In situ activation of CdS electrochemiluminescence film and its application in H₂S detection

Nanocrystals (NCs) usually suffer from weak electrogenerated chemiluminescence (ECL) emissions compared with conventional luminescent reagents like Ru(bpy)3(2+). In this work, we proposed a simple in situ activation approach by dipping CdS NCs film on glass carbon electrode (CdS NCs/GCE) in an activation solution containing H2O2 and citric acid, resulting in a ~58-fold enhancement of ECL intensity in the presence of coreactant H2O2. During activation, CdS NCs were oxidized by H2O2 to smaller ones which resulted in more surface S vacancies; meanwhile, citric acid played an important role in stabilizing NCs. The ECL enhancing mechanism was investigated in detail, and the coordination of H2O2 to surface excess Cd(2+) ions (S vacancies) on the CdS NCs surface formed in activation was the main factor which could stabilize the electrogenerated radicals, resulting in an enhanced ECL. ECL from the activated CdS NCs/GCE could be quenched in Na2S solution due to the bonding of S(II) to excess Cd(2+) ions on the surface of CdS NCs. On the basis of this, we then used the activated CdS NCs/GCE as an ECL probe for the detection of Na2S which showed good performance including a wide linear range of 5 nM to 20 μM and good anti-interference ability. Moreover, this ECL probe was successfully applied for hydrogen sulfide (H2S) detection in a biological system.