Nanoparticle Assembly at the Water-Oil Interface Induced by Spontaneous Emulsification for Microdroplet Immunoassay

Micron-sizedwater-in-oil droplets (microdroplets) have been usedfor various biochemical analyses. Many studies have been reportedon immunoassays using microdroplets because of their high versatility.A selective enrichment method using spontaneous emulsification wasdeveloped as a pretreatment method for analytical systems of microdroplets.In this study, a one-step immunoassay for microdroplets using nanoparticleassembly at the interface by spontaneous emulsification is proposed.At the interface of the microdroplet, with aqueous nanoparticle dispersion,it was found that nanoparticles with diameters less than 50 nm wereuniformly adsorbed to the microdroplet interface as a Pickering emulsion,whereas larger nanoparticles tended to aggregate in the bulk partof the microdroplet. Based on this phenomenon, a proof of conceptof the one-step immunoassay was demonstrated using rabbit IgG as theanalyte. This method is expected to be a powerful tool for trace biochemicalanalyses.

Automated summary

In this study, a one-step immunoassay for microdroplets using nanoparticle assembly at the interface by spontaneous emulsification is proposed. It was found that nanoparticles with diameters less than 50 nm were uniformly adsorbed to the microdroplet interface as a Pickering emulsion, whereas larger nanoparticles tended to aggregate in the bulk part of the microdroplet. The feasibility of this method was demonstrated using rabbit IgG as the analyte, and it is expected to be a powerful tool for trace biochemical analyses.