With their clear silica shells, diatoms would appear to somehow have a photonic purpose. Researchers at the Università di Napoli Federico II and the Istituto per la Microelettronica e Microsistemi-Unità di Napoli (both of Napoli, Italy) have found one; they have turned diatoms, or at least their shells, into photoluminescence-based gas sensors that can measure the presence and concentration of nitrogen dioxide (NO2), methane, or carbon monoxide in air. They experimented on three types of diatoms, all with micrometer-size macropores, and one with 20 to 30 nm micropores.
The silica shells were separated from the cell and deposited on a silicon substrate; a 325-nm-emitting helium-cadmium laser was the excitation source. A spectrometer and CCD camera acquired the data. The researchers measured the photoluminescence spectrum in dry air, and then introduced a gas. All the gases induced either an increase or decrease of the magnitude of the dry-air spectrum, but no change in spectral shape (thus the gas has to be known, and only one gas can be sensed at a time). The detection threshold for NO2 in one of the diatom samples reached the sub-parts-per-million level. Contact Stefano Lettieri at [email protected].