The less you want something to be, the harder it is to build. This is the barrier retaining many technologies, from batteries to optics, but a new technique developed at MIT can make nanoscale materials easier to produce, reducing larger designs. The approach uses an absorbent type of scaffold to produce 3D structures 1,000 times smaller than the original.
Until now, techniques for creating tiny 3D structures were painfully slow and limited in complexity. Most involve the use of 2D nanostructures recorded on one surface and adding successive layers to the desired 3D shape. It's basically a very slow 3D print. There are a few methods to speed up small-scale 3D printing, but they only work with certain specialized polymers that do not work in many applications. The technology of MIT is unique because it should work with almost everything – metal, polymers and even DNA.
The technology borrows from an established imaging technique called expansion microscopy; is just running backwards. Under expansion microscopy, the tissues are incorporated in hydrogel and then expanded to obtain high resolution scans. The team found that they could create large-scale objects in expanded hydrogels and then reduce them to the nanoscale. They call it "implosion manufacturing."
The process begins with a scaffold composed of an absorbent material called polyacrylate. A solution of fluorescein molecules is allowed to infiltrate the polyacrylate. These act as signaling on the scaffold (see below) when exposed to laser light. This allows researchers to attach molecules anytime they wish. The molecules can be anything like a gold nanoparticle or a quantum dot.
Everything is still "big" at that point – on the millimeter instead of the nanometer scale. To reduce construction to the desired size, researchers add acid to the solution. This eliminates the negative charges on the polyacrylate gel, causing it to contract. This drags the molecules along with it, resulting in a 10-fold reduction in each dimension for a total drop of 1,000 times in volume.
With current laboratory techniques, the team can pick up an object with a cubic millimeter volume with a resolution of 50 nanometers. For objects larger than about 1 cc, they can reach a resolution of 500 nanometers. This limit may fall with further refinements. The team is looking for ways to use this technique to create enhanced lens optics and nanoscale robotics.