Prof. Govindasamy Mugesh explains how the the cellular uptake of fluorescent probe naphthalimide was drastically improved (from 5-8% to up to 98%) by substituting two of its hydrogen atoms with iodine. The iodine atom forms a halogen bond with the MCT8 receptor that ferries the molecule across the membrane. The receptor is known to transport thyroxine, which is a thyroid hormone containing iodine, into the cells.