Protein Detection Using Quadratic Fit Analysis near the Dirac Point of Graphene Field-Effect Biosensors

Although graphene-based biosensors provide extreme sensitivity for the detection of atoms, gases, and biomolecules, the specificity of graphene biosensors to the target molecules requires surface decoration of graphene with bifunctional linkers such as pyrene derivatives. Here, we demonstrate that the pyrene functionalization influences graphene's electrical properties by yielding partial formation of bilayer graphene, which was confirmed by the Raman 2D spectrum. Based on this observation, we introduce quadratic fit analysis of the nonlinear electrical behavior of pyrene-functionalized graphene near the Dirac point. Compared to the conventional linear fit analysis of the transconductance at a distance from the Dirac point, the quadratic fit analysis of the nonlinear transconductance near the Dirac point increased the overall protein detection sensitivity by a factor of 5. Furthermore, we show that both pyrene linkers and gating voltage near the Dirac point play critical roles in sensitive and reliable detection of proteins' biological activities with the graphene biosensors.