A sensitive fluorescence biosensor was developed for microcystin-LR (MC-LR) detection using H1, H2, and H3 DNA probes as sensing elements. The aptamer in H1 can recognize the target. H2 was labeled with FAM and BHQ. The MC-LR and H1 binding will activate the H2 and H3 self-assemblies through toehold-mediated strand displacement. In the formed products (MC-LR/H1/nH2/nH3), FAM and BHQ will be separated and a high FAM fluorescence signal can be observed for the MC-LR assay. The biosensor is sensitive with a detection limit of 53 fM. We further constructed several logic circuits (AND-AND cascaded ...
