This yellow fluorescent phalloidin conjugate (equivalent to Alexa Fluor® 514-labeled phalloidin) selectively binds to F-actins. Phalloidin derivatives are convenient probes used at nanomolar concentrations for labeling, identifying, and quantitating F-actins in formaldehyde-fixed and permeabilized tissue sections, cell cultures, or cell-free experiments. Phalloidin binds to actin filaments much more tightly than to actin monomers, leading to a decrease in the rate constant for the dissociation of actin subunits from filament ends, essentially stabilizing actin filaments through the prevention of filament depolymerization.