Figure 1.

Basic biosensor designs. A. Translocation-based biosensors. Phosphoinositide (PI) sensors utilize lipid-selective binding domains that translocate to or from the membrane to report the production and degradation of specific PIs, such as PIP₃ (a). Kinase translocation reporters similarly undergo translocation into or out of the nucleus depending on the phosphorylation of kinase-specific substrate sequences within the reporter (b). SPARK, a phase separation-based kinase reporter, visualizes dynamics of kinase activity with phase separation (c). B. Single FP-based sensor. The insertion of a conformational switch into a single FP can be used to alter chromophore behavior in response to a signaling event. C. FRET-based sensor. Changes in the proximity or orientation between a pair of FPs caused by the sensing unit upon detection of a signaling event results in a change in FRET.