A lab-on-a-chip (LOC) device for detecting a target nucleic acid sequence in a sample, the LOC device having probes with a nucleic acid sequence complementary to the target nucleic acid sequence for forming probe-target hybrids, and an electrochemiluminescent (ECL) luminophore, electrodes for generating an excited state in the ECL luminophore in which the ECL luminophore emits photons of light, and, a photosensor for sensing the photons emitted from the ECL luminophore, wherein, the electrodes are plates of conductive material, the plates having peripheral edges optically coupled to the photosensor.