Interparticle Charge Transport Enhances Electrochemiluminescence of Quantum Dots

Quantum dots (QD) have been gaining popularity within the field of biomedical diagnostics research because of their unique electrochemiluminescence (ECL) properties. During the past two decades, great efforts have been devoted to the development of ECL luminophores and coreactants. However, the current understanding of ECL generation upon QDs is largely inherited from the theories developed by Bard and coworkers. Two types of charge-transfer mechanisms have been postulated for ECL generation: (i) intraparticle charge-transfer between coreactant radical and QD radical, (ii) interparticle charge-transfer between opposite-charged QD radicals. The manipulation and effective probing of these routes remain a fundamental challenge due to the extremely short lifetime of radicals and their stochastic collisions. In this chapter, we designed QD aerogels as luminophores to elucidate the charge-transfer mechanisms for ECL generation. The CdSe QD aerogel prepared via a versatile water-induced gelation strategy was used for designing novel ECL luminophores. The efficient charge transport and greatly improved ECL efficiency based on the strong electronic coupling between adjacent QDs within the aerogel networks were explored. The selectively enhanced interparticle charge-transfer route for coreactant-based ECL systems was proposed. In addition, the charge-transport-promoted ECL mechanism was further verified by designing CdSe-CdTe mixed QD aerogels, where the interparticle charge-transfer route could be clearly decoupled from the intraparticle charge-transfer route. Finally, we presented an evaluation of energy level alignments and Fermi level of QDs to further verify the interparticle charge-transfer route within the CdSe-CdTe mixed QD aerogels. The study conducted on a fundamental understanding of ECL further supports the utilization of next-generation QD-based devices.