Effect of number density on optimal design of gold nanoshells for plasmonic photothermal therapy

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.

Substrate-Mediated Broadband Tunability in Plasmonic Resonances of Metal Nanoantennas on Finite High-Permittivity Dielectric Substrate

“…Metallic nanoparticle antennas-by virtue of surface plasmon resonances in their optical responsehave already evidenced numerous exciting possibilities like directed narrow-band scattering, resonance-enhanced wideband absorption, and intense near-field confinement as well as enhancement [2,3]. These properties made the plasmonic nanoantennas feature in a wide spectrum of applications ranging from light harvesting to biological/chemical sensing, and from waveguiding to photothermal therapeutics [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Cubic, or in general rectangular cuboid, nanoparticles are usually preferable for such applications owing to their broad resonance tunability, comparatively large optical coefficients, and relative ease of fabrication [18].…”

Optimized gold nanoshell ensembles for biomedical applications

“…where Q α ( r , h ) is expressed through Mie coefficients for a coated sphere [9,22,23], which are the functions of the excitation wavelength, refractive index of the tissue, and permittivities of the nanoshell constituents.…”

“…Amongst the commonly used gold nanoparticles, silica-core gold nanoshells exhibit larger photothermal efficiency as compared to gold nanorods of equal number densities [1], whereas hollow gold nanoshells (HGNs) absorb light stronger than the silica-core gold nanoshells do [9,10]. Furthermore, HGNs are comparatively less harmful to healthy tissues neighboring a cancer site [9], which makes them prospective for both photothermal and imaging applications.…”

“…Amongst the commonly used gold nanoparticles, silica-core gold nanoshells exhibit larger photothermal efficiency as compared to gold nanorods of equal number densities [1], whereas hollow gold nanoshells (HGNs) absorb light stronger than the silica-core gold nanoshells do [9,10]. Furthermore, HGNs are comparatively less harmful to healthy tissues neighboring a cancer site [9], which makes them prospective for both photothermal and imaging applications. Although different tissue types and excitation wavelengths were analyzed before to determine the optimal dimensions of a nanoshell [10,11], no optimization has ever been performed for a nanoshell ensemble with a real size distribution.…”

Nanopharmaceuticals (part 2): products in the pipeline

“…43 The unique optical properties of gold NPs which are related to localized plasmonic excitations in metal nanostructures interacting with light 44 are currently under intense investigations as is mirrored by the high number of PubMed hits, as shown in Table 1. A large variety of nanostructures made from gold, including nanoshells, nanorods, nanospheres, and nanocages, have been used as photothermal therapeutic agents for fighting cancers (reviewed by Sikdar et al 45 ). In light of the large interest in this new strategy for anticancer therapy, it is surprising (to us) that only two clinical trials are currently listed in the NIH database, both being conducted by the same principal investigator and, moreover, both trials not aiming at destroying cancer cells but exploring LSPR for the treatment of atherosclerosis.…”