Tuning Viscosity and Spin Time to Enhance the Thinnest rGO Film Coating in SPR Sensors

This study examined the optimization of the solution viscosity and spin-coating time to produce thin and uniform rGO layers for surface plasmon resonance (SPR) sensor applications. The viscosity of the rGO solution was controlled by varying the concentration of ascorbic acid as a reducing agent in the rGO synthesis process. Then, characterization was performed using FESEM-EDX, TEM, and thickness and roughness measurements using a topography measurement system (TMS). The characterization results demonstrated that increasing the solution viscosity was directly proportional to the layer thickness, roughness, and the percentage of carbon elements, as determined by EDX mapping. The SEM and TEM analyses revealed a surface morphology that resembled wrinkled paper structures, which overlapped and folded. The SAED pattern indicated the presence of crystallinity relating to the (002), (100), and (110) crystal planes. In addition, as the spin-coating time increased, the thickness and roughness of the layer decreased; however, the thickness-to-roughness ratio increased. SPR sensor testing with the rGO layer was also conducted using ethanol solution analytes with concentrations ranging from 0 to 20%. The results demonstrated that the SPR sensor with the rGO layer exhibited a sensitivity of 2481.42 nm/RIU and a linearity of R² = 0.96.