Phase-Dependent Fluorescence Quenching Efficiency of MoS₂ Nanosheets and Their Applications in Multiplex Target Biosensing

Two-dimensional layered transition-metal dichalcogenide nanosheets have shown great potential in biosensors owing to their unique properties. Here, we exfoliated ultrathin metallic and semiconductive MoS2 nanosheets based on a chemical exfoliation method. We compared the difference of fluorescence quenching efficiency between metallic and semiconductive MoS2 nanosheets. We found that the fluorescence quenching efficiency of MoS2 nanosheets is phase-dependent. The ultrathin metallic MoS2 nanosheets with larger contents of a 1T-phase structure show higher fluorescence quenching efficiency than semiconductive MoS2 nanosheets, which can be ascribed to the higher conductivity of metallic MoS2 nanosheets. On the basis of the excellent fluorescence quenching efficiency of metallic MoS2 nanosheets and their discriminative adsorption toward single-strand DNA and double-strand DNA, a fluorescent biosensor for multiplex detection of DNA was developed. This fluorescent biosensing platform allows simultaneous fluorescence quenching of two single-strand DNA probes labeled with different fluorophores, resulting in multiplex detection of different DNA sequences in one homogeneous solution with high sensitivity.