Benedikt Bierer

Characterization of microbial current production as a function of microbe-electrode-interaction

Microbe-electrode-interactions are keys for microbial fuel cell technology. Nevertheless, standard measurement routines to analyze the interplay of microbial physiology and material characteristics have not been introduced yet. In this study, graphite anodes with varying surface properties were evaluated using pure cultures of Shewanella oneidensis and Geobacter sulfurreducens, as well as defined and undefined mixed cultures. The evaluation routine consisted of a galvanostatic period, a current sweep and an evaluation of population density. The results show that surface area correlates only to a certain extent with population density and anode performance. Furthermore, the study highlights a strain-specific microbe-electrode-interaction, which is affected by the introduction of another microorganism. Moreover, evidence is provided for the possibility of translating results from pure culture to undefined mixed species experiments. This is the first study on microbe-electrode-interaction that systematically integrates and compares electrochemical and biological data.

Odor-Sensing System to Support Social Participation of People Suffering from Incontinence.

This manuscript describes the design considerations, implementation, and laboratory validation of an odor sensing module whose purpose is to support people that suffer from incontinence. Because of the requirements expressed by the affected end-users the odor sensing unit is realized as a portable accessory that may be connected to any pre-existing smart device. We have opted for a low-cost, low-power consuming metal oxide based gas detection approach to highlight the viability of developing an inexpensive yet helpful odor recognition technology. The system consists of a hotplate employing, inkjet-printed p-type semiconducting layers of copper(II) oxide, and chromium titanium oxide. Both functional layers are characterized with respect to their gas-sensitive behavior towards humidity, ammonia, methylmercaptan, and dimethylsulfide and we demonstrate detection limits in the parts-per-billion range for the two latter gases. Employing a temperature variation scheme that reads out the layer’s resistivity in a steady-state, we use each sensor chip as a virtual array. With this setup, we demonstrate the feasibility of detecting odors associated with incontinence.

Miniature Low-Cost Carbon Dioxide Sensor for Mobile Devices

We present our recent advances on developing a miniature sensor for carbon dioxide that may be used in mobile devices. Until now, limiting factors for the implementation of gas sensors in mobile devices, such as smartphones, include their production costs and large size, which is associated with the comparatively poor sensitivity. To overcome these constraints, we employ a photoacoustic-based infrared detection technology to gauge the light intensity of a mid-infrared LED. The photoacoustic detector mainly consists of a commercially available microphone inside a hermetically sealed, carbon dioxide filled cell. To save space and minimize intensity losses, a novel waveguide is used to direct the LED radiation to the detector. The waveguide simultaneously forms the measuring chamber. Because of the high sensitivity of our device, the overall size can be reduced to a level where it is compatible with standard IC sockets. Gas measurements were performed that demonstrate the suitability of the sensor. While providing high sensitivity, the influence of humidity on the sensor signal is insignificant and influences due to temperature shifts may be compensated for.

Photo-Induced Room-Temperature Gas Sensing with a-IGZO Based Thin-Film Transistors Fabricated on Flexible Plastic Foil

We present a gas sensitive thin-film transistor (TFT) based on an amorphous Indium–Gallium–Zinc–Oxide (a-IGZO) semiconductor as the sensing layer, which is fabricated on a free-standing flexible polyimide foil. The photo-induced sensor response to NO2 gas at room temperature and the cross-sensitivity to humidity are investigated. We combine the advantages of a transistor based sensor with flexible electronics technology to demonstrate the first flexible a-IGZO based gas sensitive TFT. Since flexible plastic substrates prohibit the use of high operating temperatures, the charge generation is promoted with the help of UV-light absorption, which ultimately triggers the reversible chemical reaction with the trace gas. Furthermore, the device fabrication process flow can be directly implemented in standard TFT technology, allowing for the parallel integration of the sensor and analog or logical circuits.

MEMS-based array for hydrogen sulfide detection employing a phase transition

The monitoring of hydrogen sulfide in biogas is crucial due to its highly corrosive properties. Most notably, the lifetime of heat and power generation machinery suffers from high levels of hydrogen sulfide. Here an approach to enable large-scale, low cost deployment of selective, quasi-continuous hydrogen sulfide detection systems is presented. A chip featuring three individually controllable hotplates has been developed for this purpose. Each hotplate device consists of a heating structure and an interdigitated electrode structure, which we use to control the temperature and determine the resistivity of copper(II)oxide nanospheres, respectively. The fundamental process to determine the hydrogen sulfide concentration is based on a phase transition that occurs in the temperature regime below 200°C. The transition process may be reversed at temperatures above 300°C thus resetting the sensing layer. However, the reversal takes times, which is why we use a total of six hotplates simultaneously to enable a quasi-continuous monitoring of the hydrogen sulfide concentration.

Carbon dioxide sensor for mobile devices: A novel approach for low-power consuming, highly sensitive NDIR sensors

In this work, a miniature sensor for carbon dioxide is presented. Until now, limiting factors for the implementation of gas sensors in smartphones include their production costs, large size and the comparatively poor sensitivity. A small-scale sensor for carbon dioxide suitable for integration in a smartphone is introduced that overcomes these constraints. The sensor components are low-cost, low-power consuming only. As light source a mid-infrared LED is employed and to gauge the light intensity a photoacoustic detector consisting of a commercially available microphone inside a hermetically sealed carbon dioxide cell is used. To save space and minimize intensity losses, a novel waveguide is used to direct the LED radiation to the detector. The waveguide simultaneously forms the measuring chamber. At the same time, because of the high sensitivity of our detector, the overall size can be reduced to a level where it is compatible with standard IC sockets. Gas measurements were performed that emphasize the suitability of the sensor. While providing high sensitivity, the influence of cross-sensitivities to humidity are insignificant and influences due to temperature shifts may be compensated for.

MEMS-based platform optimized for inkjet printing of nano-sized, gas sensitive functional metal oxides to enable the measurement of gas induced changes of the heating power

Metal oxide based gas sensors are usually read-out by measuring the overall resistivity of the gas sensitive layer. However, the reaction of the gas species with the metal oxide surface does not only change the electrical conductivity but also effects the required heating power to maintain the layer’s temperature. This change in power consumption may be disregarded when using standard bulk sensor chips due to their overall high thermal mass. Nevertheless, micromachined Si based hotplate devices offer the possibility to measure these effects. Here we present results that have been obtained by using a novel hotplate platform optimized for low power consumption and inkjet printing of nano sized gas sensitive metal oxide particles. The temperature of the gas sensitive layer is controlled via the heater resistance and the power consumption is recorded with a fully automated gas measurement system. To separate changes in the heat conductivity of the gas matrix from the heat of the surface reaction, the measurements have been performed in parallel using hotplates with and without a metal oxide layer deposited onto them. Here layers composed of copper (II) oxide (CuO) have been used to highlight the possibilities of the novel approach. Determining both, the gas dependent resistivity as well as heating power yields two independent sensing quantities from one single device and might be an important cornerstone on the way towards selective metal oxide based gas sensors.