The presence of a nucleic acid target, molecule or ligand can be detected by hybridization, antigen-antibody reaction or receptor-ligand binding. This is reported by the strategic positioning of a first probe and a second probe attached to a small particle of electrical conductor, which closes an electrical circuit, thereby reporting the event. A myriad of potential applications of this technique include the identification and detection of small amounts of nucleic acids by hybridization, the detection of molecules such as toxins and carcinogens by antigen-antibody reaction and the detection of other molecules by receptor-ligand interaction. The method can also be adapted to assay the quantity of a given substance using the principle of competitive binding.