Cancer Cell Imaging and Photothermal Therapy in the Near-Infrared Region by Using Gold Nanorods

TLDR

Noble‑metal nanoparticles exhibit enhanced absorption and scattering due to surface electric fields, enabling optically active agents for imaging and photothermal therapy, especially in the near‑infrared (650–900 nm) where gold nanorods with appropriate aspect ratios absorb strongly to reduce tissue light extinction. The study demonstrates gold nanorods as dual contrast agents for molecular imaging and photothermal cancer therapy in vitro. Gold nanorods were synthesized, conjugated to anti‑EGFR antibodies, and incubated with non‑malignant HaCat cells and malignant HOC 313 and HSC 3 oral epithelial cell lines. Anti‑EGFR‑conjugated gold nanorods bind preferentially to EGFR‑overexpressing malignant cells, enabling their clear visualization by dark‑field microscopy and allowing selective photothermal ablation with roughly half the laser energy needed for non‑malignant cells, demonstrating simultaneous diagnostics and therapy.

Abstract

Due to strong electric fields at the surface, the absorption and scattering of electromagnetic radiation by noble metal nanoparticles are strongly enhanced. These unique properties provide the potential of designing novel optically active reagents for simultaneous molecular imaging and photothermal cancer therapy. It is desirable to use agents that are active in the near-infrared (NIR) region of the radiation spectrum to minimize the light extinction by intrinsic chromophores in native tissue. Gold nanorods with suitable aspect ratios (length divided by width) can absorb and scatter strongly in the NIR region (650−900 nm). In the present work, we provide an in vitro demonstration of gold nanorods as novel contrast agents for both molecular imaging and photothermal cancer therapy. Nanorods are synthesized and conjugated to anti-epidermal growth factor receptor (anti-EGFR) monoclonal antibodies and incubated in cell cultures with a nonmalignant epithelial cell line (HaCat) and two malignant oral epithelial cell lines (HOC 313 clone 8 and HSC 3). The anti-EGFR antibody-conjugated nanorods bind specifically to the surface of the malignant-type cells with a much higher affinity due to the overexpressed EGFR on the cytoplasmic membrane of the malignant cells. As a result of the strongly scattered red light from gold nanorods in dark field, observed using a laboratory microscope, the malignant cells are clearly visualized and diagnosed from the nonmalignant cells. It is found that, after exposure to continuous red laser at 800 nm, malignant cells require about half the laser energy to be photothermally destroyed than the nonmalignant cells. Thus, both efficient cancer cell diagnostics and selective photothermal therapy are realized at the same time.