Au-coated FeO core-shell nanohybrids with photothermal activity for point-of-care immunoassay for lipoprotein-associated phospholipase A on a digital near-infrared thermometer.

A portable photothermal immunoassay based on Au-coated magnetic FeO core-shell nanohybrids (Au-FeO) was developed for point-of-care (POC) testing of lipoprotein-associated phospholipase A (Lp-PLA) on a digital near-infrared (NIR) thermometer. Au-FeO photothermal materials were first synthesized through reverse micelle method, and then functionalized with polyclonal rabbit anti-human Lp-PLA antibody. A sandwiched immunoreaction was carried out in polyclonal mouse anti-human Lp-PLA antibody-coated microplate using Au-FeO-labeled antibody as the detection antibody. With formation of sandwich-type immunocomplex, the captured Au-FeO on the plate converted the light into heat under an 808-nm laser irradiation (1.5 W cm), thereby resulting in the increasing temperature of the detection solution. The temperature variations relative to surrounding temperature was determined on a portable NIR thermometer. Several labeling protocols with gold nanoparticle, FeO nanoparticle, or Au-FeO nanohybrids were investigated for determination of Lp-PLA and improved analytical features were achieved with the core-shell Au-FeO nanohybrids. Under optimum conditions, Au-FeO-based immunoassay exhibited good photothermal responses for the detection of Lp-PLA with a dynamic linear range of 0.01-100 ng mL at a low detection limit of 8.6 pg mL. Good reproducibility and intermediate precision were less than 9.7%. Other biomarkers or proteins did not interfere with responses of this system. An acceptable accuracy was acquired for analysis of human serum sample between Au-FeO-based photothermal immunoassay and commercialized human Lp-PLA ELISA kit.