Optical Properties Of Molybdenum Disulfide And Its Application In Sensing

The two-dimensional transition metal sulfide represented by molybdenum disulfide has attracted much attention as a graphene-like material.Due to the variety of size and composition defects of molybdenum disulfide,it has different applications in different fields.When the size of molybdenum disulfide nanomaterials is less than 10nm,they are called molybdenum disulfide quantum dots（MoS₂ QDs）.MoS₂ QD has strong fluorescence due to quantum size effect and edge effect,and has the advantages of simple preparation,low biological toxicity,and good biocompatibility,so it can be widely used in biosensing and environmental detection.MoS₂ NPs and MoS₂nanosheets with a size larger than 10 nm have not fluorescent properties,but they have a surface plasmon resonance（SPR）effect similar to graphene,and can extremely enhance fluorescence of surface fluorescence molecules.So MoS₂ NPs are expected to replace the easily oxidized precious metal nanomaterials to enhance fluorescence,and become a new generation of substrate materials that enhance surface fluorescence.Self-assembled membrane technology is an ordered membrane formed by non-covalent bonding.Self-assembled membranes can control the distance between the substrate material and the fluorescent molecular group by the number of assembly layers of polydimethyldiallylammonium chloride（PDDA）and sodium polystyrene sulfonate（PSS）polyelectrolyte,thereby generating a surface-enhanced fluorescent effect.Therefore,this study proposes the use of MoS₂ QDs for biosensing and temperature sensing.At the same time,large-sized MoS₂ NPs and MoS₂ nanosheets was used as surface-enhanced fluorescent substrate materials,and we combine the effect of surface fluorescence enhancement with self-assembled membrane technology to build a self-assembled sensing membrane.Also we can use the controllable distance characteristics of self-assembled films to control the distance between the substrate and the fluorescent molecules,so as to produce a surface-enhanced fluorescent effect,and explore the effect of the shape of molybdenum disulfide on the surface of the assembled film.Based on the above analysis,This article intends to carry out the following research work:（1）Blue fluorescent MoS₂ QDs were synthesized by hydrothermal method.MoS₂QDs were characterized by atomic force microscope,transmission electron microscope,X-ray photoelectron spectroscopy,fourier transform infrared spectrum,ultraviolet-visible absorption spectrum,and fluorescence spectrum.The salt resistance,acid and alkali resistance and photobleaching resistance of MoS₂ QDs were also discussed.（2）MoS₂ QDs synthesized by hydrothermal method have strong blue fluorescence,good stability and water solubility.The fluorescence intensity of MoS₂ QDs was quenched with the addition of rutin.Its relative fluorescence intensity has a good linear relationship with the rutin concentration.The linear range is 5.0×10^-7-3.2×10^-5 mol/L,and the detection limit is 3.5×10^-7mol/L.In addition,the fluorescence intensity of MoS₂QDs changes with increasing or decreasing temperature.Also,MoS₂ QDs has a good linear relationship with temperature between 20℃and 80℃.Therefore,MoS₂ QDs can be used as fluorescent sensors to achieve a high degree of selectivity to rutin,and at the same time to achieve temperature sensing.（3）The black precipitated MoS₂ NPs without fluorescent properties were synthesized by a hydrothermal method,and the MoS₂ NPs were mixed with chitosan（CS）.The distance between molybdenum disulfide nanoparticles and gold nanoclusters（Au NCs）was controlled by assembling different layers of polyelectrolyte pairs（PDDA/PSS）.Based on the plasma effect of molybdenum disulfide,a Quartz/（PDDA/PSS）2/MoS₂ NPs@CS/（PSS/PDDA）n/Au NCs SAMs assembly membrane was constructed.The fluorescence spectra,fluorescence lifetime,and laser confocal fluorescence microscopy and etc.,were used to characterize them.It was found that the assembled films based on MoS₂ NPs can enhance the fluorescence of Au NCs.Compared with the assembly film based on MoS₂ nanosheet,it was found that the fluorescence enhancement effect of MoS₂ NPs assembly substrate is better than that of MoS₂nanosheet.And Quartz/（PDDA/PSS）2/MoS₂ NPs@CS/（PSS/PDDA）n/Au NCs SAMs self-assembled membranes are used for solid-liquid interface sensing of silver ions,which improves the sensitivity of silver ions about 26 times than that the assembled membrane of unassembled MoS₂ NPs.