Abstract
We describe the design of an instrument, the OxR (for Oxygen Release), for the enzymatically specific and non-enzymatic detection and quantification of the reactive oxidant species (ROS), superoxide radicals (O2•−), and peroxides (O22−, e.g., H2O2) on the surface of Mars and Moon. The OxR instrument is designed to characterize planetary habitability, evaluate human health hazards, and identify sites with high biosignature preservation potential. The instrument can also be used for missions to the icy satellites of Saturn’s Titan and Enceladus, and Jupiter’s Europa. The principle of the OxR instrument is based on the conversion of (i) O2•− to O2 via its enzymatic dismutation (which also releases H2O2), and of (ii) H2O2 (free or released by the hydrolysis of peroxides and by the dismutation of O2•−) to O2 via enzymatic decomposition. At stages i and ii, released O2 is quantitatively detected by an O2 sensor and stoichiometrically converted to moles of O2•− and H2O2. A non-enzymatic alternative approach is also designed. These methods serve as the design basis for the construction of a new small-footprint instrument for specific oxidant detection. The minimum detection limit of the OxR instrument for O2•− and O22− in Mars, Lunar, and Titan regolith, and in Europa and Enceladus ice is projected to be 10 ppb. The methodology of the OxR instrument can be rapidly advanced to flight readiness by leveraging the Phoenix Wet Chemical Laboratory, or microfluidic sample processing technologies.
Highlights
On Earth, the production of reactive oxygen species (ROS) in soils is typically associated with the relatively high abundance of O2 (g) in the atmosphere [1]
One approach for implementing the Oxygen Release (OxR) assay for field instrument construction is to keep it compatible with the Wet Chemistry Laboratory (WCL) that flew as part of the Phoenix lander mission to Mars [30]
The OxR instrument prototype will be tested in a laboratory setting and results compared to standard laboratory procedures, followed by field testing in the Mojave Desert
Summary
On Earth, the production of reactive oxygen species (ROS) in soils is typically associated with the relatively high abundance of O2 (g) in the atmosphere [1]. O2 -sensing electrodes are based on the luminescence quenching by O2 , and are sensitive enough to measure O2 at ~1 nmole O2 per cubic cm (cm−3 ) of regolith or water, i.e., much lower than that detected by the GEX (775 nmoles cm-3 regolith) This translates to a minimum instrument detection limit for metal salts of O2 − and O2 2− of 0.01 ppm (= 10 ppb) for Martian and Lunar regolith or O2 2− in Europa and Enceladus water. This sensitivity corresponds to ~10 μg O2 − /O2 2− kg−1 Mars or Lunar surface regolith (based on a density of 1.4–1.6 g cm−3 for Mars [46,47], and for the Moon [48])
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