Automated portable array biosensor for multisample microcystin analysis in freshwater samples

An automated array biosensor based on evanescent-wave excitation has been developed for the detection of microcystins (MCs) in freshwater samples. The sensing surface consisted of microcystin-leucine-arginine (MCLR) covalently immobilized onto a planar waveguide (microscope slide). The binding of anti-MCLR monoclonal antibodies, spiked in the sample, to the immobilized MCLR was competitively inhibited by MCLR in solution and the amount of antibody bound to the patterned antigens was revealed using Cy5-labeled rabbit anti-mouse IgG. Surface chemistry has been optimized to improve biosensor performance in terms of sensitivity, regeneration ability and to avoid non specific binding for further application to environmental monitoring. The optimized biosensor assay presents an IC50 value of 0.34 ± 0.01 μg/L, a detection limit of 16 ± 3 ng/L and a dynamic range from 0.06 to 1.5 μg/L MCLR, improving the performance of previously reported devices. Cross-reactivity to other related MCs, such as microcystin-RR (MCRR, 90%), microcystin-RR desmethylated (dm-MCRR, 95%) and microcystin-YR (MCYR, 91%), was also evaluated. The automated microarray can assay up to six different samples in parallel, with a total analysis time of about 60 min. The sensing surface was regenerated with 50 mM NaOH and each chip was reused for, at least, 15 assay-regeneration cycles without significant binding capacity loss. The immunosensor has been successfully applied to the direct analysis of MCs in surface water samples and the results were in close agreement with those provided by LC-MS/MS.