A method for detecting the presence of target molecules bound to a working electrode in a first location. The first location is coated with a detection solution containing labeling molecules that include a first charge-separation moiety attached to a first molecule that binds to the target molecule. The first charge-separation moiety includes a material that generates hole-electron pairs in response to being illuminated by light in a first band of wavelengths. After removing any unbound labeling, the working electrode is immersed in a solution containing a compound that is oxidized by the generated holes. The first location is then selectively illuminated with light in the first band; and the change in the current and/or potential is measured between the working electrode and a reference electrode in contact with the solution. The first charge-separation moiety is preferably constructed from particles of a semiconducting material such as TiO2.