Volatile-organic-compound optic fiber sensor using a gold-silver vapochromic complex

Abstract

We describe a new gold-silver complex based on 2,2-bipyridine, whose formula is {Au2Ag2(C6F5)4[(C5H4N)-(C5H4N)]2}n, used to detect volatile organic compounds (VOCs) such as ethanol, methanol, and acetic acid. This organometallic material is presented in the form of bright yellow powder, and suffers a change in its optical properties when it is exposed to VOCs. A new fiber optic sensor is presented based on the properties of a new vapochromic material. The sensor works in a reflection configuration and consists of an optic fiber pigtail (core diameter is 200 µm and cladding is 230 µm) on the cleaved end of which the vapochromic material, previously mixed with a commercially available solvent, Liquicoat®, is deposited by using the dip-coating technique. Using an optical source and a photodetector, it is possible to detect and quantify the change in reflected intensity-modulated signal when the sensor is exposed to VOC inside a sealed chamber. This behavior can be related to the VOC concentration. The study of the sensor's response is made at a specific wavelength for different VOC concentrations. Limits of detection of 2.16, 1.73, and 3.73 mg/L of vapors of ethanol, methanol, and acetic acid vapors, respectively, are attained.