Researchers from Sandia National Laboratories have created a way to turn tiny amounts of gold into large, high-quality supercrystals with the potential to improve the chemical detection of drugs or explosives and the performance of sensors, lasers, and solar panels.
Metallic nanoparticles (a few millionths of a millimeter in diameter) such as gold and silver can self-assemble and crystallize into highly ordered arrays known as supercrystals. Highly ordered single supercrystals have critical applications in areas such as optics, electronics, and sensor platforms. However, the difficulty of obtaining high-quality supercrystals for production scale usage and device integration has limited their wide-scale adoption.
Sandia researchers’ solution involves a method for fabricating unusually large (millimeter-sized) supercrystals containing millions of tightly packed gold nanoparticles. The method involves binary solvent diffusion (BSD), in which the nanoparticles are exposed to two types of liquids (solvents). A toluene solution containing gold nanoparticles is topped with isopropanol (IPA), forming a liquid–liquid interface. The IPA solvent then flows (diffuses) into the toluene solvent, and as the concentration of gold nanoparticles becomes too high for all of them to remain in the solution, they slowly emerge and form large nanoparticle supercrystals. These supercrystals have a hexagonal disk shape characterized by facets (similar to those seen in cut diamonds).
In addition to supercrystals made from gold nano-particles, the scientists also successfully used the same method to create supercrystals from other nanoparticle materials such as semiconducting (e.g., cadmium selenide, lead sulfide, lead selenide) or magnetic (e.g., iron oxides, iron platinum).
The BSD method has several competitive advantages over conventional approaches to supercrystal fabrication and sensing (e.g., using single-nanoparticle or thin film substrates) that will enhance its potential for use in industry applications.