Fully automated immunoassay for detection of prostate-specific antigen using nano-magnetic beads and micro-polystyrene bead composites, ‘Beads on Beads’

Abstract Magnetic beadshave served as a conventional bioassayplatform in biotechnology. In this study, a fully automated immunoassay was performed using novel nano- and microbead- composites constructedby assembling nano-magnetic beadsonto polystyrene microbeads, designated ‘ Beadson Beads’. Nano-sized bacterial magnetic particles (BacMPs) displaying the immunoglobulin G(IgG)-binding domain of protein A (ZZ domain) were used for the construction of ‘ Beadson Beads’ via the interaction of biotin– streptavidin. The efficient assembly of ‘ Beadson Beads’ was performed by gradual addition of biotin-labeled BacMPs onto streptavidin-coated polystyrene microbeads. Approximately 2000 BacMPs were uniformly assembled on a single microbead without aggregation. The constructed ‘ Beadson Beads’ were magnetized and separated from the suspension by using an automated magnetic separationsystem with a higher efficiency than BacMPs alone. Furthermore, fully automated detection of prostate-specific antigenswas performed with the detection limit of 1.48 ng mL −1 . From this preliminary assay, it can be seen that ‘ Beadson Beads’ could be a powerful tool in the development of high-throughput, fully automated multiplexed bioassays.