Homogeneous time-resolved fluoroimmunoassay of microcystin-LR using layered WS2 nanosheets as a transducer

A homogeneous time-resolved fluoroimmunoassay method for rapid and sensitive detection of microcystin-LR (MC-LR) in water samples was developed based on the interaction between water-soluble WS2 nanosheets and the conjugate of MC-LR with a luminescent Eu3+ complex BHHBCB-Eu3+ (BHHBCB: 1,2-bis[4'-(1'',1'',1'',2'',2'',3'',3''-heptafluoro-4'',6''-hexanedion-6''-yl)- benzyl]-4-chlorosulfobenzene). The large lateral dimensions and high surface areas of two-dimensional layered WS2 nanosheets enable easy adsorption of the MC-LR-BHHBCB-Eu3+ conjugate, that lead to efficient quenching of the luminescence of Eu3+ complex via energy transfer or electron transfer process. However, the addition of monoclonal anti-MC-LR antibody can induce the formation of MC-LR-BHHBCB-Eu3+/antibody immune complex, which prevents the interaction between WS2 nanosheets and MC-LR-BHHBCB-Eu3+ to result in the restoration of Eu3+ luminescence. This signal transduction mechanism made it possible for analysis of the target MC-LR in a homogeneous system. The present method has advantages of rapidity and simplicity since the B/F (bound reagent/free reagent) separation steps, the solid-phase carrier and antibody labeling or modification process are not necessary. The proposed immunosensing system displayed a wide linear range, good precision and accuracy, and comparable sensitivity with a detection limit of 0.3 μg l−1, which satisfied the World Health Organization (WHO) provisional guideline limit of 1.0 μg l−1 for MC-LR in drinking water.