Dyeing For Gold

Forget gold-plated teeth. Researchers have now found a way to use the precious metal to dye human hair (Nano Lett., DOI: 10.1021/nl303107w). The golden hair also fluoresces red under blue light, says Philippe Walter of Pierre & Marie Curie University, in Paris, who led the team that developed the dyeing technique. The red fluorescence has to do with the fact that the gold forms nanoparticles that chemically bind to sulfur in hair’s cysteine amino acids. When blue light shines on the nanoparticles, excited electrons form a surface plasmon, which leads to the red fluorescence, Walter says. Before rushing to the nearest salon in search of golden locks, consider this: It takes seven hours of dyeing white hair to acquire the first hint of a gold tint and 16 days to get the permanent fluorescing red accent. To boot, the dyeing process requires chloroauric acid (HAuCl₄) and a strong base (pH 12.5), conditions far more caustic than the classic alkaline hair perm, which requires ammonium thioglycolate ([NH₄][OC(O)CH₂SH]) and a pH of 9 or 10. On the plus side, the amount of gold deposited in the hair isn’t prohibitively expensive—only about $30 worth for long tresses, Walter says