A water-soluble gold nanoparticle was prepared with trisodium citrate by reduction method, and using cystine as a self-assembled molecule, three dimensional net structure of gold nanoparticle with cystine was obtained. Various techniques, such as UV-Vis spectrophotometry, transmission electron microscopy, Religh light-scattering spectrum, were used to characterize gold nanoparticle and the 3D net structure. The average diameter of gold nanoparticle assembled by cystine in this 3D net structure was about 5.1 nm, bigger than that of gold nanoparticle of 4.5 nm. In order to form 3D net structure, the optimal molar ratio of gold to cystine was 1∶1, and a pH 5.1 buffer solution of sodium citrate-citric acid was required. Only approximate 14% of cystine molecules was assembled to surface of gold nanoparticle, while excessive cystine played an important role in the 3D net structure, where cystine molecule was a bridge among gold nanoparticles and ion band was a dominating factor. Compared with gold nanoparticle (518 nm), its UV-Vis absorption peak has been red-shifted to 670 nm and such 3D net structure had a nonlinear light-scattering characteristics.

Key words: cystine, gold nanoparticle, three dimensional net structure, Religh light-scattering spectrum