Periodic Surface-Enhanced Raman Scattering-Encoded Magnetic Beads for Reliable Quantitative Surface-Enhanced Raman Scattering-Based Multiplex Bioassay.

Surface-enhanced Raman scattering (SERS)-based immunoassay on encoded beads is highly attractive with the advantages of ultrasensitivity, multiplex and high throughput. However, it was a great challenge to screen out in-focus signals of the immunoconjugated SERS nanoprobes on spherical bead conveniently. Here, periodic SERS-encoded magnetic beads (PSE-MBs) were developed through droplet optofluidic technique by using monodisperse SERS-encoded magnetic nanospheres as building blocks. The designed PSE-MBs not only exhibit huge coding capacity, but also provide the strongest and reproducible SERS coding signals as "in-focus beacons". When PSE-MBs are used as capture carriers in SERS-based immunoassay, both multiple target analytes and in-focus signals of SERS nanoprobes could be easily identified according to the collected SERS coding signals. Thus, reliable quantitative analysis of multiple target analytes could be conveniently achieved by such detection protocol. Additionally, the magnetic ingredient in PSE-MBs made the operation easily during the bioassay. The multiple advantages of PSE-MBs including large coding capacity, in-focus beacons and magnetic operation endorse them to be robust capture carriers in reliable quantitative SERS-based multiplex immunoassay.