"Nanomaterials," materials with at least one dimension in the nanometer length range (roughly one billionth of one meter), are finding much use in a wide range of common (and useful) applications. These include, but are not limited to, medical biotechnology, environmental remediation, and monitoring cancer drug efficacy.
Such applications often take advantage of the fact that the properties of nanomaterials may be different from their bulk counterparts. For example, a pure gold brick is always one color.
However, the color of a solution of gold nanoparticles depends on the diameter of the nanoparticles. For example, a small change in gold nanoparticle diameter may switch the color from red to blue.
This property of gold nanoparticles has been exploited for over a decade for (bio)molecular detection purposes. A recent example is in cheaply and easily detecting melamine poisoning of food.
Toxicity danger.
A persistent worry is the potential unforseen toxicity of nanomaterials. Since their properties can be different from their bulk counterparts, why should toxicity be an exception?
Just because a bulk material (metal or nonmetal) is nontoxic doesn't mean that its nanoscale counterparts are nontoxic. For example, silica isn't toxic in bulk (e.g., beach sand and glass windows), but silica nanofilaments (asbestos) can be highly toxic over long-term exposure.
Possible toxicity of a nanomaterial needs to be addressed before it gets dumped into our bodies and into the environment. Relevant studies are in progress (and have been completed) for certain nanomaterials, but don't receive nearly the amount of funding (and "prestige") that is warranted.
Addressing the lack of knowledge regarding the toxicity of titanium oxide nanofilaments, Arnaud Magrez (Ecole Polytechnique Fédérale de Lausanne, Switzerland), Beat Schwaller (University of Fribourg, Switzerland), and coworkers have carried out such a toxicity study. They have found them to be toxic, raising concerns about the health and environmental impacts of titanium nanomaterials.
Toxicity results.
The scientists' titanium oxide nanofilaments were from 12 to 75 nanometers in diameter. They monitored the growth of a standard laboratory cell line, over the course of four days, after incubation with the nanofilaments, as a measure of toxicity.
They found that nanofilament toxicity depended on their concentration in the cell growth medium. More nanofilaments gave more toxicity, as would be expected.
In the case of 2 micrograms per milliliter nanofilaments, after two days of exposure, the scientists found that titanium nanofilaments were at least somewhat toxic (roughly 15% cell growth inhibition). However, the toxicity was less than that imparted by carbon nanofilaments (roughly 30% cell growth inhibition).
Perhaps most notably, acidifying the titanium nanofilaments greatly increased their toxicity (roughly 55% cell growth inhibition). This should not be particularly surprising, because the surface properties of a material have a large impact on their interaction with the surrounding environment.
The scientists found that the titanium nanofilaments tended to disrupt cell-cell contacts, accumulate near the cell nucleus (where genetic information is stored), and sometimes disrupted cell division. A cause of further concern is that titanium nanoparticles (in water) help to generate extremely toxic molecules when exposed to light, an issue that needs to be investigated in more detail.
How to reduce the toxicity.
Scientists often coat nanomaterials with proteins or inert polymers to target them to specific organs or cells, and to impart biocompatibility. Although uncoated titanium nanofilaments seem to be toxic, coated nanofilaments may not suffer from the same problem as long as they're evantually cleared from the body.
One should not read this article and conclude that nanomaterials are too dangerous to study and use. However, potential dangers of new nanomaterials do need to be investigated before they're put into widespread use.
for more information:
Magrez, A., Horváth, L., Smajda, R., Salicio, V., Pasquier, N., Forró, L., & Schwaller, B. (2009). Cellular Toxicity of TiO2-Based Nanofilaments ACS Nano, 3 (8), 2274-2280 DOI: 10.1021/nn9002067