Nanotech News

July 18, 2005

New Method Purifies Nanoparticles

To meet the stringent purity requirements of the U.S. Food and Drug Administration, pharmaceutical manufacturers will need robust, economical methods for cleaning up and recovering nanoparticles. While many methods exist for purifying small amounts of nanoparticles, such techniques are often difficult or uneconomical to use on even the modest scale needed to produce an approved pharmaceutical or imaging agent.

Anticipating the need for a commercially viable purification process, an international team of investigators has developed novel polymer-coated beads that can rapidly separate nanoparticles from any of the chemicals and biomolecules used to make or add function to the nanoparticles, which would include targeting molecules, drugs, and imaging agents. As an example, the investigators, led by Andrew Lyddiatt, Ph.D., easily and quickly separated 95-nanometer-diamter albumin nanoparticles from the albumin used to make the particles. The results of this research are published in the journal IEE Proceedings – Nanobiotechnology.

The key component of this system is the polymer-coated bead, and the investigators have developed a unique process to coat micron-sized beads with nanometer-thick polymer coatings. The inert polymer coating is porous and allows proteins and smaller molecules – but not the nanoparticles – to reach the inner bead, which is made of any number of commercially available materials used in purification processes. The beads are chosen based on the type of impurities that are expected to result from a given nanoparticle synthesis. In the prototype work reported in the current paper, free albumin was considered the impurity, so the researchers used a bead designed to tightly absorb proteins such as albumin. If the expected impurity would have been a molecule with a positive charge, for instance, the researchers would have chosen a bead with negative charges on its surface – opposites attract in the case of charged molecules.

In operation, the polymer-coated beads can be added to the reaction mixture used to form a labeled-nanoparticle. After a brief period of mixing, the beads and the absorbed contaminants are removed by filtration, leaving purified nanoparticles behind. If more than one contaminant is expected, multiple types of beads, each capable of absorbing a different impurity, can be used simultaneously. The beads can be processed later for reuse.

This work is detailed in a paper titled, “Subtractive chromatography for purification and recovery of nano-bioproducts.” Investigators from Bioprocessing Ltd. in Consett, United Kingdom, and the University of Mazandaran in Babol, Iran, participated in this study.

An abstract is available at the journal’s website.
View abstract.