Masruroh, Freygieon Ogiek Rizal Sukma, Syahidatun Na'imah, Mahardika Auditia Hanif, Dionysius J.D.H. Santjojo, Retna Apsari, Sulaiman Wadi Harun
The limited evanescent wave penetration depth makes the thickness of the functionalized sensing layer a critical parameter in determining the performance of surface plasmon resonance (SPR) sensors. Variations in layer thickness can significantly affect the optical properties of the sensing interface and, consequently, the SPR response. In this work, reduced graphene oxide (rGO) was synthesized through ascorbic acid reduction and spin-coated onto gold-coated prisms for ethanol-in-water detection. The influence of rGO layer thickness on SPR resonance was investigated by varying the spin-coating speed from 2200 to 3000 rpm, with higher spin speeds producing thinner rGO layers. SEM analysis revealed characteristic wrinkled surface morphology and interlayer gaps in the cross-sectional structure, confirming the formation of typical rGO layers. FTIR spectroscopy verified the successful reduction of graphene oxide, while Raman spectroscopy showed an increase in the D-to-G peak intensity ratio as the rGO layer thickness increased, indicating greater structural disorder in thicker films. SPR measurements showed that only rGO layers with thicknesses below 632.8 nm, obtained at spin speeds of 2800 and 3000 rpm, were able to support SPR excitation. The resonance angle increased with increasing rGO thickness; however, excessively thick layers hindered the interaction between incident light and surface plasmons, as evidenced by reduced SPR reflectance. Among the tested samples, the rGO-coated sensor at 3000 rpm exhibited the best performance, achieving an enhanced sensitivity of 2108°/RIU with improved linearity than uncoated sensor. This sensitivity is also higher than those reported for several carbon-based SPR sensors using the Kretschmann configuration. © 2026 The Author(s).
Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Brawijaya, Malang, Indonesia; Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Udayana, Bali, Indonesia; Department of Physics, Faculty of Science and Technology, Universitas Airlangga, Surabaya, Indonesia; Department of Electrical Engineering, Faculty of Engineering, Universiti Malaya, Kuala Lumpur, 50603, Malaysia; Research Center for Photonic and Plasmonic Materials, University of Brawijaya, Jl Veteran 12-16, Malang, 65145, Indonesia; Research Center for Advanced System and Material Technology, University of Brawijaya, Jl Veteran 12-16, Malang, 65145, Indonesia
