Thermohypersensitive polydiacetylene vesicles embedded in calcium-alginate hydrogel beads

Polydiacetylenes (PDAs) are widely adapted materials for the development of sensors with liposome-like biomimetic structures, and the sensing results are often detectable with the naked eye. In addition, PDA-based sensors encapsulated within hydrogels have been intensively studied due to their superiority over solution-embedded-type and/or solid-immobilized-type sensors. Hydrogel-type PDA sensors are more stable and equipped with physically controllable high surface areas and are thus potentially utilizable in many applications. However, PDAs have intrinsic color-transitioning properties when exposed to temperatures greater than 50-60 degrees C, which cannot be used for more practical applications. In this study, we employed a calcium-alginate polymer to maximize the utility of a PDA-based hydrogel-type sensor and discovered that the sensor can be hypersensitive to temperature increases at a lower temperature range. We report the characterization of potential factors, gelation periods, and gelation agents that correlate with the sensitivity of the so-called PDA-alginate hydrogel. We expect that our findings can be applied in future research on industrially applicable developments for the maintenance of cold-chain delivery systems, temperature-sensitive chemicals, or food. Moreover, our materials will also provide a history of temperature changes because the corresponding color will not revert back even after the temperature decreases to the normal range.