Table 2.

Monolayer-protected AuNPs that have been tested in vivo, including those protected by various mercaptan tetraethylene glycols (MTEG), such as ligands with an alkyl linker region (mercaptoundecyl-TEG, or MUTEG) and those with carboxylic acid termini (MTEG acid). Organ retention is listed in order of highest to lowest Au concentration. Only tiopronin-protected AuNPs have been found to be toxic, and most of the variants have safely cleared the system without generating an immune response in se. This is a desirable trait, indicating the potential to be made antigenic with specificity by the integration of an epitope into the organic shell.

Monolayer composition	Toxicity	Blood and urine clearance time	Immune response	Organ retention
Tiopronin (Tio)	>23 mg/kg	8 hr	none	liver, spleen, kidney
Tio:MUTEG	none	>4 wk	at high MUTEG abundance	spleen, kidney, heart, liver
Tio:MTEG acid	none	24 hr	none	liver, spleen, kidney, heart
Tio:MTEG	none	24 hr	none	liver, spleen, kidney, heart
Glutathione	none	24 hr (and later, see text)	none	liver, spleen, heart, kidney