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Gold Nanomaterials at Work in Biomedicine *
Published in Valerio Voliani, Nanomaterials and Neoplasms, 2021
Xuan Yang, Miaoxin Yang, Pang Bo, Madeline Vara, Younan Xia
Under the same assumptions, analytical solutions have been derived for a number of systems, including spherical particles, concentric core-shell spherical particles, spheroids, and cylinders with an infinite length [12]. For other geometric shapes and boundary conditions, only numerical solutions can be obtained through computational simulation. The most popular method for calculating the LSPR spectra of nanoparticles with an arbitrary shape or a complex structure, as well as their aggregates, is based on the discrete dipole approximation (DDA) [334, 335]. In this method, the nanoparticle is divided into an array of point dipoles, each of which can interact with the electric field induced by the incident light and other point dipoles. Other approaches, including the finite-difference time-domain (FDTD) method [336, 337] and boundary element method (BEM) [338], have also been developed and used in the biomedical community.
Influence of natural convection on gold nanorods-assisted photothermal treatment of bladder cancer in mice
Published in International Journal of Hyperthermia, 2020
Ean H. Ooi, Viktor Popov, Massimo Alfano, Jason K. K. Cheong
Figure 2 plots the absorption and scattering coefficients against the irradiation wavelength for a monodisperse GNR distribution with diameter and aspect ratio of 10 nm and 3.8, respectively, and volume fractions of 0.001, 0.005, and 0.01%. Peak absorbance occurred at 778 nm wavelength, which matched well the Discrete Dipole Approximation simulations and the experimental results recently reported [52]. Increasing the volume fraction of the GNR led to larger absorption and scattering coefficients; however, the wavelength at peak absorbance was not affected. The absorption and scattering coefficients corresponding to peak absorbance for the different GNR volume fractions investigated are presented in Table 2. It is worth noting that the absorption coefficient of the GNR is a few orders of magnitude higher than the absorption coefficients of the bladder and surrounding tissue.
Heat transfer from nanoparticles for targeted destruction of infectious organisms
Published in International Journal of Hyperthermia, 2018
Michael B. Cortie, David L. Cortie, Victoria Timchenko
The previous section highlighted the challenges of using isolated or dilute concentrations of nanoparticles for hyperthermia. On general grounds, many of these limitations can be overcome if agglomerates of many nanoparticles are used instead because local heating effects will, on balance, be increased. This is despite the fact that agglomeration induced by biological factors will decrease per particle heating efficiency due to changes in capture cross-section and, in the case of magnetic excitation, to changes in local viscosity [41]. There is, however, no simple analytical solution for the heat transfer in this situation. The optical extinction cross-section of a specific arrangement of particles may be numerically calculated using the discrete dipole approximation mentioned previously but some simplifying assumptions are normally made for the heat transfer. The dimensionless optical extinction efficiency of an agglomerate is generally inferior to that of a single nanoparticle, but the key point is that the absorption cross-section in physical units is much larger. In addition, the peak extinction is red-shifted, possibly into the tissue window. For the case of gold nanospheres, this is a distinct advantage as it permits excitation at wavelengths at which they would otherwise be nearly transparent [14,71–74]. The situation is compared in Figure 4 for an isolated gold nanosphere and an agglomerate.