Process for making gold nanometer probe

The invention relates to a method for making gold nanometer probe comprising, mixing chlorauric acid and citric acid trisodium in water, then adding in the citric acid trisodium solution of sodium borohydride, adding eicosane group sodium sulphate at the same time of adding in the citric acid trisodium solution of sodium borohydride, thus achieving the gold nanometer probe with particle diameter of 4-6 nanometer. The small particle size gold nanometer particle prepared by the method in accordance with the invention has small particle diameter and good monodispersity. ii