A Point-of-Care System for the Quantification of Small-Molecule Drugs in Blood

Rapid detection of small-molecule drugs in blood, such as anticoagulants, can be critical for aiding clinicians in selecting the correct treatment and dosing. While qualitative point-of-care tests are available for some drugs, quantitative blood tests are not readily available. We describe a flow-front immunoassay for quantifying small-molecule drugs in whole blood within 10 min, targeting the three direct oral anticoagulants, dabigatran, rivaroxaban, and apixaban; the oncology drug methotrexate; and the antibiotic linezolid. The method integrates a novel homogeneous optical immunoassay on a disposable cartridge, where sample flow reconstitutes reagents deposited in the filter at the solvent front, enabling sequential reagent addition. The embedded filter retains red blood cells, allowing the plasma front to migrate to a microcuvette, where the optical readout signal is detected. This system incorporates two key innovations: the immunoassay and the microcuvette. The dabigatran concentration was quantified in 52 clinical plasma samples and demonstrated comparable results to commercially available assays and mass spectrometry analysis.