Spectral Response and Sensing Capability of Bimetallic Pd-Au Core–Shell Dimers

A comprehensive investigation of both spectral characterizations and sensing performance of a Pd-Au core–shell dimer is conducted theoretically by the finite-difference time-domain (FDTD) numerical tool. The extinction spectrum of the two-particle model exhibits the excitation of three hybrid resonance modes, which introduces a reliable multi-site sensing platform for bio/chemical molecules. Altering either the core size (r_c) or the shell thickness (t) significantly impacts the overall optical properties, illustrating controlled optical tunability over a wide range of frequencies extending from the UV to the visible region. Increasing the shell thickness considerably improves sensing capability to changes in the dielectric properties of the host matrix. To maintain simultaneous and effective sensing standards at several spectral sites, a structural ratio of t ≤ (3/2)r_c should be maintained. Otherwise, the sensing performance of the high-energy site is degraded with any further increase in t. The optimal sensing performance is achieved for a core radius of r_c = 10 nm and a shell thickness of t = 15 nm, where both low- and high-energy plasmonic modes exhibit enhanced sensitivity factors. The structural tunability of the proposed bimetallic dimer provides detailed guidelines for designing plasmon-based nanosensors. Additionally, we conclude that our theoretical observations will have profound implications for the use of extinction cross-section spectra in characterizing bimetallic core–shell dimers.