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Abstract
Small gold nanorods have a significantly large absorption/scattering ratio and are especially beneficial in exploiting photothermal effects, for example in photothermal therapy and remote drug release. This work systematically investigates the influence of growth conditions on the size, growth yield, and stability of small gold nanorods. The silver-assisted seed-mediated growth method was optimized to synthesize stable small gold nanorods with a high growth yield (>85%). Further study on the influence of silver ions on the growth facilitates the growth of small gold nanorods with tunable longitudinal surface plasmon resonance from 613 to 912 nm, with average dimensions of 13–25 nm in length and 5–6 nm in diameter. Moreover, the small gold nanorods were successfully functionalized with thiol-modified hairpin oligonucleotides (hpDNA) labeled with Cy5. Fluorescence intensity measurements show an increase in the presence of target DNA and an enhanced signal/background ratio when the longitudinal surface plasmon resonance of small gold nanorods overlaps with the excitation and emission wavelength of Cy5. This coincides with a reduced fluorescence lifetime of Cy5 in the hairpin structure, indicating surface plasmon resonance-enhanced energy transfer to the small gold nanorods. This study may provide insight on the synthesis and functionalization of small gold nanorods in biomedical sensing and therapy.
Highlights
Gold nanorods have been demonstrated as promising agents for various biomedical applications including cancer diagnosis and treatment.[1−3] The choice of gold nanorods stems from their unique optical properties arising from localized surface plasmon resonance.[4,5] The longitudinal surface plasmon mode of gold nanorods depends on the particle aspect ratio[4−6] and can be tuned from the visible to the near infrared (NIR) region
The energy transfer process from the fluorophore to gold nanorods has been exploited to good effect to understand the molecular interactions between proteins, DNA, mRNA, and fluorescence lifetime-based sensing of bioanalytes.[21−23] In addition, Wei et al demonstrated the assembly of fluorophore-labeled hairpin DNA on the large gold nanorod structure for detecting mRNA in a homogenous solution.[24] hpDNA has been utilized in various biological applications because of its increased sensitivity and specificity for target recognition.[24,25]
We have demonstrated a successful synthesis of stable small gold nanorods of various sizes and aspect ratios with tunable longitudinal surface plasmon resonance from 613 to 912 nm by the silver-assisted seed-mediated growth method
Summary
Gold nanorods have been demonstrated as promising agents for various biomedical applications including cancer diagnosis and treatment.[1−3] The choice of gold nanorods stems from their unique optical properties arising from localized surface plasmon resonance.[4,5] The longitudinal surface plasmon mode of gold nanorods depends on the particle aspect ratio[4−6] and can be tuned from the visible to the near infrared (NIR) region This shape-dependent optoelectronic property manifests itself in various processes such as strong surface-enhanced Raman scattering, two-photon luminescence, surface plasmon enhanced energy transfer, and photothermal effects.[7−13] These combined with low toxicity, water solubility, and biocompatibility, have made gold nanorods a versatile nanomaterial with demonstrated applications in various areas including biological sensing, imaging, drug delivery, and cancer therapy.[14−20]. This work should facilitate the development of small gold nanorod-based agents for enhanced performance in targeted analyte sensing, biomolecular labeling, photothermal therapy, and drug delivery
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