Nanoparticles in metal complexes-based electrogenerated chemiluminescence for highly sensitive applications

This review aims to give an overview on the state of the art in the precise context of metal complexes-based ECL dyes directly adsorbed on, included in or interacting with nanoparticles of various nature. Electrogenerated chemiluminescence, or electrochemiluminescence (ECL), is the process through which species generated at electrodes undergo homogeneous high-energy electron transfer reactions to give excited states that emit light. When stable ECL probes such as ruthenium coordination complexes are used, this process can be performed several times, free of the interferences typical of photoluminescence such as the excitation light, providing a clear and stable signal suitable for highly sensitive assays. The ECL emission is initiated and controlled by the electrode potential and immobilization of the ECL probes on the electrode surface allows one to reduce the consumption of expensive reagents, simplifies the experimental design, and creates regenerable sensing devices. The organization of the electrode surface is thus the key point to optimize the device performance. Nanoparticles have proved their potential as tools to organize the ECL probes, to increase the active area and to improve the electrochemical properties of the interface. There is an extended research devoted on one hand to optimize the materials, and on the other hand to explore the wide horizon of possibilities that arise from the combination of nanoparticles and ECL probes, co-reagents, (bio)markers and other functional moieties. The results discussed in this review clearly show that the use of nanoparticles aimed to obtain signal enhancement represents one of the most interesting research lines for the development of the ECL technique. The activity in this field is so dynamic that outstanding results could reasonably be expected in the near future.