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

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.


Local field enhancement profiles of the Au nanocage (L = 50 nm and W = 13.4 nm) at the LSPR wavelength of 800 nm.(a,d) Are the conceptual schematics showing four designated planes. (b,c,e,f) show the profiles of LSPR-induced local field enhancement. The incidence is polarized along x direction.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5035923&req=5

f5: Local field enhancement profiles of the Au nanocage (L = 50 nm and W = 13.4 nm) at the LSPR wavelength of 800 nm.(a,d) Are the conceptual schematics showing four designated planes. (b,c,e,f) show the profiles of LSPR-induced local field enhancement. The incidence is polarized along x direction.

Mentions: The E field enhancement profiles for the Au nanocage are shown in Fig. 5. Four planes are chosen to render the field plots. As shown in Fig. 5a, two planes X1 and X2 are perpendicular to the polarization direction (x-axis). X1 overlaps the central symmetry plane and X2 cuts the middle of the nanowires that form the edge of the structure. Figure 5b shows uniformly enhanced field intensity in X1 across the hollow interior of the nanocage. This region can potentially be loaded with theranostic agents that can be modulated by the enhanced field. Figure 5c illustrates several strongly enhanced hot spots at the outer surface of edge nanowires, which are primarily due to the dipolar resonance in those nanowires as they are aligned parallel to the polarization. Two additional planes Y1 and Y2 are defined perpendicular to the y-axis as illustrated in Fig. 5d. Strong field enhancement profiles can be observed in the hollow interior of the Au nanocage in Fig. 5e,f. This localized field concentration in the interior of the nanocage is attributed to the strong mode coupling between adjacent Au nanowire frame elements1920. The unique advantage of the nanocage over the core-shell particle is the abundance of coupled modes existing among the Au nanowires. The nanocage provides a larger number of hot spots on its surface that can be leveraged for theranostic applications. Moreover, the surface of nanocage can be functionalized with biotargeting agents to enable selective binding to a target biomaterial, e.g. cancer cells. Specifically, by manipulating thiolate-Au monolayer chemistry, excellent compatibility between Au surfaces and various molecules and ligands can be achieved2122. During the functionalization process, fluorescent labels can be attached to the Au surface to enable spatial tracking and imaging15. The LSPR of the nanoparticles can be used to enhance fluorescent signal intensity23, i.e. to dramatically increase the signal intensity from surface-bound or encapsulated fluorescent molecules2425. The enhanced fluorescence could enable high-resolution in vivo spatial imaging and tracking.


Theoretical Comparison of Optical Properties of Near-Infrared Colloidal Plasmonic Nanoparticles
Local field enhancement profiles of the Au nanocage (L = 50 nm and W = 13.4 nm) at the LSPR wavelength of 800 nm.(a,d) Are the conceptual schematics showing four designated planes. (b,c,e,f) show the profiles of LSPR-induced local field enhancement. The incidence is polarized along x direction.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Local field enhancement profiles of the Au nanocage (L = 50 nm and W = 13.4 nm) at the LSPR wavelength of 800 nm.(a,d) Are the conceptual schematics showing four designated planes. (b,c,e,f) show the profiles of LSPR-induced local field enhancement. The incidence is polarized along x direction.
Mentions: The E field enhancement profiles for the Au nanocage are shown in Fig. 5. Four planes are chosen to render the field plots. As shown in Fig. 5a, two planes X1 and X2 are perpendicular to the polarization direction (x-axis). X1 overlaps the central symmetry plane and X2 cuts the middle of the nanowires that form the edge of the structure. Figure 5b shows uniformly enhanced field intensity in X1 across the hollow interior of the nanocage. This region can potentially be loaded with theranostic agents that can be modulated by the enhanced field. Figure 5c illustrates several strongly enhanced hot spots at the outer surface of edge nanowires, which are primarily due to the dipolar resonance in those nanowires as they are aligned parallel to the polarization. Two additional planes Y1 and Y2 are defined perpendicular to the y-axis as illustrated in Fig. 5d. Strong field enhancement profiles can be observed in the hollow interior of the Au nanocage in Fig. 5e,f. This localized field concentration in the interior of the nanocage is attributed to the strong mode coupling between adjacent Au nanowire frame elements1920. The unique advantage of the nanocage over the core-shell particle is the abundance of coupled modes existing among the Au nanowires. The nanocage provides a larger number of hot spots on its surface that can be leveraged for theranostic applications. Moreover, the surface of nanocage can be functionalized with biotargeting agents to enable selective binding to a target biomaterial, e.g. cancer cells. Specifically, by manipulating thiolate-Au monolayer chemistry, excellent compatibility between Au surfaces and various molecules and ligands can be achieved2122. During the functionalization process, fluorescent labels can be attached to the Au surface to enable spatial tracking and imaging15. The LSPR of the nanoparticles can be used to enhance fluorescent signal intensity23, i.e. to dramatically increase the signal intensity from surface-bound or encapsulated fluorescent molecules2425. The enhanced fluorescence could enable high-resolution in vivo spatial imaging and tracking.

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.