Special issue  

Applications like air quality, fire detection and detection of explosives require selective and quantitative measurements in an ever-changing background of interfering gases. One main issue hindering the successful implementation of gas sensors in real-world applications is the lack of appropriate calibration procedures for advanced gas sensor systems. This article presents a calibration scheme for gas sensors based on gas profiles with unique randomized gas mixtures.

A commercial solid electrolyte gas sensor of the type "Pt|YSZ|Pt, air" based on yttria-stabilized zirconia for colorimetric oxygen detection was operated in optimized dynamic electrochemical modes. Cyclic voltammetry and square-wave voltammetry were used for the detection of NO and O₂ in N₂ in the temperature range between 550 and 750 °C. Due to the differences of electrode kinetics of the single components it is possible to detect these redox active gases selectively and quasi-simultaneously.

In this contribution, an inexpensive and robust impedimetric NO_x sensor is presented. The impedance of a functional thick film depends selectively on the NO_x concentration in the exhaust but shows a dependency on the oxygen concentration. Therefore, an additional temperature-independent resistive oxygen sensor structure was integrated on the same sensor platform. It serves not only to determine the oxygen concentration in the exhaust, but also to correct the oxygen dependency of the NO_x sensor.

A miniaturized, field-applicable sensor system was developed for the measurement of low hydrogen (H₂) concentrations in air. The sensor system is based on the application of a newly developed miniaturized coulometric detector with gas chromatographic (GC) pre-separation after injection. By optimizing all operational parameters, it was possible to conduct reproducible and 100 % selective H₂ measurements with more than 90 % analyte turnover compared to Faraday's law.

Symmetrical Pt | YSZ | Pt–NO gas sensors were produced with frit-containing and fritless Pt electrodes and fired between 950 and 1300 °C. The sensors were operated by pulsed polarization. With fritless pastes, the sensors responded significantly higher. The firing temperature affects the sensitivity only slightly. The low NO sensitivity of the frit-containing electrodes was attributed to a blocking effect at the triple-phase boundaries that inhibits the oxygen transport through the sensor.

We present a work on gas sensors that can for example be used for the assessment of indoor air quality. These sensors suffer from deterioration by siloxanes, so we investigated these effects by a distinct operation mode and exposition to this gas that allows us to interpret different reactions on the sensor surface. We found that all processes on the sensor surface are slowed down by this treatment and a self-compensation by the evaluation of oxygen adsorption processes is likely to be found.

In a very specific way, this research paper shows how established systems – in this case a commercial soot sensor for the automotive sector – can be optimized by diving deep into the basic research. The approach here is to link macroscopic observations or signal behavior with processes taking place on the atomic level. Taking these fundamental processes into account, the sensor's specific response time could be shortened effectively by a change in operating strategy – without any design changes.

In this paper we investigate an in-line concept for continuous monitoring of sodium, potassium, calcium and urea concentrations in blood serum using ion-selective electrodes. This concept is evaluated in a preclinical study with human packed red blood cells as a test medium. It has been shown that the electrolytes can be well monitored. In addition, we present the first measurements with ion-sensitive field-effect transistors in a miniaturized sensor assembly using a novel readout electronics.