Abstract
High-energy ionizing radiation in the form of solar energetic particles and galactic cosmic rays is pervasive on the surface of planetary bodies with thin atmospheres or in space facilities for humans, and it may seriously affect the chemistry and the structure of organic and biological material. We used fluorescent microarray immunoassays to assess how different doses of electron and gamma radiations affect the stability of target compounds such as biological polymers and small molecules (haptens) conjugated to large proteins. The radiation effect was monitored by measuring the loss in the immunoidentification of the target due to an impaired ability of the antibodies for binding their corresponding irradiated and damaged epitopes (the part of the target molecule to which antibodies bind). Exposure to electron radiation alone was more damaging at low doses (1 kGy) than exposure to gamma radiation alone, but this effect was reversed at the highest radiation dose (500 kGy). Differences in the dose–effect immunoidentification patterns suggested that the amount (dose) and not the type of radiation was the main factor for the cumulative damage on the majority of the assayed molecules. Molecules irradiated with both types of radiation showed a response similar to that of the individual treatments at increasing radiation doses, although the pattern obtained with electrons only was the most similar. The calculated radiolysis constant did not show a unique pattern; it rather suggested a different behavior perhaps associated with the unique structure of each molecule. Although not strictly comparable with extraterrestrial conditions because the irradiations were performed under air and at room temperature, our results may contribute to understanding the effects of ionizing radiation on complex molecules and the search for biomarkers through bioaffinity-based systems in planetary exploration.
Highlights
The study of the effects of ionizing radiation on the organic molecules with abiotic or biological origin or even whole living beings is of major relevance in many research areas, especially in planetary exploration
Exposure of target compounds to ionizing radiation caused a loss of the immunoidentification signal, mostly due to epitope damage (Fig. 2)
This study does not show which detailed chemical modifications occurred within the molecules after irradiation, the loss of fluorescence after the immunoassay with increasing radiation doses is an indicator of any structural or chemical alteration of the antigen and/or the epitopes directly induced by ionizing radiation
Summary
The study of the effects of ionizing radiation on the organic molecules with abiotic or biological origin or even whole living beings is of major relevance in many research areas, especially in planetary exploration. In the case of Enceladus, direct measurements of ocean materials have revealed the presence of organic compounds (Postberg et al, 2009, 2011; Waite et al, 2009). Biogenic organic molecules are susceptible to chemical and physical degradation after organisms die, and this constrains their preservation potential in the geological record (Eigenbrode, 2008) This could be a major limiting factor in the search for evidence of life on planetary environments where any organic biosignatures near the surface might have been exposed to physical and chemical degradation produced by environmental factors, for example, ultraviolet and ionizing radiation or powerful oxidants such as perchlorates for timescales of millions to billions of years
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