Abstract:
We report the first demonstration of accurate real-time
non-invasive measurement of the absolute cumulative
mole fraction of metabolic carbon dioxide emitted by
Escherichia coli and Staphylococcus aureus over a period
of several hours of their life cycles using a recentlydeveloped
calibration-free wavelength modulation
spectroscopy technique. A 1mW vertical cavity surface
emitting laser is used to interrogate a single rotational
vibrational absorption line of carbon dioxide at 2003.5
nm. The measurements are immune to laser intensity
fluctuations and variable optical coupling that is
inevitable in such free-space coupled experiments that
run over 10-18 hours. The cumulative carbon dioxide
mole fraction follows the characteristic modified
Gompertz model that is typical of bacterial growth in
batch cultures. The characteristics growth parameters
are extracted from this curve. The technique can be
readily extended to study multiple volatile organic
compounds that bacteria are known to emit.