The physical and chemical properties of graphene are strongly dependent on its surface termination, and controlled tailoring of surface functional groups in this fascinating two-dimensional material will expand its applicability to a wider range of fields. One way to profit from the excellent electronic properties of graphene is through its use in field-effect transistors (FETs). In this chapter, the importance of the choice of the surface chemistry to anchor bioreceptor onto a graphene-based FET (GFET) will be systematically explained using the sensing of cardiac troponin I (cTnI) as model analyte. cTnI bioreceptor integration using diazonium chemistry and the subsequent effects on the electrical properties will be revisited. This covalent ligand attachment will be compared to noncovalent strategies based on the use of heterojunction pyrene ligands attached to graphene nanosheets for cTnI sensing. cTnI, a non-glycosylated polypeptide of 222 amino acids, is a subtype of the troponin family and its commonly used as a marker for myocardial damage as it is detected in the serum only if myocardial injury has occurred. Serum levels can indeed differentiate between low (<15 pg ml −1 ), medium (15 pg ml −1  > c-TnI <500 ml −1 ), and severe (>500 pg ml −1 ) myocardial injury in people with chest pain. It will be shown that using a cTnI aptamer as a bioreceptor results in GFET sensors adequate to differentiate low-medium and severe myocardial injury in patients' samples with high potential as point-of-care testing concept.