Abstract
Despite much research efforts being devoted to the design optimization of metallic nanoshells, no account is taken of the fact that the number of the nanoshells that can be delivered to a given cancerous site vary with their size. In this paper, we study the effect of the nanoshell number density on the absorption and scattering properties of a gold-nanoshell ensemble exposed to a broadband near-infrared radiation, and optimize the nanoshells’ dimensions for efficient cancer treatment by analyzing a wide range of human tissues. We first consider the general situation in which the number of the delivered nanoshells decreases with their mean radius R as ∝ R−β, and demonstrate that the optimal design of nanoshells required to treat cancer most efficiently depends critically on β. In the case of β = 2, the maximal energy absorbed (scattered) by the ensemble is achieved for the same dimensions that maximize the absorption (scattering) efficiency of a single nanoshell. We thoroughly study this special case by the example of gold nanoshells with silica core. To ensure that minimal thermal injury is caused to the healthy tissue surrounding a cancerous site, we estimate the optimal dimensions that minimize scattering by the nanoshells for a desired value of the absorption efficiency. The comparison of gold nanoshells with different cores shows that hollow nanoshells exhibiting relatively low absorption efficiency are less harmful to the healthy tissue and, hence, are preferred over the strongly absorbing nanoshells. For each of the cases analyzed, we provide approximate analytical expressions for the optimal nanoshell dimensions, which may be used as design guidelines by experimentalists, in order to optimize the synthesis of gold nanoshells for treating different types of human cancer at their various growth stages.
Highlights
Significant progress has been achieved over the past several decades in synthesizing highquality metallic nanoparticles of different shapes and sizes [1]
The fact that the function N(R2) we used is only an approximation to the real dependency does not alter the qualitative results of this section, which indicates that the number density of gold nanoshells is crucial for the efficacy optimization of plasmonic photothermal therapy (PPTT)
Optimal design of gold nanoshells for β = 2 In order to explain the origin of maxima in Fig. 1 and estimate the optimal design of gold nanoshells for different therapeutic usages, we focus on the situation where the density of the nanoshells is inversely proportional to their cross section area
Summary
Significant progress has been achieved over the past several decades in synthesizing highquality metallic nanoparticles of different shapes and sizes [1]. Despite the fact that a wide variety of materials and excitation wavelengths were analyzed in these studies, a number of crucial questions on the optimization of gold nanoshells still need to be answered First of all, it is not clear what would be the effect of broadband excitation on the absorption efficiency of the nanoshells and whether the use of broadband sources would benefit PPTT. The case of β = 2 is of particular heuristic and methodological interests, as it corresponds to the situation where the energy absorbed (scattered) by the ensemble becomes maximal for the same dimensions that maximize the absorption (scattering) efficiency of a single nanoshell This situation is analyzed in detail by the example of silica-core gold nanoshells exposed to the radiation with a uniform spectrum between 650 and 900 nm.
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