High sample throughput flow immunoassay utilising restricted access columns for the separation of bound and free label

A flow immunodetection system with high sample throughput capacity is described for the screening of various analytes. The immunochemical detection principle is based on the chromatographic separation of the formed immunocomplex (AbAg or AbAg*) and the free antigen (Ag) by a restricted access (RA) column, utilising size-exclusion and reversed-phase mechanism. A fluorescein labelled analyte (Ag*) was used in the competitive assay format with fluorescence detection. The speed and simplicity of the assay were the greatest advantages, allowing measurement of the analyte to be carried out in less than 1 min. The biocompatibility and capacity of the restricted access material allowed multiple injections of up to 5000, without any breakthrough of the fluorescent tracer molecule and thus need for regeneration. The flow immunoassay was developed using the well-known atrazine herbicide and some transformation products as model compounds, due to their human toxicity and widespread use. The sample throughput was 80 samples per hour and the detection limits were 1.4 nM (300 pg/ml) for atrazine (Ab I) and 2.3 nM (500 pg/ml) for the sum of triazines (Ab II–III). Different sample matrices, PBS buffer, creek water, and urine were successfully applied in the flow system without the need for any sample handling step. For plasma samples an additional clean-up step using solid-phase extraction had to be included. The resulting detection limits for atrazine in plasma and water samples using this clean-up and trace enrichment procedure were found to be 2 ng/ml and 20 pg/ml, respectively. The analysis could be performed at a sample throughput rate of 400 per 6-h working shift.