Abstract: Methods of synthesizing water-soluble thiolate-protected gold nanoparticles of uniform size and conjugates thereof are disclosed. In particular, the invention relates to a method of synthesizing homogeneous, water-soluble gold nanoparticles by using a modified Brust procedure and methods of conjugating them. Gold nanoparticles, produced by the methods of the invention, are useful in various therapeutic and imaging applications where the use of gold nanoparticles having uniform structural and optical properties is desired.