Fluorescent Calcium Indicators

The study of the function of calcium ions (Ca2+) inside cells is one of the most dynamic areas of modern cell biology. In common parlance, a transient rise in the cytosolic free Ca2+ concentration is referred to as a “Ca2+ signal”. Ca2+ signaling is essential in diverse biological processes, including mitosis, vesicular secretion (e.g., release of various neurotransmitter and hormones), motility (e.g., muscle contraction), and learning and memory (e.g., long-term potentiation and depression of synaptic transmission).   Techniques for the measurement and manipulation of Ca2+ are therefore crucial and have advanced rapidly, largely as a result of the invention of fluorescent calcium indicators.

The commonly used fluorescent Ca2+ indicators today (Fluo, Fura, and Indo) were invented in the 1980s with little improvement over the last 25 years. Scientists at TEFLabs have now developed new Ca2+ indicators that aim to remedy shortcomings in the old generation of indicators.

TEFLabs is committed to improving Ca2+ indicators and supporting scientists by:

  • providing visible-wavelength indicators that offer greatly enhanced brightness and extended dynamic range = Asante Calcium Green (ACG): Fmax/Fmin=220, which is brighter than Fluo-4 by more than 3 fold and is leakage resistant;
  • providing improved long-wavelength and near-infrared indicator families - Asante Calcium Red (ACR) and Asante Calcium NearIR (ACNIR); 
  • providing all Ca2+ indicator families in versions with enhanced performance characteristics, including low affinity, leakage resistance, and near-membrane Ca2+ sensing; and 
  • continuing innovation in fluorescent ion indicators.


Table 4.1 TEFLabs Calcium Indicators 

TEFLabs fluorescent calcium Ion Indicators


TTable 4.1 summarizes TEFLabs’ new and traditional  fluorescent Ca2+ indicator families. Within each family, TEFLabs offers indicators for a range of affinities and enhanced-performance versions. The availability of multiple versions within each family permits the researcher to select an indicator that is most appropriate for a particular experiment.

Ca2+ indicators that are excited at visible wavelengths have advantages over UV-excited indicators. Whereas UV light can cause cell damage, visible light is generally biologically benign. Moreover, much less cellular autofluorescence is excited by visible light than by UV light. The ready availability of low-cost lasers that emit visible light makes the visible indicators ideal for confocal microscopy and flow cytometry.