G-Ca-FLITS is a green fluorescence lifetime-based biosensor for quantitative imaging of intracellular Ca[2+]. G-Ca-FLITS was generated by mutagenesis of Tq-Ca-FLITS and is a fusion protein composed of the M13 calmodulin-binding peptide, a circularly permuted fluorescent protein (derived from mTurquoise2 with additional mutations) and calmodulin. For detailed kinetic and spectral properties, see FBrf0264145.