Gold Nanorods
Gold nanorods are a type of gold nanostructure characterized by their elongated, cylindrical shape, which gives them unique optical and chemical properties compared to spherical gold nanoparticles. These properties are largely influenced by their aspect ratio—the ratio of their length to their diameter—which can be precisely controlled during synthesis.
Applications
Gold nanorods are used extensively in biomedical imaging due to their strong optical absorption and scattering properties. They are particularly useful in photoacoustic imaging, where they enhance contrast significantly, providing detailed images of biological tissues.
The ability of gold nanorods to absorb light in the near-infrared region, where biological tissues are relatively transparent, allows for their use in photothermal therapy. When irradiated, they efficiently convert light into heat, destroying targeted cancer cells with minimal damage to surrounding healthy tissue.
The sensitivity of gold nanorods to changes in their local dielectric environment is exploited in biosensing applications. They can be used to detect small amounts of biological analytes, such as proteins or pathogens, by observing shifts in their plasmon resonance frequency.
Functionalized gold nanorods can be used to transport therapeutic agents directly to specific disease sites. The rods can be designed to release their payload in response to external stimuli such as light or pH changes, allowing for controlled, site-specific drug release.
Properties
- Optical Properties: Gold nanorods exhibit two types of surface plasmon resonances: transverse and longitudinal. The transverse mode occurs at shorter wavelengths and is less sensitive to changes in aspect ratio, while the longitudinal mode, which occurs at longer wavelengths, can be tuned across a wide range from visible to near-infrared by adjusting the aspect ratio. This tunability allows for the precise engineering of their optical properties.
- Enhanced Electromagnetic Fields: The ends of the nanorods, where the curvature is more pronounced, can generate enhanced electromagnetic fields. These “hot spots” are particularly beneficial for applications requiring intense local field enhancements, such as in surface-enhanced Raman scattering (SERS).
Chemical Stability and Functionalization: Like other gold nanostructures, nanorods can be easily functionalized with a variety of molecules, such as polymers, DNA, or proteins, enhancing their compatibility with different biological and chemical environments. This functionalization is key for various applications in medicine and chemistry.