Put simply, they are yet another wonder material from the realm of nanotechnology. As with carbon nanotubes, they come in a variety of forms with a legion of applications, from drug delivery to plastic additives to cleaning up environmental damage. In fact, in terms of sheer variety, dendrimers make nanotubes and fullerenes look rather dull.
Dendrimers have been around for some time - the term was first coined by Donald Tomalia and the Dow Chemical Company in the early 1980s. For most of this time they haven't been considered as nanotechnology, but then neither were nanotubes. Many people would probably file them under polymer chemistry or macromolecular chemistry (a macromolecule is basically a very large molecule, such as a protein or many polymers, as opposed to a small molecule such as water). It could also be argued, however, that dendrimers are a fine example of nanoscale engineering and hierarchical self-assembly.
But even if the synthesis of dendrimers is not considered to be nanotechnology, some of the uses to which they can be put certainly are. Precisely defined and engineered macromolecules like dendrimers hold great promise as building blocks for complex supramolecular structures with specifically designed functions. They can be considered as versatile nanoscale components for building nanoscale structures.
Dendrimers can act as nanoscale carrier molecules in the sorts of applications where nanoparticles and nanocapsules are seeing increasing use, such as drug delivery. The enormous variety of structures that can be built, with different physical - including optical and electrical - and chemical properties, make dendrimers potentially a great deal more versatile than the alternatives. In addition, they can be made with atomic precision, which becomes necessary when trying to build nanoscale structures or "devices" with sophisticated and complex functionality.
Dendrimers also find applications in more traditional areas, such as coatings and inks. Whether used in nanotechnology or traditional technology, dendrimers are synthetically versatile which explains the ever-increasing interest they are provoking. In terms of mankind's nascent, but growing, capabilities in molecular engineering, dendrimers represent the state of the art.
Dendrimers can also act as scavengers of metal ions, offering the potential for environmental clean-up operations because their size allows them to be filtered out with ultrafiltration techniques. That may be useful for cleaning up after a "dirty bomb", for example. They are also finding applications in protection and decontamination relating to biological and chemical attacks, mostly under the watchful eye of the US military.
NASA is currently researching dendrimers for detecting apoptosis, or cell death, to diagnose radiation damage in astronauts before symptoms become apparent. A commonly heard piece of nanotechnology hype is that it will give us the ability to detect cancer at the single-cell level. That's somewhat misleading since this can already be done and does not need to involve nanotechnology. However, dendrimers promise the ability to fight cancer at the cellular level, performing the tasks of detection, delivering a payload and then monitoring to check that the drug has worked. Such a creation may well warrant the use of that overused word, "nanodevice".
But the best thing about this promising new nanotechnology is the fact that it isn't new and so you can already buy dendrimers in bulk from standard chemical catalogues.