April 10, 2006
Characterizing Gold Nanoparticles
As researchers continue to develop a wide range of nanoparticle-enabled technologies for detecting and treating cancer, there is a growing need to understand how the basic physical properties of a particular nanoparticle affect biologically relevant behavior such as cellular uptake and antitumor activity. Now, two papers published in the journal Nano Letters provide a few such details that could help guide future clinical development of versatile gold nanoparticles.
Warren Chan, Ph.D., and his colleagues at the University of Toronto, investigated how the size and shape of gold nanoparticles influenced how well cells were able to take up the nanoparticles. The investigators began by preparing nanoparticles ranging from 14 nanometers to 74 nanometers in diameter and ranging in shape from round to oval to rod-shaped and then observed how well each type of particle was taken up by cells growing in culture.
Plotting the number of gold nanoparticles taken up by cells over time, the investigators were able to show that cellular uptake peaked with 50-nanometer-diameter particles. Uptake also occurred most efficiently during the first two hours of exposure to the nanoparticles and reached a plateau after four hours. Also, cells were able to take up over twice as many 50-nanometer particles as either 14-nanometer or 74-nanometer particles. Shape also had a pronounced effect on cellular uptake, with spherical nanoparticles being taken up much more efficiently than rod-shaped particles. The investigators note that protein absorption on the surface of gold nanoparticles is likely to play a role in their uptake by cells.
In a separate study, a team at Ohio University led by Hugh Richardson, Ph.D., and Alexander Govorov, Ph.D., set out to better understand how gold nanoparticles turn light into heat, a property that several groups are using to develop nanoscale thermal scalpels that kill cancer by heating them to death. To study this light-to-heat effect, the researchers developed a method for embedding gold nanoparticles into a thin film of ice and then measuring the amount of melting that occurred when the particles were irradiated with light.
Using Raman spectroscopy, the investigators were able to determine the critical light intensities at which the particles were most efficient at melting the surrounding ice. Using this method, the Ohio University team also found that heat generation depended significantly on the way in which gold nanoparticles form complexes with each other in a watery environment. Complexes containing larger numbers of particles, for example, were most efficient at melting the surrounding ice. Using the data generated from these studies, the investigators were able to develop a theoretical model that predicted heat generation as a function of complex size and light intensity. Such a model, the researchers note, should be helpful for those investigators who are attempting to develop nanoscale thermal heaters as cancer therapeutics.
The work from the Chan group is detailed in a paper titled, “Determining the size and shape dependence of gold nanoparticle uptake into mammalian cells.” This paper was published online in advance of print publication. An abstract of this paper is available through the journal’s website.
The work from the Richardson and Govorov group is detailed in a paper titled, “Thermooptical properties of gold nanoparticles embedded in ice: characterization of heat generation and melting.” This paper was published online in advance of print publication. An abstract of this paper is available through the journal’s website.