March 13, 2006
Characterizing Individual Airborne Nanoparticles
As nanoparticle-based cancer imaging and therapeutic agents wind their way through preclinical development and human clinical trials, researchers are busily developing the analytical tools that will be needed to ensure that nanoparticle manufacturing meets all future regulatory and occupational safety requirements. One regulatory standard, designed to protect the health of those employees who work with nanoparticles, is likely to require that airborne nanoparticle concentrations be kept low. Now, thanks to a new device developed at the University of Delaware, researchers will have the means to rapidly monitor airborne nanoparticles.
Murray Johnston, Ph.D., and his colleagues created a “nanoaerosol mass spectrometer” that is capable of detecting and characterizing nanoparticles in ambient air samples. The device, which is described in a paper in the journal Analytical Chemistry, is capable of analyzing the chemical composition of individual nanoparticles in real time.
This new mass spectrometer overcomes two limitations that a variety of investigators had identified in earlier attempts to use mass spectrometry to analyze airborne nanoparticles. The first limitation is that nanoparticles smaller than approximately 20 nanometers in diameter are difficult to concentrate into a small volume prior to sending them into the mass spectrometer. As a result, nanoparticle samples can be very inefficient. The second limitation is that a single nanoparticle has miniscule mass – a standard mass spectrometer would require over a million particles to yield meaningful data.
Solving these two problems required the investigators to use an aerodynamic lens that focuses an electrically charged sample of nanoparticles in air. The focused nanoparticle “beam” then passes through a magnetic field, further focusing and concentrating the nanoparticles. As the particles exit the magnetic field, they are trapped in a second magnetic field and blasted by an intense laser pulse that causes any nanoparticles that are present to disintegrate into individual atoms that are readily detected by the mass spectrometer. The precise atomic makeup of a particular nanoparticle acts as a unique chemical fingerprint of that nanoparticle.
This work is detailed in a paper titled, “Chemical characterization of individual, airborne sub-10-nm particles and molecules.” This paper was published online in advance of print publication. An abstract is available at the journal’s website.