In collaboration from the Emergency Resuscitation Research Center of the University of Chicago, we are developing a novel biosensor for an important medical application - revival of sudden cardiac arrest victims. Oxidants such as reactive oxygen species and reactive nitrogen species play critical roles in cell signaling and cell injury during pathologic conditions such as ischemia/reperfusion. Specifically, two of the most diffusible oxidants, hydrogen peroxide and nitric oxide, play important roles in ischemia/reperfusion injury. The objective of our work is to develop a highly sensitive real-time sensor for noninvasively measuring these species in human-exhaled breath as biomarkers of cell injury.

Because the concentration levels of H2O2 and NO in exhaled breath are expected to be in the parts per billion range, we selected for further development a sensitive infrared technique based on tunable diode laser absorption. We designed and built a tunable diode laser at an infrared wavelength range of 1260-1290 cm-1, where the H2O2 peak appears in the absorption spectra and where interfering species like H2O and CO2 have minimal interference. Serial dilutions of H2O2 in water were prepared from 0.01 to 0.0001 wt.%. Extreme care was taken to minimize sample contamination, deposits on cell wall, or decomposition by dust or contaminants. The vapor from the headspace of a tube with test solution was pumped into the cell to a pressure of 3 torr. Measurement results showed decreasing detection peaks for 0.01 to 0.0001 wt.% samples. The lowest concentration level (0.0001 wt.%) detected corresponds to 30 ppb in the vapor phase. Further improvement by an order of magnitude is possible by integrating the signal longer than the 1-ms time constant employed. Having reached our sensitivity goal, the University of Chicago is anxious to use the device to validate the hypothesis of noninvasive oxidant stress measurements via breath analysis.