Vapors Plucked on a Harp

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APPLIED PHYSICS: Vapors Plucked on a Harp

Ian S. Osborne

Optical or electronic devices that sniff out chemical compounds with high

sensitivity and selectivity clearly have applications in a broad range of

circumstances, from environmental monitoring to the detection of biohazards.

However, the compounds of interest may not be in pure form; often they are

diluted among multiple background substances, and such an artificial nose must

therefore be able to sort through complex mixtures. Stievater et al.

present a chemical sensor based on a micro-optomechanical bridge that can be

interrogated remotely using optics. Their device, a microharp, forms one end of

a Fabry-Perot interferometer and comprises an array of microbridges in which

each bridge is coated with a sorbent polymer sensitive to a particular analyte.

Each bridge also has a distinct length and so vibrates at an individual

frequency. When the device is placed in a test atmosphere, different compounds

bind to particular strings on the harp, changing the mass of the bridge and

thereby inducing a shift in the frequency at which it vibrates. Interrogating

the vibrational frequency of each bridge separately allows monitoring of a

vapor's chemical composition remotely, and in some cases (as for

organophosphonates) detection concentrations down to 17 parts per billion. -- ISO