Resolution enhancement of plasmonic sensors by metal-insulator-metal structures

Optical sensors based on surface plasmons have attracted much attention over the past decades owing to the wealth of applications in bio- and chemical and gas sensing. In surface plasmon resonance sensors, a single metal layer is commonly used, but its resolution is limited because of broad resonances. In this context, we have developed a sensor chip based on a stack of metals and a dielectric, e.g. a metal-insulator-metal structure, consisting of a thick insulator layer sandwiched by metal layers, that exhibits a sharp resonance due to the excitation of surface plasmon polaritons hybrid modes. We have performed both experiments and theoretical simulations to estimate the enhancement of the sensitivity of such a structure. By changing the refractive index of an aqueous solution of glucose on top of the sensor chip, we found that the use of a metal-insulator-metal structure improves the figure of merit of the sensor 7.5 times compared to that of a conventional surface plasmon resonance sensor chip. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)