Okay, we’re pretty sure that the nanoparticles they’ve come up with won’t turn you into the Borg, but they will make your urine glow. Specifically, when injected into the bodies of people who’ve recently undergone transplants, they can help identify when an organ is failing.
The particles are tiny (duh), but they’re big enough that they won’t accumulate in normal, native tissue. However, they are small enough that, when a transplanted organ is being attacked by the body, the nanoparticles will end up getting through the kidneys and into urine. The particles are fluorescent and glow under near-infrared light.
The nanoparticles are aimed at replacing biopsies, as they are more predictive and less invasive. Also, who wouldn’t want to claim they’ve been enhanced by nanotechnology? Resistance is futile, after all.