**4. Conclusion**

Graphene has been called a "wonder material" based on its electrical, mechanical, and chemical properties, and the numerous fields and applications have come to be used. It is not a surprise that the 2010 Nobel Prize for Physics was conferred to Drs. Andrew Geim and Konstantin Novoselov for their experimental work on graphene.

Based on its properties, graphene has become a much-preferred material to increase the sensitivity of SPR sensors. In this work, we present the idea of biasing a multimaterial-graphene sensor surface structure to tune the refractive index of graphene thereby providing a significant enhancement in sensitivity. In this work, we have shown that the sensitivity of a Au-MoS2-Gr sensor system can be used to detect urea of 10 nm thickness sample layer and while the refractive index of the urea changes from n = 1.332 to 1.335, a change of 3/1000. Application of electrical bias across the metal-Gr layer structure tends to provide a strong excitation of the surface plasmon, which results in a very small reflectance at the SPR angle, which facilitates far better measurement. It should be noted that this increase in sensitivity is in addition to whatever the sensitivity original unbiased graphene-metal-based sensor structure may provide. Thus, the fact that the superior and more favorable electrical and electromagnetic properties of graphene facilitate the application of electrical bias across it, resulting in a high sensitivity of the graphene-based SPR biosensor system.
