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Molecular spectroscopy and theoretical chemistry

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Contact Information

Laboratory of Physical Chemistry
Department of Chemistry
A.I. Virtasen aukio 1
(P.O. BOX 55)
FI-00014 University of Helsinki
Finland

Group leader
Prof. Lauri Halonen, D.Sc.
Phone: +358(0)2941 50280
email: lauri.halonen helsinki.fi
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Experimental work in laser spectroscopy

Breath analysis by cavity ring-down spectroscopy

We are interested in applying state-of-the-art laser spectroscopic techniques to the analysis of the human exhaled breath. The underlying motivation is to develop the breath analysis methodology for the non-invasive diagnosis and monitoring of various diseases. The exhaled breath contains hundreds of volatile species and some of these are linked to the normal and abnormal metabolism of the body. Yet others are due to environmental exposure or end up in the body via food and drink. Compared to many other biological matrices (blood, urine, tear fluid etc.) exhaled breath can be collected effortlessly and frequently, basically providing an unlimited sample volume.

The molecules we haven been recently interested in include hydrogen cyanide (HCN) and ammonia (NH3). Exhaled HCN has garnered attention because it is produced in the body by the bacterium Pseudomonas aeruginosa. PA plays an important role in the morbidity and mortality of cystic fibrosis patients who often exhibit PA infections in their airways and lungs. Exhaled HCN analysis has been proposed as a non-invasive tool for early diagnosis of the PA infection in cystic fibrosis patients [1]. Yet, PA in the lung is not the only source of HCN in the body. It has been noted that even healthy people produce significant amounts of HCN in the oral cavity. In our group we recently established a direct correlation between the HCN concentration in the oral fluid and in mouth-exhaled breath [2]. We also demonstrated that the oral HCN generation is probably of bacterial or enzymatic origin. We then continued to search for the relevant cyanogenic oral bacteria. After screening some well-known oral anaerobes, we found strains that emitted measurable levels of HCN in vitro [3]. The setup used for the in vitro study is schematically depicted in Fig. 1.


Fig. 1. Setup for in vitro HCN study of oral anaerobic bacteria. Green arrows indicate gas flow towards the optical cavity, red arrows gas flow away from the cavity and towards the vacuum pump.

NH3 is produced by the human body in amino acid metabolism and is therefore an important molecule in normal and abnormal physiology. One of the most studied applications for exhaled NH3 has been its use in following the efficacy of hemodialysis. It has been reported that mouth-exhaled NH3 levels correlate well with blood urea levels and the progress of hemodialysis can be monitored by exhaled breath ammonia measurements. We have previously developed exhaled ammonia sampling and measurement, providing background levels for ammonia in mouth and nose-exhaled breath as well as emitted from the skin [4]. We also studied the mechanism of exhaled NH3 production in detail and showed that for healthy people mouth-exhaled ammonia is dominantly generated in the oral cavity via urease catalyzed hydrolysis of urea [5]. We are presently working to demonstrate that the mechanism is valid also for end stage renal disease patients undergoing hemodialysis [6]. The observed association between blood urea and exhaled ammonia arises essentially from the correlation between blood urea and urea in saliva.

For our exhaled breath studies, we utilize both our home-built near-infrared cavity ring down spectrometer as well as commercial analyzers based on the same technology. We are also interested in extending the breath studies to mass spectrometric instrumentation (especially proton transfer reaction mass spectrometry, PTR-MS) and in using the the novel mid-infrared laser sources (OPOs and frequency combs) developed within our group.

[1] D. Smith, P. Spanel, F.J. Gilchrist and W. Lenney, "Hydrogen cyanide, a volatile biomarker of Pseudomonas aeruginosa infection", J. Breath Res. 7, 044001 (2013).
[2] W. Chen, M. Metsälä, O. Vaittinen and L. Halonen, "Hydrogen cyanide in the headspace of oral fluid and mouth-exhaled breath", J. Breath Res. 8, 027108 (2014).
[3] W. Chen, K. Roslund, C. Fogarty, P.J. Pussinen, L. Halonen, P.-H. Groop, M. Metsälä and M. Lehto, "Detection of hydrogen cyanide from oral anaerobes by cavity ring down spectroscopy", submitted for publication.
[4] F. M. Schmidt, O. Vaittinen, M. Metsälä, M. Lehto, C. Forsblom, P.-H. Groop and L. Halonen, "Ammonia in breath and emitted from skin", J. Breath Res. 7, 017109 (2013).
[5] W. Chen, M. Metsälä, O. Vaittinen and L. Halonen, "The origin of mouth-exhaled ammonia", J. Breath Res. 8, 036003 (2014).
[6] W. Chen, O. Vaittinen, L. Halonen, F. Ortiz, P.-H. Groop, M. Lehto and M. Metsälä, manucript under preparation