Optical gas sensing from polymer nanocavity

The optical sensors are claimed to be ideal for detecting trace gas concentrations due to their high signal-to-noise ratio, compact, lightweight nature, and immunity to electromagnetic interference.

Although other optical gas sensors had been developed before, the MIT team conceived an extremely sensitive, compact way to detect vanishingly small amounts of target molecules. They describe their new approach in Applied Physics Letters.

The researchers fabricated wavelength-scale photonic crystal cavities from PMMA, an inexpensive and flexible polymer that swells when it comes into contact with a target gas.

The polymer is infused with fluorescent dye, which emits selectively at the resonant wavelength of the cavity through a process called the Purcell effect. At this resonance, a specific colour of light reflects back and forth a few thousand times before eventually leaking out. A spectral filter detects this small colour shift, which can occur at even sub-nanometre level swelling of the cavity, and in turn reveals the gas concentration.