Novel Fluorescent Sensors for the Detection of Organic Molecules in Extraterrestrial Samples

Abstract

The objective of this PhD project was to develop, test and evaluate lanthanide-based fluorescent sensors that could detect organic molecules in extracts taken from carbonaceous chondrite-type meteorites. These contain solvent soluble organic molecules, some of which are potentially prebiotic and are, therefore, of interest in the search for extinct or extant life in extraterrestrial environments. The sensors are based upon the ligands DOTA and DO3A, the lanthanide complexes of which are well characterised and have been used as contrast agents and sensors in medical and biological sectors. Their application to the extracts of geological samples, and subsequent analysis by fluorescence spectroscopy, is, however, novel. After testing on individual analytes, it was shown that nucleobases and benzoic acid modified the intensity of the lanthanide emissions and modified the form of the emission spectrum of europium by sensitisation of certain transitions. The presence of these analytes affected the spectra of the DO3A lanthanide complexes more effectively, therefore, novel, structurally similar DO3A-like ligands were synthesised, chelated to lanthanides and tested. Sensors were tested with individual analytes, solution obtained from weathered mineral samples, a terrestrial rock and two carbonaceous chondrites (Murchison and ALH88045). Tests concluded that the presence of dissolved mineral species or mineral particulates in an extract would be unlikely to interfere with sensor responses. When applied to the extracts of the terrestrial and extraterrestrial rocks, the sensor responses were varied and, by comparing them to responses recorded when in the presence of individual analytes, indicated that the sensors detected the presence of structurally similar molecules. Therefore, it can be concluded that the sensors tested exhibit potential utility for analyte detection in a variety of scenarios. Using fluorescence techniques, perhaps as a ‘lab-on-a-chip’ device as part of the instrumentation on board a rover on the surface of planetary body, these sensors may be employed in the ongoing quest to detect evidence of alien life and clues as to how life began on Earth.