The search for evidence of existing or extant Life (biosignatures) is a
growing research topic and one of the main pillars of Astrobiology.
There is significant interest in the search and exploration of new
biosignatures, and increasing relevance of Potential Biosignatures.
These are specific features that although consistent with biological
processes can also be attributed to inanimate processes. Biogenic
Metallic nanoparticles (MNPs), have been intensively studied and
explored, yet their synthesis is not yet fully understood. Despite the
lack of a systematic survey on this topic, it is well known that many
microbes produce molecules with the capability of reducing metal ions.
Given the wide diversity of such molecules, we can assume that all
microbial life is capable of synthesizing them and, consequently,
producing MNPs. Researchers agree that any existing or extant life on
Mars or on other parts of the solar system, is (or was) likely
microbial. Therefore, the detection of MNPs formation, when analyzing
extraterrestrial samples (e.g., sediments, rocks), could be used to
infer the presence of biological molecules and thus be employed as a new
potential biosignature. Therefore, in short: yes, biogenic metallic
nanoparticles have a great potential of being used as biosignatures.