Spatially modulated optical fields provide the perspective of tuning nanoparticle (NP) dynamics in a colloidal suspension. Here, it is shown that the lateral interferometric optical field created by a chain of optically bound Au NPs (i.e., optical matter) can tailor the electrodynamic interactions among more Au NPs. The free-standing NP chain, which is assembled and confined by an auxiliary optical line, shapes the main trapping beam and guides the self-organization of Au NPs under an optimized polarization direction. We find that the NP chain can largely enhance the anisotropic optical binding interaction of two nearby NPs but suppress the anisotropic interaction of multiple NPs, leading to isotropic self-organization. The dynamics and structural transitions of the NPs are well-reproduced in a simulation by using a coupled finite-difference time-domain (FDTD)-Langevin dynamics approach. Our work provides a new dual-beam optical trapping and in situ laser beam shaping approach to study and control interparticle electrodynamic interactions among colloidal NPs.