A new nano-weapon delivers a low-toxicity form of arsenic that only turns into a lethal poison once it is inside a tumor.

Arsenic is a famous poison that is usually too dangerous to use as a systemic cancer treatment. This nanozyme carries a safe version of the element called arsenate and hides it from the rest of the body. Once the particles reach the acidic and unique environment of a liver tumor, they trigger a chemical reaction that converts the cargo into a highly potent toxin. This ensures that the poison is only active where it is needed to kill cancer cells. This approach could turn many other discarded toxic chemicals into high-precision medical tools.