Plasmonic Photothermal Cancer Therapy: Nanoparticle-embedded Tumor-tissue-mimicking Phantoms for Visualizing Photothermal Temperature Distribution

Plasmonic photothermal therapy (PPTT), an emerging cancer treatment, involves delivering nanoparticles (NPs) to a tumor, followed by near-infrared (NIR) irradiation to generate localized heat that destroys cancer cells. Before administering PPTT, the therapeutic parameters -- NP concentration, irradiation intensity, and duration -- need to be estimated. For this, numerical simulations are performed. However, to ensure robust computation, these simulations must be validated through photothermal experiments on tumor-tissue-mimicking phantoms replicating the optical properties of tumor tissue. For PPTT, therapeutic parameters are governed by the scattering and absorption of incident radiation by the tissue and NPs. Therefore, validation experiments can be conducted on phantoms mimicking the reduced scattering coefficient (µs') and absorption coefficient (µa) of the target tumor/tissue. Specifically, this protocol provides instructions for preparing phantoms mimicking µs' and µa of breast tumor injected with gold nanorods, surrounded by normal breast tissue. The protocol also details NIR irradiation, temperature monitoring, and validation of numerical results by comparing spatiotemporal temperatures with those measured using thermocouples. The protocols presented in this study facilitated the preparation of hydrogel-based cylindrical breast tumor-tissue phantoms with dimensions (ϕ40 x 12 mm) and a central tumor region (ϕ20 x 6 mm), comprising 1% agarose as the base matrix and intralipid as the scattering constituent and tumor region embedded with gold nanorods at 25 µg/mL concentration. Representative results from a case study illustrate the application of fabricated phantoms for validating numerical simulations for PPTT. The study concludes that the demonstrated protocols are valuable for conducting photothermal experiments aimed at optimizing and planning therapeutic parameters prior to in vivo experiments and validating numerical simulations for PPTT.