators B: Chemical}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0925-4005}, doi = {10.1016/j.snb.2018.05.136}, pages = {21 -- 27}, year = {2018}, abstract = {A chip-based amperometric biosensor referring on using the bioelectrocatalytical amplification principle for the detection of low adrenaline concentrations is presented. The adrenaline biosensor has been prepared by modification of a platinum thin-film electrode with an enzyme membrane containing the pyrroloquinoline quinone-dependent glucose dehydrogenase and glutaraldehyde. Measuring conditions such as temperature, pH value, and glucose concentration have been optimized to achieve a high sensitivity and a low detection limit of about 1 nM adrenaline measured in phosphate buffer at neutral pH value. The response of the biosensor to different catecholamines has also been proven. Long-term stability of the adrenaline biosensor has been studied over 10 days. In addition, the biosensor has been successfully applied for adrenaline detection in human blood plasma for future biomedical applications. Furthermore, preliminary experiments have been carried to detect the adrenaline-concentration difference measured in peripheral blood and adrenal venous blood, representing the adrenal vein sampling procedure of a physician.}, language = {en} } @article{BaeckerDellePoghossianetal.2011, author = {B{\"a}cker, Matthias and Delle, L. and Poghossian, Arshak and Biselli, Manfred and Zang, Werner and Wagner, P. and Sch{\"o}ning, Michael Josef}, title = {Electrochemical sensor array for bioprocess monitoring}, series = {Electrochimica Acta (2011)}, volume = {56}, journal = {Electrochimica Acta (2011)}, number = {26}, publisher = {Elsevier}, address = {Amsterdam}, pages = {9673 -- 9678}, year = {2011}, language = {en} } @article{HonarvarfardGamellaPoghossianetal.2017, author = {Honarvarfard, Elham and Gamella, Maria and Poghossian, Arshak and Sch{\"o}ning, Michael Josef and Katz, Evgeny}, title = {An enzyme-based reversible Controlled NOT (CNOT) logic gate operating on a semiconductor transducer}, series = {Applied Materials Today}, volume = {9}, journal = {Applied Materials Today}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2352-9407}, doi = {10.1016/j.apmt.2017.08.003}, pages = {266 -- 270}, year = {2017}, abstract = {An enzyme-based biocatalytic system mimicking operation of a logically reversible Controlled NOT (CNOT) gate has been interfaced with semiconductor electronic transducers. Electrolyte-insulator-semiconductor (EIS) structures have been used to transduce chemical changes produced by the enzyme system to an electronically readable capacitive output signal using field-effect features of the EIS device. Two enzymes, urease and esterase, were immobilized on the insulating interface of EIS structure producing local pH changes performing XOR logic operation controlled by various combinations of the input signals represented by urea and ethyl butyrate. Another EIS transducer was functionalized with esterase only, thus performing Identity (ID) logic operation for the ethyl butyrate input. Both semiconductor devices assembled in parallel operated as a logically reversible CNOT gate. The present system, despite its simplicity, demonstrated for the first time logically reversible function of the enzyme system transduced electronically with the semiconductor devices. The biomolecular realization of a CNOT gate interfaced with semiconductors is promising for integration into complex biomolecular networks and future biosensor/biomedical applications.}, language = {en} } @article{OezsoyluKizildagSchoeningetal.2020, author = {{\"O}zsoylu, Dua and Kizildag, Sefa and Sch{\"o}ning, Michael Josef and Wagner, Torsten}, title = {Differential chemical imaging of extracellular acidification within microfluidic channels using a plasma-functionalized light-addressable potentiometric sensor (LAPS)}, series = {Physics in Medicine}, volume = {10}, journal = {Physics in Medicine}, number = {100030}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2352-4510}, doi = {10.1016/j.phmed.2020.100030}, pages = {8}, year = {2020}, abstract = {Extracellular acidification is a basic indicator for alterations in two vital metabolic pathways: glycolysis and cellular respiration. Measuring these alterations by monitoring extracellular acidification using cell-based biosensors such as LAPS plays an important role in studying these pathways whose disorders are associated with numerous diseases including cancer. However, the surface of the biosensors must be specially tailored to ensure high cell compatibility so that cells can represent more in vivo-like behavior, which is critical to gain more realistic in vitro results from the analyses, e.g., drug discovery experiments. In this work, O2 plasma patterning on the LAPS surface is studied to enhance surface features of the sensor chip, e.g., wettability and biofunctionality. The surface treated with O2 plasma for 30 s exhibits enhanced cytocompatibility for adherent CHO-K1 cells, which promotes cell spreading and proliferation. The plasma-modified LAPS chip is then integrated into a microfluidic system, which provides two identical channels to facilitate differential measurements of the extracellular acidification of CHO-K1 cells. To the best of our knowledge, it is the first time that extracellular acidification within microfluidic channels is quantitatively visualized as differential (bio-)chemical images.}, language = {en} } @article{EngelmannPourshahidiShalabyetal.2022, author = {Engelmann, Ulrich M. and Pourshahidi, Mohammad Ali and Shalaby, Ahmed and Krause, Hans-Joachim}, title = {Probing particle size dependency of frequency mixing magnetic detection with dynamic relaxation simulation}, series = {Journal of Magnetism and Magnetic Materials}, volume = {563}, journal = {Journal of Magnetism and Magnetic Materials}, number = {In progress, Art. No. 169965}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0304-8853}, doi = {10.1016/j.jmmm.2022.169965}, year = {2022}, abstract = {Biomedical applications of magnetic nanoparticles (MNP) fundamentally rely on the particles' magnetic relaxation as a response to an alternating magnetic field. The magnetic relaxation complexly depends on the interplay of MNP magnetic and physical properties with the applied field parameters. It is commonly accepted that particle core size is a major contributor to signal generation in all the above applications, however, most MNP samples comprise broad distribution spanning nm and more. Therefore, precise knowledge of the exact contribution of individual core sizes to signal generation is desired for optimal MNP design generally for each application. Specifically, we present a magnetic relaxation simulation-driven analysis of experimental frequency mixing magnetic detection (FMMD) for biosensing to quantify the contributions of individual core size fractions towards signal generation. Applying our method to two different experimental MNP systems, we found the most dominant contributions from approx. 20 nm sized particles in the two independent MNP systems. Additional comparison between freely suspended and immobilized MNP also reveals insight in the MNP microstructure, allowing to use FMMD for MNP characterization, as well as to further fine-tune its applicability in biosensing.}, language = {en} } @article{PourshahidiEngelmannOffenhaeusseretal.2022, author = {Pourshahidi, Ali Mohammad and Engelmann, Ulrich M. and Offenh{\"a}usser, Andreas and Krause, Hans-Joachim}, title = {Resolving ambiguities in core size determination of magnetic nanoparticles from magnetic frequency mixing data}, series = {Journal of Magnetism and Magnetic Materials}, volume = {563}, journal = {Journal of Magnetism and Magnetic Materials}, number = {In progress, Art. No. 169969}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0304-8853}, doi = {10.1016/j.jmmm.2022.169969}, year = {2022}, abstract = {Frequency mixing magnetic detection (FMMD) has been widely utilized as a measurement technique in magnetic immunoassays. It can also be used for the characterization and distinction (also known as "colourization") of different types of magnetic nanoparticles (MNPs) based on their core sizes. In a previous work, it was shown that the large particles contribute most of the FMMD signal. This leads to ambiguities in core size determination from fitting since the contribution of the small-sized particles is almost undetectable among the strong responses from the large ones. In this work, we report on how this ambiguity can be overcome by modelling the signal intensity using the Langevin model in thermodynamic equilibrium including a lognormal core size distribution fL(dc,d0,σ) fitted to experimentally measured FMMD data of immobilized MNPs. For each given median diameter d0, an ambiguous amount of best-fitting pairs of parameters distribution width σ and number of particles Np with R2 > 0.99 are extracted. By determining the samples' total iron mass, mFe, with inductively coupled plasma optical emission spectrometry (ICP-OES), we are then able to identify the one specific best-fitting pair (σ, Np) one uniquely. With this additional externally measured parameter, we resolved the ambiguity in core size distribution and determined the parameters (d0, σ, Np) directly from FMMD measurements, allowing precise MNPs sample characterization.}, language = {en} } @article{AchtsnichtSchoenenbornOffenhaeusseretal.2019, author = {Achtsnicht, Stefan and Sch{\"o}nenborn, Kristina and Offenh{\"a}usser, Andreas and Krause, Hans-Joachim}, title = {Measurement of the magnetophoretic velocity of different superparamagnetic beads}, series = {Journal of Magnetism and Magnetic Materials}, volume = {477}, journal = {Journal of Magnetism and Magnetic Materials}, number = {1}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0304-8853}, doi = {10.1016/j.jmmm.2018.10.066}, pages = {244 -- 248}, year = {2019}, abstract = {The movement of magnetic beads due to a magnetic field gradient is of great interest in different application fields. In this report we present a technique based on a magnetic tweezers setup to measure the velocity factor of magnetically actuated individual superparamagnetic beads in a fluidic environment. Several beads can be tracked simultaneously in order to gain and improve statistics. Furthermore we show our results for different beads with hydrodynamic diameters between 200 and 1000 nm from diverse manufacturers. These measurement data can, for example, be used to determine design parameters for a magnetic separation system, like maximum flow rate and minimum separation time, or to select suitable beads for fixed experimental requirements.}, language = {en} } @article{HaegerBongaertsSiegert2022, author = {Haeger, Gerrit and Bongaerts, Johannes and Siegert, Petra}, title = {A convenient ninhydrin assay in 96-well format for amino acid-releasing enzymes using an air-stable reagent}, series = {Analytical Biochemistry}, journal = {Analytical Biochemistry}, number = {624}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1096-0309}, doi = {10.1016/j.ab.2022.114819}, pages = {Artikel 114819}, year = {2022}, abstract = {An improved and convenient ninhydrin assay for aminoacylase activity measurements was developed using the commercial EZ Nin™ reagent. Alternative reagents from literature were also evaluated and compared. The addition of DMSO to the reagent enhanced the solubility of Ruhemann's purple (RP). Furthermore, we found that the use of a basic, aqueous buffer enhances stability of RP. An acidic protocol for the quantification of lysine was developed by addition of glacial acetic acid. The assay allows for parallel processing in a 96-well format with measurements microtiter plates.}, language = {en} } @article{PoghossianJablonskiKochetal.2018, author = {Poghossian, Arshak and Jablonski, Melanie and Koch, Claudia and Bronder, Thomas and Rolka, David and Wege, Christina and Sch{\"o}ning, Michael Josef}, title = {Field-effect biosensor using virus particles as scaffolds for enzyme immobilization}, series = {Biosensors and Bioelectronics}, volume = {110}, journal = {Biosensors and Bioelectronics}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0956-5663}, doi = {10.1016/j.bios.2018.03.036}, pages = {168 -- 174}, year = {2018}, abstract = {A field-effect biosensor employing tobacco mosaic virus (TMV) particles as scaffolds for enzyme immobilization is presented. Nanotubular TMV scaffolds allow a dense immobilization of precisely positioned enzymes with retained activity. To demonstrate feasibility of this new strategy, a penicillin sensor has been developed by coupling a penicillinase with virus particles as a model system. The developed field-effect penicillin biosensor consists of an Al-p-Si-SiO₂-Ta₂O₅-TMV structure and has been electrochemically characterized in buffer solutions containing different concentrations of penicillin G. In addition, the morphology of the biosensor surface with virus particles was characterized by scanning electron microscopy and atomic force microscopy methods. The sensors possessed a high penicillin sensitivity of ~ 92 mV/dec in a nearly-linear range from 0.1 mM to 10 mM, and a low detection limit of about 50 µM. The long-term stability of the penicillin biosensor was periodically tested over a time period of about one year without any significant loss of sensitivity. The biosensor has also been successfully applied for penicillin detection in bovine milk samples.}, language = {en} } @article{AboulnagaZouSelmeretal.2018, author = {Aboulnaga, Elhussiny A. and Zou, Huibin and Selmer, Thorsten and Xian, Mo}, title = {Development of a plasmid-based, tunable, tolC-derived expression system for application in Cupriavidus necator H16}, series = {Journal of Biotechnology}, volume = {274}, journal = {Journal of Biotechnology}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0168-1656}, doi = {10.1016/j.jbiotec.2018.03.007}, pages = {15 -- 27}, year = {2018}, abstract = {Cupriavidus necator H16 gains increasing attention in microbial research and biotechnological application due to its diverse metabolic features. Here we present a tightly controlled gene expression system for C. necator including the pBBR1-vector that contains hybrid promoters originating from C. necator native tolC-promoter in combination with a synthetic tetO-operator. The expression of the reporter gene from these plasmids relies on the addition of the exogenous inducer doxycycline (dc). The novel expression system offers a combination of advantageous features as; (i) high and dose-dependent recombinant protein production, (ii) tight control with a high dynamic range (On/Off ratio), which makes it applicable for harmful pathways or for toxic protein production, (iii) comparable cheap inducer (doxycycline, dc), (iv) effective at low inducer concentration, that makes it useful for large scale application, (v) rapid, diffusion controlled induction, and (vi) the inducer does not interfere within the cell metabolism. As applications of the expression system in C. necator H16, the growth ability on glycerol was enhanced by constitutively expressing the E. coli glpk gene-encoding for glycerol kinase. Likewise, we used the system to overcome the expression toxicity of mevalonate pathway in C. necator H16. With this system, the mevalonate-genes were successfully introduced in the host and the recombinant strains could produce about 200 mg/l mevalonate.}, language = {en} } @article{IkenAhlbornGerlachetal.2013, author = {Iken, Heiko and Ahlborn, Kristina and Gerlach, Frank and Vonau, Winfried and Zander, Wilhelm and Schubert, J{\"u}rgen P. and Sch{\"o}ning, Michael Josef}, title = {Development of redox glasses and subsequent processing by means of pulsed laser deposition for realizing silicon-based thin-film sensors}, series = {Electrochimica acta}, journal = {Electrochimica acta}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1873-3859 (E-Journal); 0013-4686 (Print)}, pages = {Available online 30.8.2013}, year = {2013}, language = {en} } @article{MuribYeapEurlingsetal.2016, author = {Murib, M. S. and Yeap, W. S. and Eurlings, Y. and Grinsven, B. van and Boyen, H.-G. and Conings, B. and Michiels, L. and Ameloot, Marcel and Carleer, R. and Warmer, J. and Kaul, P. and Haenen, K. and Sch{\"o}ning, Michael Josef and Ceuninck, W. de and Wagner, P.}, title = {Heat-transfer based characterization of DNA on synthetic sapphire chips}, series = {Sensors and Actuators B: Chemical}, volume = {230}, journal = {Sensors and Actuators B: Chemical}, number = {230}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0925-4005}, doi = {10.1016/j.snb.2016.02.027}, pages = {260 -- 271}, year = {2016}, abstract = {In this study, we show that synthetic sapphire (Al₂O₃), an established implant material, can also serve as a platform material for biosensors comparable to nanocrystalline diamond. Sapphire chips, beads, and powder were first modified with (3-aminopropyl) triethoxysilane (APTES), followed by succinic anhydride (SA), and finally single-stranded probe DNA was EDC coupled to the functionalized layer. The presence of the APTES-SA layer on sapphire powders was confirmed by thermogravimetric analyis and Fourier-transform infrared spectroscopy. Using planar sapphire chips as substrates and X-ray photoelectron spectroscopy (XPS) as surface-sensitive tool, the sequence of individual layers was analyzed with respect to their chemical state, enabling the quantification of areal densities of the involved molecular units. Fluorescence microscopy was used to demonstrate the hybridization of fluorescently tagged target DNA to the probe DNA, including denaturation- and re-hybridization experiments. Due to its high thermal conductivity, synthetic sapphire is especially suitable as a chip material for the heat-transfer method, which was employed to distinguish complementary- and non-complementary DNA duplexes containing single-nucleotide polymorphisms. These results indicate that it is possible to detect mutations electronically with a chemically resilient and electrically insulating chip material.}, language = {en} }