MIT Develops Optical Gas Sensors with Ten in a Million Parts Sensitivity
24 June 2014
Researchers from the Massachusetts Institute of Technology (MIT) have developed a method to detect extremely low concentrations of gases with optical sensors that use microscopic polymer light resonators expanding in the presence of specific elements.
A team from the Institute's Quantum Photonics Laboratory in Cambridge have fabricated cavities ten micrometers by 600 nanometers wide in a poly methyl methacrylate (PMMA) film 400 nanometers thick. These wavelength-scale photonic crystal cavities swell when they make contact with a specific type of target gas.
The polymer itself emits light selectively at a resonant wavelength after being infused with fluorescent dye. During this process, called the Purcell effect, a specific color of light bounces back and forth, reflected a thousand times within the polymer before leaking into a spectral filter which is able to detect subtle color shifts even if they occur at a sub-nanometer level in the cavity. This reveals the concentration of gas.
The method provides high versatility because the PMMA lends itself to treatment making it interact specifically with a wide variety of target chemicals. Therefore, sensor systems based on that approach can be applied in multiple settings - from the chemical industry, through homeland security to medical uses.
The technology's possible adaption in various industries is also very likely, because the polymers are easily reusable: once the gas that swells them is removed, they shrink back to their previous length. Currently, the method can achieve sensitivity of ten parts per million but, according to the research team, through refining it can become even more precise, detecting gases with part-per-billion concentration levels.