SO2 Gas Sensing by Nanometer-Thick Soap Films Using Conductometry and Fluorimetry

Conductometric and fluorometric sensing of SO2 gas using common black films (CBF) of nanometer thickness (<20 nm) with large specific surface area (about 108 m-1) was shown. For conductometry, H2O2 molecules in the soap film oxidized SO2 and increased the conductance by producing H3O+, HSO4-, and SO42- ions. Limit of detection (LOD) for this assay was 70 parts per billion (ppb), and a linear signal-concentration relation was seen up to 1 ppm (ppm) of SO2 in the air. In the 1-25 ppm range, a monotonic yet nonlinear increasing correlation was seen. For fluorimetry, SO2 reacted quantitatively with Rhodamine B hydrazide in CBF to form highly fluorescent Rhodamine B molecules. The LOD was 100 ppb, and a linear signal-concentration relation was seen for 0.1-25 ppm of SO2 in the air. Sensing of SO2 released by wine and beer samples was also demonstrated.