FM 1-43FX membrane probe is an FM 1-43 membrane probe analog that has been modified to contain an aliphatic amine. That modification makes the probe fixable with aldehyde-based fixatives (formaldehyde, glutaraldehyde, etc.). FM 1-43 membrane probe is widely used both for identifying actively firing neurons and for investigating the mechanisms of activity-dependent vesicle cycling. Unmodified FM 1-43 membrane probe is available as 1 mg in a single vial (T-3163) and as 1 mg packaged into 10 vials, each containing 100 μg (T-35356).