Rolling circle amplification integrated with suspension bead array for ultrasensitive multiplex immunodetection of tumor markers.

Multiplex detection of ultra-low abundant tumor markers is extremely important for early diagnosis and therapy evaluation. Herein, an ultrasensitive multiplex immunoassay was developed by combination of rolling circle amplification (RCA) and suspension bead array (SBA) technology. Based on a conventional sandwich-type immunoreaction on beads, the detection antibodies were conjugated with DNA primers, so RCA could be implemented to generate long-stranded DNA with abundant repeated sequences allowing for hybridization with fluorochrome-labeled oligonucleotide probes. Thus the fluorescence signal of immunocomplexes on the encoded beads can be greatly enhanced. Using the as-developed immuno-RCA suspension bead array (iRCA-SBA), simultaneous analysis of multiple tumor markers was achieved with the limits of detection of 3.1 pg/mL (∼0.1 pM) for prostate specific antigen (PSA), 9.1 pg/mL (∼50 fM) for carcinoembryonic antigen (CEA), and 0.66 pg/mL (∼9 fM) for α-fetoprotein (AFP), which are two to three orders of magnitude lower than those obtained by the conventional SBA method. The dynamic range were 4.5, 4.7, and 5.5 orders of magnitude for PSA, CEA, and AFP, respectively. Tests on clinical serum samples demonstrate that the tumor marker concentrations measured by the newly developed iRCA-SBA assay agreed well with those obtained by the conventional SBA method. These results indicate that the iRCA-SBA assay significantly increased the detection sensitivity and dynamic range without sacrificing the reliability and accuracy of conventional SBA. Upon the integration with iRCA, SBA could find more applications in the detection of low abundance protein biomarkers for early diagnosis of cancer and other diseases.