Aqueous Gold Nanoparticle Solutions for Improved Efficiency in Electrogenerated Chemiluminescent Reactions

The efficiency of the high-energy electrogenerated chemiluminescence (ECL) tris(2,2′-bipyridine)ruthenium(II)/oxalate reaction was determined in the presence of citrate-coated gold nanoparticle (AuNPs) aqueous solutions. The ECL efficiency (ΦECL) for this reaction is enhanced by the addition of increasing amounts of AuNPs, followed by a sharp decrease when [AuNPs] is higher than 1.6 × 10–8 M. To explain this ΦECL/[AuNPs] trend, photoluminescent (PL) quenching, transmission electronic microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) measurements were also performed as well as redox potentials for the [Ru(bpy)3]3+/2+ couple. Two facts were noteworthy: First, there is an increase in ΦECL, which accompanies an energy transfer effect by coupling between the Ru(II) complex ECL emission band and the AuNPs surface plasmon resonance (SPR)-induced band. This coupling, which we have called the ECL-SPR effect, enabled the quantifying of a coefficient (KECL-SPR, ECL-SPR effectiveness) for the improved ΦECL of the tris(2,2′-bipyridine)ruthenium(II)/oxalate reaction, which turned out to be about 3.5 times higher than the quenching constant for the [Ru(bpy)3]2+/Au@citrate system. This ECL-SPR effectiveness is the basis for applying the ECL-SPR coupling effect in a given reaction. Specifically, it measures the degree to which an ECL reaction has been improved. Second, a metal nanostructure is generated in the solution due to a sufficiently strong electrostatic binding between the Ru(II) complex and the AuNPs, which is revealed through TEM and EDS measurements and the redox potential trend.