In this thesis, single-layer graphene (SLG)-based field-effect devices were built to realize two different sensors: a pH sensor and a sensor measuring the concentration of the chemokine CXCL8 in clinical samples. CXCL8 is a signal protein that has various promising new applications in the field of disease diagnostics.20 For building these devices, a recently proposed new functionalization approach for graphene was employed.78 The approach is based on the assembly of an all-carbon van der Waals (vdW) heterostructure of carbon nanomembrane (CNM) and SLG. The effect of different substrates including SiO2, poly(ethylene 2,6-naphthalate) (PEN) and SiC and different types of SLG including graphene grown by chemical vapor deposition (CVD), epitaxial graphene, and nanoporous graphene (NPSLG) on the sensor response was investigated. Devices of increasing complexity were designed and investigated. At first, devices for measurements in vacuum. As a next step, devices for measurements of the pH value, and as final step the devices for biosensing. The fabrication of devices included their successive optimization based on transport measurements, electrical impedance spectroscopy (EIS) measurements, and surface sensitive characterization techniques. The device concept was the solution-gated field-effect transistor (SGFET),33 which has promising applications for point-of-care devices247 and lab-onchip technology.