Sensitive Chemical Optic Sensor Using Birefringent Porous Glass for the Detection of Volatile Organic Compounds

A simple design involving a birefringent porous glass oriented between two crossed polarizers serves as the foundation for an optically based sensitive broad-spectrum chemical sensor. Volatile organic compounds (VOCs) such as acetonitrile vapors can be readily detected at concentrations of as low as 50 ppm. Changes are observed in polarized light transmitted by the anisotropic porous material constituting the sensor, upon exposure to VOC-bearing air, as intensity changes at a defined wavelength or as changes in spectral content (color) detectable by the eye. The optical effects resulting from exposure to various vapors are reversible and may result from adsorption of solvent vapors with attendant reduction of anisotropy. The microporous structure as well as the surface chemistry of the sensor may be controlled for tuning the response to VOCs for industrial applications. Miniaturization of the sensor using low-cost materials such as plastic or glass optical fibers, Polaroid films, and birefringent porous glass is demonstrated. The sensor described in this paper could use ambient light as source and the eye as detector (color change) or electronically controlled light emission and detection for better sensitivity and real time monitoring of VOCs. Such intrinsic explosion proof sensors could be used to safely monitor VOC levels in remote environments.