Visual Detection of Cesium Ions in Domestic Water Supply or Seawater using a Nano-optode

Cesium, in particular radioactive Cs 137 is currently a significant environmental problem in Japan following the incident at the Fukushima-Daiichi nuclear power plant caused by the Great East Japan earthquake. Although radioscopes and gamma ray cameras have been developing to visualize radioactive species or contamination, it is not necessarily a simple matter to locate sources of contamination under high levels of background radiation. However, supramolecular approaches for environmental sensing of analyses are useful in the design of high-resolution molecular sensors. Here, we have developed an optical imaging technique for cesium ions involving an optode system in environmental water. An optode membrane was prepared incorporating a calix[6]arene derivative, which showed excellent selectivity toward cesium ions in aqueous solutions, even in water supplied for domestic use or seawater. Furthermore, this membrane was fabricated using nanoparticles with a diameter of ca. 100 nm. The nano-optode also gave an excellent response to cesium ions. Therefore, this optode provides a higher spatial resolution than existing radioscopes and gamma ray cameras under high level radioactive environments.