Minimizing Formaldehyde Use in the Synthesis of Gold−Silver Core−Shell Nanoparticles

The majority of formaldehyde used in the synthesis of gold−silver core−shell nanoparticles does not function as a reducing agent. Instead, the formaldehyde reacts with ammonium hydroxide to form a polymer, which binds to the gold nanoparticle cores and results in an asymmetric coating of silver. The resultant nanoparticles absorb in the near infrared. Understanding this mechanism allowed us to decrease the formaldehyde used 100-fold, providing a greener synthesis