Optimum Dimensions for Au Nanoframe Tuning in the Near-Infrared Second Window Range for Biomedical Applications: A Numerical Study

Au nanoparticles are favored in biomedical applications owing to their low cost and negligible cytotoxicity to biological cells. Nanoframes outshine their solid counterparts because of their porosity, which produces pronounced redshifts in their local surface plasmon resonance (LSPR). This feature enables the utilization of nanoframes in photothermal-based therapy, where LSPR excitation of particles within the near-infrared range (NIR) is essential. LSPR redshift in nanoframes is highly sensitive to their dimensions. A slight difference in the nanoframe dimension can result in substantial redshift, potentially pushing its LSPR beyond or below the required NIR range. We perform a systematic numerical study to investigate the optimum dimensions within a range of 1–100 nm for a spherical frame (SpF) and standard cubic frame (CF) to precisely tune their LSPR within the NIR-II window (1000–1400 nm). Our findings indicate that SpF exhibits a shorter LSPR redshift than CF’s at a certain porosity limit that is related to the geometry of the frame. Moreover, SpF displays higher LSPR sensitivity in the NIR region compared to CF. These insights provide valuable guidance for nanoframe design tailored for photothermal-based biomedical applications.