A green method for synthesizing one type of these structures involves adding kappa-carrageenan (“care-uh-JEE-nin”) to a sample and blasting it with ultrasound. The growth of these structures can be halted via addition of capping ligands. These structures form thin films whose localized surface plasmons are the basis of surface-enhanced Raman spectroscopy. A metal is treated with citrate to form these structures in the Turkevich method. They’re not (10[1])micelles, but drugs encased in these structures can be PEGylated to permeate the blood-brain barrier. A suspension of these structures that gradually changes from red to blue due to Ostwald ripening is called colloidal gold. For 10 points, name these particles whose diameter is roughly 9 orders of magnitude smaller than a meter. ■END■