H. G. Mengers, F. Völker, L. M. Blank

Decoding Bacillus subtilis’ Volatilome Under Acid Stress, in Real Time with SESI-Orbitrap
This study reveals the acid stress volatilome of Bacillus subtilis using real-time SESI-Orbitrap MS, offering unprecedented temporal resolution (0.3 Hz) during pH shock in resting cells. Over 450 compounds were tracked across 16,000 data points, uncovering both immediate and delayed VOC responses. Acetoin dominated, as expected, but a novel signal (C₄H₆O) also emerged. This work highlights SESI’s power to monitor microbial stress responses via off-gas VOCs, non-invasively, instantly, and at the molecular scale.

J. Zeng, N. Stankovic, K. D. Singh, R. Steiner, U. Frey, T. Erb, P. Sinues

Breath Pharmacometabolomics of Propofol Anesthesia in Children
This pilot study demonstrates that on-site SESI-HRMS breath analysis can robustly track propofol and its metabolites in pediatric patients, with exhaled signals showing strong correlation to serum concentrations (R² ≥ 0.65). Beyond pharmacokinetics, SESI revealed surgery-induced metabolic responses, including elevated fatty aldehydes—markers of oxidative stress and lipid peroxidation. Conducted in children undergoing IV anesthesia, this work highlights real-time, non-invasive breath profiling as a promising tool for individualized anesthetic monitoring and metabolic assessment during surgery.

R. Bourgeois, K. Rohrbach, Y. Baumann, N. Perkins, E. Seidl, S. Micic, A. Moeller

Remote Breath Profiling of Preschool Asthma Using SESI-HRMS
This pioneering study demonstrates that SESI-HRMS combined with offline Nalophan-based breath collection can detect asthma-specific VOC markers in preschool children (ages 3–6). Out of 375 previously identified asthma-specific m/z features, 125 were re-detected, with 16 showing statistically significant differences between symptomatic patients and healthy controls. Several markers mapped to known metabolic pathways, and classification performance (AUC 0.77) confirms diagnostic potential. This is the first validation of SESI-based asthma diagnostics in young children using a remote, non-invasive method—a promising step toward early, accurate respiratory disease detection.

H. G. Mengers

Decoding the Yeast Volatilome: From CO₂ Conversion to Real-Time SESI Profiling
This thesis explores the diverse and underexplored volatilome of Saccharomyces cerevisiae, combining metabolic engineering with advanced gas-phase analysis. Highlights include CO₂-to-formate conversion during fermentation using a Ru-catalyst system (yielding 26% conversion), and bio-based production of volatile acetaldehyde via ADH-deleted yeast strains at industrially relevant rates (100 mg/g/h). Volatile stripping and capture were achieved using custom in situ water traps. Crucially, SESI-Orbitrap MS was established as a sensitive, real-time tool to detect volatiles, including heat-labile allicin from garlic and >200 fermentation-derived compounds at 0.4 Hz resolution. This work showcases SESI’s potential in online bioprocess monitoring, from early detection of volatile metabolites to mapping dynamic metabolic shifts such as ethyl ester formation during carbon source transitions.

Hendrik G. Mengers, Martin Zimmermann & Lars M. Blank

We use secondary electrospray ionisation high-resolution Orbitrap mass spectrometry (SESI-Orbitrap MS) to monitor the complete yeast volatilome every 2.3 s. Over 200 metabolites were identified during growth in shake flasks and bioreactor cultivations, all with their unique intensity profile. Special attention was paid to ethanol as biotech largest product and to acetaldehyde as an example of a low-abundance but highly volatile metabolite. Volatilome shifts are visible, e.g. after glucose depletion, fatty acids are converted to ethyl esters in a detoxification mechanism after stopped fatty acid biosynthesis. This work showcases the SESI-Orbitrap MS system for tracking microbial physiology without the need for sampling and for time-resolved discoveries during metabolic transitions.

Jiayi Lan, Giorgia Greter, Bettina Streckenbach, Markus Arnoldini, Renato Zenobi & Emma Slack

We demonstrate that secondary electrospray ionization mass spectrometry can be used to non-invasively monitor metabolic activity of the intestinal microbiome of a live, awake mouse. This was achieved via analysis of the headspace volatile and semi-volatile metabolome of individual gut microbiota bacterial species growing in pure culture, as well as from live gnotobiotic mice specifically colonized with these microbes. The microbial origin of these compounds was confirmed by feeding of heavy-isotope labeled microbiota-accessible sugars. This reveals that the microbiota is a major contributor to the released metabolites of a whole live mouse, and that it is possible to capture the catabolism of sugars and cross-feeding within the gut microbiota of a living animal using volatile/semi-volatile metabolite monitoring.

Jisun HJ Lee, Jiangjiang Zhu

The analysis of exhaled breath (breathomics) has gained attention as a useful technique to measure the human VOC profile altered as a result of dietary interventions. In this mini-review, we examined recent clinical trials that performed promising dietary interventions, SCFAs analysis in plasma/feces, and VOC profile analysis in exhaling breath to understand the relationship between dietary intervention and metabolic health.

Jisun H. J. Lee and Jiangjiang Zhu

Gut microbiota plays essential roles in maintaining gut homeostasis. The composition of gut microbes and their metabolites are altered in response to diet and remedial agents such as antibiotics. However, little is known about the effect of antibiotics on the gut microbiota and their volatile metabolites. In this study, we evaluated the impact of a moderate level of ampicillin treatment on volatile fatty acids (VFAs) of gut microbial cultures using an optimized real-time secondary electrospray ionization coupled with high-resolution mass spectrometry (SESI-HRMS).

J. Zhu, H. D. Bean, J. Jiménez-Díaz, and J. E. Hill

Bacterial pneumonia is one of the leading causes of disease-related morbidity and mortality in the world, in part because the diagnostic tools for pneumonia are slow and ineffective. To improve the diagnosis success rates and treatment outcomes for bacterial lung infections, we are exploring the use of SESI-MS breath analysis as a rapid, noninvasive method for determining …

J. Zhu, J. E. Hill

Escherichia coli O157:H7 (EC O157:H7), as well as its recently emerging non-O157 relatives, are a notorious group of pathogenic bacteria associated with foodborne outbreaks. In this study, we demonstrated that secondary electrospray ionization mass spectrometry (SESI-MS) could be a rapid and accurate detection technology for foodborne pathogens …