Toward understanding of transfer mechanism between electrochemiluminescent dyes and luminescent quantum dots.

Electrochemiluminescence resonance energy transfer (ECL-RET) based on dye-quantum dot (QD) hybrids, is a very powerful tool for chemical sensing and probing many important biological processes. In this work, we have investigated both electrochemiluminescence (ECL) and photoluminescence (PL) properties of the hybrid system, in which tris(2,2'-bipyridypruthenium(II) ([Ru(bpy)(3)](2+))/2-(dibutylamino)ethanol (DBAE) and QD are employed as the ECL donor and acceptor, respectively. Unexpectedly, we find that ECL of the [Ru(bpy)(3)](2+)/DBAE system can be efficiently quenched by various types of QDs. In addition, ECL quenching in the [Ru(bpy)(3)](2+)/DBAE system is independent of the core size and the surface charge of QDs, indicating that the quenching effect does not originate from resonance energy transfer between the [Ru(bpy)(3)](2+)/DBAE system and QDs. Photoluminescence properties of the hybrid system under electrochemical control and electron spin resonance (ESR) measurements further reveal that a charge transfer between QDs and the radical-state DBAE is responsible for ECL quenching in the [Ru(bpy)(3)](2+)/DBAE system. Contrary to previously published information, we propose that electron transfer, rather than energy transfer, dominates in the hybrid system under electrochemical control. We further demonstrate that such electron transfer could be switched to energy transfer by controlling the distance between [Ru(bpy)(3)](2+)/DBAE ECL and QDs. The energy/electron transfer process between [Ru(bpy)(3)](2+)/DBAE ECL and QDs is implemented to develop a novel platform for immune sensing.