Protonex™ Red 670-Latex Bead Conjugates exhibit unique pH-dependent fluorescence properties. Unlike most existing fluorescent dyes that typically increase in fluorescence at higher pH levels, Protonex™ Red 670-Latex Bead Conjugates become significantly more fluorescent under acidic conditions. This characteristic makes them an ideal tool for studying phagocytosis and its modulation by drugs or environmental factors. The beads display minimal fluorescence outside of cells, eliminating the need for wash steps and enhancing their utility for live-cell imaging. Protonex™ Red 670-Latex Bead Conjugates are particularly effective in highlighting acidic cellular compartments such as phagosomes, lysosomes, and endosomes, where they emit a bright red fluorescence. Additionally, Protonex™ Red 670-Latex Bead Conjugates can be used in combination with green fluorescent dyes like GFP, Fluo-8®, calcein, or FITC-labeled antibodies for multiplexed cell functional analysis. Their spectral properties are similar to those of Cy5, allowing for the use of common Cy5 filter sets in assays involving Protonex™ Red 670, further facilitating their integration into existing experimental setups.