Dual Fluorescence Sensor for Trace Oxygen and Temperature with Unmatched Range and Sensitivity

An optical dual sensor for oxygen and temperature is presented that is highly oxygen sensitive and covers a broad temperature range. Dual sensing is based on luminescence lifetime measurements. The novel sensor contains two luminescent compounds incorporated into polymer films. The temperature-sensitive dye (ruthenium tris-1,10-phenanthroline) has a highly temperature-dependent luminescence and is incorporated in poly(acrylonitrile) to avoid cross-sensitivity to oxygen. Fullerene C70 was used as the oxygen-sensitive probe owing to its strong thermally activated delayed fluorescence at elevated temperatures that is extremely oxygen sensitive. The cross-sensitivity of C70 to temperature is accounted for by means of the temperature sensor. C70 is incorporated into a highly oxygen-permeable polymer, either ethyl cellulose or organosilica. The two luminescent probes have different emission spectra and decay times, and their emissions can be discriminated using both parameters. Spatially resolved sensing is achieved by means of fluorescence lifetime imaging. The response times of the sensor to oxygen are short. The dual sensor exhibits a temperature operation range between at least 0 and 120 °C, and detection limits for oxygen in the ppbv range, operating for oxygen concentrations up to at least 50 ppmv. These ranges outperform all dual oxygen and temperature sensors reported so far. The dual sensor presented in this study is especially appropriate for measurements under extreme conditions such as high temperatures and ultralow oxygen levels. This dual sensor is a key step forward in a number of scientifically or commercially important applications including food packaging, for monitoring of hyperthermophilic microorganisms, in space technology, and safety and security applications in terms of detection of oxygen leaks

Methods and techniques to measure molecular oxygen in plants

Designing and developing sensors for molecular oxygen (O2) has turned into a large, interdisciplinary field of research, with significant progress seen in the past decades. Until the early 1980s, the field of O2 sensing was dominated by polarographic electrode sensors, among which the most popular Clark-type electrode found wide application in plant science. Nevertheless, the great demand for more sophisticated, intracellularly applicable O2 sensors for real-time measurements in plants cannot be satisfied by the predominant techniques. Thus, optical sensors applying an O2-specific reduction of luminescent probes or dyes provide novel, promising tools and open new perspectives on the cellular or even subcellular level of O2 measurements. This chapter aims to give a comprehensive overview on the variety of methods and systems available in the field of O2 sensing with respect to application in plant tissue. Different types of the earlier polarographic electrode technique as well as emerging alternatives will be discussed, including fluorescent proteins as potential, genetically encoded intracellular O2 sensors. Due to the tremendous variety of materials and formats, the young field of optical O2 sensing will receive particular attention directing the focus towards the progress that has been made in developing new probes and dyes. Moreover, the current state of fluorescence measurements will be explored, particularly novel, plant-specific measurement modalities that mask plant autofluorescence. For the potential user, important practical aspects are also presented, revealing the limitations of the existing methods and further encouraging more interdisciplinary research in O2 sensing