Conventional lateral flow assays consist of a single planar strip with sample, conjugate, nitrocellulose, and absorbent pads arranged in series. All reagents and sample flow through one continuous capillary path. This architecture made LFAs ubiquitous in point-of-care diagnostics, but it also couples immunorecognition and signal generation into a brief, poorly controlled time window as the fluid front passes the test line.

As a result, the only WHO-endorsed urine-based POC test for tuberculosis (LF-LAM) achieves only ~40-50% sensitivity overall, restricting its use to seriously ill people living with HIV with CD4 cell counts below 200 cells/mm³.

Signal-enhancement approaches like enzyme-based amplification with chromogenic substrates can improve sensitivity, but they typically add reagent loadings or timed incubations that undermine sample-in-answer-out simplicity. The dual-flow architecture solves this.