Understanding the structure-property relationship of multielement nanoparticles is vital for developing novel nanodevices. In the present paper, via a combination of a basin hopping global sampling method, a symmetry-orbit shell optimization technique, and density functional theory reoptimizations, we determine the energetically most stable CuAg face-centered cubic nanoparticles. The calculated structures show a clear tendency toward CucoreAgshell chemical ordering by populating the more cohesive Cu in the core region and of Ag in the shell region. Further, using time-dependent density functional theory (TDDFT) calculations, we analyze the band edge optical excitations of the nanoparticles with pyridine molecule on top. With the help of charge difference density plots, we found dramatic modifications in the electron density distribution of the nanoparticles. We believe that the present theoretical findings will be useful for the development of novel nanosensors.