Gold Nanoparticles for Photothermal Cancer Therapy

Abstract

Gold is a multifunctional material that has been utilized in medicinal applications for centuries because it has been recognized for its bacteriostatic, anticorrosive, and antioxidative properties. Modern medicine makes routine, conventional use of gold and has even developed more advanced applications by taking advantage of its ability to be manufactured at the nanoscale and functionalized because of the presence of thiol and amine groups, allowing for the conjugation of various functional groups such as targeted antibodies or drug products. It has been shown that colloidal gold exhibits localized plasmon surface resonance (LPSR), meaning that gold nanoparticles can absorb light at specific wavelengths, resulting in photoacoustic and photothermal properties, making them potentially useful for hyperthermic cancer treatments and medical imaging applications. Modifying gold nanoparticle shape and size can change their LPSR photochemical activities, thereby also altering their photothermal and photoacoustic properties, allowing for the utilization of different wavelengths of light, such as light in the near-infrared spectrum. By manufacturing gold in a nanoscale format, it is possible to passively distribute the material through the body, where it can localize in tumors (which are characterized by leaky blood vessels) and be safely excreted through the urinary system. In this paper, we give a quick review of the structure, applications, recent advancements, and potential future directions for the utilization of gold nanoparticles in cancer therapeutics.

Keywords: cancer therapeutics; gold; hyperthermia; nanoparticles; photo-active property.

Figure 1

Particle diameter of Au on the absorption spectra and the plasmon bandwidth. (A) UV/ Visual absorption spectra of 9, 22, 48, and 99 nm gold nanoparticles in water. All spectra are normalized at their absorption maxima, which are 517, 521, 533, and 575 nm, respectively. (B) The plasmon bandwidth Δλ as a function of particle diameter. Re-printed with permission from American Chemistry Society Publications 1999 (Link and El-Sayed, 1999).

Figure 2

Color of gold nanorods with different aspect ratios. The small difference in the aspect ratio shows distinctive transmitted colors in the samples. Re-printed with permission from Elsevier 2005 (Pérez-Juste et al., 2005).

Figure 3

Fabrication of gold nanostars with different shapes. TEM images of gold nanostars prepared at 30°C are shown in the left panel. The authors were able to create different shapes by adding (a) 1, (b) 3, and (c) 6 mL of HEPES solution (0.1 M). The scale bar indicates 10 nm. (d) Normalized extinction spectra of gold nanostars with different volumes of HEPES. (e) The main extinction peak and FWHM (full width at half-maximum) as a function of HEPES volume. Re-printed with permission from American Chemistry Society Publications 2014 (Liu et al., 2014).

Figure 4

Diversity of gold nanostructures. (A) Nanospheres. (B) Nanocubes. (C) Nanobranches. (D) Nanorods (aspect ratio = 2.4 ± 0.3). (E) Nanorods (aspect ratio = 3.4 ± 0.5). (F) Nanorods (aspect ratio = 4.6 ± 0.8). (G) Nanobipyramids (aspect ratio = 1.5 ± 0.3). (H) Nanobipyramids (aspect ratio = 2.7 ± 0.2). (I) Nanobipyramids (aspect ratio = 3.9 ± 0.2). (J) Nanobipyramids (aspect ratio = 4.7 ± 0.2). Re-printed with permission from American Chemistry Society Publications 2008 (Chen et al., 2008).

Figure 5

Normalized extinction spectra of the gold nanostructures. (A) Spectra a–e correspond to nanospheres (aspect ratio = 2.4 ± 0.3), nanocubes (aspect ratio = 3.4 ± 0.5), and nanorods with aspect ratios of 4.6 ± 0.8. (B) Spectra a–d correspond to nanobipyramids with different aspect ratios (as shown 1.5 ± 0.3, 2.7 ± 0.2, 3.9 ± 0.2, and 4.7 ± 0.2, respectively) and nanobranches (spectra e). Re-printed with permission from American Chemistry Society Publications 2008 (Chen et al., 2008).