Sensitivity Enhancement of Hybrid Two-Dimensional Nanomaterials-Based Surface Plasmon Resonance Biosensor

Abstract

In this work, we designed structures based on copper nanosubstrate with graphene and two-dimensional transition metal dichalcogenides (TMDC) in order to achieve an ultrasensitive surface plasmon resonance biosensor. This system contains seven components: SF11 triangular prism, BK-7 glass, Chromium (Cr) adhesion layer, thin copper film, layers of one of the types of transition metal dichalcogenides: MoS₂, MoSe₂, WS₂ or WSe₂ (defined as MX₂), graphene, sensing layer with biomolecular analyte. Copper was chosen as a plasmonic material because it has a higher conductivity than gold which is commonly used in plasmonic sensors. Moreover, copper is a cheap and widespread material that is easy to produce on a large scale. We have carried out both theoretical and numerical sensitivity calculations of these kinds of structures using the Goos-Hänchen (GH) shift method. GH shift is lateral position displacement of the p-polarized reflected beam from a boundary of two media having different indices of refraction under total internal reflection condition and its value can be retrieved from the phase change of the beam. The SPR signal based on the GH shift is much more sensitive compared to other methods, including angular and wavelength scanning, due to much more abrupt phase change of the SPR reflected light than its intensity ones. By optimizing the parameters of the SPR sensing substrate, such as thickness of copper, number of layers of 2D materials and excitation wavelength, we theoretically showed an enhanced sensitivity with a detection limit 10^-9 refractive index unit (RIU).

Keywords: biosensors; graphene; plasmonics; surface plasmon resonance.

Figure 1

Schematic picture of Cu—TMDCs—graphene enhanced SPR biosensor system. The difference of GH shift for TM and TE waves are measured in order to improve the signal to noise ratio since the signals for TE waves can be used as a reference.

Figure 2

Reflectivity of the structure with 5 layers of WSe₂ and 35 nm of Cu depending on the angle of incidence (degrees).

Figure 3

Phase calculations (a) and GH shift values (b) of the structure with 5 layers of WSe₂ and 35 nm of Cu depending on the angle of incidence (degrees).

Figure 4

The sensitivity values of the enhanced model by number of TMDC layers with 40 nm of copper: (a) The wavelengths are 600 nm and 660 nm for MoS₂ layers; (b) the schematic structure; (c) The wavelengths are 600 nm, 660 nm, and 785 nm for MoSe₂ layers; (d) The wavelength is 600 nm for WSe₂ layers and 40 nm of Cu.

Figure 5

The sensitivity values of the enhanced model with 1 layer of graphene by TMDC layers and thickness of copper: (a) The wavelengths are 633 nm and 785 nm for MoS₂ layers with 45 nm of copper; (b) the schematic structure; (c) The wavelengths are 600 nm and 785 nm for MoSe₂ layers with 40 nm of copper; (d) The wavelength is 633 nm for MoSe₂ layers with 45 nm of copper.

Figure 6

The sensitivity values of the enhanced model with 2 layers of graphene by TMDC layers and thickness of copper: (a) The wavelengths are 600 nm and 633 nm for MoS₂ layers with 40 nm of copper; (b) the schematic structure; (c) The wavelength is 1024 nm for MoSe₂ layers with 35 nm of copper.

Figure 7

The sensitivity values of the enhanced model with 2 layers of graphene by TMDC layers and thickness copper: (a) The wavelength is 1024 nm for WSe₂ layers with 35 nm of copper; (b) the schematic structure; (c) The wavelength is 1024 nm for WSe₂ layers with 45 nm of copper.