A rapid diagnostic test (RDT) is widely used in global health programs to monitor and diagnose Malaria by detecting the presence of the histidine-rich protein 2 (PfHRP2) antigen, which is secreted by the parasite Plasmodium falciparum\textit{Plasmodium falciparum}Plasmodium falciparum. This diagnostic test is a lateral flow immunoassay utilizing monoclonal antibodies (MCAs).
Which statement correctly describes the biochemical mechanisms occurring on the test strip when a positive blood sample (containing PfHRP2) is applied?
The PfHRP2 antigen binds directly to the immobilized antibodies on the test line first, which then release a colored enzyme that migrates to the control line to produce a color change.
Mobile gold-conjugated monoclonal antibodies bind to the PfHRP2 antigen, forming a complex that is captured by immobilized anti-PfHRP2 antibodies at the test line, while excess mobile antibodies bind to immobilized antibodies at the control line.
The patient's blood sample contains host antibodies against PfHRP2 that carry the antigen to the control line, where they react with gold-labeled secondary antigens.
Immobilized antibodies on the test line detach upon binding to PfHRP2 and carry the colored gold markers to the control line, where they form a double line.