Development of a highly sensitive enzyme-linked immunosorbent assay for atrazine Performance evaluation by flow injection immunoassay

Application of screen-printed electrodes as transducers in affinity flow-through sensor systems

An affinity flow-through sensor system based on a heterogeneous competitive affinity assay for the determination of low molecular weight compounds is described using the examples of biotin and atrazine determination. The binding proteins, either streptavidin or a biotinylated monoclonal antibody, were immobilized on a biotinylated screen-printed electrode, where the competition between the analyte and an analyte-enzyme-conjugate took place. Determination of the bound enzyme was done through the supply of suitable enzyme substrates and electrochemical determination of an enzyme reaction product. In the assays described here, peroxidase was used as enzyme label. As hydrogen peroxide and hydroquinone were used as enzyme substrates, the amount of enzyme retained at the screen-printed graphite electrode was determined amperometrically at a reducing potential of -600 mV vs a screen-printed platinum electrode. The activation of the electrode by biotinylation was done in a batch procedure outside the system, before the electrode was inserted. All following steps of the assay were performed automatically in an unsegmented flow-through system through an appropriate delivery of required reagents. The system was optimized mainly through the determination of biotin. This assay was based on the competition between biotin and biotinylated peroxidase for the binding sites of streptavidin. The method showed a linear range from 0.045 to 2 micrograms/l (r2 = 0.9997, n = 7) with RSD lower than 3.8%. The system was modified further by using a biotinylated monoclonal antibody against atrazine for analyte recognition and performing a competitive assay between atrazine and a triazine-peroxidase-conjugate. The linear range was from 0.01 to 10 micrograms/l, with IC50 = 0.4 microgram/l and RSD lower than 4.6%. The method was also applied to atrazine spiked water samples. Regeneration of the sensor surface was based on removal of streptavidin in both assays.

Influence of the hapten design on the development of a competitive ELISA for the determination of the antifouling agent Irgarol 1051 at trace levels

Enzyme-linked immunosorbent assays (ELISAs) with a high detectability have been developed for determination of the antifouling agent Irgarol 1051. The features of the resulting assays have been rationalized by using molecular mechanic calculations (MM2+) to correlate the chemical structure of different immunizing haptens and the corresponding avidities of the obtained antisera. The ability of Irgarol 1051 to compete for the antibody binding sites with 11 horseradish peroxidase enzyme tracers, differing in the chemical structures of the hapten, has been investigated. The present paper demonstrates that high-quality antibodies and, therefore, immunoassays reaching very low detection limits could be predicted by molecular modeling studies of the analyte conformations and of the immunizing haptens' geometries, hydrogen-bonding capabilities, and electronic distributions. Two of the ELISAs obtained have been optimized to obtain reproducible immunoassays. The dynamic ranges of both assays are between 30 and 200 ng/L, and the limits of detection are approximately 16 ng/L. The reported immunoassays have been evaluated and validated by analyzing spiked and real seawater samples. Irgarol 1051 has been found to be present in two of the geographical locations analyzed at concentration levels dependent on the time of year. The analytical results obtained with these immunoassays have been validated by chromatographic methods.

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.