Colloidal Graphene as a Transducer in Homogeneous Fluorescence-Based Immunosensor for Rapid and Sensitive Analysis of Microcystin-LR

Herein, we reported the assembly of colloidal graphene (CG) and microcystin (MC)-LR-DNA bioconjugates to develop a homogeneous competitive fluorescence-based immunoassay for rapid and sensitive detection of MC-LR in water samples. Initially, the MC-LR-DNA probe was quickly adsorbed onto the CG surface through the strong noncovalent pi-pi stacking interactions and can be effectively quenched benefiting from the high quenching efficiency of CG. In contrast, the competitive binding of anti-MC-LR with MC-LR-DNA destroyed the graphene/MC-LR-DNA interaction, thus resulting in the restoration of fluorescence signal. This signal transduction mechanism made it possible for analysis of the target MC-LR. Taking advantage of the colloidal nature of the as-prepared graphene, the assay was carried out in homogeneous solution throughout, which avoided numerous immobilization, incubation, and washing steps that were necessary to traditional heterogeneous immunoassays, thereby reducing the whole assay time (within less than 35 min) and allowing a much better antigen-antibody interaction. Moreover, due to the direct competitive mode, the assay did not involve any antibody labeling or modification process, which would be beneficial to preserve the binding affinity of antigen-antibody. Under optimal conditions, the proposed immunosensor can be applied for quantitative analysis of MC-LR with a detection limit of 0.14 mu g/L, which satisfied the World Health Organization (WHO) provisional guideline limit of 1 mu g/L for MC-LR in drinking water, thus providing a powerful tool for rapid and sensitive monitoring of MC-LR in environmental samples.