Advanced Chemical Synthesis: From Turkevich to Seed-Mediated Growth
The production of high-quality AuNPs requires extreme precision to ensure uniform size and shape. Two primary "bottom-up" chemical approaches dominate the field:
The Turkevich Method: The most widely used technique for producing spherical nanoparticles. It involves reducing a gold salt (chloroauric acid) using sodium citrate in boiling water. The citrate acts as both a reducing agent (donating electrons to form gold atoms) and a stabilizing agent (coating the particles to prevent them from clumping together).
Seed-Mediated Growth: To create complex geometries like rods, cubes, or bipyramids, researchers use this two-step process. First, small "seed" particles are formed. These seeds are then placed in a "growth solution" containing more gold salt and a surfactant like CTAB (Cetyltrimethylammonium bromide). The surfactant directs the gold to attach only to certain faces of the seed, "growing" it into a specific shape.