An overview of synthetic strategies and current applications of gold nanorods in cancer treatment.

Photothermal therapy, also referred to as optical hyperthermia or photothermal ablation, is an emerging strategy for treating solid tumours. Colloidal gold converts the absorbed light into localized heat via a non-radiative mechanism, surface plasmon resonance, which ablates the solid tumours. Several plasmon resonating nanostructures, including gold nanoparticles (AuNPs), gold nanorods (AuNRs), gold nanoshells, gold nanocages, copper sulphide and carbon nanotubes, have shown potential for photo-activated cancer therapy. Generally, spherical AuNPs display absorption maxima between 500-550 nm, making them inefficient due to low tissue penetration. On the other hand, AuNRs absorb light in the near-infrared (NIR) region that penetrates deeper with higher spatial precision, and causes no damage to the surrounding healthy tissues due to the low energy absorption of NIR light by normal tissue. Moreover, the absorption range of light can be fine-tuned to the NIR region by adjusting the aspect ratios of AuNRs. However, large-scale synthesis and stability of this colloidal system still poses challenges for clinical translation. In this review, we discuss various strategies applied up to now for the synthesis of AuNRs. Current trends in the pre-clinical development of multifunctional AuNRs with emphasis on preparation and application strategies in cancer therapy have been delineated.