ATP has essential roles in cell signalling and energy homeostasis and biosensors to detect it have many potential applications. Here, the authors develop a new ATP sensor that can be targeted to the membrane or cytosol.

FRET sensors hardly achieve visualization of spatiotemporal dynamics of protein activity in vivo. Here the authors present intensiometric small GTPase biosensors based on dimerization-dependent fluorescent proteins that enable monitoring of activity of small GTPases in the brains of behaving mice at a single spine resolution.

VARNAM is a red-shifted genetically encoded voltage sensor based on the Ace opsin. It is applied in Drosophila, mouse brain slices and behaving mice. It can be readily combined with blue-light-sensitive tools for dual-color applications.

The synOptopatch approach enables all-optical access to synaptic communication via mutually exclusive expression of an optogenetic actuator and a voltage sensor in pre- and postsynaptic neurons, respectively.

This protocol describes how to combine up to four genetically encoded fluorescent sensors to image redox landscapes. The procedure describes applications in live imaging and flow cytometry of cultured cells, and in vivo imaging in zebrafish larvae.