The lungs are an incredibly efficient way to deliver toxic chemicals into the bloodstream. However, there are researchers who would like to use the power of the lungs for good. They are testing out different ways nanoparticles could be used to deliver drugs through the lungs or diagnose diseases.
True nanotechnology is not only about size, but also about how nanoscale particles are engineered. Surface charges, or even a therapeutic drug along for the ride, can have an impact on the way a nanoparticle behaves inside the lungs and whether it remains there to do some damage or is released harmlessly out of the body.
So the researchers, writing in Nature Biotechnology, describe their experiments with near-infrared fluorescent nanoparticles that they systematically varied in chemical composition, shape, size and surface charge, biodistribution and elimination. They found that particles larger than 34nm did not easily move out of the lungs to the lymph nodes, where they can potentially be transferred into the bloodstream. When it comes to particles smaller than 34nm, surface charges come into play. Electronically neutral particles can easily move from the lungs to lymph nodes within three minutes and pass through the urine after half an hour. Positively charged surfaces prevented nanoparticle movement.
So, you want to design a nanoparticle that delivers drugs quickly, then goes away, make them 5nm and not positively charged. You want a nano drug delivery device that stays in the lungs longer, make them larger and positively charged. The danger zone appears to be particles between 6nm and 34nm that are not positively charged. They can migrate through the body and do some damage.