Enhanced Lateral Flow Immunoassay for Pesticide Paraquat Based on Combining Magnetite and Gold Nanoparticles

A lateral flow immunoassay (LFIA) utilizing two types of marker conjugates-magnetite nanoparticles (MNPs) with specific antibodies and gold nanoparticles (GNPs) with anti-species antibodies-was proposed and realized for the detection of the pesticide paraquat. In this assay, the MP conjugate is used to concentrate the target analyte from the tested sample and then to form labeled immune complexes at the test strip, while the GNP conjugate is then applied for the integration into the formed complexes in the binding zone. The magnetic preconcentration allows for working with large volumes of samples, and the following treatment by the GNP conjugate enhances the coloration by five times for reliable analyte revelation in lower concentrations. In the course of the assay implementation, its conditions have been optimized, and the efficiency of the paraquat determination in orange samples was confirmed. The achieved detection limits were 1.2-3.7 ng/mL for visual assessment and 0.12-0.48 ng/mL for the instrumental one, with paraquat detection rates ranging from 96% to 120%. The implementation of the assay in combination with the stage of magnetic concentration allows for the collection of paraquat from large volumes of samples and detects it in this way in concentrations up to two orders of magnitude smaller.