NOVEL FLUORESCENT SENSORS FOR THE DETECTION OF ORGANIC MOLECULES IN EXTRA-TERRESTRIAL SAMPLES Roy C. Adkin, James I. Bruce and Victoria K. Pearson Twitter: @RCAdkin Aim of the Research Development of a fluorescent lanthanide complex which will interact with meteoritic organic species in situ and/or in the aqueous phase Background • Organic material is found in carbonaceous chondrite (CC) meteorites: <5% by mass (~14000 different molecules (Schmitt-Kopplin et al., 2010)) • Although (most) confirmed as extra-terrestrial in origin due to: – Isotope ratios (H/D, C, N, O) – Structural isomerisation and diversity e.g. racemic ratio, branching – Compounds present in higher concentrations but rare on Earth, e.g., isovaline, pseudoleucine etc. (Kvenvolden et al., 1970) • No defined environment of formation for what is seen in meteorites although several possible cosmological provinces suggested • BUT, minerals are formed under distinct chemical and physical conditions so can be used as environmental indicators (Velde, 2000) • Understanding mineral/organic associations more could help clarify organic compound source regions and formation processes The problem • We know a relationship exists; – Amount of matrix vs bulk organic material indicated by C and N content (e.g. Anders et al., 1973) – Removal of minerals by dissolution releases more organic material (e.g. Sephton and Gilmour, 2001) – Basic labelling reveals organic material predominately associated with matrix (e.g. Pearson et al., 2007) • Organic molecular inventory and concept of mineral/organic material associations elucidated by destructive analysis of carbonaceous chondrites Development of a new, non-destructive, in situ analytical tool is required… Fluorescence - Overview Emitted light < energy and > λ than the light absorbed Usually, emission ceases almost instantaneously as irradiation is terminated (ns to μs timescale) The sensor – Introducing the lanthanides • Lanthanides (Ln) are elements, e.g. europium (Eu) and terbium (Tb) - amongst the most luminescent elements in the Periodic Table • Extensively used in biomedical imaging techniques • Lanthanide metal ion coupled to an organic ligand • • • ‘Fingerprint’ emission spectrum consisting of line-like peaks or bands – indicative of the element Have long fluorescent lifetimes – the time between termination of irradiation and cessation of emission (ms) Ln must be stable, chemically inert yet subject to physical interactions The sensor – ligand: DOTA Commercially available 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraethanoic acid The sensor – EuDOTA and TbDOTA Preliminary research Sources of intrinsic CC fluorescence • Some minerals exhibit fluorescent properties • Presence of Eu or Tb can activate, enhance or intensify that fluorescence • Identify organic and inorganic CC components whose excitation and emission λ may be similar to Eu and Tb • Organic excitation below that of Eu and Tb so not a concern • Mineral fluorescence, activated and intrinsic, can be background corrected Preliminary research – DOTA experimentation 1) DOTA was synthesised 2) Suitable analytes were chosen representative of all classes of organic molecules identified in CCs taking into consideration: – The number and type of reactive sites and functional groups – Likelihood of interaction with the sensor – structure/size – Whether they are terrestrially rare or potentially prebiotic – Solubility in water Results of DOTA experiments and discussion • 1 mM LnDOTA solution mixed with a range of meteoritic organic molecules at concentrations expected in CCs • Spectra showed no peak shifts but a slight, yet trendless, variation in intensity • Lack of spectral deviation • No interaction with metal centre? • Lanthanide/analyte interaction but fluorescence not altered by presence of analyte? • Limit of detection? • Concentrations consistent with chondritic organic matter (µM, 10-6 mol dm-3, to nM, 10-9 mol dm-3) may be too low for detection by this sensor Fluorimetric analysis – Equimolar (1 mM) EuDOTA/analyte analysis Fluorimetric analysis – Equimolar (1 mM) TbDOTA/analyte analysis DOTA Fluorimetric analysis – Conclusion • Would expect analytes to increase fluorescent intensity due to displacement of water molecules • No discernible trend regarding analyte structure; • It was expected that conjugated and aromatic analytes could increase fluorescent intensity by absorption of excitation energy • Hypothesis: DOTA ligand does not afford interactions • Steric hindrance • Ln atom is too well enveloped • Cannot be sure of limit of detection • Solution? – Use DO3A ligand…one less pendant arm The new ligand – DO3A Fluorimetric analysis – EuDOTA/TbDO3A comparison 200000 180000 160000 Fluorescent intensisty 140000 120000 TbDO3A TbDOTA 100000 80000 60000 40000 20000 0 450 500 550 Fluorescent emission wavelength, nm 600 650 Fluorimetric analysis – Eu3+(aq)/EuDOTA/EuDO3A comparison EuDO3A fluorimetric analysis – EuDO3A and all analytes EuDO3A fluorimetric analysis – EuDO3A and all analytes (L)-serine (L)-tyrosine (L)-threonine EuDO3A/EuDOTA fluorimetric analysis - conclusions • EuDOTA and EuDO3A have shown intensity increase with certain structures or chemical classes only • Identification of structures or functional groups is feasible • Individual molecular specificity may not be achievable Future work • Produce standards for mixtures of: – Similar compound classes (e.g. all amino acids or all carboxylic acids etc.) – Similar or analogous structures (e.g. hypoxanthine and cytosine or adenine and 2,4-diaminopyrimidine etc.) – Complex mixtures of classes and structures • Introduce LnDOTA and LnDO3A complexes to these mixtures • Measure the effects on Ln fluorescent properties Future work (continued) • Development of other ligand molecules • change nature of the pendant arms - facile ligand modifications - broaden the scope of interactions with analytes - selectivity and sensitivity • Development of methodology for future solid sample analysis Thank you for listening. Any questions? Twitter: @RCAdkin Email: Roy.Adkin@open.ac.uk Fluorimetric analysis – Analyte structures (L)-serine (L)-threonine (L)-ornithine (L)-tyrosine (L)-aspartic acid Benzoic acid Fluorimetric analysis – Analyte structures Maleic Acid Fumaric acid Cytosine Adenine Itaconic acid Hypoxanthine N-guanylurea 2,4-diaminopyrimidine