<p>We present a hybrid plasmonic nanostructure that functions as a multi-band and spectrally tunable sensor, operating in the visible and near-infrared region. The study is based entirely on finite-difference time-domain simulations. The system employs a double-layer triangular symmetric gold nanodisk array configuration, which is designed to support the hybridization of localized plasmon modes between top and bottom nanostructures. By adjusting the structural parameters including the thickness of the dielectric spacer layer, both the absorption intensity and peak position can effectively be modulated. The observed spectral behavior is further verified by analyzing the corresponding electromagnetic field distributions. The sensing capability is demonstrated by varying the refractive index of the surrounding dielectric medium. Results indicate that the proposed structure not only achieves near-perfect absorption across multiple spectral bands, but also enables high-sensitivity detection. This multi-band operational system is promising for applications in areas such as biosensing, photodetection, and infrared energy harvesting.</p>