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 × 10−8 M of streptavidin by measuring the fluorescence intensity without the requirement of an additional labeling step.

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