The blood-brain barrier (BBB) is a marvelous piece of evolutionary engineering designed to keep the inside of your skull pristinely clean by segregating the nervous and circulatory systems. The downside to this nearly impermeable membrane is that it is as adept at blocking therapeutic molecules as it is against harmful chemicals and microbes. However, a team from Canada's National Research Council (NRC) believe they've finally found the key that unlocks the body's Fort Knox. They're called "single domain antibodies" (SDA) -- molecular fragments capable of binding to larger molecules -- and they reportedly trick the BBB into thinking that most any molecule they're attached to is copacetic. So instead of having to wrap disease fighting medicines in carrier molecules like microscopic Trojan Horses, as has been the preferred method for the past two decades, these single domain antibodies act more like molecular security badges instead.