P10 - Propofol Detection with Metal Oxide Semiconductor Gas Sensors

16. Dresdner Sensor-Symposium 2022
2022-12-05 - 2022-12-07
(Bio-)Medizinische Sensorik
C. Bur, H. Lensch, A. Schütze - Saarland University, Saarbrücken/ D
99 - 104


Breath analysis as a non-invasive tool has the potential to become a powerful tool for early detection and monitoring of diseases. Of great interest is the detection of cancer, diabetes, pulmonary diseases, renal dysfunction, and COPD (chronic obstructive pulmonary disease) as well as early detection of sepsis and inflammation. There are already some biomarkers identified and linked to certain diseases, like acetone for diabetes, hydrogen for lactose intolerance, or nitrous gases for asthma. However, in many cases there is not a single biomarker but rather changes in the concentration of multiple exhaled volatile organic compounds (VOCs) which need to be detected. For cancer detection, changes in VOC profiles between a test and a reference group have frequently been studied. In the breath of healthy humans more than 800 different VOCs have been found with concentrations ranging from several ppt (parts per trillion) up to a few ppm (parts per million). Table 1 summarized major compounds of human breath. Besides endogenous sources of VOCs the inhaled air also has a significant impact on the composition of the exhaled air. Besides early detection of diseases, the analysis of exhaled air can be used for drug monitoring with the aim to correlate the breath concentration of the given drug or a metabolite to the plasma concentration. The large number of VOCs together with a wide range of concentrations of different target substances poses a serious challenge for the measurement system. Several techniques have been studied for breath analysis with analytical methods like gas chromatography coupled with mass spectrometry (GC/MS) being the gold standard due its high sensitivity and selectivity. For real time analysis Selected Ion Flow Tube MS (SIFT-MS) or Proton Transfer Reaction MS (PTR-MS) are used. However, these instruments are complex, high-end priced and require trained personnel so that they are mostly used for research purposes. In drug monitoring, bedside, non-invasive, and ideally online monitoring of exhaled air could have a high therapeutic relevance calling for more cost-effective technologies. For the intravenous anesthetic propofol, ion mobility spectrometry (IMS) has been studied intensively. A correlation of the concentration in exhaled air to the plasma concentration was reported and a pharmacokinetic model was suggested to predict the time-delayed and exhaled concentration of propofol. Another promising technology are semiconductor gas sensors based on metal oxides (MOS). Being low-cost, small sized with low power consumption, and easy to integrate make them highly attractive for portable and simple to use hand-held devices. These could also be used in non-clinical environments, i.e., medical practices or even at home. Besides being highly sensitive, MOS-sensors are non-selective. By using temperature-cycled operation (TCO) [17] we could show that a single MOS sensor is capable of quantifying single VOCs in the low ppb-range in a complex and varying background of interfering VOCs, hydrogen (H2) and carbon monoxide (CO), e.g. for indoor air quality applications. Dynamic operation together with signal processing based on machine learning and a complex lab calibration with randomized gas mixtures are the basis to achieve a performance of MOS sensors which is comparable to analytics but with the advantage of being low-cost and offering real time and online monitoring. To demonstrate the potential of MOS sensors for drug monitoring, two commercially available MOS sensors, i.e. ZMOD4410 (indoor air sensor) and ZMOD4510 (outdoor air sensor) from Renesas, Dresden, Germany, are studied in this work for propofol quantification in a simulated atmosphere under lab conditions.