Calcium indicator proteins include the single fluorophore sensor GCaMP11,16,17 and several families of Förster resonance energy transfer based sensors18-22. However, none of these protein-based indicators have yet surpassed the sensitivity and speed of commonly used synthetic calcium indicators (e.g., Oregon Green Bapta-1-AM, OGB1-AM). Therefore, depending on the experimental goals, investigators choose between sensitive synthetic indicators delivered by invasive chemical or physical methods, or less sensitive protein sensors delivered with genetic methods.
