and 2mL of 25mM chloroauric acid.30 Following preparation of the gold colloid, a rotary evaporator was used to concentrate the nanoparticles before mixing them with the silica nanoparticles. Formaldehyde was then used to grow the gold shell, by acting as a reducing agent for the gold in the chloroauric acid. Finally, 20L of 5M thiolated polyethylene glycol was used to increase the biocompatibility of the nanoshells by preventing the body from having an “immune response”. Filtration and centrifugation were used to purify the nanoshells before suspending them in phosphate buffer saline.31
Chloroauric acid, thiolated PEG and APTES all contribute to this being a particularly costly method, however materials such as formaldehyde, ethanol, ammonia and sodium hydroxide would most likely be found in a typical laboratory, which reduces the impact of the higher cost materials. However, as before, it was assumed that the highest purity was required which would obviously increase the cost. The method of preparing these gold nanoshells is also far simpler than others, for example to Fe3O4-polymer-gold nanoshells, and no time is consumed in leaving the reaction mixture for hours at a time.
This section will discuss the ways in which the NIR-absorbing nanostructures detailed in the above section can be applied in cancer diagnosis and treatment, from photothermal therapy, to contrast agents in imaging, to drug delivery systems
After synthesis of the multi-layered gold nanoshells, proposed by Gao et al and discussed above, their applicability in photothermal therapy was studied both in vitro (outside of the body) and in vivo (inside of the body). Breast cancer tumour cells were chosen for this study. First, the effectiveness of the nanoshells was tested in vitro by treating four groups of breast cancer cells under a microscope, the results of which are shown in Figure 11 below. It can be seen clearly that neither the gold nanoshells or 808nm laser light alone (C2 and C3) caused a significant effect, however when combined, as in C4, only 10% remained capable of surviving.
For the in vivo study, mice with breast cancer tumours were injected with either saline (as a control) or the multi-layered gold nanoshells, and exposed to laser radiation of 808nm.

As shown in the image above, the tumour regions in mice treated with multi-layered gold nanoshells were significantly hotter after laser irradiation than in those which had been treated with saline – the tumour regions treated with multi-layered gold nanoshells reached temperatures of 58C, whilst those treated with saline only reached temperatures of 38C.

The study carried out by Gao et al is particularly extensive as it studies the effects of the nanoshells in response to NIR light both in and outside of the body, giving it an advantage over the majority of studies which