We have acquired positive results in a controlled study to investigate the effects of substrate surface modification on the growth-induced flux-pinning nanostructures in YBa2Cu3O7−δ (YBCO) films. Nanoscale iridium (Ir) particles were applied to single-crystal SrTiO3 substrate surfaces using dc-magnetron sputtering. Superconducting properties of YBCO films grown on the Ir-modified substrates, measured by transport and magneto-optical imaging, have shown substantial improvement in the critical current densities (Jc) at 77 K over those on untreated, control substrates. Results also show a nearly uniform enhancement of Jc over all orientations of magnetic field. Present results are found to be consistent with cross-sectional transmission electron microscopy investigations. Ultimately, the objective of this approach is to produce enhancements in the properties of coated conductors by a simple pretreatment of the substrate surface.