Extended Data Fig. 2: Gold chelating orders of 6 amino acids, 2-mercaptoethanol (2-ME), and D-penicillamine (D-P).
From: Genetically encoded tags for direct synthesis of EM-visible gold nanoparticles in cells
a, Tests of AuNPs synthesis with the six mixtures of 0.2 mM 6 typical amino acids and 0.5 mM HAuCl4, reduced by 1 mM NaBH4, the solutions all changed to purple or dark brown color, indicating the formation of AuNPs. b, Tests of AuNPs synthesis with the additional 140 mM 2-ME to the six mixtures of the 0.2 mM amino acids and 0.5 mM HAuCl4, reduced by 1 mM NaBH4; Only the sample with cysteine changed color to brown (an indication of AuNPs formation), other specimens remained colorless (no AuNPs formed). c, Tests of AuNPs synthesis with the additional 30 mM D-P to the six mixtures of the 0.2 mM amino acids and 0.5 mM HAuCl4, reduced by 1 mM NaBH4; No AuNPs formed in all the six samples. These results implied a gold chelating order (from weak to strong): -COOH, -NH2 group of amino acid< thiol group of 2-ME < thiol group of cysteine < thiol group of D-P. The results in b and c also demonstrated the capabilities of 2-ME and D-P for auto-nucleation suppression. Representative images for (a-c) were selected from n = 4 independent experiments with similar results.
