Electrochemical immunosensor for ultrasensitive detection of microcystin-LR based on graphene–gold nanocomposite/functional conducting polymer/gold nanoparticle/ionic liquid composite film with electrodeposition

The study developed an electrochemical immunosensor for ultrasensitive detection of microcystin-LR in water. Graphene oxide and chloroauric acid were alternately electrodeposited on the surface of glassy carbon electrode for 20 cycles to fabricate graphene–gold nanocomposite. The composite was characterized and its apparent heterogeneous electron transfer rate constant (37.28±0.16 cm s−1) was estimated by Laviron's model. To immobilize microcystin-LR antibody and improve the electrical conductivity, 2,5-di-(2-thienyl)-1-pyrrole-1-(p-benzoic acid) and chloroauric acid were electrodeposited on the modified electrode in sequence. The ionic liquid was then dropped on the electrode surface and finally microcystin-LR antibody was covalently connected to the conducting polymer film. Experiment showed the electrochemical technique offers control over reaction parameters and excellent repeatability. The graphene–gold nanocomposite and gold nanoparticles enhance electron transfer of Fe(CN)63−/4− to the electrode. The ionic liquid, 1-isobutyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide, improves stability of the antibody. The sensor displays good repeatability (RSD=1.2%), sensitive electrochemical response to microcystin-LR in the range of 1.0×10-16–8.0×10−15 M and detection limit of 3.7×10−17 M (S/N=3). The peak current change of the sensor after and before incubation with 2.0×10−15 M of microcystin-LR can retain 95% over a 20-weeks storage period. Proposed method presents remarkable improvement of sensitivity, repeatability and stability when compared to present microcystin-LR sensors. It has been successfully applied to the microcystin-LR determination in water samples with a spiked recovery in the range of 96.3–105.8%.

► Proposed strategy to fabricate the graphene–gold nanocomposite and sensor is green and controllable.
► Graphene–gold nanocomposite remarkably enhance the electron transfer rate.
► The antibody was covalently immobilized on the electrode using functional conducing polymer.
► The ionic liquid improves biocompatibility of the microenvironment for the antibody.
► The sensor for microcystin-LR offers the best sensitivity and stability up to now.