Blue-shift ultrasensitivity using rhombus-shape plasmonic crystal on Si3N4 membrane
Foozieh Sohrabi1,2, Dordaneh Etezadi2, Yasaman Jahani2, Ershad Mohammadi2,3, Bahareh Ghadiani2, Mahdi Tamizifar2, Seyedeh Mehri Hamidi1,*
Harnessing ultrasensitivity from optical structures to detect tiny changes in the targeted samples is the main goal of scientists in the field of sensor design. In this study, an uncommon rhombus-shape plasmonic structure is proposed for providing blue-shift ultrasensitivity. The physical origin of this optical response relies on multi-faces of gold rhombus and their electromagnetic coupling with their induced images in a high-refractive-index substrate (Si3N4). A characteristic of blue-shift emerges as the Fano resonance in the reflection spectrum. We have experimentally shown that this novel structure has the surface sensitivity to the refractive index difference in the order of 10-5. This characteristic have been applied for non- and conditioned- cell culture medium with refractive difference in this order. Such a level of sensitivity is interesting for enhanced fingerprinting of minute quantities of targeted molecules and the interfacial ion redistribution.