A localized surface plasmon resonance (LSPR)-based optical biosensor in connection with a multispot copper-capped nanoparticle array (MC-NPA) chip was proposed and developed. The copper (Cu) films, used as a shell, formed a "cap-like" layer on the top of the silica nanoparticles, used as a core, in an orderly fashion, to form the surface called a "Cu-capped nanoparticle array chip". The plasmonic properties of this nanostructure type were initially investigated while controlling the shell thickness of the deposited Cu. Also, we quantified the sensitivity of MC-NPA chip to changes in bulk refractive index (RI). As a result of its LSPR properties, the MC-NPA chip displayed a sensitivity of 67.8 nm per RI unit, and the wavelength shift of the LSPR spectrum peak was sensitive to the RI of the surrounding bulk medium, such as the biomolecular layers. Using MC-NPA chips, multiplex sensing of target DNAs from reference bacteria and clinical samples was possible in a quantitative manner with a detection limit of 10 fM (50 zmol). The optical biosensor developed in this study represents a unique approach to performing LSPR that utilizes a simple and cost-effective optical setup with disposable chips.