Complementary Photothermal Heating Effects Observed between Gold Nanorods and Conjugated Infrared-Absorbing Dye Molecules

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.