Abstract Alzheimer's disease (AD) is a neurodegenerative disorder with a high negative impact in terms of cost and social issues. New kinds of noninvasive, reliable, easy‐to‐use, and cheap biosensors are highly desired. In this work, the use of graphene oxide (GO) sheets functionalized with the peg 4 ‐KLVFF peptide conjugate is reported as a sensing layer for the detection of Aβ 42 protein, a key AD biomarker. An optimized synthetic protocol provides a suitable GO/peptide‐functionalized layer without extensively modifying the planar structure of GO. The nature of the bonds involved in the functionalization process is highlighted through Fourier Transform Infrared Spectroscopy (FTIR) and X‐ray photoelectron spectroscopy (XPS) analyses. The covalently functionalized material (GO@peg 4 ‐KLVFF) is deposited by dielectrophoresis (DEP) between two metal electrodes, forming the sensitive layer. The devices show a selective and linear electrical response as a function of Aβ 42 concentrations. The selectivity toward Aβ 42 is validated using two different scrambled sequences of the amyloid‐β peptides (Aβ 42s , Aβ 40s ) as well as the Tau 26–44 peptide. The different electrical behaviors are discussed in detail and explained by simulating, at the molecular level, the interaction of the different Aβ peptides with GO and KLVFF. Potential chemical interactions are explored, including charge transfer between the peptides and GO.