Metal Affinity-Enabled Capture and Release Antibody Reagents Generate a Multiplex Biomarker Enrichment System that Improves Detection Limits of Rapid Diagnostic Tests

Multi-antigen rapid diagnostic tests (RDTs) are highly informative, simple, mobile, and inexpensive, making them valuable point-of-care (POC) diagnostic tools. However, these RDTs suffer from several technical limitationsthe most significant being the failure to detect low levels of infection. To overcome this, we have developed a magnetic bead-based multiplex biomarker enrichment strategy that combines metal affinity and immunospecific capture to purify and enrich multiple target biomarkers. Modifying antibodies to contain histidine-rich peptides enables reversible loading onto immobilized metal affinity magnetic beads, generating a novel class of antibodies coined “Capture and Release” (CaR) antibody reagents. This approach extends the specificity of immunocapture to metal affinity magnetic beads while also maintaining a common trigger for releasing multiple biomarkers. Multiplex biomarker enrichment is accomplished by adding magnetic beads equipped with CaR antibody reagents to a large sample volume to capture biomarkers of interest. Once captured, these biomarkers are magnetically purified, concentrated, and released into a RDT-compatible volume. This system was tailored to enhance a popular dual-antigen lateral flow malaria RDT that targets <i>Plasmodium falciparum</i> histidine-rich protein-II (HRPII) and <i>Plasmodium</i> lactate dehydrogenase (<i>p</i>LDH). A suite of <i>p</i>LDH CaR antibody reagents were synthesized, characterized, and the optimal CaR antibody reagent was loaded onto magnetic beads to make a multiplex magnetic capture bead that simultaneously enriches <i>p</i>LDH and HRPII from <i>Plasmodium falciparum</i> parasitized blood samples. This system achieves a 17.5-fold improvement in the dual positive HRPII/pan-<i>p</i>LDH detection limits enabling visual detection of both antigens at levels correlating to 5 p/μL. This front-end sample processing system serves as an efficient strategy to improve the sensitivity of RDTs without the need for modifications or remanufacturing