Disposable screen-printed electrodes for the immunochemical detection of polychlorinated biphenyls

Three different electrochemical approaches for the detection of α-naphthol (amperometry, chronoamperometry and differential pulse voltammetry), using screen-printed carbon electrodes, were compared with respect to measurable range, detection limit, reproducibility, sample throughput and suitability for in field use. The highest sensitivity (252 nA/μM) with a calculated detection limit of 0.1 μM, combined with a remarkable ‘time for sample measurement’ (5.5 s) was achieved with differential pulse voltammetry. The standard error over the whole measured range (0.5–100 μM) was below 5%. The scan speed and the pulse amplitude of the differential pulse voltammetric method were optimised using a simplex method. The optimised electrochemical procedure was then used to evaluate the detection of low levels of alkaline phosphatase: this enzyme catalyses the hydrolysis of α-naphthyl phosphate to α-naphthol. Using 2 min as incubation time for the enzyme reaction, a linear calibration curve in the range 1–10−5 U/ml was obtained with a calculated detection limit of 2.1 × 10−6 U/ml. The standard error for the 10−2 U/ml enzyme standard was 6.8%. Finally a competitive enzyme immunoassay for polychlorinated biphenyls based on alkaline phosphatase was performed using the optimised electrochemical detection of α-naphthol. The assay measurable range was 0.01–10 μg/ml, and the detection limit was 0.01 μg/ml (BxB0%=10).