Paper-based multi-well depletion ELISA.

Enzyme-linked immunosorbent assay (ELISA) is widely employed for detecting target molecules in bioassays including the serological assays that measure specific antibody titers. However, ELISA tests are inherently limited to centralized laboratories staffed with trained personnel as the assay workflow requires multiple steps to be performed in a specific sequence. Here, we report a dipstick ELISA test that automates this otherwise laborious process and reports the titer of a target molecule in a digital manner without the need for an external instrument or operator. Our assay measures titer by gradually immuno-depleting the target analyte from a flowing sample effectively diluting the residual target - a process conventionally achieved through serially diluting the whole sample in numerous, time-consuming pipetting steps performed manually. Furthermore, the execution of the depletion ELISA process is automated by a built-in flow controller which sequentially delivers different reagents with preset delays. We apply the technology to develop assays measuring (1) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody titers (IgM/IgG antibodies to nucleocapsid and spike protein) and (2) troponin I, a cardiac biomarker.