Antibody-based methods for surfactant screening

Abstract

This brief overview summarises the immunoassay-based results obtained in the course of two years of the European INCO-Copernicus project BIOTOOLS. The project is aimed at simplifying the procedures for detection of surface active compounds (SAC) using, among others, antibody-based methods, i.e., microtiter plate-based enzyme-linked immunosorbent assays (ELISA), polarisation fluoro immunoassays (PFIA), and enzyme flow injection immunoassays (FIIA). Thirty-three rabbits were immunised with five different sulphophenyl moieties and three p-hydroxyphenyl moieties conjugated to protein immunogens to produce analytical antibodies against linear alkylbenzene sulphonates (LAS) and nonylphenol (NP). Although most of the antibodies exhibited binding reaction in indirect ELISA, only a few showed the required assay sensitivity. The best antibodies for LAS exhibited a 50% binding inhibition at IC₅₀ 19.8 µg L^–1 in indirect ELISA. Similar inhibition was observed for direct ELISA using peroxidase tracers. Antibodies against NP allowed the establishment of an indirect assay operating in the mg L⁻¹ range. A rapid and simple protocol for the screening of NP and LAS using homogeneous PFIA is described. The assay time for 10 samples was 7 minutes, thus allowing fast detection of the selected SAC at the mg L^–1 level. A generic competitive FIIA system, using a protein G column for separation of free and antibody-bound β-galactosidase (β-Gal) tracer, was developed for the screening of LAS, NP, and nonylphenol decaethoxylate (NPEO₁₀). The FIIA had a sample throughput (STP) of 5–10 samples per hour, with limits of detection (LOD) for LAS, NP, and NPEO₁₀ of 19.5, 52, and 2.4 µg L^–1, respectively. The developed FIIAs were applied to spiked rain and surface water.