Nanoscale Heat Control: Studying Thermal and Steady-State Properties in Colloidal Gold Nanoparticles for Biomedical Applications

This paper investigates theoretically and experimentally the thermal and steady-state properties of colloidal gold nanoparticles (AuNPs) under the excitation of electromagnetic (EM) light. Theoretically, it investigates absorption and extinction phenomena by discrete dipole approximation (DDA), focusing on the efficient conversion of photon energy into thermal energy during the absorption phase for AuNPs sizing from 5 to 10 nm. Size-dependent behavior is observed, with smaller AuNPs exhibiting effective light-to-heat conversion. As size increases to 40 nm, scattering becomes prominent, influencing total extinction values. The study introduces photothermal parameters for designing nanomaterials and analyzes steady-state temperature and absorption cross section (σ abs ) as a function of NP size and power density. Controlling temperature elevations is demonstrated, emphasizing the importance of understanding the absorption process for efficient heat generation. The study introduces a figure of merit, steady-state factor (S 2 F), which increases with NP size but declines beyond 80 nm. Steady-state time (τ) exponentially increases with NP size. To validate the theoretical results obtained by DDA, this paper experimentally measured the absorption cross-section, steady-state temperature, S 2 F, and heat generation for 20 and 30 nm AuNPs. It found that the variations between experimental and theoretical results are within 15% for 20 nm and 27% for 30 nm AuNPs. Overall, the research provides valuable insights into optimizing AuNPs for diverse applications in nanotechnology and biomedicine.