Enhancing Analytical Potential of Electrochemiluminescence By the Silica Nanoparticle Approach
Authors: Valenti Giovanni , Marcaccio Massimo , Rampazzo Enrico , Kesarkar Sagar , Prodi Luca , Paolucci Francesco 
Published: February 2020

Electrochemiluminescence (ECL) is a leading technique in bioanalysis.1 Since the excited species are produced with an electrochemical stimulus rather than with a light excitation source, ECL displays improved signal-to-noise ratio compared to photoluminescence, with minimized effects due to light scattering and luminescence background.2

In the quest for ever-increasing sensitivities, ECL can ideally be coupled to nanotechnology and supramolecular chemistry to develop new systems and strategies for analyte determination also in very complex matrices. For instance, we have recently shown a supramolecular approach to detect sarcosine, a potential prostate cancer biomarker, in urines, with good sensitivity and very high selectivity.3 Dye-doped silica nanoparticles (DDSNs), semiconductor nanocrystals, or polymer dots were also advantageously used as ECL-active systems.4,5 In particular, DDSNs present many advantages: they can be obtained with accessible synthetic schemes, are intrinsically hydrophilic, and, thanks to silica chemistry, are prone to bioconjugation. Very bright systems can be obtained with this approach since silica is inert from the photophysical point of view, and DDSNs assume the photophysical properties of the dye(s) molecules accumulated within the nanoparticle.5 In DDSNs, light emission is influenced by the combination of several factors that make DDSNs complex multichromophoric structures, such as the coexistence of dye populations experimenting with slightly different environments and the occurrence of intraparticle energy transfer processes (mainly resonance energy transfer or quenching). When ECL comes into play, the scenario is even more complicated by the presence of the coreactant−NP interactions, since the coreactant needs to approach the NP surface and to react with the dyes buried within the silica at different extent. A scenario of such a complexity was then approached at the theoretical level by developing suitable mechanistic models for ECL generation6 while, at the same time, the influence of doping level and particle charging on ECL efficiency was evaluated. The results showed that the ECL intensity of a nanosized system cannot be merely incremented acting on doping, since other parameters come into play.7 These studies provide valuable indications for the design of more efficient ECL nano- and microsized labels for ultrasensitive bioanalysis.
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