A method for remotely switching on chemical reactions using magnetic fields is described in a paper published online this week in the new journal Nature Catalysis. The technique reported allows the release of molecules at specific locations and times, with potential applications in selective drug delivery.

Enzymes normally react quickly with a specific target, known as the substrate. It is possible to attach a drug molecule to the substrate that will only be released once the substrate comes into contact with the enzyme. However, under normal conditions, selectivity is a problem: the drug will be released as soon as the enzyme and substrate are in the same location.

Sergiy Minko and colleagues have now overcome this problem by attaching enzymes and substrates to separate iron oxide nanoparticles. They encased these particles in a polymer coat to ensure they could not interact. The authors show that in the absence of a magnetic field, as expected, no interaction between the nanoparticle-linked enzyme and nanoparticle-linked substrate occurs and that no drug is released. However, once the magnetic field is switched on, the nanoparticles are forced together and their polymer coats merge, allowing the required chemical reactions to take place and the drug to be released. The authors then used the method in a proof-of-principle study to show it can be used to kill cancer cells by releasing the chemotherapy drug doxorubicin.