New immunochemical approach to low-molecular-mass analytes determination

One of the goals of the new automated immunoassay analysers is to perform direct analysis in complex matrices thus overcoming traditional limits of homogeneous immunoassays: reduced sensitivity and ability to determine above all proteins and antibodies. The aim of this work was to demonstrate the feasibility of quantitative homogeneous immunoassay for small analytes in a complex matrix with a rapid and easy assay by exploiting an agglutination reaction. We studied the steroid hormone progesterone, and used new technology, the Copalis™, which uses a special optical-sizing flow particle analysis and a semiconductor laser as a light source. We used polystyrene microbeads coated with the antigen as markers and put them in competition with the analyte in solution for the analytical antiserum. We synthesised and tested different conjugates of progesterone-bovine serum albumin, optimising all the experimental parameters. We performed a short pre-treatment of the serum and we obtained a detection limit of 0.011 ng cm−3 and a working range between 0.026 and 43 ng cm−3. We estimated human serum specimens and, with minor experimental revisions, the amounts of progesterone found agreed accurately with AutoDELFIA™ analysis. The recoveries are good. All the experimental steps are easy, rapid and enable us to process many samples contemporarily.