Fig. 1

Proposed refractive index sensor for formalin detection: (a) top view, (b) 3D view, and (c) front view of the design and (d) depicts the design materials used in the sensor. Key parameters include: structure length and width, T = 20 μm for the structure’s thickness, a SiO2 layer with a thickness of J = 1 μm, analyte thickness S = 4 μm, graphene metasurfaces layer height set to 0.34 nm, and a central circle radius C = 4.3 μm.