Fig. 11. (a) Cell viability of non-tumorigenic HEK 293T cells with various concentrations of GO, GO–PVP, GO–PVP–Fe₃O₄, GO–PVP–Fe₃O₄–QSR and QSR, and (b) cell viability of human breast cancer MDA MB 231 cells with various concentrations of GO, GO–PVP, GO–PVP–Fe₃O₄, GO–PVP–Fe₃O₄–QSR and QSR.