A genetically encoded near-infrared fluorescent calcium ion indicator

We report an intensiometric, near-infrared fluorescent, genetically encoded calcium ion (Ca2+) indicator (GECI) with excitation and emission maxima at 678 and 704 nm, respectively. This GECI, designated NIR-GECO1, enables imaging of Ca2+ transients in cultured mammalian cells and brain tissue with sensitivity comparable to that of currently available visible-wavelength GECIs. We demonstrate that NIR-GECO1 opens up new vistas for multicolor Ca2+ imaging in combination with other optogenetic indicators and actuators. NIR-GECO1, the first near-infrared genetically encoded calcium ion (Ca2+) indicator, enables improved Ca2+ imaging in conjunction with blue-light-activated optogenetic tools and multiplexed imaging in cell cultures and tissue slices.