Ultrasensitive label-free electrochemical biosensor for detecting linear microcystin-LR using degrading enzyme MlrB as recognition element

A label-free electrochemical biosensor was firstly constructed to detect linear microcystin-LR (L-MC-LR) with high sensitivity. Degradation enzyme MlrB was used as recognition element for specific recognition of L-MC-LR. The electrode was modified with -COOH functionalized multi-walled carbon nanotube to increase the specific surface area and improve the conductivity, which was then applied to immobilize MlrB. The electrochemical signal was changed with the reaction between MlrB and L-MC-LR, which was recorded by using square wave voltammetry. The electrochemical biosensor showed superior sensitivity, with a dynamic range of 1 pg/mL to 100 ng/mL and a detection limit of 0.127 pg/mL. Moreover, the fabricated electrochemical biosensor exhibited excellent specificity toward L-MC-LR in real water samples. The concentrations of spiked L-MC-LR were 0.100, 5.00, 50.0 ng/mL, and the recovery rates were 95.0-104% with relative standard deviation (RSD) of 0.900-2.30% and 74.0-93.0% with RSD of 2.30-3.50% in lake water and tap water, respectively. Furthermore, the selectivity, reproducibility, and stability demonstrated the potential of degradation enzymes as recognition element in detection of cyanotoxins.