Biopolymer capsules bearing polydiacetylenic vesicles as colorimetric sensors of pH and temperature

We report the creation of biopolymer capsules that show a colorimetric response to changes in pH and temperature. Polymerized diacetylenic (PDA) vesicles are embedded within capsules formed by complexing the cationic biopolymer, chitosan, with an anionic surfactant. The PDA vesicles impart their colorimetric properties to the capsules while remaining embedded within the capsule lumen. Accordingly, the capsules show a blue color at low pH (∼6) or temperature (∼25 °C) whereas the color changes to purple at medium pH (∼8) or temperature (∼45 °C) and finally to red at high pH (∼10) or temperature (∼60 °C). These capsule-based sensors are easy to prepare, low-cost, and can be easily tailored for various applications.