Daniel Oran and Samuel G. Rodriques, Massachusetts Institute of Technology (MIT), Cambridge, USA, and colleagues have created nanoobjects by shrinking. They first assembled 3D objects in a special polyacrylate/polyacrylamide hydrogel. They soaked the hydrogel with a solution containing light-sensitive fluorescein molecules. With ultrafine-focused laser pulses, they anchored molecules in the gel. Then, the fluorescein solution is washed out, only the laser-anchored molecules remained in the hydrogel. They used these molecules as a docking point, for example, to attach metal atoms, plastics, or other building materials of the desired construct. The 3 D structure of the desired object can thus be created with high precision.

Then the gel and its contents are shrunk. Thee researchers soaked the hydrogel for several hours with an acid or a solution with cations such as magnesium chloride. This treatment abolishes the rejection of negative charges in the hydrogel that previously kept the gel components at a distance. As a result, the gel contracts and also reduces the 3D construct created in it. The team achieved resolutions in the tens of namometers and complex, non-self-supporting 3D geometries.

According to the researchers, this method, called Implosion Fabrication (ImpFab), is doable with common technology and allows completely new nanoclusters. They see the first concrete applications in specialized nanoscale lenses, future applications could include nanoelectronics and nanorobots.

• 3D nanofabrication by volumetric deposition and controlled shrinkage of patterned scaffolds,
  Daniel Oran, Samuel G. Rodriques, Ruixuan Gao, Shoh Asano, Mark A. Skylar-Scott, Fei Chen, Paul W. Tillberg, Adam H. Marblestone, Edward S. Boyden,
  Science 2018.
  https://doi.org/10.1126/science.aau5119