Tris(2,2'-bipyridyl)ruthenium (II) complex as a universal reagent for the fabrication of heterogeneous electrochemiluminescence platforms and its recent analytical applications

Rapid and simple viral protein detection by functionalized 2D MoS2/graphene electrochemiluminescence aptasensor

In this work we present the development of an electrochemiluminescence aptasensor based on electrografting molybdenum disulphide nanosheets functionalized with diazonium salt (MoS2-N2+) upon screen-printed electrodes of graphene (SPEs GPH) for viral proteins detection. In brief, this aptasensor consists of SPEs GPH electrografted with MoS2-N2+ and modified with a thiolated aptamer, which can specifically recognize the target protein analyte. In this case, we have used SARS-CoV-2 spike protein as model protein. Electrochemiluminescence detection was performed by using the [Ru(bpy)3]2+/TPRA (tripropylamine) system, which allows the specific detection of the SARS-CoV-2 spike protein easily and rapidly with a detection limit of 9.74 fg/mL and a linear range from 32.5 fg/mL to 50.0 pg/mL. Moreover, the applicability of the aptasensor has been confirmed by the detection of the protein directly in human saliva samples. Comparing our device with a traditional saliva antigen test, our aptasensor can detect the spike protein even when the saliva antigen test gives a negative result.

Complex electrochemiluminescence patterns shaped by hydrodynamics at a rotating bipolar electrode

Electrochemiluminescence (ECL) is a powerful analytical approach that enables the optical readout of electrochemical processes. Over the last few years, ECL has gained considerable attention due to its large number of applications, including chemical sensing, bioanalysis and microscopy. In these fields, the promotion of ECL at bipolar electrodes has offered unprecedented opportunities thanks to wireless electrochemical addressing. Herein, we take advantage of the synergy between ECL and bipolar electrochemistry (BE) for imaging light-emitting layers shaped by hydrodynamics, polarization effects and the nature of the electrochemical reactions taking place wirelessly on a rotating bipolar electrode. The proof-of-principle is established with the model ECL system [Ru(bpy)3]2+/tri-n-propylamine. Interestingly, the ECL-emitting region moves and expands progressively from the anodic bipolar pole to the cathodic one where ECL reactants should neither be generated nor ECL be observed. Therefore, it shows a completely unusual behavior in the ECL field since the region where ECL reagents are oxidized does not coincide with the zone where ECL light is emitted. In addition, the ECL patterns change progressively to an "ECL croissant" and then to a complete ring shape due to the hydrodynamic convection. Such an approach allows the visualization of complex light-emitting patterns, whose shape is directly controlled by the rotation speed, chemical reactivity and BE-induced polarization. Indeed, the bipolar electrochemical addressing of the electrode breaks the circular symmetry of the reported rotating system. This unexplored and a priori simple configuration yields unique ECL behavior and raises new curious questions from the theoretical and experimental points of view in analytical chemistry. Finally, this novel wireless approach will be useful for the development of original ECL systems for analytical chemistry, studies of electrochemical reactivity, coupling microfluidics with ECL and imaging.

Electrogenerated chemiluminescence from luminol-labelled microbeads triggered by in situ generation of hydrogen peroxide

We developed a sensing strategy that mimics the bead-based electrogenerated chemiluminescence immunoassay. However, instead of the most common metal complexes, such as Ru or Ir, the luminophore is luminol. The electrogenerated chemiluminescence of luminol was promoted by in situ electrochemical generation of hydrogen peroxide at a boron-doped diamond electrode. The electrochemical production of hydrogen peroxide was achieved in a carbonate solution by an oxidation reaction, while at the same time, microbeads labelled with luminol were deposited on the electrode surface. For the first time, we proved that was possible to obtain light emission from luminol without its direct oxidation at the electrode. This new emission mechanism is obtained at higher potentials than the usual luminol electrogenerated chemiluminescence at 0.3-0.5 V, in conjunction with hydrogen peroxide production on boron-doped diamond at around 2-2.5 V (vs Ag/AgCl).

Redox-mediated electrochemiluminescence enhancement for bead-based immunoassay

Electrochemiluminescence (ECL) is a highly sensitive mode of detection utilised in commercialised bead-based immunoassays. Recently, the introduction of a freely diffusing water-soluble Ir(iii) complex was demonstrated to enhance the ECL emission of [Ru(bpy)3]2+ labels anchored to microbeads, but a comprehensive investigation of the proposed 'redox-mediated' mechanism was not carried out. In this work, we select three different water-soluble Ir(iii) complexes by virtue of their photophysical and electrochemical properties in comparison with those of the [Ru(bpy)3]2+ luminophore and the TPrA co-reactant. A systematic investigation of the influence of each Ir(iii) complex on the emission of the Ru(ii) labels on single beads by ECL microscopy revealed that the heterogeneous ECL can be finely tuned and either enhanced up to 107% or lowered by 75%. The variation of the [Ru(bpy)3]2+ ECL emission was correlated to the properties of each Ir(iii)-based mediator, which enabled us to decipher the mechanism of interaction and define guidelines for the future design of novel Ir(iii) complexes to further enhance the ECL emission of bead-based immunoassays. Ultimately, we showcase the potential of this technology for practical sample analysis in commercial instruments by assessing the enhancement of the collective ECL intensity from a bead-based system.