Development of immunoassays to determinate sulfamethoxazole residues in wastewaters

Different immunoassays have been developed to monitor sulfamethoxazole (SMX), an antibiotic frequently detected in water. The immunoassays were developed and optimized in two different formats: ELISA in polystyrene 96-well plate and microarray on compact disc (CD) support. Competitive microimmunoassays were performed by direct adsorption of immunoreagents on the polycarbonate surface of a low-reflectivity CD. Results were displayed using nanogold-labeled immunoglobulins and silver staining developer. High sensitivity was achieved with both formats: LD 0.001 ng mL(-1) in the ELISA-plate, and 0.09 ng mL(-1) in the CD format. The novel CD methodology presents advantages such as simplicity, sensitivity, portability, analytical capacity (2560 spots per disc), in addition to reductions in immunoreagents required, costs and time for analysis. Both proposed methods were applied to determine SMX at nanograms per litre level in wastewater samples without previous preconcentration. Finally, the determination of several fortified wastewater samples using the CD format protocol showed a mean recovery of 87%, which confirms that this assay format is a good screening tool to detect sulfamethoxazole in water samples rapidly and reliably.