A cytosolically localized far-red to near-infrared rhodamine-based fluorescent probe for calcium ions.

Ca2+ is one of the most important second messengers in cells. A far-red to near-infrared (NIR) Ca2+ fluorescent probe is useful for multi-color imaging in GFP or YFP-expressing biosamples. Here we developed a cytosolically localized far-red to NIR rhodamine-based fluorescent probe for Ca2+, CaSiR-2 AM, while rhodamine dyes are basically localized to mitochondria or lysosomes in cells.