A true-color electrochemiluminescent (ECL) imaging strategy was designed for a multi-immunoassay of
proteins by coupling highly efficient
polymer dots (Pdots) with dual
DNA amplification. The Pdots were prepared by nanoprecipitation of poly[(9,9-dioctylfuorenyl-2,7-diyl)- alt-co-(1,4-benzo-{2,1',3}-
thiadiazole)] in the presence of
poly(styrene- co-maleic anhydride) and functionalized with DNA1 that hybridized with black hole quencher-labeled DNA2 to self-quench the ECL emission. The Pdots modified Au/ITO
electrode showed 100-fold stronger ECL emission than the Pdots modified ITO
electrode. After the capture antibody immobilized on Au/ITO slide recognized the target
protein and then reacted with
biotin-labeled antibody,
streptavidin and
biotin-labeled
oligonucleotide, respectively, a large number of DNA1 functionalized Pdots could be introduced onto the slide surface by rolling circle amplification of the
oligonucleotide to trigger the enzymatically cyclic release of the Pdots from the self-quenched probes to
solution in the presence of Exo III. The dual
DNA amplification produced a greatly amplified ECL signal for true-color ECL imaging. Using
carcinoembryonic antigen, cytokeratin-19-fragment, and
neuron-specific enolase as a
lung cancer-specific
biomarker panel, the ECL imaging-based multi-immunoassay exhibited excellent performance with a linear range of 1 pg mL-1 to 500 ng mL-1 and limits of detection of 0.17, 0.12, and 0.22 pg mL-1, respectively. The proposed method could accurately detect these
biomarkers in clinical human serum samples for
lung cancer screening. The Pdots-based true-color ECL imaging approach possessed the advantages of visual analysis along with wide detection range and high sensitivity and thus has great potential in clinical application.