Optical fibre sensors based on vapochromic gold complexes for environmental applications

A new vapochromic material based on a gold-silver complex and diphenylacetyl, of formula [Au₂Ag₂(C₆F ₅)₄(C₆H₅CCC₆H ₅)], has been developed and used for the detection of some volatile organic compounds (VOCs). The material is presented in the form of dark green powders. When the powders are in presence of VOC, its colour changes, yielding to a change in its optical properties. The sensor consists of an optical fibre pigtail onto the cleaved end of which the vapochromic material was deposited. The fibre has a core diameter of 200 μm and a plastic cladding. A commercially available solvent, Liquicoat^c is used to create a solution, capable of being fixed onto the fibre. The fibre optic sensor is employed in a reflection scheme, so the other extreme of the optical fibre pigtail is connected to an optical coupler, completing the set-up with an optical source to generate the interrogating signal and an optical detector to measure the received intensity-modulated signal. The behavior of the sensor has been studied for different wavelengths for different concentrations of several VOC. Changes up to 2.5 dB in the reflected optical power were detected.