Use of graphene oxide as an active layer on a tapered fibre for detection of volatile liquid vapours: ammonium hydroxide, trimethyl phosphate, and 1,4-thioxane

This paper investigates the application of a G-Flake graphene oxide (GO) layer as an innovative coating material for optical fibre tapers, enhancing the sensor sensitivity to various volatile liquid vapours. The results confirm that this combination is effective because the formation of a monolayer of adsorbed gas alters light propagation in the tapered optical fibre. These changes are detectable across a broad wavelength spectrum, ranging from visible to infrared. In this study, three volatile liquids – trimethyl phosphate (TMP), 1,4-thioxane (THX), and ammonium hydroxide (NH4OH) – were tested using pure THX and TMP without dilution, while NH4OH was applied as a 25% solution. The gases used in the research simulate chemical warfare agents, such as sulphur mustard and sarin. The authors used the differential method to analyse the results, which revealed the formation of characteristic peak pairs around a wavelength of 795 nm. The peak heights and the distance between them varied over time in response to exposure to the selected vapours. Additionally, the amplitude of the transmitted power changes linearly in the first 30–45 min, with the highest power change rate observed for TMP (0.026 dBm/min at 789.2 nm). The greatest contrast between maximum and minimum power levels was observed for TMP, reaching 4.45 dBm. An approach was presented that demonstrates how a tapered fibre covered with GO can be used as the basis for developing a low-cost gas and vapour sensor.