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Penicillin detection by means of field-effect based sensors: EnFET, capacitive EIS sensor or LAPS?
(2001)
Penicillin detection by means of field-effect based sensors: EnFET, capacitive EIS sensor or LAPS?
(2000)
Optoelectronic Properties of Nanostructured Ensembles Controlled by Biomolecular Logic Systems
(2008)
Optimization of the immobilization of bacterial spores on glass substrates with organosilanes
(2016)
Spores can be immobilized on biosensors to function as sensitive recognition elements. However, the immobilization can affect the sensitivity and reproducibility of the sensor signal. In this work, three different immobilization strategies with organosilanes were optimized and characterized to immobilize Bacillus atrophaeus spores on glass substrates. Five different silanization parameters were investigated: nature of the solvent, concentration of the silane, silanization time, curing process, and silanization temperature. The resulting silane layers were resistant to a buffer solution (e.g., Ringer solution) with a polysorbate (e.g., Tween®80) and sonication.
Bacillus subtilis and Bacillus licheniformis are widely used for the large-scale industrial production of proteins. These strains can efficiently secrete proteins into the culture medium using the general secretion (Sec) pathway. A characteristic feature of all secreted proteins is their N-terminal signal peptides, which are recognized by the secretion machinery. Here, we have studied the production of an industrially important secreted protease, namely, subtilisin BPN′ from Bacillus amyloliquefaciens. One hundred seventy-three signal peptides originating from B. subtilis and 220 signal peptides from the B. licheniformis type strain were fused to this secretion target and expressed in B. subtilis, and the resulting library was analyzed by high-throughput screening for extracellular proteolytic activity. We have identified a number of signal peptides originating from both organisms which produced significantly increased yield of the secreted protease. Interestingly, we observed that levels of extracellular protease were improved not only in B. subtilis, which was used as the screening host, but also in two different B. licheniformis strains. To date, it is impossible to predict which signal peptide will result in better secretion and thus an improved yield of a given extracellular target protein. Our data show that screening a library consisting of homologous and heterologous signal peptides fused to a target protein can identify more-effective signal peptides, resulting in improved protein export not only in the original screening host but also in different production strains.
Optimization of passivation layers for corrosion protection of silicon-based microelectrode arrays
(2000)
A light-addressable potentiometric sensor (LAPS) is a field-effect-based potentiometric device, which detects concentration changes of an analyte solution on the sensor surface in a spatially resolved way. It uses a light source to generate electron–hole pairs inside the semiconductor, which are separated in the depletion region due to an applied bias voltage across the sensor structure and hence, a surface-potential-dependent photocurrent can be read out. However, depending on the beam angle of the light source, scattering effects can occur, which influence the recorded signal in LAPS-based differential measurements. To solve this problem, a novel illumination unit based on a field programmable gate array (FPGA) consisting of 16 small-sized tunable infrared laser-diode modules (LDMs) is developed. Due to the improved focus of the LDMs with a beam angle of only 2 mrad, undesirable scattering effects are minimized. Escherichia coli (E. coli) K12 bacteria are used as a test microorganism to study the extracellular acidification on the sensor surface. Furthermore, a salt bridge chamber is built up and integrated with the LAPS system enabling multi-chamber differential measurements with a single Ag/AgCl reference electrode.
The immobilization of NAD+-dependent dehydrogenases, in combination with a diaphorase, enables the facile development of multiparametric sensing devices. In this work, an amperometric biosensor array for simultaneous determination of ethanol, formate, d- and l-lactate is presented. Enzyme immobilization on platinum thin-film electrodes was realized by chemical cross-linking with glutaraldehyde. The optimization of the sensor performance was investigated with regard to enzyme loading, glutaraldehyde concentration, pH, cofactor concentration and temperature. Under optimal working conditions (potassium phosphate buffer with pH 7.5, 2.5 mmol L-1 NAD+, 2.0 mmol L-1 ferricyanide, 25 °C and 0.4% glutaraldehyde) the linear working range and sensitivity of the four sensor elements was improved. Simultaneous and cross-talk free measurements of four different metabolic parameters were performed successfully. The reliable analytical performance of the biosensor array was demonstrated by application in a clarified sample of inoculum sludge. Thereby, a promising approach for on-site monitoring of fermentation processes is provided.
Online-Messsysteme für die automatisierte Charakterisierung von feldeffektbasierten Biosensoren
(2007)
A variety of transition metals, e.g., copper, zinc, cadmium, lead, etc. are widely used in industry as components for wires, coatings, alloys, batteries, paints and so on. The inevitable presence of transition metals in industrial processes implies the ambition of developing a proper analytical technique for their adequate monitoring. Most of these elements, especially lead and cadmium, are acutely toxic for biological organisms. Quantitative determination of these metals at low activity levels in different environmental and industrial samples is therefore a vital task. A promising approach to achieve an at-side or on-line monitoring on a miniaturized and cost efficient way is the combination of a common potentiometric sensor array with heavy metal-sensitive thin-film materials, like chalcogenide glasses and polymeric materials, respectively.
N-Acyl-amino acids can act as mild biobased surfactants, which are used, e.g., in baby shampoos. However, their chemical synthesis needs acyl chlorides and does not meet sustainability criteria. Thus, the identification of biocatalysts to develop greener synthesis routes is desirable. We describe a novel aminoacylase from Paraburkholderia monticola DSM 100849 (PmAcy) which was identified, cloned, and evaluated for its N-acyl-amino acid synthesis potential. Soluble protein was obtained by expression in lactose autoinduction medium and co-expression of molecular chaperones GroEL/S. Strep-tag affinity purification enriched the enzyme 16-fold and yielded 15 mg pure enzyme from 100 mL of culture. Biochemical characterization revealed that PmAcy possesses beneficial traits for industrial application like high temperature and pH-stability. A heat activation of PmAcy was observed upon incubation at temperatures up to 80 °C. Hydrolytic activity of PmAcy was detected with several N-acyl-amino acids as substrates and exhibited the highest conversion rate of 773 U/mg with N-lauroyl-L-alanine at 75 °C. The enzyme preferred long-chain acyl-amino-acids and displayed hardly any activity with acetyl-amino acids. PmAcy was also capable of N-acyl-amino acid synthesis with good conversion rates. The best synthesis results were obtained with the cationic L-amino acids L-arginine and L-lysine as well as with L-leucine and L-phenylalanine. Exemplarily, L-phenylalanine was acylated with fatty acids of chain lengths from C8 to C18 with conversion rates of up to 75%. N-lauroyl-L-phenylalanine was purified by precipitation, and the structure of the reaction product was verified by LC–MS and NMR.
A novel photoexcitation method for the light-addressable potentiometric sensor (LAPS) is proposed to achieve a higher spatial resolution of chemical images. The proposed method employs a combined light source that consists of a modulated light probe, which generates the alternating photocurrent signal, and a ring of constant illumination surrounding it. The constant illumination generates a sheath of carriers with increased concentration which suppresses the spread of photocarriers by enhanced recombination. A device simulation was carried out to verify the effect of constant illumination on the spatial resolution, which demonstrated that a higher spatial resolution can be obtained.
Novel organic membrane-based thin-film microsensors for the determination of heavy metal cations
(2006)
A first step towards the fabrication and electrochemical evaluation of thin-film microsensors based on organic PVC membranes for the determination of Hg(II), Cd(II), Pb(II) and Cu(II) ions in solutions has been realised. The membrane-coating mixture used in the preparation of this new type of microsensors is incorporating PVC as supporting matrix, o-nitrophenyloctylether (o-NPOE) as solvent mediator and a recently synthesized Hg[dimethylglyoxime(phene)]2+ and Bis-(4-hydroxyacetophenone)-ethylenediamine as electroactive materials for Hg(II) and Cd(II), respectively. A set of three commercialised ionophores for Cd(II), Pb(II) and Cu(II) has been also used for comparison. Thin-film microsensors based on these membranes showed a Nernstian response of slope (26-30 mV/dec.) for the respective tested cations. The potentiometric response characteristics (linear range, pH range, detection limit and response time) are comparable with those obtained by conventional membranes as well as coated wire electrodes prepared from the same membrane. The realisation of the new organic membrane-based thin-film microsensors overcomes the problem of an insufficient selectivity of solid-state-based thinfilm sensors.
Novel concepts for flow-rate and flow-direction determination by means of pH-sensitive ISFETs
(2001)
Chemical imaging systems allow the visualisation of the distribution of chemical species on the sensor surface. This work represents a new flexible approach of read out in a light-addressable potentiometric sensor (LAPS) with the help of a digital light processing (DLP) set-up. The DLP, known well for video projectors, consists of a mirror-array MEMS device which allows fast and flexible generation of light patterns. With the help of these light patterns the sensor surface of the LAPS device can be read out sequentially in a raster like scheme (scanning LAPS). The DLP approach has several advantages compared to conventional scanning LAPS set-ups, e.g., the spot size, the shape and the intensity of the light pointer can be changed easily and no mechanical movement is necessary, which reduces the size of the set-up and increases the stability and speed of measurement.
Amino acid-based surfactants are valuable compounds for cosmetic formulations. The chemical synthesis of acyl-amino acids is conventionally performed by the Schotten-Baumann reaction using fatty acyl chlorides, but aminoacylases have also been investigated for use in biocatalytic synthesis with free fatty acids. Aminoacylases and their properties are diverse; they belong to different peptidase families and show differences in substrate specificity and biocatalytic potential. Bacterial aminoacylases capable of synthesis have been isolated from Burkholderia, Mycolicibacterium, and Streptomyces. Although several proteases and peptidases from S. griseus have been described, no aminoacylases from this species have been identified yet. In this study, we investigated two novel enzymes produced by S. griseus DSM 40236ᵀ . We identified and cloned the respective genes and recombinantly expressed an α-aminoacylase (EC 3.5.1.14), designated SgAA, and an ε-lysine acylase (EC 3.5.1.17), designated SgELA, in S. lividans TK23. The purified aminoacylase SgAA was biochemically characterized, focusing on its hydrolytic activity to determine temperature- and pH optima and stabilities. The aminoacylase could hydrolyze various acetyl-amino acids at the Nα -position with a broad specificity regarding the sidechain. Substrates with longer acyl chains, like lauroyl-amino acids, were hydrolyzed to a lesser extent. Purified aminoacylase SgELA specific for the hydrolysis of Nε -acetyl-L-lysine was unstable and lost its enzymatic activity upon storage for a longer period but could initially be characterized. The pH optimum of SgELA was pH 8.0. While synthesis of acyl-amino acids was not observed with SgELA, SgAA catalyzed the synthesis of lauroyl-methionine.
Enzyme-catalyzed reactions have been designed to mimic various Boolean logic gates in the general framework of unconventional biomolecular computing. While some of the logic gates, particularly OR, AND, are easy to realize with biocatalytic reactions and have been reported in numerous publications, some other, like NXOR, are very challenging and have not been realized yet with enzyme reactions. The paper reports on a novel approach to mimicking the NXOR logic gate using the bell-shaped enzyme activity dependent on pH values. Shifting pH from the optimum value to the acidic or basic values by using acid or base inputs (meaning 1,0 and 0,1 inputs) inhibits the enzyme reaction, while keeping the optimum pH (assuming 0,0 and 1,1 input combinations) preserves a high enzyme activity. The challenging part of the present approach is the selection of an enzyme with a well-demonstrated bell-shape activity dependence on the pH value. While many enzymes can satisfy this condition, we selected pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase as this enzyme has the optimum pH center-located on the pH scale allowing the enzyme activity change by the acidic and basic pH shift from the optimum value corresponding to the highest activity. The present NXOR gate is added to the biomolecular “toolbox” as a new example of Boolean logic gates based on enzyme reactions.
The aim of the present study was the characterisation of three true subtilisins and one phylogenetically intermediate subtilisin from halotolerant and halophilic microorganisms. Considering the currently growing enzyme market for efficient and novel biocatalysts, data mining is a promising source for novel, as yet uncharacterised enzymes, especially from halophilic or halotolerant Bacillaceae, which offer great potential to meet industrial needs. Both halophilic bacteria Pontibacillus marinus DSM 16465ᵀ and Alkalibacillus haloalkaliphilus DSM 5271ᵀ and both halotolerant bacteria Metabacillus indicus DSM 16189 and Litchfieldia alkalitelluris DSM 16976ᵀ served as a source for the four new subtilisins SPPM, SPAH, SPMI and SPLA. The protease genes were cloned and expressed in Bacillus subtilis DB104. Purification to apparent homogeneity was achieved by ethanol precipitation, desalting and ion-exchange chromatography. Enzyme activity could be observed between pH 5.0–12.0 with an optimum for SPPM, SPMI and SPLA around pH 9.0 and for SPAH at pH 10.0. The optimal temperature for SPMI and SPLA was 70 °C and for SPPM and SPAH 55 °C and 50 °C, respectively. All proteases showed high stability towards 5% (w/v) SDS and were active even at NaCl concentrations of 5 M. The four proteases demonstrate potential for future biotechnological applications.
Ein lichtadressierbarer potentiometrischer Sensor (LAPS) kann die Konzentration eines oder mehrerer Analyten ortsaufgelöst auf der Sensoroberfläche nachweisen. Dazu wird mit einer modulierten Lichtquelle die Halbleiterstruktur des zu untersuchenden Bereiches angeregt und ein entsprechender Photostrom ausgelesen. Durch gleichzeitige Anregung mehrere Bereiche durch Lichtquellen mit unterschiedlichen Modulationsfrequenzen können diese auch zeitgleich ausgelesen werden. Mit der neuen, hier vorgestellten Ansteuerungselektronik integriert in einem "Field Programmable Gate Array" (FPGA) ist es möglich, mehrere Leuchtquellen gleichzeitig mit unterschiedlichen, während der Laufzeit festlegbaren Frequenzen, Phasen und Lichtintensitäten zu betreiben. Somit kann das Frequenzverhalten des Sensors untersucht und die Konzentration des Analyten über das Oberflächenpotential mit Hilfe von Strom/Spannungs-Kurven und Phase/Spannungs-Kurven bestimmt werden.
Proceedings of the 2nd Humboldt Kolleg, Hammamet, Tunisia Organizer: Alexander von Humboldt Stiftung, Germany. pdf 184 p. Welcome Address Dear Participants, Welcome to the 2nd Humboldt Kolleg in “Nanoscale Science and Technology” (NS&T’12) in Tunisia, sponsored by the "Alexander von Humboldt" foundation. The NS&T’12 multidisciplinary scientific program includes seven "hot" topics dealing with "Nanoscale Science and Technology" covering basic and application-oriented research as well as industrial (market) aspects: - Molecular Biophyics, Spectroscopy Techniques, Imaging Microscopy - Nanomaterials Synthesis for Medicine and Bio-chemical Sensors - Nanostructures, Semiconductors, Photonics and Nanodevices - New Technologies in Market Industry - Environment, Electro-chemistry, Bio-polymers and Fuel Cells - Nanomaterials, Photovoltaic, Modelling, Quantum Physics - Microelectronics, Sensors Networks and Embedded Systems We are deeply indebted to all members of the Scientific Committee and General Chairs for joint Sessions and to all speakers and chairmen, who have dedicated invaluable time and efforts for the realization of this event. On behalf of the Organizing Committee, we are cordially inviting you to join the conference and hope that your stay will be fruitful, rewarding and enjoyable. Prof. Dr. Michael J. Schöning, Prof. Dr. Adnane Abdelghani
An array of electrically isolated nanoplate field-effect silicon-on-insulator (SOI) capacitors as a new transducer structure for multiparameter (bio-)chemical sensing is presented. The proposed approach allows addressable biasing and electrical readout of multiple nanoplate field-effect capacitive (bio-)chemical sensors on the same SOI chip, as well as differential-mode measurements. The realized sensor chip has been applied for pH and penicillin concentration measurements, electrical monitoring of polyelectrolyte multilayer formation, and the label-free electrical detection of consecutive deoxyribonucleic acid (DNA) hybridization and denaturation events.
The incorporation of nanomaterials that are biocompatible with different types of biological compounds has allowed the development of a new generation of biosensors applied especially in the biomedical field. In particular, the integration of film-based nanomaterials employed in field-effect devices can be interesting to develop biosensors with enhanced properties. In this paper, we studied the fabrication of sensitive nanofilms combining ZnO nanocrystals and carbon nanotubes (CNTs), prepared by means of the layer-by-layer (LbL) technique, in a capacitive electrolyte-insulator-semiconductor (EIS) structure for detecting glucose and urea. The ZnO nanocrystals were incorporated in a polymeric matrix of poly(allylamine) hydrochloride (PAH), and arranged with multi-walled CNTs in a LbL PAH-ZnO/CNTs film architecture onto EIS chips. The electrochemical characterizations were performed by capacitance–voltage and constant capacitance measurements, while the morphology of the films was characterized by atomic force microscopy. The enzymes glucose oxidase and urease were immobilized on film’s surface for detection of glucose and urea, respectively. In order to obtain glucose and urea biosensors with optimized amount of sensitive films, we investigated the ideal number of bilayers for each detection system. The glucose biosensor showed better sensitivity and output signal for an LbL PAH-ZnO/CNTs nanofilm with 10 bilayers. On the other hand, the urea biosensor presented enhanced properties even for the first bilayer, exhibiting high sensitivity and output signal. The presence of the LbL PAH-ZnO/CNTs films led to biosensors with better sensitivity and enhanced response signal, demonstrating that the adequate use of nanostructured films is feasible for proof-of-concept biosensors with improved properties that may be employed for biomedical applications.
The possibility of using the atomic-force microscopy as a method for detection of the analytical signal from plasticized polymeric sensor membranes was analyzed. The surfaces of cadmium-selective membranes based on two polymeric matrices were examined. The digital images were processed with multivariate image analysis techniques. A correlation was found between the surface profile of an ion-selective membrane and the concentration of the ion in solution.
In comparison to single-analyte devices, multiplexed systems for a multianalyte detection offer a reduced assay time and sample volume, low cost, and high throughput. Herein, a multiplexing platform for an automated quasi-simultaneous characterization of multiple (up to 16) capacitive field-effect sensors by the capacitive–voltage (C–V) and the constant-capacitance (ConCap) mode is presented. The sensors are mounted in a newly designed multicell arrangement with one common reference electrode and are electrically connected to the impedance analyzer via the base station. A Python script for the automated characterization of the sensors executes the user-defined measurement protocol. The developed multiplexing system is tested for pH measurements and the label-free detection of ligand-stabilized, charged gold nanoparticles.
Die qualitative und quantitative Detektion von Zielsubstanzen innerhalb einer wässrigen Probe ist für viele Fragestellungen von Interesse, etwa bei der Detektion von Kontaminationen in Trinkwasser in Krisensituationen. Hierbei ist es nicht nur wichtig, dass Pathogene möglichst sensitiv detektiert werden können, sondern auch, dass die Analyse schnell erfolgt, um Betroffenen im Katastrophenfall zügig sicheres Trinkwasser zu Verfügung stellen zu können. Da bei einem solchen Szenario nicht von einer in der Nähe befindlichen funktionierenden Laborinfrastruktur ausgegangen werden kann, ist es wichtig, dass die Messung direkt vor Ort erfolgen kann. Im Rahmen dieser Arbeit wurde untersucht, ob eine derartige Schnellanalytik mithilfe von superparamagnetischen Beads (MBs) und der magnetischen Frequenzmischtechnik möglich ist. Dabei werden die MBs mit Hilfe von primären Antikörpern an die Zielsubstanz gebunden und mit sekundären Antikörpern an die Poren-Oberfläche eines Polyethylen-Filters fixiert (Sandwich-Immunoassay). So kann die Quantifizierung der Zielsubstanz auf eine magnetische Messung der immobilisierten MB-Marker zurückgeführt werden. Die magnetische Frequenzmischtechnik basiert auf der Anregung der Probe mit Magnetfeldern zweier verschiedener Frequenzen. Die durch die nichtlineare Magnetisierungsform der superparamagnetischen MBs entstehenden Mischfrequenzen werden typischerweise mithilfe einer zweistufigen Lock-in-Detektion analysiert (analoge Demodulation), die in einem Magnetreader als Handheldgerät realisiert wurde. Zusätzlich zu dieser Technik wurde das Prinzip der direkten Digitalisierung des gesamten Antwortsignals mit anschließender Fourier-Analyse der erzeugten Mischfrequenzen experimentell umgesetzt, um die Amplituden und Phasen mehrerer Mischfrequenzen simultan zu erfassen. Eine Möglichkeit zur Sensitivitätssteigerung ist die magnetische Aufkonzentration, indem vor der magnetischen Analyse eine Separation der MBs aus einem größeren Probenvolumen mittels magnetischem Feldgradienten durchgeführt wird. Zur Charakterisierung verschiedener kommerzieller MBs hinsichtlich ihrer magnetischen Separierbarkeit wurde ein Aufbau zur Messung ihrer magnetophoretischen Beweglichkeiten realisiert und ihre Geschwindigkeiten im Gradientenfeld mikroskopisch gemessen.Da eine Probe oftmals nicht nur auf eine einzige Zielsubstanz, sondern simultan auf mehrere verschiedene Pathogene hin untersucht werden soll, wurden verschiedene Ansätze entwickelt und getestet, die einen solchen multiparametrischen magnetischen Immunoassay ermöglichen. Einerseits wurde eine räumliche Separation der Bindungsbereiche für verschiedene Zielsubstanzen realisiert, die sequentiell ausgewertet werden können. Andererseits wurde die Unterscheidung von verschiedenen Zielsubstanzen anhand der Charakteristika der an sie gebundenen, verschieden funktionalisierten MB-Typen untersucht. Für eine solche Unterscheidung wurde zum einen die Anregefrequenz der magnetischen Frequenzmischtechnik während einer Messung variiert. Damit konnte gezeigt werden, dass sich verschiedene MB-Sorten anhand der Phase ihrer Frequenzmischsignale voneinander unterscheiden lassen. Weiterhin wurde gezeigt, dass sich der Signalverlauf einer binären Mischung zweier verschiedener MB-Typen als gradueller Übergang der Verläufe der beiden reinen MB-Lösungen ergibt. Eine weitere Analysemethode für einen multiparametrischen Immunoassay besteht darin, ein zusätzliches einstellbares statisches magnetisches Offsetfeld zu verwenden. Hierfür wurden mehrere Aufbauten auf Basis von Permanent- und Elektromagneten simuliert, konstruiert und charakterisiert. Mithilfe von Simulationen konnte gezeigt werden, dass eine auf diesem Verfahren beruhende Unterscheidung für MBs mit unterschiedlichen magnetischen Partikelmomenten möglich ist. Als direkte Anwendung des hier entwickelten Magnetreaders in Zusammenspiel mit der digitalen Demodulation wurde ein magnetischer Assay gegen die B-Untereinheit des Choleratoxins in Trinkwasser mit einem niedrigen Detektionslimit von 0,2 ng/ml demonstriert.
Magnetic immunoassays employing Frequency Mixing Magnetic Detection (FMMD) have recently become increasingly popular for quantitative detection of various analytes. Simultaneous analysis of a sample for two or more targets is desirable in order to reduce the sample amount, save consumables, and save time. We show that different types of magnetic beads can be distinguished according to their frequency mixing response to a two-frequency magnetic excitation at different static magnetic offset fields. We recorded the offset field dependent FMMD response of two different particle types at frequencies ƒ₁ + n⋅ƒ₂, n = 1, 2, 3, 4 with ƒ₁ = 30.8 kHz and ƒ₂ = 63 Hz. Their signals were clearly distinguishable by the locations of the extremes and zeros of their responses. Binary mixtures of the two particle types were prepared with different mixing ratios. The mixture samples were analyzed by determining the best linear combination of the two pure constituents that best resembled the measured signals of the mixtures. Using a quadratic programming algorithm, the mixing ratios could be determined with an accuracy of greater than 14%. If each particle type is functionalized with a different antibody, multiplex detection of two different analytes becomes feasible.
In modern bioanalytical methods, it is often desired to detect several targets in one sample within one measurement. Immunological methods including those that use superparamagnetic beads are an important group of techniques for these applications. The goal of this work is to investigate the feasibility of simultaneously detecting different superparamagnetic beads acting as markers using the magnetic frequency mixing technique. The frequency of the magnetic excitation field is scanned while the lower driving frequency is kept constant. Due to the particles’ nonlinear magnetization, mixing frequencies are generated. To record their amplitude and phase information, a direct digitization of the pickup-coil’s signal with subsequent Fast Fourier Transformation is performed. By synchronizing both magnetic beads using frequency scanning in magnetic frequency mixing technique magnetic fields, a stable phase information is gained. In this research, it is shown that the amplitude of the dominant mixing component is proportional to the amount of superparamagnetic beads inside a sample. Additionally, it is shown that the phase does not show this behaviour. Excitation frequency scans of different bead types were performed, showing different phases, without correlation to their diverse amplitudes. Two commercially available beads were selected and a determination of their amount in a mixture is performed as a demonstration for multiplex measurements.
The present work describes a novel multiple sensor-type system for the real-time analysis of aseptic sterilisation processes employing gaseous hydrogen peroxide (H2O2) as a sterilant. The inactivation kinetics of Bacillus atrophaeus by gaseous H2O2 have been investigated by means of a methodical calibration experiment, taking into account the process variables H2O2 concentration, humidity and gas temperature. It has been found that the microbicidal effectiveness at H2O2 concentrations above 2% v/v is largely determined by the concentration itself, while at lower H2O2 concentrations, the gas temperature and humidity play a leading role. Furthermore, the responses of different types of gas sensors towards the influencing factors of the sterilisation process have been analysed within the same experiment. Based on a correlation established between the inactivation kinetics and the sensor responses, a calorimetric H2O2 sensor and a metal-oxide semiconductor (MOX) sensor have been identified as possible candidates for monitoring the microbicidal effectiveness of aseptic sterilisation processes employing gaseous H2O2. Therefore, two linear models that describe the relationship between sensor response and microbicidal effectiveness have been proposed.
It is well known that biochemical and biotechnological processes are strongly dependent and affected by a variety of physico-chemical parameters such as pH value, temperature, pressure and electrolyte conductivity. Therefore, these quantities have to be monitored or controlled in order to guarantee a stable process operation, optimization and high yield. In this work, a sensor chip for the multiparameter detection of three physico-chemical parameters such as electrolyte conductivity, pH and temperature is realized using barium strontium titanate (BST) as multipurpose material. The chip integrates a capacitively coupled four-electrode electrolyte-conductivity sensor, a capacitive field-effect pH sensor and a thin-film Pt-temperature sensor. Due to the multifunctional properties of BST, it is utilized as final outermost coating layer of the processed sensor chip and serves as passivation and protection layer as well as pH-sensitive transducer material at the same time. The results of testing of the individual sensors of the developed multiparameter sensor chip are presented. In addition, a quasi-simultaneous multiparameter characterization of the sensor chip in buffer solutions with different pH value and electrolyte conductivity is performed. To study the sensor behavior and the suitability of BST as multifunctional material under harsh environmental conditions, the sensor chip was exemplarily tested in a biogas digestate.
In this work, a multi-sensor chip for the investigation of the sensing properties of different types of metal oxides towards hydrogen peroxide in the ppm range is presented. The fabrication process and physical characterization of the multi-sensor chip are described. Pure SnO2 and WO3 as well as Pd- and Pt-doped SnO2 films are characterized in terms of their sensitivity to H2O2. The sensing films have been prepared by drop-coating of water-dispensed nano-powders. A physical characterization, including scanning electron microscopy and X-ray diffraction analysis of the deposited metal-oxide films, was done. From the measurements in hydrogen peroxide atmosphere, it could be shown, that all of the tested metal oxide films are suitable for the detection of H2O2 in the ppm range. The highest sensitivity and reproducibility was achieved using Pt-doped SnO2.
Calibration plot of a SnO2, WO3, Pt-, and Pd-doped SnO2 gas sensor for H2O2 concentrations in the ppm range.