Kazuhiko Ishihara, Ph.D.

Nanoparticles are particles that are smaller than 100 nanometers. They are typically obtained from metals and, because of their tiny size, have unique properties that make them useful for biomedical applications. However, without treatment to make their surfaces biologically inert, their effectiveness is severely limited. Researchers led by Kazuhiko Ishihara at the University of Tokyo have pioneered the use of MPC polymers to modify the surfaces of nanoparticles. In a recent article published in the journal Science and Technology of Advanced Materials, they reviewed current ways in which polymeric nanoparticles can be used to transport a type of small nanoparticles called quantum dots into cells.

MPC polymers are large molecules made from chains of 2-methacryloyloxyethyl phosphorylcholine (MPC). Bioactive nanoparticles whose surfaces have been modified with them can be used as anti-tumor compounds, gene carriers, contrast agents that improve MRI images, and protein detectors. MPC polymers mimic cellular membranes and allow the delivery of bioactive molecules that are normally not very soluble in water or that might produce unwanted biological side effects. When scientists attach MPC polymers to the surface of inorganic nanoparticles, they can make substances that are easily delivered into the blood or other tissue.

Ishihara’s group has recently used this process with quantum dots to produce nanoparticles that can outperform traditional organic fluorescent dyes in biomedical imaging. Using a simple solvent-evaporation technique, they were able to fabricate polymer nanoparticles that contained a core of quantum dots enmeshed in the nanoparticle polymer PLA (poly L-lactic acid), which was then surrounded by a layer of an MPC-polymer derivative called PMBN. This combination produced particles that maintained the same levels of fluorescence in a solution after being stored for more than six months at 4 degrees Celsius, and that functioned in environments of varying acidity. While traditional organic dyes lose their fluorescence with repeated illumination, the polymer quantum dot nanoparticles did not.