Development and characterization of an enzyme-linked DNA aptamer-magnetic bead-based assay for human IGF-I in serum

DNA aptamer sequences were selected and screened for affinity against recombinant human insulin-like growth factor-I (rhIGF-I) using an ELISA-like aptamer-based assay (ELASA). When the top four aptamers were paired against one another in all possible sandwich assay combinations using capture aptamers on magnetic beads (MBs), one sandwich combination appeared superior. This combination produced a reliably sensitive assay with a probable limit of detection < 16 ng/mL even in human serum. The assay did not require separation of rhIGF-I from IGF binding proteins (IGFBP) in human serum, suggesting that the capture and reporter aptamers may bind an exposed IGF-I epitope in the IGF-I-IGFBP complex.