Immobilization of polydiacetylene onto silica microbeads for colorimetric detection

Colorimetric polydiacetylene (PDA) undergoes a rapid blue-to-red color transition in response to a variety of environmental perturbations. It has been immobilized on planar substrates to serve as sensing devices for many biological applications. On the other hand, microbeads have been recognized to be a viable alternative to planar substrates for a variety of bioassays and have demonstrated a number of advantages over their planar counterpart. However, it remains a tremendous challenge to immobilize PDA on microbeads without changing its colorimetric properties because PDA is highly sensitive to the environment. In this work, PDA was immobilized onto silica microbeads using 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and CaCl2 as incorporation and pretreatment agents. It was found that the amount of PDA immobilized on silica microbeads increased with a decrease of the PDA/DMPC molar ratio and an increase of CaCl2 concentration. PDA retained its colorimetric properties after immobilization on the microbeads and underwent a blue-to-red color change upon exposure to phospholipase. These PDA/silica microbeads can be readily used for bead-based assay of biomolecules such as proteins, peptides, and many more.