Interaction of graphene electrolyte gate field-effect transistor for detection of cortisol biomarker

We report on the development of graphene-based electrolyte-gate field-effect transistor (EGFET) for detection of cortisol hormone, a biomarker of stress. The EGFET was fabricated using silicon wafer as the substrate and conventional photolithography method was used to pattern the source, drain, and gate of the EGFET. Graphene was drop-coated on the sensing area of EGFET and was annealed to improve adhesion on the substrate. Graphene surface was functionalized with bifunctional linker molecule, l-pyrenebutanoic acid succinimidyl ester (PBASE). PBASE serve as linker, where the aromatic pyrenyl group of PBASE binds to the basal plane of graphene by π-π interaction, while the other end, succinimide group of PBASE binds to the amino group of cortisol antibody covalently via amide bond. Cortisol antibody was immobilized on the graphene surface for specific and sensitive detection of cortisol target hormone and ethanolamine was used to prevent non-specific binding. The device was introduced with varying concentration of cortisol target to study the effect of concentration on the graphene surface. Atomic Force Microscopy (AFM) was used to characterized the surface morphology of graphene nanoplatelets. The crystallinity structure and defect on the deposited graphene and the PBASE functionalized graphene was characterized using Raman Spectroscopy. The interaction between graphene with each modification step and the effect of varying concentration were studied in terms of the change in current-voltage measurement.