Spurred by the anthrax hysteria of 2001, the U.S. government has thrown billions of dollars into developing new equipment and technologies to detect chemical and biological warfare agents. Now the Air Force has a plan that, if it actually works, would render all those billions obsolete.

A new solicitation from the service describes the need for “nanoparticle-based sensors that can be deployed in biological environments for the real-time detection of agents of interest.” In other words, the Air Force wants an instant, in vivo detector for every single toxic chemical and nasty germ on the face of the earth – from smallpox to nerve agents.

The chemical detection part is only slightly less wild than the rest of the proposal. Currently, the military has a variety of ways to detect and identify chemical agents, from stationary detectors that monitor the air for toxic clouds at a distance, or handheld devices that travel with a soldier and give off a warning in the event of a chemical exposure. But detecting biological agents is another feat entirely – living organisms are orders of magnitude more complex, constantly changing, and take much longer to identify. Typical lab tests can take hours (if not days) to analyze, process, and confirm a specific biological agent, and that’s only if the lab knows exactly what antigen it’s looking for.

This sensor, therefore, seems beyond any reasonable stretch of the imagination. It would pack all existing chemical agent detecting capabilities into a tiny cell. It would solve the hugely daunting problem of identifying not just one, but hundreds of dangerous biological organisms (many which look indistinguishable from harmless germs). And most significantly, it would do this all in real time.

The strategy the Air Force proposes is based on a system perfected by nature for life in complex environments: bimolecular switches. These switches turn on and off all the time, controlling how our cells work and how we respond to our environments. For example, specific proteins in our nose bind to odor molecules (whether they’re wafting off freshly baked bread or rotting meat) and let us detect different smells.

The turning on and off these switches is usually accompanied by a change in shape – “off” the biomolecule lies flat, “on” and it gets folded; “off” it’s circular, “on” it’s square. In some cases the specific change triggers a signal – the folded or square position may activate some other enzyme, or open a channel in a cell. Scientists have even engineered artificial switches to start glowing or give off some kind of electrochemical or biochemical signal once they are switched “on.”

The idea then, is to design “sensor systems that can enter living cells and complex environments and remain in an ‘off’ state until exposure to a target leads to a [signal].” These nano-sized sensors would float around the bloodstream until they ran into some toxic chemical or disease-causing germ. At that point, they would bind, change shape, and give off some kind of “readout,” which could presumably be measured (perhaps showing up on a lab test).

The Air Force claims it wouldn’t dole out these biosensors willy-nilly – only when troops are likely to run into dangerous biological or chemical warfare agents. However, it likes to keep its options open: “ideally, this sensor should be easy to implant and non-toxic so as to be administered even under appropriate suspicion.”

The project will be tricky, to say the least. Biomolecular switches have been designed for very specific uses before – for example a few years ago bio-engineers genetically combined two proteins (one that attached to glucose, one that glowed), to create a molecular switch that would light up when it encountered sugar. But the Air Force wants a sensor with “broad applicability to detect changes caused by known and unknown threats.”

Like making a key for a lock you’ve never seen, designing an uber-specific microscopic agent to track down an “unknown threat” may prove slightly difficult. So good luck, Air Force. On this project, you’re gonna need it.

Photo: U.S. Army