Have I described a "nanoparticle"? Am I a "nanotechnologist"? Well, I wouldn't say so: I would say that I'm just another biologist, since what I've described is Herceptin, a humanized monoclonal antibody manufactured by Genentech, one of several now in clinical use or trial.
I'm always teasing nanotech enthusiasts, partly because they seem to be taking an end-run on my decade-long skepticism of the field by slapping their label on what used to be called biotechnology. For some good examples, check out this very interesting post by chemist Derek Lowe:
You might get the impression that there's a clear boundary to the field, and that "Departments of Nanotechnology" are springing up. Actually, it's more something that's coming on fast in many fields at once. . .I've cherry-picked the examples that best support my point, which is that what distinguishes "nanotech" from other fields of engineering (and largely fails to distinguish it from biotech, as I emphasized in a post last year) is its dearth of "design."
A group at Oregon has modified a standard lysozyme enzyme, changing the sequence of one three-dimensional loop. This causes a huge shift in the protein's entire structure, changing the conformation at its far end as if it had been levered. Now that they've found a good system, they're working on similar proteins where this could be accomplished just by changing the pH, to make an artificial protein-based mechanical switch. . .
At Georgia Tech, they're studying how DNA condenses into nanometer-sized particles. A common shape is a doughnut-like toroid, and they're getting a handle on what causes their variations in size and thickness. This will be important for understanding gene delivery systems and the behavior of polynucleotides in vivo. . .
A multi-center collaboration between several Japanese groups and Cold Spring Harbor shows the turning of a natural protein-based rotary motor. It's done with a single molecule of each unit, since (as the authors point out) if you tried to do this study the old-fashioned way, with a bulk sample, all the motors would be in different phases of their rotation and you wouldn't be able to get much useful data.
After all, the only departure from reality in my cryptic description of Herceptin, above, was my repeated use of the term "design." No human "designed" Herceptin -- the hard work was done by the immune system of a mouse, following in microcosm the exact same mutation-and-selection cycle that "designed" the mouse itself, in the course of days rather than billions of years.  The same applies to all the molecular "machines" that Derek describes above -- they were designed by evolution, which works very differently from a Ford Motors design team, and now scientists and engineers are unplugging them from their natural setting and putting them to work elsewhere. Is this nanotech? Well, I suppose it is if it means you'll give me venture capital dollars for it, otherwise I'd still call it biotech -- it's not like molecular biologists are uncomfortable with very small molecules, after all.
It's funny, since I grew up on a sci-fi vision of the future in which nanotech and biotech were pitted against one another, as in Bruce Sterling's Shapers vs. Mechanists stories. Increasingly it looks like they will be one and the same, unless one term or the other becomes more faddish with investors or targeted by Luddites.