Assessment of Near-infrared Penetration Depth and Photothermal Efficiency of Organic and Inorganic Materials in Tissue-mimicking Phantoms

This study evaluated how deeply near-infrared light (NIR) can penetrate skin tissue in photothermal therapy (PTT) using an acrylamide-based phantom that mimics skin tissue. We loaded the phantom with varied photothermal agents (PTAs) such as indocyanine green (ICG), IR788, PA2, and gold nanorod (AuNR). The temperature change of the PTAs under a NIR laser irradiation was assessed at different phantom lid thicknesses, resulting in temperature drop is proportional to lid-thickness. Moreover, Pearson's correlation coefficient indicated that the temperature change and transmittance were directly related, having high values. The trends observed in the study were consistent with the respective photothermal conversion efficiency values of the PTAs. The results suggest that AuNR is superior to ICG and IR788sIPN as a PTA for absorbing energy from laser irradiation in the phantom. The acrylamide-based phantom provides a valuable platform for further research into the performance of PTAs for PTT under tissue conditions.