On‐Paper Enzyme‐Linked and Metal‐Linked Immunosorbent Assays for Low‐Cost Decentralized Testing of Carcinoembryonic Antigen

Abstract This work reports two simplified paper‐based approaches for immunosensing of carcinoembryonic antigen (CEA) in serum. On‐paper enzyme‐linked immunosorbent assay (p‐ELISA) (using enzymatic generation of a colored product) and metal‐linked immunosorbent assay (p‐MeLISA) (using gold nanoparticles (AuNPs) as labels) were implemented using low‐cost diagnostic bio‐conjugated paper mini disks as platforms for the fast colorimetric immunosensing of CEA in human serum. The colour intensity was captured with a commercial scanner and analyzed using an open‐source software. Different parameters of the preparation of the bioconjugated disks and of the immunoassays were studied and, under the selected conditions, LODs of 0.4 ng mL −1 with p‐ELISA and 0.1 ng mL −1 with p‐MeLISA were achieved while recoveries of CEA in serum samples were in the range from 88 to 112 % with coefficient of variation of <12 %. The assay time was 90 s for p‐ELISA and 85 s for p‐MeLISA. The immunoassays exhibited satisfactory selectivity in the presence of other cancer biomarkers and good stability under storage. Thanks to simple and rapid fabrication and modification, simple analysis protocol, affordability (<0.05 € per device), equipment‐free quantification, low sample and reagents requirments, stability and satisfactory analytical characteristics, these approaches are fit‐for‐purpose for assay of CEA in serum at the point‐of care in resource‐limited settings.