The selection of gold nanomaterials (GNMs) for potential use in photothermal therapeutic applications depends on a few parameters including their morphology, size, and surface functionalization. We report experimental and theoretical studies of the photothermal efficiency of GNMs of a few different morphologies, including gold nanoparticles (AuNPs) of the spherical shape, gold nanorods (GNRs), and gold nanourchins (GNUs), as well as spherical gold nanoparticle conjugates (AuNPC), where 20 nm AuNPs were functionalized with an IR 808 dyes. The photothermal conversion efficiencies (η) were obtained by using the experimental results from the heating of GNMs with an IR 808 nm laser. We demonstrate that the surface functionalization of spherical gold nanoparticles of 20 nm size increases their photothermal efficiency by a factor of 4 as compared to the same size spherical AuNPs.
We present a method for measuring the optical absorption cross section ($$\sigma_{abs}$$ σ abs ) of gold nanoparticles (GNPs) based on optically heating the solution of GNPs with an 808 nm near-infrared (NIR) laser and measuring the temperature increase of the solution. We rely on the theoretical calculations based on the heat diffusion equations and experimental measurements based on the energy balance equations to measure the $$\sigma_{abs}$$ σ abs and the temperature distribution of single GNPs. Several morphologies, including gold nanospheres (GNSs), spherical gold nanoparticle conjugate (AuNPC), which are 20 nm GNSs surface-functionalized with an IR 808 dye, gold nanorods (GNRs), and gold nanourchins (GNUs), were studied. The study found that a single 20 nm GNS has the lowest $$\sigma_{abs}$$ σ abs and temperature distribution as compared to 100 nm GNUs. By increasing the size of GNSs from 20 to 30 nm, the magnitude of $$\sigma_{abs}$$ σ abs as well as temperature distribution increases by a factor of 5. The $$\sigma_{abs}$$ σ abs values of 20 and 30 nm GNSs calculated by Mie theory and the experimentally measured are in a good agreement. GNRs with equivalent radius ($$R_{eq}$$ R eq ) 9.16 nm show the second lowest $$\sigma_{abs}$$ σ abs . By increasing the $$R_{eq}$$ R eq by a factor of 2 to 19.2 nm, the measured $$\sigma_{abs}$$ σ abs and temperature distribution also increased by a factor of 2. We also estimated $$\sigma_{abs}$$ σ abs for GNUs with diameters at 80 and 100 nm, which also have higher $$\sigma_{abs}$$ σ abs values. This work confirms that we can use temperature to accurately measure the $$\sigma_{abs}$$ σ abs of a variety of GNPs in solution.
Nonlinear optical response of metal-semiconductor Zn0.8Co0.2O/Au nanocomposite films was studied experimentally and theoretically. Z-scan measurements revealed a positive nonlinear index of refraction of the composite film. Fluorescent spectroscopy measurements exhibited a narrow sharp peak that might be attributed to exciton peak of semiconductor nanostructured thin film enhanced by nearby gold nanoparticles. Classical electrodynamic calculations of a quantum dot in close proximity to a gold nanoparticle agree well with the experimentally observed normalized quantum efficiency.
We theoretically study particle-substrate interactions under laser irradiation. Van der Waals, electrostatic double layer and a laser induced dipole in the nanoparticle and an image dipole in the substrate were considered to be the major components of the total interaction potential. It was shown that laser-induced attractive potential energy between the particle and substrate reduces the potential barrier which increases the probability for metal nanoparticles to be deposited onto the substrate.
Due to their biocompatibility, ease of surface modification, and heating capabilities, gold nanomaterials are considered excellent candidates for the advancement of photothermal therapy techniques and related applications in cancer treatment. Various morphologies of gold nanomaterials have been shown to heat when exposed to high-powered laser irradiation, especially that which is from the near-infrared (NIR) region. While these lasers work well and are effective, light-emitting diodes (LEDs) may offer a safe and low-powered alternative to these high energy lasers. We investigated the heating capability of NIR-dye conjugated gold nanorods when exposed to an 808 nm LED light source using polyethylene glycol (PEG)-coated gold nanorods as the control. In this way, since the rods exhibited a surface plasmon resonance peak between 795 and 825 nm for both the PEG-coated rods and the dye-conjugated rods, which are fairly close to the frequency of the 530 mW, 850 nm LED light source, we were able to reveal the heating effect of the dye modification. While both morphologies heat when irradiated with the LED light, we demonstrated that the addition of an NIR dye increases the rate of heating and cooling, compared to the PEGylated counterpart. To our knowledge, the complementary effect given by the conjugated NIR-dye has not been previously reported in the literature. The targeting abilities of the NIR-dye combined with the increased heating rate of the modified particles used in this proof-of-concept work suggests that these particles may be exceptional candidates for theranostic applications.
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