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Novel self-assembly processes for nanotech applications
Jan. 10, 2003
AMHERST, Mass. ' Researchers at the University of Massachusetts Amherst have developed a series of novel techniques in nanotechnology that hold promise for applications ranging from highly targeted pharmaceutical therapies, to development of nutrition-enhanced foods known as "nutraceuticals," to nanoscopic sensors that might one day advance medical imaging and diagnostics. The research, published in the Jan. 10 issue of Science, was funded by the U.S. Department of Energy and the National Science Foundation.
The team included faculty members Thomas Russell and Todd Emrick of the department of polymer science and engineering, and Anthony Dinsmore of the department of physics, and graduate students Yao Lin and Habib Skaff, both of polymer science and engineering. "Our findings open new avenues to revolutionize technology by the controlled fabrication of nanoscopic materials having unique optical, magnetic and electronic properties," said Russell.
The study details three major findings:
- A novel method to create robust capsules from nanometer-sized particles;
- A new technique to make nanoscopic particles water-soluble; and
- Functionalizing regions of the capsules with tailored properties, such as luminescence.
Emrick's research explores the behavior of nanoparticles to which ligands ' organic molecules and polymers ' have been attached. Russell is an expert in the surface and interfacial properties of polymers, and polymer-based nanostructures. Dinsmore specializes in colloidal assemblies and interface physics. "This is a productive collaboration in that we really have all the bases covered in terms of synthesis, understanding of interfacial activity and mediation, and the physics issues including surface tension and particle interactions," Emrick said.
The study details a new method for assembling nanoparticles into robust, three-dimensional structures by encapsulating and stabilizing water droplets. Nanoparticles suspended in oil will self-assemble around a droplet of water, fully coating it with a shell. Although scientists have long known that particles tend to assemble at fluid interfaces, "the idea of using liquid interfaces as scaffolds is exciting and tremendously useful since researchers can tailor or modify the nanoparticles from both sides of the interface," explained Dinsmore. "We have much more surface area to work with for adding or removing specific particles."
"Nanoparticles have exciting properties due to their small size, and they can be prepared in various shapes and sizes. What's really key is that you attach ligands that extend from the nanoparticles like hairs, in order to preserve the nanoscopic integrity of the particles and prevent them from clustering," Emrick said. "Changing the nature of these organic ligands can really modify the behavior of the particles. You can endow the nanoparticles, and thus the capsules that they form upon interfacial assembly, with a wide range of properties based on which ligands are attached." The effect of the ligands on the interactions of nanoparticles with the surrounding environment is crucial in medical applications. "These organic molecules will dictate the solubility, miscibility, and charge transport properties of the particles," Emrick said.
UMass researchers also developed a method to take these nanoparticles, which are oil-soluble, and make them water-soluble, simply by shining light on them. "Developing nanoparticles that are water-soluble has significant implications for medicine in the biosensors area," Emrick said. "Using luminescent material, as we did, could lead to advances in very sophisticated medical-imaging techniques as the fluorescent nature of these particles allows them to be viewed and tracked over time."
Finally, the UMass team discovered that when nanoparticles of different sizes compete for assembly at the interface, the bigger ones win, and segregate or cluster into patches on the droplet surface. "This opens a range of possibilities for developing nanoscopic capsules that have certain properties in specific areas," said Dinsmore. "You could build in an area with permeability, magnetism, or conductivity, so that one area would be functionally distinct."
University of Massachusetts at Amherst
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