Development and application of highly sensitive anti-immune complex ELISAsfor microcystins in tap water

We developed an anti-immune complex (IC) ELISA applicable to direct determi nation of trace amounts of microcystins (MCs) in tap water. Comparison of t wo assay formats revealed that the use of anti-immune complex monoclonal an tibody (MAB) in the coating step to trap anti-MC MAB-MC complexes improved the sensitivity as well as precision. The detection limit and quantitative range of the IC ELISA was 2 pg ml(-1) and 2-100 pg ml(-1) of microcystin-LR (MCLR), respectively, indicating the most sensitive of all the methods for detecting MCs reported to date. Additionally, the IC ELISA maintained good reliability through its quantitative range, as evidenced by low coefficien ts of variation (5.0-10.8 and 4.9-10.2% for intra- and interassay, respecti vely). The IC ELISA showed good cross-reactivity to microcystin-RR and micr ocystin-YR, suggesting major MCs found in the environment can be detected b y this method. Recovery tests in which quantitative range of MCLR were adde d to tap water resulted in a mean recovery of 99%, with a mean standard dev iation of 5.7%; therefore the IC ELISA performed well in the analysis of ta p water samples. ELISA analysis of tap water samples collected in China and Japan revealed that, among 17 samples tested, two samples collected in Chi na were positive for MCs at 4.9-14 pg ml(-1). These results suggest that th e newly developed IC ELISA can be used to monitor trace amounts of MCs in t ap water.