Gold nanoparticle (NP) assisted photothermal therapy (PTT) has been actively studied as a minimally invasive approach for treating cancer. With the contemporary fabrication techniques, NPs in a greater spectrum of shapes and sizes become accessible. Thus, laying out some design principles may provide a better start for future implementations.
We compare the optical absorption properties of experimentally realized NP shapes (e.g. rod, tube, disk, ring, and sphere), in the NIR-I and NIR-II biological transparency windows. The optical response of randomly oriented NP ensembles is numerically studied by a boundary element method (MNPBEM) [1]. Unlike many of the existing studies that evaluate the photothermal performance of a NP by its resonant orientation, the present work shows that the random orientation of the NP in host environment has to be taken into account for a realistic assessment and may lead to somewhat counterintuitive results. In particular, we demonstrate that nanodisks can surpass nanorods in terms of photothermal conversion efficiency with almost 3 folds improvement compared to experimentally reported nanorod samples [2, 3]. The improvement is further enhanced in core-shell geometries (nanorings, nanotubes).
Our study highlights several benchmarks that is relevant to the application environment (i.e. cancer tissue) such as NP size which effects cellular intrusion and retention, and NP dose/mass which is correlated with cytotoxicity. In light of these limitations, we compare the size-dependent tunability of the plasmon resonance in different geometries. We show that mass-sensitive applications favor nanorod design (λres α mNP) instead of nanodisks (λres α mNP2) at higher wavelengths, i.e. NIR-II.
Conventional PTT as a standalone therapy is currently being challenged by synergistic approaches that require simultaneous utilization of multiple therapeutic schemes (e.g. chemotherapy, immunotherapy and photodynamic therapy) and imaging modalities (NP-assisted optical/thermal imaging). The present work also addresses the optimization of multifunctional NP designs for theranostic applications, e.g. image-guided PTT which utilizes gold NPs both as photothermal transducers and optical contrast agents.
[1] J. R.Cole, et al. J. Phys. Chem. C, 113, 12090 (2009).
[2] M. A. Mackey, et al. J. Phys. Chem. B, 118, 1319 (2014).
[3] L. M. Maestro, et al. RSC Adv., 4, 54122 (2014).
Photonic & plasmonic nanomaterials , Nanoscale photothermal effects , Nanomedicine