Nano Lett. 12, 602–609 (2011)

Nanoscale plasmonic interferometers comprising two grooves either side of a central slit in a thin silver film can function as tiny biochemical sensors that suit dense integration on a chip, according to Jing Feng and colleagues from Brown University in the USA. Light illuminating the structure strikes the grooves and excites surface plasmon polaritons, which interfere with light passing through the central slit. The two slit-groove paths act as tiny arms of a miniature interferometer. Light transmission through the slit depends on the illumination wavelength, the refractive index of the medium and the slit-groove distances, and thus can be used to detect small changes in refractive index due to changes in chemical concentration or composition. The researchers performed tests with a proof-of-concept sensor chip containing thousands of such plasmonic interferometers per square millimetre. Results indicate that the sensor can not only resolve refractive index changes as small as ∼3 × 10−7, but also detect glucose in water with a concentration of 0.1–140 mg ml−1 in sample volumes as small as 20 fl. The researchers anticipate that such sensors could serve as useful high-throughput devices for a wide variety of biomedical sensing tasks.