AbstractA pencil graphite electrode (PeGE) modified with copper nanoparticles (CuNPs) was employed for sensitive electrochemical detection of adenine (Ade). The CuNPs were synthesized by the chemical reduction of copper (II) sulphate by borohydride in the presence of polyvinylpyrrolidone (PVP) and immobilized onto the electrode surface by means of physical adsorption. The cyclic voltammetry (CV) results illustrate that the CuNP‐modified PeGE provides at least fivefold increase of Ade oxidation peaks compared to the bare PeGE. The detection limit in CV corresponds to value of 200 nM. The accumulation of Ade through the complex with Cu (I) allows us to introduce the novel biosensor for the determination not only of adenine but also purines capable to form analogical Cu (I) complexes.