Boron-Doped Diamond Electrode Outperforms the State-of-the-Art Electrochemiluminescence from Microbeads Immunoassay

Electrochemiluminescence (ECL) is a powerfultransduction technique where light emission from a molecularspecies is triggered by an electrochemical reaction. Application tobiosensors has led to a wide range of electroanalytical methods withparticular impact on clinical analysis for diagnostic and therapeuticmonitoring. Therefore, the quest for increasing the sensitivity whilemaintaining reproducible andeasy procedures has broughtinvestigations and innovations in (i) electrode materials, (ii)luminophores, and (iii) reagents. Particularly, the ECL signal isstrongly affected by the electrode material and its surfacemodification during the ECL experiments. Here, we exploit boron-doped diamond (BDD) as an electrode material in microbead-basedECL immunoassay to be compared with the approach used in commercial instrumentation. We conducted a careful characterizationof ECL signals from a tris(2,2 '-bipyridine)ruthenium(II) (Ru(bpy)32+)/tri-n-propylamine (TPrA) system, both homogeneous (i.e.,free diffusing Ru(bpy)32+) and heterogeneous (i.e., Ru(bpy)32+bound on microbeads). We investigated the methods to promoteTPrA oxidation, which led to the enhancement of ECL intensity, and the results revealed that the BDD surface properties greatlyaffect the ECL emission, so it does the addition of neutral, cationic, or anionic surfactants. Our results from homogeneous andheterogeneous microbead-based ECL show opposite outcomes, which have practical consequences in ECL optimization. Inconclusion, by using Ru(bpy)32+-labeled immunoglobulins bound on microbeads, the ECL resulted in an increase of 70% and adouble signal-to-noise ratio compared to platinum electrodes, which are actually used in commercial instrumentation for clinicalanalysis. This research infers that microbead-based ECL immunoassays with a higher sensitivity can be realized by BDD.