The Protonex™ Red 670-E. coli Conjugate is a ready-to-use reagent designed to study phagocytosis and phagosome acidification in live cells. This conjugate combines E. coli particles, a biologically relevant model of bacterial uptake, with Protonex™ Red 670, a novel pH-sensitive fluorophore that remains non-fluorescent at neutral pH and becomes highly fluorescent upon entering acidic environments such as maturing phagosomes and phagolysosomes. As a standalone reagent, it enables users to integrate phagocytic detection into their own custom assays. The Cy5-like excitation/emission properties of Protonex™ Red 670 make it compatible with a wide range of fluorescence imaging and detection systems. These conjugates can be used in combination with green fluorescent dyes like GFP, Calbryte™ 520, calcein AM, or FITC-labeled antibodies for multiplexed cell functional analysis. It is ideal for immunological research, drug discovery, and mechanistic studies of innate immune function, autophagy, or bacterial clearance.