You injure yourself and inevitably it hurts. But instead of heading to the medicine cabinet you're already starting to feel better, as your sense-act-treat patch kicks in and releases a pain killer. That's a scenario that Joseph Wang and colleagues at the University of California-San Diego, US, are trying to turn into a reality.

In collaboration with Evgeny Katz at Clarkson University, US, the team have wired up a biofuel cell that is activated by injury biomarkers and then releases a drug from one of the electrodes. The integrated system uses Boolean logic to regulate the release of the drug and only delivers as much of the drug as is needed. Both logically responsive fuel cells and logically controlled drug release have been achieved before, but this is the first time that the two have been combined.

The team decided to produce a biofuel device that responded to lactic acid, as excess amounts of this molecule are released in the event of abdominal trauma. They created a system consisting of a biofuel cell that has an enzyme based logic gate on its anode and a drug containing cathode. When both lactic acid and lactate dehydrogenase (LDH) are present, LDH catalyses the production of pyruvate from lactic acid, using NAD⁺ as an oxidising agent. The NADH that is subsequently formed by the reaction can then feed electrons into the fuel cell. In this way, LDH and lactic acid act as an AND gate, and the drug at the cathode - in this case paracetamol - is only released when the injury biomarker lactic acid is detected and the circuit is completed. 

The work was funded by the Office of Naval Research and Wang explains that the goal is to design a complete 'nanopharmacy' that can monitor and treat soldiers on the battlefield, perhaps as a patch on the arm.

'The field of molecular logic is growing nicely now with good applications beginning to emerge,' says A P de Silva, who works on molecular logic at Queen's University, Belfast, UK. 'Joe Wang's paper is one of these.'   

There's still a long way to go for practical use as various improvements are made, but maybe one day the medicine cabinet itself will be a thing of the past.

Laura Howes

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