Ultra-sensitive detection of microcystin-LR with a new dual-mode aptasensor based on MoS2-PtPd and ZIF-8-Thi-Au

A novel dual-mode aptasensor was fabricated for ultra-sensitive detection of microcystin-LR (MC-LR). The direct method was developed using chronoamperometry for quick detection. A glass carbon electrode (GCE) was first modified with MoS2-PtPd nanoparticles (NPs). MoS2-PtPd was used as a substrate for a higher loading of aptamers and to amplify the signal by catalytic activity toward H2O2. The aptamer was then assembled onto the modified electrode surface to work as a recognition probe to bind MC-LR. To increase the sensitivity of the aptasensor, we developed an indirect method for ultra-sensitive detection through synthesizing and utilizing novel zeolitic imidazolate framework (ZIF)-8-thionine (Thi)-Au as signal material for the first time. This signal material not only possessed the high conductivity of Au NPs, but also produced current signal from a redox reaction by Thi. The complementary strand of the aptamer was immobilized on the surface of ZIF-8-Thi-Au and their compounds hybridized with the aptamer on the MoS2-PtPd modified GCE. MC-LR would replace ZIF-8-Thi-Au compounds by competition binding with the aptamer. The electrical signal would decrease then and be detected by SWV. Under optimal conditions, the linear ranges of the indirect and direct methods were respectively 0.01-50 and 0.1-50 ng mL(-1). And LOD of the indirect and direct method were respectively 0.006 and 0.045 ng mL(-1) (signal-to-noise ratio= 3). The aptasensor ensured the accuracy of the detection outcome through comparing the results of the two modes and provided a potentially reliable and ultra-sensitive detection method of MC-LR in water environments.