Protonex™ Red 670, NHS ester The fluorescence intensity will dynamically change with the environmental pH value: the fluorescence signal is extremely weak under alkaline conditions, while the fluorescence intensity reaches its maximum value in acidic environments. When the dye binds to cell surface receptors or antibodies, it remains in a non fluorescent state due to the neutral pH environment outside the cell. The dye is immediately activated when transported to an acidic environment (pH decreases) through the endosomal pathway, and emits strong red fluorescence under red laser excitation. (Ex/Em=643/660nm)