CP and infection: BEEF-CP as a Ca2+-selective sensor exhibits several advantages for practical applicability, such as (i) appropriate cell internalization [44]; (ii) the effective concentration of the dye is 2–20 times lower (0.5–0.05 μM) compared with other widely used compounds (> 1 μM); and (iii) it is free of toxic leaving groups and, hence, infection processes are not affected by the chelation of Ca2+ using the novel dye, unlike in the case of working concentrations for BAPTA-AM; and (iv) appropriate spectrophysical characteristics and sufficient pH insensitivity around the physiological pH.