Size Effect on Photothermal Heating Ability of Gold Bipyramids

Abstract Gold nanoparticles (AuNPs) exhibit photothermal properties that are fundamental to biomedical and catalytic fields. However, the relationship between photothermal heating efficiency and nanoparticle characteristics often features a non‐intuitive behavior, being dependent on experimental parameters, sample scale (microscopic versus macroscopic), and material phase (solid or liquid). Using gold bipyramids (AuBPs) as a model system and employing a combination of experimental and computational approaches, photothermal heating is investigated as a function of nanoparticle dimensions while maintaining comparable optical properties. The computational analysis revealed an inverse correlation between the achievable maximum temperature at the single‐particle level versus multi‐particle systems. At the macroscopic scale, it is observed that photothermal heating efficiency follows an inverse proportionality with nanoparticle volume, with notable deviations occurring at reduced nanoparticle sizes. This deviation suggests the emergence of additional energy relaxation pathways. To outline practical implications of these findings, processable agarose films containing AuBPs capable of enhancing the performance of light‐powered Stirling engine are developed.