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A microscopic device developed by an Alberta-based team features a tiny spatula-like arm that rotates in response to a magnetic field. The movement is detected by shining laser light across the length of the device. Such a device could one day be used to create hand held sensors that detect different substances based on their magnetic properties. The entire device is about 14 millionths of a metre long -- less than the diameter of a human hair.

Nathanael Wu/National Institute for Nanotechnology

A woman is at a party and realizes someone may have slipped something into her drink. Even if she tosses it, her uncertainty and worry remain. She wonders: Has someone tried to drug me?

In the future, it may be possible to get an answer by discreetly dabbing a few drops onto a smartphone and getting an on-the-spot chemical readout of what's in the drink. A portable but sensitive device for performing such tests could be realized with the help of a tiny magnetic sensor developed by a team of Alberta-based researchers.

"At this moment we're far from actually doing that, but there aren't any physical reasons why that won't work," said Mark Freeman, a University of Alberta physicist who has worked out the technology that underlies the idea.

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In 2008, Dr. Freeman and his team developed a tiny magnetic sensing device, called a torque magnetometer, on a piece of silicon chip that is smaller than the diameter of a strand of human hair. The device features a tiny spatula-shaped arm suspended on a narrow band of material that twists ever so slightly when the arm is pulled up or down by a magnetic field.

Now, Dr. Freeman has joined forces with scientists at the University of Calgary and the National Institute for Nanotechnology to add a nanoscale optical system that can measure the position of the arm to extraordinary precision by setting up a pattern of laser light along its length. The system is so sensitive it can record a displacement in the tip of the spatula as small as the diameter of a proton. In a paper published Monday in the journal Nature Nanotechnology, the scientists document their latest version of the device and demonstrate its ability to sense magnetic forces at scales far smaller than the device itself.

There could be a host of uses for such a tool, the researchers say, including probing and characterizing the magnetic properties of new materials that are being developed for future applications in electronics and quantum computing.

But the most imaginative use may be in the area known as magnetic spectrometry. Because different species of atoms have magnetic properties that can be distinguished from one another, it's possible to use magnetism to tell them apart. The method can be used like a chemical fingerprint. Such measurements are performed today with bench-sized or even room-sized machines. The Alberta researching team appears to have hit upon a way to shrink the capability down to a microscopic device that could be carried around to determine the composition of different materials.

"This device is the first of its kind in the world," said Paul Barclay, an associate professor at the University of Calgary's Institute for Quantum Science and Technology who led the development of the optical system used in the device. "There haven't been many examples of people being able to harness this level of sensitivity that these kinds of systems provide to learn something new."

The advance is an example of the continuing drive to miniaturize the tools that scientists have long used to measure the properties of matter in hopes of creating powerful and convenient devices, both for industrial and consumer use, that resemble the gadgets wielded by characters in science fiction.

When technologies become portable, they also become increasingly attractive for space exploration, Dr. Freeman noted. "And similarly for terrestrial applications, there are lots of magnetic particles in the environment, in sediments, rocks, etc., that could be examined in the field with such a tool."

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Drug tests may be farther off on the horizon, but Dr. Barclay added that one way or another it's hard to imagine the kind of sensor developed by the Alberta researchers not finding a role in the future.

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