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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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Absorption cross section spectra σabs of particles vs. variation of the domain period and dimensions.(a) σabs of the SiO2@Au particle with Rc = 27.3 nm and ts = 3.7 nm vs. variation of the domain period P. The inset shows the results predicted by Mie theory. (b–d) σabs of three NIR colloids with the same volume Vp vs. variation of dimensions: (b) SiO2@Au core-shell particles, (c) Au nanoframes and (d) Au nanorods.
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f2: Absorption cross section spectra σabs of particles vs. variation of the domain period and dimensions.(a) σabs of the SiO2@Au particle with Rc = 27.3 nm and ts = 3.7 nm vs. variation of the domain period P. The inset shows the results predicted by Mie theory. (b–d) σabs of three NIR colloids with the same volume Vp vs. variation of dimensions: (b) SiO2@Au core-shell particles, (c) Au nanoframes and (d) Au nanorods.

Mentions: We first study the LSPR tunability of the three nanostructures as a function of their dimensional parameters. The total particle volume is held fixed at Vp = (50 nm)3 for all particles. It is important to note that the fixed particle volume applies throughout this work and hence the volume fractions of the different colloids are identical. We also assume that the colloids are sufficiently dilute so that interparticle photonic coupling is negligible. We begin by investigating the LSPR tunability of the SiO2@Au structure. We calibrate and validate the 3D computational model for this structure using Mie theory. To this end, Fig. 2a shows an analysis of the absorption spectrum of a SiO2@Au particle as a function of the size of the computational domain (Fig. 1d). Here, the length P that defines the square cross section of the computational domain, i.e. traverse to the direction of propagation, is systematically increased until the computed absorption spectrum equals that obtained using Mie theory. This occurs when P = 2000 nm as seen in the inset of Fig. 2a. This value of P is used throughout this work unless specified otherwise. This preliminary calibration is necessary because symmetry boundary conditions (BCs) are imposed on the lateral sides of the computational domain (i.e. transverse to the direction of propagation) to simplify the analysis. However, these BCs give rise to undesired interparticle coupling, which can contribute to the field solution and needs to be minimized by choosing a sufficiently large spacing between the particles (i.e. sufficiently large P) as described in the Method section.


Theoretical Comparison of Optical Properties of Near-Infrared Colloidal Plasmonic Nanoparticles
Absorption cross section spectra σabs of particles vs. variation of the domain period and dimensions.(a) σabs of the SiO2@Au particle with Rc = 27.3 nm and ts = 3.7 nm vs. variation of the domain period P. The inset shows the results predicted by Mie theory. (b–d) σabs of three NIR colloids with the same volume Vp vs. variation of dimensions: (b) SiO2@Au core-shell particles, (c) Au nanoframes and (d) Au nanorods.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Absorption cross section spectra σabs of particles vs. variation of the domain period and dimensions.(a) σabs of the SiO2@Au particle with Rc = 27.3 nm and ts = 3.7 nm vs. variation of the domain period P. The inset shows the results predicted by Mie theory. (b–d) σabs of three NIR colloids with the same volume Vp vs. variation of dimensions: (b) SiO2@Au core-shell particles, (c) Au nanoframes and (d) Au nanorods.
Mentions: We first study the LSPR tunability of the three nanostructures as a function of their dimensional parameters. The total particle volume is held fixed at Vp = (50 nm)3 for all particles. It is important to note that the fixed particle volume applies throughout this work and hence the volume fractions of the different colloids are identical. We also assume that the colloids are sufficiently dilute so that interparticle photonic coupling is negligible. We begin by investigating the LSPR tunability of the SiO2@Au structure. We calibrate and validate the 3D computational model for this structure using Mie theory. To this end, Fig. 2a shows an analysis of the absorption spectrum of a SiO2@Au particle as a function of the size of the computational domain (Fig. 1d). Here, the length P that defines the square cross section of the computational domain, i.e. traverse to the direction of propagation, is systematically increased until the computed absorption spectrum equals that obtained using Mie theory. This occurs when P = 2000 nm as seen in the inset of Fig. 2a. This value of P is used throughout this work unless specified otherwise. This preliminary calibration is necessary because symmetry boundary conditions (BCs) are imposed on the lateral sides of the computational domain (i.e. transverse to the direction of propagation) to simplify the analysis. However, these BCs give rise to undesired interparticle coupling, which can contribute to the field solution and needs to be minimized by choosing a sufficiently large spacing between the particles (i.e. sufficiently large P) as described 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.


Related in: MedlinePlus