A New Way to Discover and Test Nanoparticles
This article was originally published in the Northwestern University Feinberg School of Medicine News Center.
A Northwestern University research team is developing a tool to rapidly test millions and perhaps even billions of different nanoparticles at one time to zero in on the best particle for a specific use – from harvesting the sun’s energy to delivering drugs directly where they’re needed.
When materials are miniaturized, their properties – optical, structural, electrical, mechanical and chemical – change, offering new possibilities. But determining what nanoparticle size and composition are best for a given application, such as catalysts, biodiagnostic labels, pharmaceuticals and electronic devices, is a daunting task.
“As scientists, we’ve only just begun to investigate what materials can be made on the nanoscale,” said Chad Mirkin, PhD, a professor of Medicine in the Division of Hematology/Oncology at Northwestern University Feinberg School of Medicine and founding director of the International Institute for Nanotechnology. Mirkin is also a member of the Robert H. Lurie Comprehensive Cancer Center of Northwestern University and co-director of the Northwestern University Center for Cancer Nanotechnology Excellence.
“Screening a million potentially useful nanoparticles, for example, could take several lifetimes. Once optimized, our tool will enable researchers to pick the winner much faster than conventional methods. We have the ultimate discovery tool.”
Combinatorial nanoparticle libraries are much like a gene chip, Mirkin explained, where thousands of different spots of DNA are used to identify the presence of a disease or toxin. To make nanoparticle libraries in a very controlled way, Mirkin and his team used Dip-Pen Nanolithography, a technique developed at Northwestern in 1999 that deposits polymer dots loaded with different metal salts on a surface. The researchers then heated the polymer dots, reducing the salts to metal atoms and forming a single nanoparticle.
Thousands of reactions can be done simultaneously, providing results in just a few hours. Furthermore, Mirkin and his team’s libraries will enable scientists to rapidly make and screen millions to billions of nanoparticles of different compositions and sizes for physical and chemical properties.
“The ability to make libraries of nanoparticles will open a new field of nanocombinatorics, where size – on a scale that matters – and composition become tunable parameters,” Mirkin said, who is considered a world leader in nanotechnology research and its application. “This is a powerful approach to discovery science.”
Expanding the Palette
To help analyze the complex compositions, size and shape of the nanoparticles down to the sub-nanometer level, the team turned to Vinayak Dravid, PhD, Mirkin’s longtime friend and collaborator. Dravid, founding director of the Northwestern University Atomic and Nanoscale Characterization Experimental (NUANCE) Center, contributed his expertise and the advanced electron microscopes of NUANCE to map the trajectories of the nanoparticles.
“I liken our combinatorial nanopatterning approach to providing a broad palette of bold colors to an artist who previously had been working with a handful of dull and pale black, white and grey pastels,” said Dravid, a co-author on the study and the Abraham Harris Professor of Materials Science and Engineering in the McCormick School of Engineering.
Using five metallic elements – gold, silver, cobalt, copper and nickel – the Northwestern team developed an array of unique structures by varying every elemental combination.
Some of the compositions can be found in nature, but more than half of them have never existed before on Earth. And when pictured using high-powered imaging techniques, the nanoparticles appear like an array of colorful Easter eggs, each compositional element contributing to the palette.
By using the Northwestern technique, the team could control the size of the nanoparticle. This control of both size and composition of nanoparticles is very important, Mirkin stressed. With this control, the scientists used the tool to systematically generate a library of 31 nanostructures using the five different metals.
Now, scientists can begin to study these nanoparticles as well as build other useful libraries consisting of billions of structures that subtly differ in size and composition.
These structures could become new materials with a range of applications, from harvesting solar energy to powering fuel cells and beyond.