Enhanced color sensitivity by coupling of surface plasmon and fabry-perot resonances for spectrometer-free and label-free biosensing

Abstract

Plasmonic sensors have received much attention in recent years since they are highly sensitive to the refractive index changes of surrounding dielectric and can be applied to spectrometer-free biosensing. In particular, the sensing based on the color factors and the imaging is considered as a powerful method due to its simplified sensing process as well as high sensitivity with high spatial resolution. Herein, we report on improvement in the color sensitivity to the refractive index changes by employing an aluminum-silicon dioxide-aluminum (AOA) structure consisted of the Fabry-Perot (FP) cavity sandwiched between double surface plasmonic (SP) layers. The coupling of SP and FP resonances in aluminum nanohole arrays and silicon dioxide cavity lead to the synergistic or attenuated change in transmission spectra and colors. Therefore, as optimizing the coupling of the resonances to increase the color change, it is possible to obtain enhanced color sensitivity and more accurate refractive index prediction. Color sensitivities up to 122.29 (L*), 169.58 (a*), and 174.72 (b*) RIU−1 of the CIELAB color space are achieved through imaging process and statistical analysis. Uniform and sensitive sensing factors of AOA sensors can distinguish the concentration difference of bovine serum albumin (BSA) with a limit of detection of 9 × 10-4 RIU. Moreover, this approach confirms the possibility of being used for in vivo detection by observing the intracellular structure of HEK-293 cells. Our AOA sensor suggests a great potential to be utilized as a spectrometer-free, label-free, and functionalization-free detection of the refractive index and the transparent biomaterials. © 2020 Elsevier B.V.