Laser spectroscopy for breath analysis: towards clinical implementation.

Detection and analysis of volatile compounds in exhaled breath represents an attractive tool for monitoring the metabolic status of a patient and disease diagnosis, since it is non-invasive and fast. Numerous studies have already demonstrated the benefit of breath analysis in clinical settings/applications and encouraged multidisciplinary research to reveal new insights regarding the origins, pathways, and pathophysiological roles of breath components. Many breath analysis methods are currently available to help explore these directions, ranging from mass spectrometry to laser-based spectroscopy and sensor arrays. This review presents an update of the current status of optical methods, using near and mid-infrared sources, for clinical breath gas analysis over the last decade and describes recent technological developments and their applications. The review includes: tunable diode laser absorption spectroscopy, cavity ring-down spectroscopy, integrated cavity output spectroscopy, cavity-enhanced absorption spectroscopy, photoacoustic spectroscopy, quartz-enhanced photoacoustic spectroscopy, and optical frequency comb spectroscopy. A SWOT analysis (strengths, weaknesses, opportunities, and threats) is presented that describes the laser-based techniques within the clinical framework of breath research and their appealing features for clinical use.

Ethylene production by Botrytis cinerea in vitro and in tomatoes.

A laser-based ethylene detector was used for on-line monitoring of ethylene released by the phytopathogenic fungus Botrytis cinerea in vitro and in tomato fruit. Ethylene data were combined with the results of a cytological analysis of germination of B. cinerea conidia and hyphal growth. We found that aminoethoxyvinylglycine and aminooxyacetic acid, which are competitive inhibitors of the 1-aminocyclopropane-1-carboxylic acid pathway, did not inhibit the ethylene emission by B. cinerea and that the fungus most likely produces ethylene via the 2-keto-4-methylthiobutyric acid pathway. B. cinerea is able to produce ethylene in vitro, and the emission of ethylene follows the pattern that is associated with hyphal growth rather than the germination of conidia. Ethylene production in vitro depended on the L-methionine concentration added to the plating medium. Higher values and higher emission rates were observed when the concentration of conidia was increased. Compared with the ethylene released by the fungus, the infection-related ethylene produced by two tomato cultivars (cultivars Money Maker and Daniela) followed a similar pattern, but the levels of emission were 100-fold higher. The time evolution of enhanced ethylene production by the infected tomatoes and the cytological observations indicate that ethylene emission by the tomato-fungus system is not triggered by the ethylene produced by B. cinerea, although it is strongly synchronized with the growth rate of the fungus inside the tomato.

Comparison of models describing light dependence of N(2) fixation in heterocystous cyanobacteria.

The abilities of four models to describe nitrogenase light-response curves were compared, using the heterocystous cyanobacterium Nodularia spumigena and a cyanobacterial bloom from the Baltic Sea as examples. All tested models gave a good fit of the data, and the rectangular hyperbola model is recommended for fitting nitrogenase-light response curves. This model describes an enzymatic process, while the others are empirical. It was possible to convert the process parameters between the four models and compare N(2) fixation with photosynthesis. The physiological meanings of the process parameters are discussed and compared to those of photosynthesis.