Double amplification upon immuno-gold nanoparticles promoted trace measurement of ricin by biolayer interferometry

The upsurge of biotoxin threat worldwide stressed challenges in the first response to date. Implementing sensitive, specific, and rapid sensing methods is very worthwhile. An emerging optical sensing technique, biolayer interferometry (BLI), has the merits of real-time, fluidics-free, label-free detection, shows its great potential for highly sensitive measurement of biotoxins via a simple, fast and straightforward way. In this article, we contributed a double amplification strategy upon immuno-gold nanoparticles (immunoGNPs) in BLI, which promoted a measurement of trace ricin based on the modified monoclonal antibodies sandwiched sensing mode. ImmunoGNPs fuel signal amplification by a three-fold action: the enhanced differential interference pattern, multivalent binding effect, and improved intrinsic nanozyme catalytic activity. Under a complete optimization, the sensitivity was 1000-fold improved in comparison with the direct immunoassay, with the limit of detection as low as 5 pM (0.3 ng/mL) and a linear range reaching three orders of magnitude. All the whole measurement procedures were completed within 15 min. Moreover, with the aid of GNPs, mAb with low affinity and high dissociation rate can provide sensitivity as good as mAb with high affinity and low dissociation rate, revealed multivalent binding effect by enhancing avidity several orders of magnitude via reducing the dissociation rate constant. It supported a feasible way to rescue mAb with weak affinity dominated by a fast dissociation behavior in the sensing field. We also proved the applicability of this BLI assay in practical samples such as crude biotoxins and intoxicated human plasma.