Figure 2.

The “typical” gold nanoparticle (GNP). The most used GNPs are the nanospheres. The gold core is sometimes covered with an imaging tag (i.e., Raman tags, fluorescent tag). Then, the GNPs are often covered by a polyethylene glycol (PEG) and/or silica shell. Finally, on the GNP surface, several molecules can be conjugated serving as blood-brain barrier (BBB) crossing internal enhancers or as chemotherapy agents.