Nanotech News

March 13, 2006

Rapid Purification and Size Separation of Nanoparticles

There are many challenges that must be met for nanoparticles to become important technological tools for detecting and treating cancer. One such challenge is the need to develop methods for purifying nanoparticles after their synthesis is complete and to separate the resulting nanoparticles according to their size. Now, using a technique known as diafiltration, investigators at the University of Oregon have developed a means of purifying and size separating water-soluble nanoparticles in a single, environmentally benign process.

Reporting its work in the Journal of the American Chemical Society, a team led by James Hutchinson, Ph.D., describes its development of a continuous flow apparatus containing a diafiltration membrane as its active component. A diafiltration membrane separates mixtures according to molecular size, which the investigators reasoned could yield a method that accomplishes purification and size separation in a single step.

Indeed, when the researchers ran crude mixtures of gold nanoparticles through their commercial diafiltration apparatus, they found that they were able to efficiently remove impurities from the nanoparticle mixtures. In fact, diafiltration achieved better purification with less solvent and waste and in less time than conventional methods such as dialysis, centrifugation, and chromatography. For example, diafiltration used only 4 liters of water per gram of nanoparticle, compared to the approximately 15 liters of organic solvent used in conventional methods. Also, diafiltration required a mere 15 minutes to produce 1 gram of pure nanoparticle product, compared to 3 days for other methods.

Diafiltration was also able to separate a mixture of nanoparticles into batches with narrow size distributions. In one experiment, for example, the investigators were able to separate 1.5 millimeter diameter nanoparticles from 3.0 millimeter diameter particles. The researchers noted that their size separation studies identified the potential for improving the capabilities of diafiltration by developing new membranes designed specifically for separating nanoparticles.

This work is detailed in a paper titled, “Rapid purification and size separation of gold nanoparticles via diafiltration.” This paper was published online in advance of print publication. An abstract is available at the journal’s website.
View abstract.