Phalloidin is a mushroom-derived toxin which can be used to label F-actin of the cytoskeleton with fluorochrome (λ_ex=495 nm, λ_em=520 nm). In Vitro: Phalloidin staining will not work with methanol-fixed cells, probably because of the disruption of actin filament integrity, but it will work with cells fixed in 0.2% glutaraldehyde in PBS. For fluorescein isothiocyanate (FITC)-Phalloidin (or rhodamine isothiocyanate [RITC]-Phalloidin), the excitation wavelength maximum will be near 495 nm (or 550 nm) and the emission wavelength maximum will be ~520 nm based on H₂O at pH 8.0 as the solvent (575 nm with methanol as the solvent). The emission spectrum of fluorescein can depend on the environmental pH and/or ionic strength^[1].