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Theoretical Comparison of Optical Properties of Near-Infrared Colloidal Plasmonic Nanoparticles

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ABSTRACT

We study optical properties of near-infrared absorbing colloidal plasmonic nanostructures that are of interest for biomedical theranostic applications: SiO2@Au core-shell particles, Au nanocages and Au nanorods. Full-wave field analysis is used to compare the absorption spectra and field enhancement of these structures as a function of their dimensions and orientation with respect to the incident field polarization. Absorption cross-sections of structures with the same volume and LSPR wavelength are compared to quantify differential performance for imaging, sensing and photothermal applications. The analysis shows that while the LSPR of each structure can be tuned to the NIR, particles with a high degree of rotational symmetry, i.e. the SiO2@Au and nanocage particles, provide superior performance for photothermal applications because their absorption is less sensitive to their orientation, which is random in colloidal applications. The analysis also demonstrates that Au nanocages are advantaged with respect to other structures for imaging, sensing and drug delivery applications as they support abundant E field hot spots along their surface and within their open interior. The modeling approach presented here broadly applies to dilute colloidal plasmonic nanomaterials of arbitrary shapes, sizes and material constituents and is well suited for the rational design of novel plasmon-assisted theranostic applications.

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Plasmonic nanostructures and the computational model.(a) SiO2@Au core-shell particles, (b) Au nanocages, (c) Au nanorods. (d) Computational domain showing the polarization and propagation direction of the incident field.
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f1: Plasmonic nanostructures and the computational model.(a) SiO2@Au core-shell particles, (b) Au nanocages, (c) Au nanorods. (d) Computational domain showing the polarization and propagation direction of the incident field.

Mentions: We used 3D full-wave computational models to study the NIR plasmonic behavior of the three nanostructures shown in Fig. 1. In our analysis, we place more emphasis on optical absorption rather than scattering as we are interested in photothermal applications in which the absorption is the dominant factor that determines the efficiency of the system. In addition, we consider subwavelength nanoparticles for which absorption dominates scattering. The comparison between intensities of absorption and scattering can be found in the Supplementary Information. The core-shell particles consist of a silica (SiO2) core with a radius Rc and a gold shell with a thickness ts as shown in Fig. 1a. The Au nanocages are cubic with twelve frame elements in the form of square Au nanowires, as shown in Fig. 1b. The nanocage geometry is defined by its length L, which defines the size of the cube, the width W that defines the cross-sectional area of the nanowire, and the aspect ratio R = L/W. In the literature, this structure is also referred to a nanoframe14. The nanorod geometry, shown in Fig. 1c, consists of a cylindrical body of radius Rd with hemispherical dome-shaped caps at either end. The total length of the nanorod is H. An example of the computational domain for this analysis is shown in Fig. 1d. Here, a single core-shell particle is centered at the origin of the domain and immersed in a carrier fluid, which we take to be H2O. The computational model is described in detail in the Method section.


Theoretical Comparison of Optical Properties of Near-Infrared Colloidal Plasmonic Nanoparticles
Plasmonic nanostructures and the computational model.(a) SiO2@Au core-shell particles, (b) Au nanocages, (c) Au nanorods. (d) Computational domain showing the polarization and propagation direction of the incident field.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5035923&req=5

f1: Plasmonic nanostructures and the computational model.(a) SiO2@Au core-shell particles, (b) Au nanocages, (c) Au nanorods. (d) Computational domain showing the polarization and propagation direction of the incident field.
Mentions: We used 3D full-wave computational models to study the NIR plasmonic behavior of the three nanostructures shown in Fig. 1. In our analysis, we place more emphasis on optical absorption rather than scattering as we are interested in photothermal applications in which the absorption is the dominant factor that determines the efficiency of the system. In addition, we consider subwavelength nanoparticles for which absorption dominates scattering. The comparison between intensities of absorption and scattering can be found in the Supplementary Information. The core-shell particles consist of a silica (SiO2) core with a radius Rc and a gold shell with a thickness ts as shown in Fig. 1a. The Au nanocages are cubic with twelve frame elements in the form of square Au nanowires, as shown in Fig. 1b. The nanocage geometry is defined by its length L, which defines the size of the cube, the width W that defines the cross-sectional area of the nanowire, and the aspect ratio R = L/W. In the literature, this structure is also referred to a nanoframe14. The nanorod geometry, shown in Fig. 1c, consists of a cylindrical body of radius Rd with hemispherical dome-shaped caps at either end. The total length of the nanorod is H. An example of the computational domain for this analysis is shown in Fig. 1d. Here, a single core-shell particle is centered at the origin of the domain and immersed in a carrier fluid, which we take to be H2O. The computational model is described in detail in the Method section.

View Article: PubMed Central - PubMed

ABSTRACT

We study optical properties of near-infrared absorbing colloidal plasmonic nanostructures that are of interest for biomedical theranostic applications: SiO2@Au core-shell particles, Au nanocages and Au nanorods. Full-wave field analysis is used to compare the absorption spectra and field enhancement of these structures as a function of their dimensions and orientation with respect to the incident field polarization. Absorption cross-sections of structures with the same volume and LSPR wavelength are compared to quantify differential performance for imaging, sensing and photothermal applications. The analysis shows that while the LSPR of each structure can be tuned to the NIR, particles with a high degree of rotational symmetry, i.e. the SiO2@Au and nanocage particles, provide superior performance for photothermal applications because their absorption is less sensitive to their orientation, which is random in colloidal applications. The analysis also demonstrates that Au nanocages are advantaged with respect to other structures for imaging, sensing and drug delivery applications as they support abundant E field hot spots along their surface and within their open interior. The modeling approach presented here broadly applies to dilute colloidal plasmonic nanomaterials of arbitrary shapes, sizes and material constituents and is well suited for the rational design of novel plasmon-assisted theranostic applications.

No MeSH data available.