Reaction-based turn-on electrochemiluminescent sensor with a ruthenium(II) complex for selective detection of...

Hydrogen sulfide (H2S) has been drawing increasing attention because it plays an important role in the nervous system and has been deemed as a third endogenous gas signal molecule besides nitric oxide (NO) and carbon monoxide (CO). In this study, using a ruthenium complex, [Ru(bpy)2(bpy-DPA)Cu](4+) (where bpy = 2,2'-bipyridine and bpy-DPA = 4-methyl-4'-[N,N-bis(2-picolyl)aminomethylene]-2,2'-bipyridine) as recognition unit, we report a new reaction-based turn-on electrochemiluminescent (ECL) sensor to selectively detect extracellular H2S in rat brain, coupled with in vivo microdialysis for dialysate sampling. To prepare the sensor for sensing endogenous H2S, [Ru(bpy)2(bpy-DPA)](2+) is first designed and synthesized, showing high ECL efficiency with tri-n-propylamine (TPA) as a coreactant and quenching after reaction with Cu(2+) (forming [Ru(bpy)2(bpy-DPA)Cu](4+)). Then a Nafion membrane is coated on the surface of glassy carbon (GC) electrode and [Ru(bpy)2(bpy-DPA)Cu](4+) is confined onto the Nafion membrane through ion exchange. The resulting [Ru(bpy)2(bpy-DPA)Cu](4+)/Nafion/GC sensor exhibits a low ECL signal. The [Ru(bpy)2(bpy-DPA)Cu](4+)/Nafion/GC sensor demonstrates enhanced ECL signal after reacting with volatile H2S due to the high-affinity binding between sulfur and Cu(2+), returning to [Ru(bpy)2(bpy-DPA)](2+)/Nafion/GC. The changes of ECL signal at the sensor depend linearly on the concentration of Na2S in the range from 0.5 to 10 μM, with a detection limit of 0.25 μM. Moreover, the sensor demonstrates high selectivity, free from interference especially by other nonvolatile thiol-containing species, such as cysteine and glutathione. The basal dialysate level of H2S in the microdialysate from the cortex of adult male Sprague-Dawley rats is determined to be 2.3 ± 0.9 μM (n = 4). This method is reliable and is envisaged to help understand the regulation of H2S in physiological and pathological events.