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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.

No MeSH data available.


Related in: MedlinePlus

NIR absorption cross section vs. particle orientation.Geometry and coordinates of spatial orientation of (a) nanoframe and (b) nanorod; σabs vs. spatial orientation (φ, θ) for (c) Au nanoframe and (d) Au nanorod.
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f3: NIR absorption cross section vs. particle orientation.Geometry and coordinates of spatial orientation of (a) nanoframe and (b) nanorod; σabs vs. spatial orientation (φ, θ) for (c) Au nanoframe and (d) Au nanorod.

Mentions: Next, we study the absorption of the nanostructures as a function of their orientation relative to the incident polarization. This is important because colloidal particles have random orientations that can impact their absorption. The SiO2@Au particles are centrosymmetric and therefore their absorption cross section is independent of orientation. However, nanocages and especially nanorods, have less rotational symmetry and their absorption changes with orientation. We use angles φ and θ to define the rotation of the particles relative to the x- and z-axis, respectively, as shown in Fig. 3. In Fig. 3a,b, the unit vector n is shown that is normal to the top area of the nanocage and along the principle axis of the nanorod, respectively. The angle φ lies in the x-y plane and is measured from the x-axis to the projection of n onto x-y plane, whereas 90° − θ is the angle between n and the z-axis.


Theoretical Comparison of Optical Properties of Near-Infrared Colloidal Plasmonic Nanoparticles
NIR absorption cross section vs. particle orientation.Geometry and coordinates of spatial orientation of (a) nanoframe and (b) nanorod; σabs vs. spatial orientation (φ, θ) for (c) Au nanoframe and (d) Au nanorod.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5035923&req=5

f3: NIR absorption cross section vs. particle orientation.Geometry and coordinates of spatial orientation of (a) nanoframe and (b) nanorod; σabs vs. spatial orientation (φ, θ) for (c) Au nanoframe and (d) Au nanorod.
Mentions: Next, we study the absorption of the nanostructures as a function of their orientation relative to the incident polarization. This is important because colloidal particles have random orientations that can impact their absorption. The SiO2@Au particles are centrosymmetric and therefore their absorption cross section is independent of orientation. However, nanocages and especially nanorods, have less rotational symmetry and their absorption changes with orientation. We use angles φ and θ to define the rotation of the particles relative to the x- and z-axis, respectively, as shown in Fig. 3. In Fig. 3a,b, the unit vector n is shown that is normal to the top area of the nanocage and along the principle axis of the nanorod, respectively. The angle φ lies in the x-y plane and is measured from the x-axis to the projection of n onto x-y plane, whereas 90° − θ is the angle between n and the z-axis.

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.


Related in: MedlinePlus