Fig.8 Principle of FRET-based GECI and single fluorescent protein GECI.
Calcium Indicators The calcium ion indicator is the key to calcium imaging. Currently, commonly used calcium ion indicators can be divided into two categories, which are chemical fluorescent calcium ion indicators and genetically encoded calcium ion indicators (GECIs). l Chemical Indicators Chemical indicators are small molecules that can chelate calcium ions. All these molecules are based on an EGTA homologue called BAPTA, with high selectivity for calcium (Ca2+) ions versus magnesium (Mg2+) ions. The commonly used chemical indicators are Oregon Green-1, Fura-2, Indo-1, Fluo-3, and Fluo-4.
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Calcium Imaging