The Construction Of Three Complex Interfaces Based On Graphene Or MoS₂ For Electrochemical Analysis Application

As we all know, due to the excellent electron conductivity, high specific surface area and the most important property of two-dimensional（2D） layered structure etc., graphene has been wide used in many fields, such as energy storage, catalysis, sensing and so on, which showed excellent performance. With the flourish of 2D sized graphene, the 2D layered analogous graphene nanomaterials such as molybdenum disulfide（MoS₂） and 2D covalent organic covalent gradually attract people’s attention. These 2D materials with a graphene-like structure and unique properties, possess excellent application potential in many fields. In addition, the conductive polymers represented by polyaniline, have very wide application space in catalysis and electrochemical sensing aspects due to their outstanding electrical conductivity and excellent electrochemical activity. The integration of nanomaterials can often get better performance, which break through the limitations of a single nanomaterial in applications.In this paper, 2D nanomaterials or the composites based on them were used as the supporting substrate, and a series of electrochemical sensors were prepared for studying the performance in the application of sensing detection of small biological molecules, DNA and other small molecules. This paper is divided into the following sections:（1） Using flavin mononucleotide sodium（FMNS） as the stabilizer for the dispersion of graphene prepared by thermal reduction method in aqueous solution, we obtained the nanocomposite of graphene and FMNS named GR@FMNS that can stably uniformly dispersed in aqueous solution. Due to the good conductivity and large surface area, graphene has a lot of advantages in terms of sensing applications. But the less surface functional groups of graphene make it difficult to disperse in an aqueous solution, which greatly limits its application scope. The integration of graphene with flavin mononucleotide solved the problem of graphene’s stable dispersion in aqueous solution. Besides, flavin mononucleotide itself has electrochemical activity that can be used as a signal for an electrochemical senso. Accordingly, we prepared an electrochemical DNA sensor based on GR@FMNS nanocomposite. By means of the signals of external indicator, [Fe（CN）6]3-/4-, the nanocomposite’s own electrochemical signals and π-π* stacking interaction between graphene and DNA, this electrochemical DNA sensor can achieve dual signal detection. This dual signal detection method greatly improves the stability and reliability of the detection, and possess high sensitivity as well. Using the signal of [Fe（CN）₆]3-/4- and the self-signal of flavin mononucleotide as the detection signals, in the concentration range of 10-6 mol L^-1 10-16 mol L^-1, they showed good linear relationships respectively: Ipa（10-5 A） = 0.1514 lg(C / mol L^-1) + 0.171, R2 = 0.9976 and Ipa（10-5 A） = 0.3278 lg(C / mol L^-1)- 0.6815, R2 = 0.9963, and the detection limits are 7.4 × 10-17 mol L^-1 and 8.3 × 10-17 mol L^-1. Besides, this method displayed high selectivity, which can distinguish the single-base mismatched DNA and three-base mismatched DNA. Our work provides a good way for the detection of vibrio in the sea, which is of great significance for the prevention and treatment of diseases caused by vibrio. We believe that this method can be extended to the sensing analysis of other DNA or biological molecules.（2） Molybdenum disulfide/polyaniline（MoS₂/PANI） nanocomposites were prepared by chemical oxidation polymerization of aniline on the surface of 2D thin-layered MoS₂ nanomaterial. The prepared MoS₂/PANI nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectrum. A new type of electrochemical sensor based on MoS₂-PANI nanocomposite was developed for the sensing detection of chloramphenicol. Due to the interaction between MoS₂ and PANI nanomaterial, compared with a single MoS₂ or PANI nanomaterial, MoS₂/PANI nanocomposite shows superior electronic conductivity, exhibit better electrochemical performance, and synergistic catalytic effect for the electrochemical oxidation and reduction processes of chloramphenicol. Accordingly, as a new electrode material, it can be used to construct an electrochemical chloramphenicol sensor. The electrocatalytic signal of nanomaterials for chloramphenicol was used as the detection response signal, a series of experimental conditions, such as modified materials, the amount of MoS₂ and reaction time in preparation of nanocomposite, and the p H of solution had been optimized at first, and then a series of concentrations of chloramphenicol had been detected to get the detection range and detection limit, as well as the detection sensitivity, stability and the capability of the application in real samples. The results indicated that the electrochemical chloramphenicol sensor based on MoS₂/PANI nanocomposite showed high sensitivity, and good stability. The detection range of chloramphenicol was 1.0 × 10-7 mol L^-1 1.0 × 10-4 mol L^-1, the detection limit reached 6.9 × 10-8 mol L^-1, and it can be used for the detection of chloramphenicol in real samples.（3） Adopting pulse potentiostatic method, poly（m-aminobenzene sulfonic acid）-MoS₂（PABSA-MoS₂） nanocomposites were prepared based on m-aminobenzene sulfonic monomer and thin-layered MoS₂. While during the oxidative polymerization of m-ABSA, thin-layered MoS₂ nanosheets were partly reduced, as a result, their electrocatalysis properties were enhanced. The resulting PABSA-MoS₂ nanocomposites exhibited synergistic catalytic activity. We constructed electrochemical sensors based on MoS₂-PABSA nanocomposites for sensing analysis of dopamine. Using electrocatalytic signals as the detection signals, we carried out a series of optimization experiments, such as: modifying materials, time and potential of PABSA’s polymerization, and the p H of solution etc. conditions. Under the optimal conditions, different concentrations of dopamine were detected, and the sensitivity, detection range and detection limit of the electrochemical sensors were investigated. Experimental results showed that the electrochemical sensors based on PABSA-MoS₂ nanocomposites exhibit good performance for the sensing detection of dopamine. The detection limit was as low as 0.32 μmol L^-1, in the concentration ranges of 1 50 μmol L^-1 and 50 1000 μmol L^-1 showed good linear relationships: Ip（μA） = 0.2218 C(μmol L^-1) + 0.1047, R2 = 0.9984, and Ip（μA） = 0.0439 C(μmol L^-1) + 10.07, R2 = 0.9944, respectively. Besides, it displayed good reproducibility and stability.