Ligand immobilization on polydiacetylene-coated and surface-enhanced Raman scattering-encoded beads for label-free detection

A better understanding of protein-protein interactions can be obtained from multiplex protein detection technologies, and spectrally encoded beads can provide fast and efficient means for this type of detection methods. However, high-throughput detection is challenging due to the requirement of using labeled secondary proteins to detect protein binding events. We have previously reported that polydiacetylene-coated surface-enhanced Raman scattering-encoded beads (PDA-SERS beads) can provide an enhanced encoding capacity owing to their SERS properties as well as their potential for label-free detection from the PDA layer. In this study, we introduced ligands to the PDA-SERS beads by using methods for making free-floating vesicles and planar solid substrates, which enabled the detection of target proteins by PDA fluorescence in a PDA-SERS beads system. By using PDA-SERS beads immobilized with biotin, the fluorescence intensities of biotin-conjugated PDA-SERS beads were increased with an increase in the concentration of streptavidin. And, we could detect 2 × 10^-8M of streptavidin by measuring the fluorescence intensity without the requirement of an additional labeling step.