What phagocytic particles are best for assaying phagocytic activity of macrophages?

Latex beads, zymosan, and E. coli are a few of the most commonly used particles for phagocytosis assays. Latex beads and zymosan can be labeled with a dye such as FITC, while E. coli can be made to express GFP. These particles can also be opsonized with IgG if necessary.