Construction of portable electrochemical immunosensors based on graphene hydrogel@polydopamine for microcystin-LR detection using multi-mesoporous carbon sphere-enzyme labels

Abstract

As one of the most common toxins of the toxigenic Cyanobacteria, microcystin-LR (MC-LR) has raised global concerns in water monitoring, environmental detection, toxicology research and epidemiology research. In this work, a portable electrochemical MC-LR immunosensor was fabricated for the detection of MC-LR. Firstly, graphene hydrogel@polydopamine (GH@PDA) was prepared by self-polymerization of dopamine on graphene oxide, followed by a hydrothermal reaction. The modification of polydopamine (PDA) not only acts as an important modifier of the inner structure of the hydrogel, but can also prevent graphene aggregation during further treatments. The transformation to GH@PDA by the hydrothermal reaction was a green synthesis, and this process can be also used to capture biomolecules based on nucleophilic reactions or Schiff base reactions between the catechol groups of PDA and the amino groups of antigens. Secondly, mesoporous carbon spheres, which were loaded with thionine as the electron mediator followed by captured Au nanoparticles, were used to immobilize horseradish peroxidase and secondary antibodies, providing a strong electrochemical response. Using this dual-amplification strategy, the immunosensor can detect MC-LR as a competitive method in the range from 0.01 to 10 μg L⁻¹, with a detection limit of 0.0097 μg L⁻¹. This method also showed good accuracy, acceptable precision and reproducibility. The proposed strategy provides biocompatible immobilization and sensitive recognition for the detection of chemical compounds, pollutants and food contaminants and for clinical diagnosis.