Matrix effects on the microcystin-LR fluorescent immunoassay based on the evanescent wave all-fiber immunosensor (EWAI) and their elimination methods were studied. The results indicated that PBS and humic acid did not affect the monitoring of samples under the investigated conditions. When the pH was less than 6 or higher than 8, the fluorescence signals detected by immunosensor systems were obviously reduced with the decrease or increase of pH. When the pH ranged from 6 to 8, IC(50) and the linear working range of MC-LR calculated from the detection curves were 1.01∼1.04 μg/L and 0.12∼10.5 μg/L, respectively, which was favourable for an MC-LR immunoassay. Low concentrations of Cu(2+) rarely affected the detection performance of MC-LR. When the concentration of CuSO(4) was higher than 5 mg/L, the fluorescence signal detected by EWAI clearly decreased, and when the concentration of CuSO(4) was 10 mg/L, the fluorescence signal detected was reduced by 70%. The influence of Cu(2+) on the immunoassay could effectively be compromised when chelating reagent EDTA was added to the pre-reaction mixture.
Keywords: Matrix effects; Microcystin-LR; fluorescent immunoassay; optical biosensor.