Assessing biomarker syngeneity: An in situ approach using monoclonal antibodies

Lipid biomarkers preserved in ancient rocks have the potential to reveal much about ancient ecosystems. However, establishing that the compounds of interest are syngenetic has proven to be an analytically challenging task. Traditional biomarker analyses rely on extraction of large quantities of powdered rock, making the association of molecules with sedimentary fabrics difficult, if not impossible. As an alternative approach, here we show that monoclonal antibodies that bind specifically to geolipids can be used as molecular probes for in situ detection and localization of such compounds. Monoclonal antibodies that bind to squalene and cross-react with the biomarker squalane were evaluated for labeling sediment-associated hydrocarbons. The anti-squalene antibodies were shown by dot immunoblotting with composed standards to cross-react also with other isoprenoids, such as phytol and its diagenetic products, suggesting reactivity towards acyclic isoprenoids. Then, the anti-squalene antibodies were shown to react with naturally occurring crude oils and, via an immunofluorescence-labeling approach, to bind to isolated organic-rich laminae in rocks from the Eocene Green River Formation known to contain squalane among other linear isoprenoids. These results suggest that squalane, or structurally similar organic biomarkers that cross-react with the antibodies, are confined to discrete organo-sedimentary fabrics within those rocks, providing evidence for their syngeneity. Depending on the specificity and sensitivity of the antibody/geolipid pair, an in situ antibody detection approach may be useful for establishing biomarker syngeneity in older rocks.