TUESDAY, 10 MAY 2011. Photonic crystals have alternating regions of high and low dielectric constants that only allow certain wavelengths to propagate through the material. As a result of this crystalline nature, these new sensors are coloured, and their colour changes when they adsorb organic compounds. They are less than 0.1mm in diameter, but are sensitive enough to detect common solvents such as toluene at concentrations of one part per million.
The production of a small, sensitive, efficient and cost-effective sensor has long been a much-needed improvement for the gas masks worn by emergency workers. These respirators protect the user by filtering air through a canister filled with activated charcoal. Airborne toxins stick to the filters but the point at which they become saturated is only estimated on safety protocols based on the amount of time the respirator has been in use. A sensor that is carbon-based would be ideal for indicating exactly when a respirator's filters have been saturated and is therefore no longer providing protection  .
Written by Stephanie Boardman