Gas-Shearing Microfluidic Fabrication of Polydiacetylene–Alginate Colorimetric Sensor Beads

Polydiacetylenes (PDA) are highly regarded for their unique colorimetric and fluorescent responses, making them ideal for sensor development. Despite their potential, conventional methods for fabricating biocompatible PDA-encapsulated hydrogel sensor beads often fail to offer precise control over bead size and morphology. This study introduces a coflow gas-shearing microfluidic system that effectively overcomes these limitations, enabling the controlled production of polydiacetylene/alginate (PDA/Alg) and polydiacetylene/polydimethylsiloxane/alginate (PDA/PDMS/Alg) microbeads. Through systematic variation of gas pressure, liquid flow rates, and nozzle sizes, the mechanisms of droplet breakup and generation are explored. This process is validated through numerical modeling based on the Weber number, which enhances our understanding of droplet size distribution and flow regimes. The solvatochromic properties of PDA/Alg microbeads are assessed, highlighting their potential as polar solvent sensors and discussing the solvatochromic mechanism in terms of intermolecular interactions and the dissolution of unpolymerized monomers. Additionally, PDA/PDMS/Alg microbeads exhibit a semireversible thermochromic response under repeated cycles of heating, cooling, and UV exposure. This response is attributed to the formation of new PDA domains inside the PDMS phase upon UV exposure onto the red-phase microbeads. Overall, this study successfully demonstrates a straightforward and effective microfluidic approach for producing well-defined stimulus-responsive PDA–hydrogel microbeads.