Dual-modal visual/photoelectrochemical all-in-one bioassay for rapid detection of AFP using 3D printed microreactor device

An elaborated 3D printing "all-in-one" dual-modal immunoassay (3D-AIO) has been constructed for the colorimetric and photoelectrochemical (PEC) detection of alpha-fetoprotein (AFP), which integrates all step-analysis functional components (including immune/enzyme reaction, separation and detection) together using automatic microfluidics. The released ascorbic acid (AA) from the enzyme-linked immunoreactions can induce the aggregation of gold nanoparticles (AuNPs) by reducing cystine into cysteine, serving as the reporting agent of colorimetric assay. Meanwhile, the released AA induces hole-trapping of the photoactive nanostructured ZnIn2S4 (ZIS), thus triggering a noticeable photocurrent enhancement at ZIS modified screen printed electrode (labeled as ZIS/SPE) slotted in PEC detection chamber. By smart controlling, the colorimetric assays exhibits a distinguishable color change once AFP contents in serum exceed its cut-off value (20 ng mL(-1)), achieving fast screening and rapid identification purpose for plasma samples as negative or positive, especially in point of care (POC) analysis. And then the PEC immunoassay could be used for more accurate quantitative analysis with the detection limit as low as 0.01 ng mL(-1) (S/N = 3). The proposed assay offered bimodal readout for realizing both qualitative fast screening and quantitative PEC determination of AFP concentration, thereby meeting the requirements of quick and precise POC analysis. The direct detection of AFP from human blood makes it promising for on-site POC diagnostics.