The electrochemiluminescence (ECL) reaction sequence employed here is illustrated in Figure , following a scheme we had previously investigated. In this framework, ECL-active tris(bipyridine)ruthenium(II), or [Ru(bpy)3] 2+ , is suspended in solution within a nanofluidic channel with a height of 100 nm. Along a 20 µm channel segment, elec-; each electrode is individually addressed. [Ru(bpy)3] 2+ undergoes oxidation at the top electrode and reduction at the bottom electrode: