<p>This paper represents a computational analysis of spherical core–shell nanoparticles (NPs), focusing on their localized surface plasmon resonance (LSPR) characteristics for applications in biological sensing, photonics, hyperthermia and thermal nano-heaters. Based on Mie theory, PyMieLab software is used to explores the tunability of the thermoplasmonic response of TiO₂@Au nanoparticles in four different media (<i>n</i> = 1.00, 1.33, 1.44 and 1.53) by systematically varying core sizes from 10 to 40&#xa0;nm and shell thicknesses from 2 to 10&#xa0;nm. Optical and thermoplasmonic characteristics and derivative spectroscopy are explored under controlled illumination at various LSPR wavelengths. The observed spectra are found in the wavelength range of 539 to 1429&#xa0;nm. Notably, the cross-section spectra shift towards longer wavelengths (red-shift), reaching a maximum value of 4.44 × 10⁻¹⁴ m² at 1429&#xa0;nm and 5.16 × 10⁻¹⁴ m² at 690&#xa0;nm wavelengths for 2 and 10&#xa0;nm gold shell with a 40-nm core radius in a 1.53 embedded medium. Using the inflection point method in derivative spectroscopy, point 3 shows the highest sensitivity with increased core radii, while 5 and 10&#xa0;nm shell thicknesses exhibit the greatest sensitivity at point 1 with changes in the surrounding refractive indices. Further, percentage increase in <i>RIS</i> is revealed between 82.6 and 196.1&#xa0;nm/RIU (137%) and 82.6 to 239.8&#xa0;nm/RIU (190%) with 10&#xa0;nm core as well as shell sizes. Furthermore, heat power and temperature elevation with different intensities, i.e. 1 × 10³ W/cm², 5 × 10³ W/cm² and 1 × 10⁴ W/cm² gradually increases with core–shell ratio as well as surrounding media. The results indicate that these core–shell nanoparticles could serve as effective heat sources in various applications including photothermal cancer therapy, bio-sensing, photo-catalysis, heating devices, thermoplasmonic welding devices and disinfection of medical equipment.</p>