Nano-sized Lab Sorts Particles On the Run

The sunglasses you are wear, the vitamin you took with your breakfast, the cell phone in your pocket may all have one thing in common--a component or part built with nanotechnology. The science of materials produced from the atom up at the nanoscale has exploded over the past two decades. But the pace of this infusion may get even faster thanks to a new measurement concept developed by the National Institute of Standards and Technology (NIST) and Cornell University.

Nanotechnology is being used to make all kinds of new and improved products, fortify manufacturing processes and even change long standing medical procedures. The list of applications for the science that builds on the unique qualities of nanoparticles is growing every day. You might not think from the way nanotechnology has infiltrated our lives that there is a challenge to living lives full of nano. But in fact, the complex and expensive processes needed to measure and describe particles – the building blocks of the technology – is slowing down the rate at which new applications can land in hands of consumers, patients and users.

The size of the nanoparticle matters significantly. For every one, its size and shape determines its properties, utility and even perhaps its safety. The conventional methods for measuring these particles can be slow. But that may change in the next few years because of a new concept just proved by a team led by Sam Stavis, Ph.D. from NIST. The technique integrates the process on a “lab on a chip.” It has potential to accelerate advances in biology, medicine, engineering, physics and materials science, all fields that use nanotechnology.

The foundation for the Dr. Stavis’s new nanoscale lab is a 4-inch wafer of glass. Using similar techniques to the ones used by the semiconductor industry to “paint on” circuitry, Stavis uses a process called grayscale photolithography to build a 3-D structure on the chip. First a layer of light sensitive chemical called “photoresist” is spread across the chip. With a a precisely calibrated “stencil”, light hits the photoresist and channels of varying widths are created across the wafer. The whole structure of 20 channels is shaped like a staircase and the channels range in size form 10 nanometers to 650 nanometers.

With another wafer placed on top, the channels-on-a-chip have become a chamber-on-a -chip. Stavis injects a solution with different size nanoparticles. Inside the chamber, the particles are pushed across the channel by an electric charge. As each particle hits a stair that matches it in diameter it falls into the corresponding channel. One after the other, nanoparticles drop into the right channel like coins in a change-sorting machine. The particles have been dyed with fluorescent paint so the team can photograph them with an electron microscope. The photo arrays the particles along a scale the channel rows are set to collect the particles that can only be seen under an electron microscope.

“You can mass produce and give people references better than the electron microscope and chromatography,” said Stavis. While the new lab-on-a-chip won’t replace these tools, this nanoscale tool for nanoparticles has potential for speed, flexibility, and portability without sacrificing accuracy achieved with the conventional tools.