Inkjet-printed point-of-care immunoassay on a nanoscale polymer brush enables subpicomolar detection of analytes in blood

Significance Sensitive quantitation of protein biomarkers plays an important role in modern clinical decision making. This work introduces an inkjet-printed assay platform built on a nonfouling, nanoscale polymer brush, which eliminates nonspecific binding, the largest source of noise in surface-based assays. The assay goes to completion after adding a drop of blood (with no additional reagents or mixing), and the assay can be read with a smartphone-based detector. This technology is significant because it enables high-performance diagnostic testing in blood with minimal infrastructural requirements. Furthermore, its fully printed nature makes it highly customizable and thus broadly applicable to a wide range of diagnostic targets. The ELISA is the mainstay for sensitive and quantitative detection of protein analytes. Despite its utility, ELISA is time-consuming, resource-intensive, and infrastructure-dependent, limiting its availability in resource-limited regions. Here, we describe a self-contained immunoassay platform (the “D4 assay”) that converts the sandwich immunoassay into a point-of-care test (POCT). The D4 assay is fabricated by inkjet printing assay reagents as microarrays on nanoscale polymer brushes on glass chips, so that all reagents are “on-chip,” and these chips show durable storage stability without cold storage. The D4 assay can interrogate multiple analytes from a drop of blood, is compatible with a smartphone detector, and displays analytical figures of merit that are comparable to standard laboratory-based ELISA in whole blood. These attributes of the D4 POCT have the potential to democratize access to high-performance immunoassays in resource-limited settings without sacrificing their performance.