A far-red fluorescent probe based on a phospha-fluorescein scaffold for cytosolic calcium imaging.

The far-red emissive fluorescent probe CaPF-1 based on a phospha-fluorescein scaffold enables the detection of cytosolic calcium ions in living cells. The probe can be excited in the red region (λabs = 636 nm) and exhibits a sufficiently high fluorescence turn-on response in the far-red region (λem = 663 nm) upon complexation with calcium ions. The hydrophilic and anionic characteristics of this phospha-fluorescein fluorophore allowed the cytosolic localization of CaPF-1. Moreover, it was possible to visualize histamine-induced calcium oscillation in HeLa cells using CaPF-1.