We're all going to be hearing a lot about nanoparticles in the next few years (some may feel as if they've already heard quite enough, but there's nothing to be done about that). The recent report of preliminary siRNA results using them as a delivery system will keep things moving along with even more interest. So it's worth checking out this new paper, which illustrates how we're going to have to think about these things.

The authors show that it's not necessarily the carefully applied coat proteins of these nanoparticles that are the first thing a cell notices. Rather, it's the second sphere of endogenous proteins that end up associated with the particle, which apparently can be rather specific and persistent. The authors make their case with admirable understatement:

The idea that the cell sees the material surface itself must now be re-examined. In some specific cases the cell receptor may have a higher preference for the bare particle surface, but the time scale for corona unbinding illustrated here would still typically be expected to exceed that over which other processes (such as nonspecific uptake) have occurred. Thus, for most cases it is more likely that the biologically relevant unit is not the particle, but a nano-object of specified size, shape, and protein corona structure. The biological consequences of this may not be simple.

Update: fixed this post by finally adding the link to the paper!