Abstract
Ultrasensitive and quantitative detection of cancer biomarkers is an unmet challenge because of their ultralow concentrations in clinical samples. Although gold nanoparticle (AuNP)-based immunoassays offer high sensitivity, they were unable to quantitatively detect targets of interest most likely due to their very narrow linear ranges. This article describes a quantitative colorimetric immunoassay based on glucose oxidase (GOx)-catalyzed growth of 5 nm AuNPs that can detect cancer biomarkers from attomolar to picomolar levels. In addition, the limit of detection (LOD) of prostate-specific antigen (PSA) of this approach (93 aM) exceeds that of commercial enzyme-linked immunosorbent assay (ELISA) (6.3 pM) by more than 4 orders of magnitude. The emergence of red or purple color based on enzyme-catalyzed growth of 5 nm AuNPs in the presence of target antigen is particularly suitable for point-of-care (POC) diagnostics in both resource-rich and resource-limited settings.