The World Health Organization (WHO) has set forth a global call for eradicating malaria, caused majorly by the protozoan parasites and . The lack of diagnostic biomarkers for , especially those that differentiate the parasite from , significantly hinders elimination. Here, we show that tryptophan-rich antigen (PvTRAg) can be a diagnostic biomarker for diagnosing in malaria patients. We report that polyclonal antibodies against purified PvTRAg protein show interactions with purified PvTRAg and native PvTRAg using Western blots and indirect enzyme-linked immunosorbent assay (ELISA). We also developed an antibody-antigen-based qualitative assay using biolayer interferometry (BLI) to detect vivax infection using plasma samples from patients with different febrile diseases and healthy controls. The polyclonal anti-PvTRAg antibodies were used to capture free native PvTRAg from the patient plasma samples using BLI, providing a new expansion range to make the assay quick, accurate, sensitive, and high-throughput. The data presented in this report provides a proof of concept for PvTRAg, a new antigen, for developing a diagnostic assay for identification and differentiation from the rest of the species and, at a later stage, translating the BLI assay into affordable, point-of-care formats to make it more accessible.