Designing genetically encodable Ca2+ sensors

Designing genetically encodable Ca²⁺ sensors have played profound roles for scientists to decode cell activity changes in living animals. There are many different methods to achieve such goals, and one of the most powerful methods is to use single chain fluorescence proteins (e.g. GFP) fused with calmodulin (CaM) and one of its specific binding peptide. Such approach has been enabling scientists to be able to image Ca²⁺ signals with broad dynamic ranges and with specific kinetic rates. Please research recent developments in this Ca²⁺ signal imaging research field, and explain the design principles and applications of the methods, and provide your views of future developments.