Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 118, Issue 7, Pages 3696-3707Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp408793a
Keywords
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Funding
- NSF EPSCOR [NSF EPS 1004083]
- Department of Education for a Graduate Assistance in Areas of National Need (GAANN) Fellowship [P200A090323]
- NSF [EPS 1004083]
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Plasmon resonances of anisotropic multibranched nanostructures are governed by their geometry, allowing morphology-directed selective manipulation of the optical properties. In this work, we have synthesized multibranched gold nanoantennas (MGNs) of variable geometry by a one-step seedless approach using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as a capping and reducing agent. This approach enables us to modulate the MGNs' geometry by controlling three different parameters: concentration of HEPES, concentration of Au3+, and pH of HEPES buffer. By altering the MGNs morphology with minimal increase in the overall dimensions, the plasmon resonances were tuned from the visible to the near-infrared. The MGNs plasmon resonances demonstrated a nonintuitive blue-shift when pH > pK(a) of HEPES which we attributed to emergence of charge transfer oscillations formed when MGNs cluster to dimers and trimers. Further, due to the presence of multiple sharp protrusions, the MGNs demonstrated a refractive index sensitivity of 373 nm/RIU, which is relatively high for this class of branched nanostructures of similar size. Finally, the sharp protrusions of MGNs also give rise to intense photothermal efficiencies; similar to 53 degrees C was achieved within 5 min of laser illumination, demonstrating the efficacy of MGNs in therapeutic applications. By modulating the mass density of MGNs, the laser flux, and time of illumination, we provide a detailed analysis of the photothermal characteristics of MGNs.
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