UCLA

Core/shell nanorods based on a plasmonic gold nanorod core with a thin dielectric shell were designed, synthesized and characterized to demonstrate their potential in photovoltaics and cancer therapy applications.

For solar cell applications, the light scattering properties of Au nanorods were combined with an electrically insulating silica (SiO₂ ) layer to form a core/shell architecture. The Au nanorod core was coated with a SiO₂ shell in order to isolate the conductive metal surface of the gold from the conductive photo-polymers in the active layers of organic photovoltaic (OPV) devices. The aspect ratio of the Au nanorod core was spectrally tailored so that the peak extinction wavelength of the Au/SiO₂ core/shell nanorod coincided with wavelength regions in which the photovoltaic material absorbed poorly. Specifically, octadecyltrimethoxysilane (OTMS)-functionalized Au/SiO₂ core/shell nanorods were spectrally tailored and incorporated into two OPV polymer systems: poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCB60M) and poly[2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,4-b]dithiophene-alt-5-dibutyloctyl-3,6-bis(5-bromothiophen-2-yl) pyrrolo[3,4-c]pyrrole-1,4-dione] (PBDTT-DPP:PC60BM). For the P3HT:PC60BM polymer with a band edge at ~ 670 nm, the incorporation of Au/SiO2 core/shell nanospheres (radius = 20 nm) resulted in a 2.7% improvement in photon conversion efficiency (PCE). The incorporation of the core/shell nanorods (radius = 10 nm) with an aspect ratio (AR) ~ 2.5 (extinction peak, ëpeak = 670 nm) resulted in a 7.1% improvement in PCE. For the PBDTT-DPP:PC60BM polymer with a band edge at ~ 830 nm, the incorporation of Au/SiO₂ core/shell nanospheres resulted in a 9.2% improvement, while that of core/shell nanorods (radius = 8 nm) of AR ~ 4 (extinction peak, ëpeak = 830 nm) resulted in a 14.4% improvement in PCE. The performance enhancements were corroborated by external quantum efficiency (EQE) measurements.

For cancer therapy applications, the strong light absorption properties of Au nanorods were combined with the upconverting light emission properties of rare earth doped-yttria (RE:Y₂O₃) in order to create hybrid plasmonic/fluorescent core/shell nanorods for dual bio-imaging and photo-thermal therapy applications. Specifically, Au/SiO₂/Yb:Er:Y₂O₃ core/shell nanorods were synthesized, optically characterized and tested for photo-thermal therapy both in-vitro and in-vivo. The plasmonic/fluorescent Au/SiO₂/Yb:Er:Y₂O₃ core/shell nanorods have a unique optical signature when excited with 980 nm laser irradiation, exhibiting both the broadband photoluminescence characteristic of Au interband transitions and the sharp emission lines characteristic of the Er^{3+ 4}F_9/2 -> ⁴I_15/2 energy transition. The Au/SiO₂/Yb:Er:Y₂O₃ showed a nearly two fold increase in emission compared to SiO₂/Yb:Er:Y₂O₃ nanospheres at a wavelength of 655 nm (Er^{3+ 4}F_9/2 -> ⁴I_15/2 energy transition). Au/SiO₂/Yb:Er:Y₂O₃ core/shell nanorods were shown to exhibit photothermal properties upon 980 nm laser irradiation which reduced cell viability in cyto-toxicity assays and induced selective hyperthermia in breast cancer cells both in-vitro and in-vivo.