Absolute non-invasive measurement of CO2 mole fraction emitted by E. coli and S. aureus using calibration-free 2f WMS applied to a 2004 nm VCSEL

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.