Paper-based quantum dot-linked immunosorbent assay of carcinoembryonic antigen with dual fluorescence/electrochemical detection

A novel paper-based quantum dot-linked immunosorbent assay (p-QDLISA) with dual-mode fluorescent/electrochemical detection was developed for quantification of carcinoembryonic antigen (CEA) in serum in which CdS-type quantum dots (CdS QDs) were used as labels. The sandwich-type immunoassay involved modification of the surface of paper minidisks with capture anti-CEA antibody, immunoreaction with CEA in the sample, binding with biotinylated reporter anti-CEA and, finally, reaction with streptavidin-conjugated CdS QDs. Optical detection involved broadband UV illumination of the disks, capture of the fluorescence intensity with a smartphone camera and image analysis using an open-source software. Electrochemical detection was performed by positioning the paper disks on top of a 3-electrode electrochemical paper-based device (ePAD) and acidically dissolving the CdS QDs; the released Cd(II) was measured by anodic stripping voltammetry (ASV). Different parameters associated with the preparation of the bioconjugated paper disks, the immunoassays and the detection were studied . The limits of detection (LODs) for CEA were 0.18 ng mL −1 and 0.003 ng mL −1 for the fluorescence and electrochemical detection. The methodologies showed adequate selectivity in the presence of other cancer biomarkers and good stability under storage. The advantages of the p-QDLISA with dual-mode fluorescent/electrochemical detection over existing immunosensing methodologies are discussed. Hence, the developed QDLISA can be readily applied to CEA monitoring at the point-of-care.