Capillary electrophoresis-based immunoassay with electrochemical detection as rapid method for determination of saxitoxin and decarbamoylsaxitoxin in shellfish samples

A simple and sensitive capillary electrophoresis (CE) based immunoassay (IA) with electrochemical (EC) detection method is presented for the assay of saxitoxin and decarbamoylsaxitoxin in shellfish samples. The method was based on competitive reactions between horseradish peroxidase (HRP)-labeled antigen (Ag*) and free antigen (Ag) with a limited amount of antibody (Ab). After incubation, the unbound Ag* and the bound enzyme-labeled complex (Ag*–Ab) were separated by CE and then the system of HRP catalyzing H2O2/o-aminophenol (OAP) reaction was adopted for EC detection. Using CEIA with EC detection, equilibrium of competitive reaction was reached in 30 min, and the analytical results were further obtained within 6 min. The linear range and the detection limit were 0.8–66.6 ng/mL and 4.3–9.2 μg/kg for saxitoxin, and 1.2–83.5 ng/mL and 7.7–16.5 μg/kg for decarbamoylsaxitoxin, respectively. The method was applied to quantitative analysis of saxitoxin and decarbamoylsaxitoxin in shellfish samples with rapid and simple pretreatment, and the results were consistent with the same samples analyzed through enzyme-linked immunosorbent assay (ELISA) and the mouse bioassay. Recoveries of saxitoxin and decarbamoylsaxitoxin in shellfish samples were 92.5–107.6% and 94.8–113.3% for saxitoxin and decarbamoylsaxitoxin, respectively. The method is thus proposed as a fast and sensitive assay for the determination of saxitoxin and decarbamoylsaxitoxin in shellfish samples.