3D-FEM simulations based on Maxwell's equations were performed using COMSOL Multiphysics software (Wave Optics Module). Material refractive indices were taken from Rakic's Brendel-Bormann model for Au and Ag, and the Hale and Querry model for H2O (surrounding medium). The relative permittivity within the intragap region was set to 2. Geometrical parameters of the Au-NNP structure are provided in Extended Data Fig. , and the volume of the silver body was fixed at 48,638 nm .The electrostatic potential energy (ue) was calculated by integrating over the corresponding volume using the equation: ue = 0.5ε0|E| 2 , where ε0 is the permittivity of free space, and E is the E-field vector. In Figure , the surrounding region refers to a spherical space with a radius of 100 nm around the nanoparticle.