The development of highly tunable plasmonic nanostructures is paramount for advancing photothermal applications in oncology. This study theoretically investigates the optical and thermoplasmonic properties of silica-core nanoparticles coated with successive copper and gold shells (SiO2/Cu/Au) when embedded within distinct biological media: healthy and infected breast tissues (types 1 and 2). The nanoparticles' optical response is exquisitely sensitive to both their geometry and their surrounding environment. We established that the Surface Plasmon Resonance (SPR) serves as a robust indicator of the host tissue, shifting from \(535{\text{ nm}}\) in healthy to \(540{\text{ nm}}\) in cancerous media, accompanied by superior absorption in the latter. This intrinsic sensitivity is complemented by a high degree of structural tunability. Systematically reallocating the internal dimensions by increasing the silica core radius while thinning the metallic shells enabled a controlled red-shift of the SPR peak deep into the near-infrared (up to \(575{\text{ nm}}\) ), together with a pronounced amplification of absorption. This geometric tuning directly translates to a marked enhancement in the local electric field (Faraday's number) and photothermal conversion efficiency (Joule's number). The photothermal performance was assessed under two distinct irradiation regimes. Continuous-wave (cw) exposure revealed a key diagnostic capability: a paradoxical thermal response where the nanoparticles induced a more substantial temperature rise in healthy ~65 °C versus cancerous ~43 °C tissue. This thermal differential acts as a robust signature for tissue discrimination. Transitioning to a femtosecond-pulsed regime revealed an operational mode defined by rapid thermal decay (~7–8 ns) and tight spatial confinement of heat, a feature highly advantageous for targeted therapies. The convergence of tunable plasmonics with a dual, modality-dependent thermal response solidifies the identity of these (SiO2/Cu/Au) nanostructures as a highly versatile theranostic tool, providing a robust foundation for developing more sophisticated interventions in breast cancer.
