Novel signal-on immunosensors for rapid and sensitive detection of Microcystin-LR

Microcystins are a group of hepatotoxins produced by cyanobacteria present in surface water. We developed two Quenbodies (Q-bodies) as effective and reliable fluorescent sensors to detect microcystin with leucine and arginine (MC-LR) within 3 min. The designed single-chain variable region of antibody 3A8 was used to prepare Q-bodies by conjugating the fluorescent dye ATTO520 or tetramethylrhodamine (TAMRA) to its N-terminus. The fluorescence of Q-bodies was quenched by the internal tryptophan residues of antibody via photo-induced electron transfer, whereas it significantly increased upon the binding of MC-LR. The limit of detection and EC₅₀ were 0.45 ng/mL and 20.43 ng/mL, respectively, for TMARA-labeled Q-body, and 8.6 ng/mL and 251.6 ng/mL for ATTO520-labeled Q-body. Combining the Q-bodies enabled sensitive and wide-range detection of MC-LR. The recovery rates for river water samples spiked with MC-LR ranged from 94.8% to 120.0%, suggesting their potential applications in MC-LR monitoring in nature.