We report on preparing poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) gradient substrate, wherein molecular weight (MW) and grafting density (a) Of the surface-anchored PDMAEMA chains vary continuously in two orthogonal directions. Such a specimen is used to control the assembly of charged gold nanoparticles. Increasing MW and a of the grafted PDMAEMA cause an enhanced binding of the nanoparticles to PDMAEMA, thus leading to an orthogonal number density gradient of surface-bound gold nanoparticles.