Abstract
We investigated the penetration and thermotherapy efficiency of different surface coated gold
nanorods (Au NRs) in multicellular tumor spheroids. The current data show that negatively
charged Au NRs, other than positively charged Au NRs, can penetrate deep into the tumor
spheroids and achieve a significant thermal therapeutic benefit.
Gold nanorods (Au NRs) are well-developed nanomaterials that have various applications in
biomedical research, such as cell imaging, drug and gene delivery and thermal therapy,
because of their biocompatibility and unique optical properties.1–4 In thermal therapy, the
localized surface plasmon resonance (LSPR) effect enables Au NRs to convert luminous
energy into heat when activated by laser at a specific wavelength.5
The LSPR maximum can
be tuned to the near-infrared (NIR, 700–900 nm)6
region by controlling the aspect ratio and
size of the Au NRs.7
Thus, the laser powerfully penetrates through human tissues and can
reach deep sites in the lesions. Additionally, it is harmless to cells without Au NRs.4, 8
The bio-distribution of Au NRs in tumor tissues is still unclear. Most tumor cells, unlike
normal tissue cells, are not reached by vasculature: blood and lymphatic vessels.9
Many
effective in vitro drugs fail to be used in clinical settings because of the poor distribution at
the tumor site; therefore, they could only achieve an effective concentration in the cells close
to the vasculatures.9
The ability of Au NRs to penetrate the tumor tissues and accumulate at
sites distant to the blood vessels is essential for the success of the thermal therapy.
Previous studies have reported that the surface chemistry is a key factor affecting the
cellular uptake and tissue penetration of nanomaterials.10–13 In this study, the relationship
between the surface chemistry and the penetration ability of Au NRs was investigated. We
synthesized Au NRs with three different polymer coatings: cetyltrimethylammonium
bromide (CTAB), polystyrene sulfonate (PSS) and poly (diallyldimethylammonium
chloride) (PDDAC). All Au NRs have an aspect ratio of 4, while the LSPR maximum