among natural mechanisms of cell deaths , disease or toxicity , one of the most common method is through overloading of certain biological metals such as calcium , iron and zinc . we propose to utilize this natural mechanism of cell death against cancer by utilizing the well known phenomenon of enhanced permeation and retention effect and metal - binding nanoparticle moieties that can self - degrade under certain biological conditions such as ph . more specifically , we show that one can form nanoparticles that consist of polymerized citric acid and various different types of metals including , but not limited to , iron , calcium , zinc , silver and magnesium , displaying acid - stability and self - degradation leading to constituent metal release when ph rises closer to the neutral ph of 7 or higher . we also show that these nanoparticles with different metal compositions have distinct cytotoxicity against various different types of cancer cell lines , including b16f10 melanoma , h460 human lung cancer , t98g kidney cancer , ramos leukemic cancer , etc . in vitro . we also show evidence of in vivo anti - cancer activity of our nanoparticles containing various different metals using mouse model studies .