Inverse DVD-R grating structured SPR sensor platform with high sensitivity and figure of merit

The figure of merit (FOM, 1/RIU) 112.34 is achieved in the Au-covered epoxy grating (Au/Epoxy) with the inverse structure of the original track pitch DVD-R. The feasible exfoliation of the cured epoxy resin from the Au-covered polycarbonate (PC) gratings (Au/PC) of DVD-R grating creates a narrow deep channel structure. As well as Au/PC, newly created Au/Epoxy gratings glow beautifully with rainbow-colored stripes on the surface due to the constructive interference of visible light. The SEM and 3D-AFM images show that the surface distortion of the Au/Epoxy grating is −0.58 (negative) and that of the Au/PC grating is 0.14 (positive). The Au/Epoxy grating exhibits 872.01 nm/RIU with slightly lower sensitivity than the Au/PC grating (887.59 nm/RIU). However, the Au/Epoxy grating shows a total of 7.76 ± 0.53 nm with up to full width half maximum (FWHM) for the SPR dip during the detection test, so a high FOM of 112.34 can be achieved. In addition, the FDTD simulation shows the experimental results as well as the relevant results of the SPR deep wavelength and FWHM. Finally, the Au/Epoxy grating shows a more pronounced resonance for methanol concentration measurements than the Au/PC grating due to the high FOM and strong adhesion between the Au layer and the epoxy substrate.