Direct Optical Detection of Factor Xa Activity in Minimally Processed Whole Blood

The ability to measure factor Xa activity directly in whole blood samples offers a path toward point-of-care monitoring and personalized anticoagulant dosage, potentially reducing bleeding risk and other anticoagulant-associated complications. We present a strategy to enable direct optical detection of factor Xa in minimally processed whole blood samples. Our strategy relies on a custom FRET-pair labeled DNA-peptide substrate, allowing FRET ratio to be monitored as an indicator of factor Xa activity. Substrates are tethered to a tapered-fiber sensor to allow evanescent detection of fluorescence directly at the sensor surface, minimizing background media interference and enabling detection directly in blood samples. After characterizing the custom substrate and demonstrating the correlation of fiber-based measurements to an existing chromogenic assay, we demonstrate the detection of endogenous factor Xa activity in >85% whole blood. Finally, we demonstrate the detection of therapeutic concentrations of enoxaparin, a widely used anticoagulant, directly in 90% whole blood in less than an hour and correlate these measurements to activated partial thromboplastin time (aPTT) testing. Together, these results indicate a promising strategy to achieve point-of-care factor Xa detection, enabling personalized anticoagulant treatment and reducing adverse outcomes.