Multifunctional Fe3O4@Au supraparticle as a promising thermal contrast for an ultrasensitive lateral flow immunoassay

An ultrasensitive lateral flow immunoassay (LFIA) strip has been developed based on a multifunctional photothermal contrast Fe3O4@Au supraparticle (Fe3O4@Au SP) for quantitative Ochratoxin A (OTA) detection. The Fe3O4@Au SP composite not only shows a better photothermal effect over Fe3O4 and gold nanoparticles, but possesses magnetic property and excellent ability to directly adsorb protein (antibody). Under 808 nm irradiation, photothermal images of the test strips are recorded by a portable Infrared thermal camera. A quantitative analysis is easily achieved based on the thermal changes, which are proportional to the concentrations of analytes. Under an optimal condition, a wide linear detection range from 1 pg mL⁻1 to 1μgmL⁻1 and a limit of detection (LOD) at 0.12 pg mL⁻1 have been achieved with OTA as a model analytes. The practical application potential has also been validated by detection of OTA in spiked corn, peanut, and soybean extractives with overall recoveries ranging from 98.6% to 115% and coefficient of variations (CVs) between 6.06% and 12.73%. The photothermal LFIA renders a rapid, sensitive, and quantitative bio-/chemo-sensing platform with only a portable laser source and a thermal camera.