Jonathan Cohen/ BU Photo
Nanoparticles are far too small to see. Can they be sensed?
Dr. Omowunmi Sadik, a Nigerian-born chemist and director of the Center for Advanced Sensors and Environmental Systems at the State University of New York, Binghamton, says the answer is yes.
She is developing sensors that can detect and identify the presence of manmade nanoparticles. She has received a $400,000 grant from the Environmental Protection Agency to support her research.
Nanotechnology, the science of manipulating materials as small as one billionth of a meter, has been incorporated into at least hundreds of consumer products ranging from strong lightweight bicycle frames and gold clubs to construction materials and anti-aging creams.
Researchers consider nano-sized materials valuable for exhibiting extraordinary properties that larger amounts of the same substances often do not. Nano-sized gold changes color, for example, while carbon nanotubes are both strong and flexible. Nanoparticles have a high surface area to volume ratio, making them more reactive as well. They’ve also raised health and safety concerns among some activists and watchdogs pushing for more research and greater government regulation about the emerging field; within the human body nanoparticles are potentially small enough to cross the blood brain barrier or get stuck in lungs or other places where they’d be difficult to remove. Like the field of nanotechnology itself, the quest for hard data on its health and environmental threats is just emerging.
Sadik is among those with concerns. In her project she plans to design new ways to detect engineered nanoparticles as a way to get a better handle on what risks they may pose.
“My main concern is that we don’t have enough information about these products,” Sadik said. The goal is to avoid a situation “where people have been exposed to these materials without understanding the implications, something that happened with PCBs and CFCs.”
By far the most commonly used nanoparticle is nanosilver, which can serve as an antibacterial agent in products like odor eater socks and food packaging. A recent study showed that the silver can detached during washing and entering the water supply.
“One can imagine that the sensors could be used to generate some sort of awareness of how much of the contaminants had been removed by the treatment,” Sadik said. Sensors, she said “would be a good tool for [water] treatment plants.”
The lab is conducting basic research which typically takes place well before products are commercialized.
As one example of a sensor, Sadik described a way to test for a type of nanosized crystal known as a quantum dot. “We have prepared unique ‘flexible polymeric membranes’ that are altered in the presence of particular nanoparticles. By detecting how the polymer has altered it’s possible to quantify the amount of nanoparticles present,” she said.
Such processes could be useful if government regulations require labeling products for nanotech content, the way nutritional information
now appears on food products. That kind of regulation isn’t likely to happen soon, however. “Our focus is more on risk assessment,” which can be entirely voluntary, Sadik said.
“It’s not uncommon for us to go to Wal-mart, for example, to buy filters,” which can weed out bacteria and traces of metal. She said it’s possible to imagine such filters including nanotech sensors that might alert users to the presence of nanoparticles by changing color. Nanosensors would also be potentially useful at facilities like water treatment plants and factories where nanoparticles are manufactured.
Dr. Nora Savage, an environmental engineer with the EPA’s Office of Research and Development, said detecting the presence of nanomaterials is a public safety issue. “The program officers have identified detecting and monitoring and quantifying these things in the environment as a priority but that doesn’t mean they’re saying we’re going to make regulations.”
“People sometimes seem to mistake the agency for seeking someone to blame and that’s not what we’re doing,” Savage said. “We’re seeking the source so we can control and mitigate the exposure.” This is particularly tricky in the case of certain nanoparticles, which occur naturally but can also be manufactured.
“What really makes nanoparticles so exciting as a scientific field is that they’re so small and we can control the size and shape,” Sadik said. But she cited studies showing that carbon nanotubes haveasbestos-like properties in animals and that mammalian cells overexposed to certain nanoparticles die instantly. “If it happens to cells, it’s going to happen to us as well.”
“There haven’t been any problems [with nanotech] because we have focused a lot on the development,” Sadik said. “There’s always this lag between design and development, and there’s also a lag between development and [a negative impact on] human health”
“Nobody knows what the impact of cell phones is going to be in the next 15, 20 years, but it doesn’t stop us from using them anyway,” Sadik said.
OK, here goes-
First, the definition of risk is :
Risk = Hazard x Exposure
There are lots of compounds that are hazardous. If we tried to control all
of them, our economy and research would slow to a crawl- or worse. Hence
the concept of risk which translates to worrying about compounds that are
present in enough quantities to actually cause harm to a human being or the
environment. The idea that a gram of a substance, no matter how toxic,
really being something that could affect many people is simply misguided,
although that seems to be the EPAs viewpoint as of late (based on a meeting
I attended in DC a month ago on a talk given by Jeff Morris.)
I have some reservations about the comparison between carbon nanotubes and
asbestos in your article. Neglecting the mechanism issues, the first and
most major stumbling block is exposure. Asbestos is a useful fiber with
excellent insulative properties and reasonable mechanical properties, plus,
and most important- it's cheap! The fact that asbestos was less than a
dollar a pound enabled it to be used in products ranging from automotive
brakes to building insulation. This was a fiber that was sold in multi
million ton quantities on an annual basis. Even as recently as 1992, global
asbestos production was some 3.5 million tons. In contrast, the cheapest
carbon nanotubes are in the $20-30/lb range, and some versions are still in
the $1000s/gram. Given the price structure of carbon nanotubes (and no
dramatic price breaks below the current floor are likely given the
production costs) carbon nanotubes will never be anything more than an
insignificant volume in goods compared to asbestos, since total carbon
nanotube production is still less than 500 tons globally. So there's a vast
difference in the amount of asbestos in the world, and the amount of carbon
nanotubes, and it's going to stay that way for the foreseeable future.
In terms of cell culture studies used to predict the toxicity of
nanomaterials, there are really two separate problems. First, how well does
cell culture accurately model the human body? And second, have there been
studies which show the toxicity of carbon nanotubes in animals?
In terms of cell culture- ask a toxicologist how accurate are cell culture
studies at predicting human toxicity and I suspect you'll get a good belly
laugh. Two major problems with cell culture studies:
1) Cell cultures are two dimensional and cells in organisms grow into
three dimensional structures. Newer work on three dimensional cell cultures
has shown that these cultures are generally far more robust than their
simpler two dimensional analogues.
2) Toxicity in humans or animals relies on mechanisms to uptake the
compound in question. Compounds which are highly soluble and readily
excreted are generally less toxic than compounds which are less soluble. Cell
cultures have no way of distinguishing between these two types of compounds.
Thus, animal studies remain the gold standard of toxicology of unknown
compounds. Needless to say, animal studies are much more expensive than
cell culture.
In terms of the toxicity of carbon nanotubes based on animal studies- be
cognizant that there's a lot of disagreement in the science community as to
the significance of those studies. Few if any, have been done to a rigorous
standard. Instead, they have been done in a quick and dirty fashion for
publications and grant funding. Studies which have shown toxicity of carbon
nanotubes in a rat lung essentially showed that the animal suffocated since
it's lungs were full of carbon nanotubes- which had been placed there by
researchers. Normal respiration didn't get any detectable nanotubes in the
lung. (Pure nanotubes are expensive- the researchers didn't have an
unlimited budget.) Furthermore, its highly unlikely that humans will come
into contact with pure carbon nanotubes outside a manufacturing environment
since they will be incorporated into products.
In terms of Dr. Sadik's contention that it will be possible to develop
sensors for nanomaterials- that's pretty far fetched. While it may be
possible to develop sensors for a particular nanoscale compound, its not
easy to detect nanoparticles in the environment. If you need to talk to
people working on this, try NIOSH- folks there are doing some good work. Nor
is there any data out there suggesting that there is some overall mechanism
that makes all nanoparticles toxic. As an example, the most common
nanoparticle on the planet is sea spray. Think it's a problem?