羧基荧光素的pKa为6.5，被用作pH指示剂。激发光谱以及对pH的荧光反应类似于BCECF。羧基荧光素可用作示踪染料。染料是膜不透性的，可通过显微注射等方式进入细胞。

5-(and-6)-FAM (full name: 5-(and-6)-Carboxyfluorescein mixed isomer) has a pKa of 6.5 and can be used as a pH indicator. Its excitation spectrum and fluorescence response to pH are similar to those of BCECF. Carboxyfluorescein can also be used as a tracer dye. The dye is membrane-impermeant and can be loaded into cells by microinjection or scrape loading.

• λ_Ex/λ_Em (pH 9) = 492/514 nm
• ε (pH 9) = 82,000
• Yellow orange solid soluble in pH>6 water
• Store at 4°C and protect from light, especially in solution
• C₂₁H₁₂O₇
• MW: 376
• [72088-94-9]