Chromatic detection of Cs ions using polydiacetylene-based vesicles containing crown-ether-like ethylene glycol units

Radioactive Cs-137, which have a half-life of about 30.17 years, are a major source of nuclear pollution and should be detected and removed. For this purpose, a colorimetric, polydiacetylene (PDA) vesicle-based sensor was synthesized to detect Cs ions. The polymer vesicles consisted of commonly used 10,12-pentacosadiynoic acid (PCDA) and its derivatives. One of the derivatives that contained tetraethylene glycol (TEG) units at the end of the PCDA side chain, and thus it acted as a chelating agent that surrounded the Cs ion like a crown ether. As a result, the main chain of the PDA was distorted by the chelation of TEG and Cs ions, resulting in a blue-red color change. To provide selectivity to the PDA vesicles, another derivative was incorporated to the PDA vesicles with controlled amount, which was not responsive to alkali metal ions. The changes in the colorimetric response of the vesicles were not observed in the presence of other alkali metal ions such as Na, K, and Rb ions, indicating that the TEG units fitted well in size with the ionic radius of the Cs ion, resulting in high selectivity. Solid-state PDA film was also fabricated to provide selective detection of Cs ions.