Exploring strategies to confine magneto-immunoassays enzymatic products on gold interdigitated microelectrodes (G-IDE) for enhanced sensitivity: application to detection of respiratory syncytial virus (RSV).

Magnetic particles (MP) combined with screen-printed electrodes (SPE) are widely used for enzyme-labelled magneto-immunoassays enabling quantitative electrochemical detection of analytes. In contrast, thin-film electrodes are less frequently implemented, despite their reported high sensitivity. This study aims to identify the key parameters required for the effective use of gold interdigitated microelectrodes (G-IDE) in the sensitive electrochemical detection of sandwich magneto-immunoassays. As a model system, we selected the fusion protein of respiratory syncytial virus (F-RSV), a major causative agent of viral respiratory infections and the second leading cause of mortality in infants beyond the neonatal period. The results demonstrate that successful detection using G-IDE requires only a fraction of the MP typically employed with SPE, combined with volumes of substrate solution down to 3-10 μL, and enzymatic detection times of only a few seconds. Two signal-enhancement strategies were synergistically combined: redox cycling-based detection of enzymatic products occurring at G-IDE and physical confinement of MP during the enzymatic reaction to generate highly concentrated products. These approaches were evaluated using two configurations: accumulation of MP in a microwell positioned on top of the G-IDE, and deposition of MP onto a paper-based disc subsequently transferred to the electrode surface. While the former approach required minimal user manipulation, the latter achieved superior analytical performance, yielding a detection limit of 0.09 ng mL-1 and F-RSV quantification correlating with the reference ELISA measurements (R2 = 0.998). Finally, the applicability of the proposed detection strategy to complex matrices was addressed through the analysis of 20 clinical samples. Overall, these results confirm the potential of G-IDE for the development of sensitive electrochemical magneto-immunosensors.