Effect of the polyelectrolyte coating on the photothermal efficiency of gold nanorods and the photothermal induced cancer cell damage.

Coating gold nanorods (GNRs) with polyelectrolytes is an effective approach to make them biocompatible for potential use in photothermal treatment (PTT) of cancer. The authors report the effect of coating of the GNRs with polystyrene sulphonate (PSS-GNRs) and PSS plus poly di-allyl di-methyl ammonium chloride (PDDAC-GNRs) on its photothermal conversion efficiency (PTE), cellular uptake and subsequently the photothermal induced cytotoxicity in human oral cancer cells (NT8e). Coating of GNRs with PSS led to decrease in PTE by ∼30% and further coating it with PDDAC led to its increase to similar level, with respect to as- prepared GNRs. The cellular uptake of PDDAC-GNRs in cancer cells was double than that for PSS-GNRs. PTT of cancer cells after treatment with 60 pM of either PDDAC-GNRs or PSS-GNRs resulted in cytotoxicty of ∼90%. At higher concentration of 120 pM, while PSS-GNRs showed no further change, for PDDAC-GNR the photothermal induced cytotoxicity decreased to ∼50%. The broadening of longitudinal surface plasmon peak of PDDAC-GNRs and appearance of dark clusters in cells under bright-field microscope suggested intracellular clustering of PDDAC-GNRs. In conclusion, despite high PTE and cellular uptake of PDDAC-GNRs, its intracellular clustering (due to acidic pH ) adversely affect the PTT of cancer cells.