Bioinspired design of a polymer gel sensor for the realization of extracellular Ca(2+) imaging.

Although the role of extracellular Ca(2+) draws increasing attention as a messenger in intercellular communications, there is currently no tool available for imaging Ca(2+) dynamics in extracellular regions. Here we report the first solid-state fluorescent Ca(2+) sensor that fulfills the essential requirements for realizing extracellular Ca(2+) imaging. Inspired by natural extracellular Ca(2+)-sensing receptors, we designed a particular type of chemically-crosslinked polyacrylic acid gel, which can undergo single-chain aggregation in the presence of Ca(2+).