Cellobiose Dehydrogenase Aryl Diazonium Modified Single Walled Carbon Nanotubes: Enhanced Direct Electron Transfer through a Positively Charged Surface

One of the challenges in the field of biosensors and biofuel cells is to establish a highly efficient electron transfer rate between the active site of redox enzymes and electrodes to fully access the catalytic potential of the biocatalyst and achieve high current densities. We report on very efficient direct electron transfer (DET) between cellobiose dehydrogenase (CDH) from Phanerochaete sordida (PsCDH) and surface modified single walled carbon nanotubes (SWCNT). Sonicated SWCNTs were adsorbed on the top of glassy carbon electrodes and modified with aryl diazonium salts generated in situ from p-aminobenzoic acid and p-phenylenediamine, thus featuring at acidic pH (3.5 and 4.5) negative or positive surface charges. After adsorption of PsCDH, both electrode types showed excellent long-term stability and very efficient DET. The modified electrode presenting p-aminophenyl groups produced a DET current density of 500,mu A cm(-2) at 200 mV vs normal hydrogen reference electrode (NHE) in a 5 mM lactose solution buffered at pH 3.5. This is the highest reported DET value so far using a CDH modified electrode and comes close to electrodes using mediated electron transfer. Moreover, the onset of the electrocatalytic current for lactose oxidation started at 70 mV vs NHE, a potential which is 50 mV lower compared to when unmodified SWCNTs were used. This effect potentially reduces the interference by oxidizable matrix components in biosensors and increases the open circuit potential in biofuel cells. The stability of the electrode was greatly increased compared with unmodified but cross-linked SWCNTs electrodes and lost only 15% of the initial current after 50 h of constant potential scanning

A Novel Biochemical Route for Fuels and Chemicals Production from Cellulosic Biomass

The conventional biochemical platform featuring enzymatic hydrolysis involves five key steps: pretreatment, cellulase production, enzymatic hydrolysis, fermentation, and product recovery. Sugars are produced as reactive intermediates for subsequent fermentation to fuels and chemicals. Herein, an alternative biochemical route is proposed. Pretreatment, enzymatic hydrolysis and cellulase production is consolidated into one single step, referred to as consolidated aerobic processing, and sugar aldonates are produced as the reactive intermediates for biofuels production by fermentation. In this study, we demonstrate the viability of consolidation of the enzymatic hydrolysis and cellulase production steps in the new route using Neurospora crassa as the model microorganism and the conversion of cellulose to ethanol as the model system. We intended to prove the two hypotheses: 1) cellulose can be directed to produce cellobionate by reducing β-glucosidase production and by enhancing cellobiose dehydrogenase production; and 2) both of the two hydrolysis products of cellobionate—glucose and gluconate—can be used as carbon sources for ethanol and other chemical production. Our results showed that knocking out multiple copies of β-glucosidase genes led to cellobionate production from cellulose, without jeopardizing the cellulose hydrolysis rate. Simulating cellobiose dehydrogenase over-expression by addition of exogenous cellobiose dehydrogenase led to more cellobionate production. Both of the two hydrolysis products of cellobionate: glucose and gluconate can be used by Escherichia coli KO 11 for efficient ethanol production. They were utilized simultaneously in glucose and gluconate co-fermentation. Gluconate was used even faster than glucose. The results support the viability of the two hypotheses that lay the foundation for the proposed new route

Delayed voltammetric with respect to amperometric electrochemical detection of concentration changes in microchannels

The time response of an electrode incorporated into a fluidic channel to variations in analyte concentration of the outer-sphere redox probe ferrocenemethanol was investigated both for amperometry (AMP) and cyclic voltammetry (CV). The experimental data show that the temporal resolution of CV is not as good as that of AMP, as CV cannot properly detect fast concentration transients. The delayed response of CV was previously reported, for neurotransmitters, and mostly attributed to the adsorption of the analyte on the electrode surface. By using an outer-sphere redox couple, we show that mass transport also significantly delays the response of CV. The experimental delay time in CV was understood from mass transfer limitations due to the relaxation of the diffusion layer during repeated potential scanning. Furthermore, a robust protocol for the analysis of fast concentration transients was established, using the impulse and modulation transfer functions of the system. This method was found to be more precise than the mere analysis of undifferentiated traces in the time domain. As a proof of concept, the effect of increased viscosity was investigated, showing that AMP was more sensitive than CV to these variations. Overall, this analysis underlines further the enhanced temporal sensitivity of AMP over CV, at the expense of decreased chemical resolution, potentially having implications for in situ electrochemical detection of biologically relevant molecules

A comparison of calculation methods to determine the degree of summer overheating in residential buildings taking ventilation systems into account

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersDie derzeit gültige ÖNORM B 8110-3: "Wärmeschutz im Hochbau.Wärmespeicherung und Sonneneinflüsse" [ONO99] beinhaltet zwei Nachweisverfahren zur Vermeidung der sommerlichen Überwärmung von Räumen: den Nachweis über den Tagesverlauf der Raumtemperatur mit einem geeigneten Rechenprogramm und den Nachweis über die mindesterforderliche speicherwirksame Masse (=vereinfachter Nachweis). In dieser Norm gilt sommerliche Überwärmung als vermieden, wenn die empfundene Raumtemperatur während einer Hitzeperiode die Grenztemperatur von +27°C am Tage und +25°C in der Nacht nicht überschreitet.Diese beiden Nachweise und Jahressimulationen mit BuildOpt_VIE wurden in der Arbeit verglichen. In den Simulationen mit BuildOpt_VIE wurden Klimadaten, Bauweisen, Fenstergrößen, Orientierungen der Fensterfassaden, Verschattungen, innere Wärmequellen und Lüftungsszenarien variiert.Die erhaltenen Daten wurden nach globaler Behaglichkeit mit PMV-Index (Predicted Mean Vote) und PPD-Index (Predicted Percentage of Dissatisfied) sowie mit der Kategorisierung nach ÖNORM EN 15251 [ONO07b] bewertet.The current Austrian Standard ÖNORM B 8110-3: "Wärmeschutz im Hochbau. Wärmespeicherung und Sonneneinflüsse" [ONO99] (Heat protection in buildings. Thermal energy storage and solar influence) includes two verification methods for avoiding interior overheating in summer: the verification of the daily change in room temperature by means of a suitable calculation programme and the verification of the minimum required thermal storage mass (a simplified verification method).Following the aforementioned standard, avoidance of summer internal overheating is met if the perceived room temperature during a heat wave does not exceed the daily boundary temperature of +27°C and the nightly boundary temperature of +25°C.In this thesis, the verification methods and annual simulations have been compared using BuildOpt_VIE. In the simulations using BuildOpt_VIE, different scenarios have been created by varying climate data, construction assemblies, window size, window orientation, shading, internal heat sources, and ventilation.The outcomes have been evaluated according to global comfort standards using the PMV-Index (Predicted Mean Vote) and PPD-Index (Predicted Percentage of Dissatisfied) as well as the ÖNORM EN 15251 [ONO07b].11

Positioning of sonar or echosounding data of small-scale water bodies using GPS and MEMS IMU

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in engl. SpacheZur hydrographischen Vermessung von großen und mittleren Gewässern werden zumeist Sonar- und Echolotsysteme eingesetzt. Für die Verortung von Echolotdaten werden häufig RTK-GPS oder Totalstationen eingesetzt. Für die Verortung von Sonardaten benötigt man zusätzlich die räumliche Orientierung des Sonarsystems. In dieser Arbeit wurde die Eignung eines kostengünstigen Messsystems basierend auf einem Einfrequenz-GPS-Empfänger und einer MEMS IMU zur Bestimmung der Position und Orientierung eines hydroakustischen Sensors untersucht. Zusätzlich wurde ein Magnetometer zur azimutalen Stabilisierung des Messsystems eingesetzt. Kostengünstige Inertialsysteme weisen große Fehler auf, die mit Hilfe von der Positions- und Geschwindigkeitsinformation aus GPS-Beobachtungen ausgeglichen werden können. Die Kombination der Sensordaten erfolgte in der institutseigenen Kalman Filter Software. Zur Einbindung der Azimutbeobachtungen mussten neue Algorithmen in die Software eingearbeitet werden. Das Kalman Filter benötigt genaue Rauschparameter zur Charakterisierung der IMU-Qualität; diese Parameter wurden in einem Laborversuch mit Hilfe der Allan Varianz abgeschätzt. Eine hydrographische Vermessung wurde durchgeführt um reale Messdaten für die weitere Analyse zu erhalten. Die Messdaten wurden in der adaptierten Software prozessiert. Die Analyse der prozessierten Messdaten und der daraus abgeleiteten Gewässersohle zeigte, dass die erwünschte Genauigkeit von 10 cm (1-sigma) bei einer Wassertiefe von 15m mit dem untersuchten kostengünstigen Messsystem erreich bar ist. Im Zuge der Arbeit wurde jedoch auch Verbesserungspotential identifiziert, vor allem betreffend die Verarbeitung von Daten, die während der Wendemanöver anfallen.The most economical methods for surveying medium and large inland water bodies are based on sonar and echo sounding systems. Today RTK-GPS or total stations are used to position the echo sounding system.3D orientation is needed as well to position sonar data.In this thesis the development of an integrated low-cost navigation system based on GPS and MEMS inertial sensors for the determination of position and attitude of the echo sounding system is investigated. A magnetometer is used to estimate the azimuth and is essential to stabilize the whole measurement system. Low-cost inertial sensors exhibit large errors which can be compensated using information on position and velocity as provided by GPS. The data of the individual sensors are combined in a Kalman filter software. New algorithms to include azimuth observations were added to the software.The Kalman filter relies on the correct quantification of the noise parameters of the MEMS IMU, which were determined in a laboratory test using the Allan Variance method.A hydrographic survey was carried out in order to assess the algorithms using real data. The assessment shows that the proposed system should be further improved especially with respect to measurements during sharp turns. However, the results also indicate that the desired accuracy of 10 cm (1-sigma) with water depths of 15 m can be achieved using single-frequency GPS, a MEMS IMU and a magnetometer for positioning and orienting the hydrographic sensors.6