The GCaMP-R Family of Genetically Encoded Ratiometric Calcium Indicators

ACS Chem Biol. 2017 Apr 21;12(4):1066-1074. doi: 10.1021/acschembio.6b00883. Epub 2017 Mar 1.


We report on GCaMP-Rs, a new family of genetically encoded ratiometric calcium indicators that extend the virtues of the GCaMP proteins to ratiometric measurements. We have engineered a tandem construct of calcium-dependent GCaMP and calcium-independent mCherry fluorescent proteins. The tandem design assures that the two proteins localize in the same cellular compartment(s) and facilitates pixelwise ratiometric measurements; however, Förster resonance energy transfer (FRET) between the fluorophores reduces brightness of the sensor by up to half (depending on the GCaMP variant). To eliminate FRET, we introduced a rigid α-helix, the ER/K helix, between GCaMP and mCherry. Avoiding FRET significantly increases the brightness (notably, even at low calcium concentrations), the signal-to-noise ratio, and the dynamic range.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Calibration
  • Chickens
  • Fluorescence Resonance Energy Transfer
  • HEK293 Cells
  • Humans
  • Kinetics
  • Luminescent Proteins / metabolism*


  • Luminescent Proteins
  • red fluorescent protein
  • Calcium