Destruction and control of Toxoplasmagondii Tachyzoites using gold nanosphere/antibody conjugates

[Extract] Gold nanoparticles are of interest for experimental photothermal therapies because they are biocompatible, can be functionalized with an antibody, and will strongly absorb light from suitably tuned lasers.1–8 These attributes can be exploited to heat up and destroy specific cells to which nanoparticles have been attached. To date, most interest in using gold nanoparticles in this way has been directed at the treatment of cancer. However, we have recently extended the paradigm to attach gold nanorods to a parasitic protozoan, the infectious extracellular tachyzoite form of Toxoplasma gondii (T. gondii).8 There are, however, some problematic issues associated with the use of nanorods, such as their positive surface charge. In the present work we show that the targeting and destruction of T. gondii may be more simply achieved with simple antibody-functionalized gold nanospheres. These aggregate upon binding to the protozoan target with two unexpected but useful side effects: a red-shift of the peak optical extinction of the gold and an inhibition of the infectivity of the tachyzoites