Formation of Gold-Hydrosol in Dilute Surfynol 485

By mixing HAuCl₄ aqueous solution (0.1-6 mM) with Surfynol 485 aqueous solution (1-54 mM) at room temperature, neat gold-hydrosol was formed after a time lag, ca. 10 min. The primary factor for the formation of gold-hydrosol was the molar ratio of Surfynol 485 to HAuCl₄, whose optimum value was 9-12. The gold-hydrosol, thus prepared, was transparent wine red and its maximum wave length of absorption was 520-540 nm. The diameter of gold-hydrosol particle was 10-30 nm and its electric charge was negative. The behaviour of gold-hydrosol was not significantly changed by dialyzing with water.