Bi-verse relationship between gold nanoparticles and intracellular pH

Gold nanoparticles (AuNPs) are extensively used in biomedicine and as therapeutic agent as they can be drug carriers, imaging agents, gene-regulating agents, and photoresponsive therapeutics. On the other hand, especially when dealing with intracellular activity, fundamental parameters such as the pH must be taken into account and may be conveniently used to direct the action of the AuNPs. Cancer and normal cells, among other things, are characterized by different pH in several intracellular compartments, a difference can be conveniently used to modulate the action inside the cells of AuNPs (possibly functionalized for higher cancer recognition), for instance by regulating the associated drug release, the intrinsic fluorescence properties or the aggregation related aspect-ratio in plasmonic photo-thermal therapy. However, AuNPs may also be employed in a reversed perspective, i.e. for introducing acidifying agents to cause a decrease in pH beyond the tolerance level of cancer cells. In this mini-review the most recent findings are reported on the biverse effects of intracellular pH and gold nanoparticles.