Effect of agitation in magneto-assay performance

G. Ruiz-Vega, E. Baldrich.

Sensors and Actuators B: Chemical , 247, 718–726.



Magnetic particles (MP) are extensively used to improve immunocapture and immunodetection. Com-pared to two-dimensional surfaces, MP provide wider active areas, efficient mixing with the sample,and target separation from other sample components. Nevertheless, MP handling is more tedious thanclassical techniques, such as ELISA, in which tens/hundreds of samples are simultaneously processed.Accordingly, MP handling automation seems essential for the exploitation of magneto-detection in realdiagnostics. This entails implementation of appropriate agitation strategies to prevent MP sedimentationand guarantee maximal target binding efficiency, minimal non-specific adsorption, and acceptable resultreproducibility. Attempts to automate magnetic-based agitation have been reported. However, we couldnot find studies comparing the effect of different agitation procedures in magneto-immunobinding effi-ciency, which could be useful to define the most appropriate strategy for integration of MP handling inautomated detection platforms.Here, we optimized a classical ELISA for detection of myeloperoxidase (MPO) that took 3 h andgenerated a limit of detection (LOD) of 4.87 ng mL1. This assay was then formatted into a 30-minmagneto-immunoassay that had an LOD of 1.65 ng mL1. MPO magneto-immunodetection was next per-formed under different agitation conditions. The results showed that sample volume had a high effectin the incubations performed under rotation, with signals 50% higher in 0.5–1 mL than in 100 L sam-ples. On the contrary, vortex agitation generated similar signals for the different volumes tested (100 L,500 L and 1 mL), which entailed a 50% enhancement in target recovery in 100 L samples compared torotation. This demonstrated that sample volume had different effect in magneto-immunobinding effi-ciency under different agitation conditions and suggested that magneto-assay automation could benefitfrom combinations of agitation types, selected in accordance to analyte type and sample volume.