Like so much of technology, the hype and fear around nanoparticles says they will either revolutionize the world we live in or embody the newest high tech scourge. The truth is somewhere in the middle, but both sides have valid points.
Nanotechnology is sort of a catch-all term. Scientists have been able to create precise chemicals on an increasingly smaller scale, until they reached the nano level.
For reference, microns are used to measure the wavelength of visible light particles, are a thousand times bigger than nanoparticles, which are on the scale of one billionth of a meter. Nanoparticles, molecules with less than a few hundred atoms, are so small that some principles of biology begin to be waived.
The concept behind nanomedicine is fairly simple. Any drug given to a person has to have certain chemical characteristics, otherwise it won't go anywhere.
If a drug is given orally, it has to have suitable properties in order to be taken either with, or without food. It must travel from the stomach to the bloodstream, survive processing by the liver and kidneys, and go to the proper place.
If you want a drug to affect special locations, like the brain, you need even more specific properties.
Throughout the history of pharmaceuticals, scientists have consistently run into this problem. Many drugs work great in the laboratory, but don't meet the criteria to work in the body. Some drugs are processed completely by the liver, or are quickly voided by the kidney. Other drugs never leave the intestine if given orally. Some of these obstacles can be removed by intravenous (IV) delivery, but not always.
Nanoparticles avoid all of these problems. Due to its tiny size, it can travel anywhere in the body without resistance. This allows free access to cellular mechanisms, a previously unknown level of control for medicines. While a great deal of work would have to be done, potential benefits are limitless.
Scientists have struggled with finding medicines to target many kinds of viral infections. From the herpes virus family to HIV, some kinds of viral evolution focus on hiding from the immune system in the nucleus, where medications are unable to reach them. Nanoparticles have no such limitations, and could be used like antibiotics are for bacteria, permanently curing these lifelong viral infections.
With some slight modification, nanoparticles have been used to enhance medical imaging in radiology. Specialized gold nanoparticles have been used in one study to enhance images of brain tumors, showing exactly where the cancer cells were distributed.
Two nanomedicines already developed for use in chemotherapy are Doxil (doxorubicin) and Abraxane (paclitaxel). Doxil is large at 100 nanometers when compared to Abraxane, at 10 nanometers. But the small size of nanomedicines means they would be found in sweat, blood, tears, and cerebrospinal fluid. The same chemical property that makes it so perfect for treating cancers resistant to chemotherapy also means that you can't avoid it.
Similar to the issues found in using nanoparticles as chemotherapy, other scientists experimenting with nanoparticles quickly found out that the free ranging nature of these tiny molecules is both a blessing and a curse.
Several studies and papers have found that nanoparticles quickly diffuse throughout the lungs, and enter the bloodstream. Great, perhaps, for a nanomedicine that could treat asthma, but not so great for anybody working in a nanomedicine factory.
Experiments on plants found that significant amounts of nanoparticles end up in the nucleus, where they attach themselves to the DNA. There are several places you don't want strange particles ending up, and DNA is high on that list. Enough mutations from problems with the DNA in a cell can kill the cell, or begin a slow progression into cancer.
Otherwise, when a large enough dose of a caustic chemotherapy nanoparticle is given to treat a cancer effectively, you might end up damaging the brain, which is normally very protected from objects in the bloodstream. Cells in high blood volume organs like the kidneys, lungs, and heart might become damaged just from accumulation alone.
While some nanoparticles focus on certain types of cells, it's hard to completely avoid these problems. Some of the best research experiments use an intermediary to guide nanoparticles directly to the targeted cell, a technique that holds a lot of promise but is still quite experimental.
Some studies have found ways to limit the diffusion of nanomedicines by altering the properties of the blood vessels. Further research in this area holds the most promise for specialized areas such as cancers that have become resistant to chemotherapy, and several chemotherapy nanoparticles have already been approved by the FDA.
Similar to the debates surrounding the early days of nuclear research, it's hard to weigh the potential risks without knowing all of the potential benefits, and we won't know the full story for quite some time. The FDA has released guidelines for additional testing for the use of nanoparticles. While not yet implemented, new requirements testing for toxicity in sensitive areas like the brain, and long term studies for organ damage, should also be strongly considered.