A critical analysis on the sensitivity enhancement of surface plasmon resonance sensors with graphene

TL;DR

This paper critically examines how different models of graphene affect the perceived sensitivity enhancement in surface plasmon resonance sensors, revealing that only an inaccurate isotropic model suggests significant improvements.

Contribution

The study compares three models of graphene in SPR sensors and shows that only the isotropic approximation falsely indicates sensitivity gains, emphasizing the need for accurate modeling.

Findings

Isotropic model predicts significant sensitivity increase.

Accurate models show negligible sensitivity enhancement.

Model choice critically affects perceived sensor performance.

Abstract

The use of graphene in surface plasmon resonance sensors, covering a metallic (plasmonic) film, has a number of demonstrated advantages, such protecting the film against corrosion/oxidation and facilitating the introduction of functional groups for selective sensing. Recently, a number of works have claimed that few-layer graphene can also increase the sensitivity of the sensor. However, graphene was treated as an isotropic thin film, with an out-of-plane refractive index that is identical to the in-plane index. Here, we critically examine the role of single and few layers of graphene in the sensitivity enhancement of surface plasmon resonance sensors. Graphene is introduced over the metallic film via three different descriptions: as an atomic-thick two-dimensional sheet, as a thin effective isotropic material (same conductivity in the three coordinate directions), and as an non-isotropic layer (different conductivity in the perpendicular direction to the two-dimensional plane). We find that only the isotropic layer model, which is known to be incorrect for the optically modelling of graphene, provides sizeable sensitivity increases, while the other, more accurate, models lead to negligible contribution to the sensitivity.