Highly sensitive surface plasmon resonance-based sensor using green synthesized Fe3O4/rGO interface layer utilizing plant leaf extracts for alcohol compound detection

Abstract

In this study, a fast response, real time, accurate, and non destructive alcohol detection method using surface plasmon resonance (SPR) technique was purposed. The SPR measurement was performed using 5-layers Krestchmann configuration with a layer structure of prism/Au thin film/Fe₃O₄/rGO nanocomposite/alcohol compounds/air. The Fe₃O₄/rGO nanocomposite was successfully synthesized using the green route utilizing Moringa oleifera and Amaranthus viridis leaf extract. X-ray diffraction analysis showed the nanocomposite has a face-centered cubic with an inverse spinel structure with a crystallite size of 5.6–5.8 nm. The size of Fe₃O₄ NPs in the Fe₃O₄/rGO nanocomposite was variated from 10.6–13.0 nm and showed that there is no impurities in the sample. Fourier transform infra-red analysis also validates the existence of Fe₃O₄ and rGO indicated by the FeO and CC bond, respectively. The interaction between Fe₃O₄ and rGO can also be observed through the coordinational bonding FeOC, which is validated by the presence of FeO and CO bonds. The optical properties were studied using ultraviolet–visible spectroscopy, which shows an energy gap of 2.36 eV. Magnetic properties of Fe₃O₄/rGO nanocomposite show a superparamagnetic characteristic with the saturation magnetization of 40.53 emu/g, magnetic susceptibility of 3.62 $\times$ 10⁻², and the domain size is 6.22 nm. The SPR angle shifts when applied with Fe₃O₄/rGO nanocomposite. The addition of alcohol compound further shifted the SPR angle by 0.22°, 0.61°, and 1.19° for methanol, ethanol, and IPA, respectively. This noticeable shift shows a possibility for early detection to differentiate these 3 compounds. The presence of a magnetic field further shifts the SPR angle by 0.08°, 0.08°, and 0.10° for 40, 60, and 80 Oe, which indicates an increase in sensitivity. Therefore, the combination of applied magnetic field and green synthesized Fe₃O₄/rGO nanocomposite as an eco-friendly interface layer are potential to enhance the sensitivity of SPR to detect the alcohol compounds.