The invention relates to an apparatus and to a method for detecting and/or quantifying mercuric ions, Hg2+. The apparatus of the invention is of the type comprising an electrical device comprising two electrodes and a substrate comprising at least one surface made of an organic or inorganic semiconductor material, the electrodes being in electrical contact with said organic or inorganic semiconductor material, and a device for measuring the variation in the conduction current between the two electrodes, and wherein at least one compound which complexes mercuric ions Hg2+, selected from a dithia-dioxa-monoaza crown ether compound, an N,N-di(hydroxyethyl)amine, an N,N-di(carboxyethyl)amine, and mixtures of two at least of these compounds, is bonded to said semiconductor material or to an electrode of said electrical device. The invention finds application in the field of the detection of mercuric ions, in particular.