We have fabricated low-temperature grown GaAs (LT-GaAs)-based plasmonic photoconductive antennas by RF sputtering of Au nanoparticles and have evaluated their terahertz detection properties. Localized surface plasmon resonance enhances the electric fields near the surface and increases the optical absorption of nanoparticles. The resonance frequency depends on the density of electrons, the effective electron mass, and the size and shape of the nanoparticles. Therefore, we tried to develop a high-sensitivity LT-GaAs photoconductive detector (PCD), which is effective over a wide range of wavelengths, by RF sputtering of Au nano-islands with a variety of aspect ratios from 1.2 to 5.1 on the dipole gap region of the PCD. As a result, we succeeded in increasing the sensitivity by 29% and 40% in the amplitude of observed terahertz pulse for 800 nm and 1560 nm femtosecond laser excitations, respectively.