Electrogenerated chemiluminescence of lucigenin enhanced by the modifications of electrodes with self-assembled monolayers and of solutions with surfactants

Electrogenerated chemiluminescence (ECL) of lucigenin (Luc2+·2NO−3, N,N′-dimethyl-9,9′-biacridinium dinitrate) in dioxygen-saturated alkaline aqueous solutions of pH 10 has been examined utilizing modifications of electrodes (i.e. self-assembled monolayer (SAM)-modified gold electrodes) and of solutions (i.e. micellar solutions containing a nonionic surfactant, Triton X-100) for the first time. In both cases of the modifications, enhanced ECL was observed, and the ECL was considered to be derived from the decomposition of a dioxetane-type intermediate formed by the radical–radical coupling reaction between an electrogenerated superoxide ion (O2−) and a one-electron reduced form of Luc2+ (i.e. a radical cation, Luc+). The surface modification of gold electrodes was achieved with dimercaptosuccinic acid (DMSA) and dl-thioctic acid (dl-TA) having carboxyl end groups. The amount of ECL at dl-TA-SAM-modified electrodes was about five times as great as that at the bare electrode. The enhancement of ECL at the SAM-modified electrodes would be due to the concentration effect of positively charged Luc2+ ions, the prevention of adsorption of the electrogenerated chemiluminescent product (i.e. N-methylacridone (NMA)) and the two-electron reduced form of Luc2+ (Luc0) on the electrode surfaces, and the effective generation of O2−. On the other hand, the amount of ECL in the micellar solution increased by about six times in comparison with that in the solution containing no surfactant. The enhanced ECL in micellar solutions would result mainly from the inhibition of adsorption of NMA and Luc0 insoluble in water on electrode surfaces.