Protonex™ Red 780, NHS ester

Protonex™ Red 780 NHS ester is an excellent building block for developing a target-specific conjugate that can be used for monitoring a pH-sensitive biological event. Protonex™ Red 780 dye works by changing its fluorescence intensity depending on the pH of the environment. Protonex™ Red 780 is minimally fluorescent at a basic pH and maximally fluorescent at an acidic pH. When Protonex™ Red 780 is bound to a receptor or an antibody on the cell surface, it is essentially non-fluorescent because the extracellular pH is neutral. However, when the receptor or antibody is internalized into the cell in response to a stimulus, it enters the endosomal pathway, where the pH is acidic. This causes Protonex™ Red 780 to become highly fluorescent and emit near-infrared light when excited by a red laser. By measuring the fluorescence intensity of Protonex™ Red 780, one can monitor the activation and trafficking of receptors or antibodies in live cells.