Non-invasive biomedical analysis: VOCs are in the air - from cellular metabolism to crowd monitoring

Volatile organic compounds (VOCs) have been described as biomarkers for a broad range of applications from “microscopic” detection of cellular metabolism to “macroscopic” monitoring of emissions from human populations. VOCs may act as disease markers and can help to assess human exposure to exogenous contaminants. VOCs can be used to monitor bacterial or cellular growth in vitro and in vivo. Along with recent developments in analytical instrumentation such as laser spectroscopy or real time MS new areas of biomedical VOC applications have emerged.

This network session is intended to address the role of specialized applications and innovative instrumentation in VOC research. This includes aspects of medical breath research as well as crowd monitoring by means of atmospheric chemistry.

Abstract Content

Abstract Content

Volatile organic compounds (VOCs) emitted from bacterial cultures can reveal information on species and metabolism. As VOC concentrations are in the low ppbV range, pre-concentration techniques are required for GC-MS analyses. This study was intended to compare SPME and NTME for VOC analysis from cultures of Mycobacterium avium paratuberculosis (MAP).For SPME, a 75 µm CAR/PDMS fibre was exposed to 20 ml headspace over cultures for 20 min at ??°C. For NTME, 20 ml were sampled bidirectionally through a needle packed with DVB, Carbopack X, and Carboxen 1000. Pure media samples served as controls. After thermal desorption VOCs were identified and calibrated by means of GC-MS in the range of 1 up to 500 ppbV by pure reference substances.73 VOCs in the low ppbV range were identified as potential biomarkers. 36 VOCs were found with both methods. Most alcohols were assessed only by NTME. Limits of detection ranged from 0.09 to 69.52 ppbV (Median = 0.82 ppbV) for NTD and 0.06 to 74.54 ppbV (Median = 1.06 ppbV) for SPME. R² of calibrations with the NTD showed a mean of 0.995 (±0.019 SD) and 0.998 (±0.015 SD) for SPME. VOC patterns determined by both methods revealed differences between bacteria and pure media samples. SPME and NTME were suitable for VOC preconcentration from bacterial cultures. Due to the principal modes of action (distribution vs. extraction) selectivity depends on physico-chemical properties of the substances. In VOC profiling, preconcentration techniques have to be chosen in accordance to the target biomarkers.

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It is often difficult to characterize or monitor biological cultures without impairment of cell growth or destruction of the whole sample. Non-invasive trace analysis of volatile organic compounds (VOCs) emitted from biological cultures could offer a solution. We designed hermetically closed Teflon boxes with customized port connections for micro extraction devices. Depending on cell type and -number the inner air volume of the boxes could be adjusted by means Teflon blocks. Preconcentration of volatile substances was realized through bidirectional needle trap micro extraction (NTME). Substances were separated by means of gas chromatography (GC), identified and quantified by means of mass spectrometry . To detect differences between media and media with cultures two identical boxes for parallel measurement were used. Heatmaps were used to visualize differences within the large amount of data.Dilution-free sampling by means of NTME resulted in RSDs < 5%. Concentrations of VOCs were determined in the range of 1 ppb – 10ppb. Differences between cultures and media were most pronounced for oxygen and sulphur containing compounds. Media emitted significantly higher concentrations of hydrocarbons than cultures.Air tight Teflon boxes with customized sampling ports enabled reproducible and reliable sampling from bacterial or cell culture headspace. Due to low methodological variations provided by the improved setup emissions from cell cultures could clearly be separated from those from blank media and ambient air. As even small variations in VOC concentrations can be assessed, VOC analysis could be used for destruction-free monitoring of culture growth.