Non-covalently Functional Modification Of Graphene And For Sensing Applications

As a member of the carbon nanomaterial family,graphene has aroused wide attention because of its unique structure and excellent properties.It has been widely studied in various fields,especially in the field of electrode materials related to electrical conductivity.Since?-?interactions and large van der Wals forces between the layers,graphene is prone to agglomerate,which limits its application as an electrode material.Utilizing the covalent or non-covalent bonds,hydrophilic molecules or groups are combined with graphene to solve this problem.At the same time,the modifiers introduced can also provide additional functions for graphene and open up a new way to develop sensors.In view of the cumbersome operation of covalent modification,the limited amount of modifiers introduced and the vulnerability of graphene's intrinsic structure,this paper chooses polymeric ionic liquid as the medium of non-covalent modification of functional molecules,cyclodextrins with molecular recognition function,aspartame with good biocompatible dipeptide molecule and methylene blue with artificial mimetic enzymes function as modifiers to non-covalently combine graphene.Their applications in electrochemical sensing and fluorescence sensing were studied.The specific research works are as follows:1.A hybrid nanocomposite?SBE-?-CD/PILs-rGO?was prepared by the modification of sulfobutyl cyclodextrin?SBE-?-CD?and polymeric ionic liquids?PILs?onto reduced graphene oxide?rGO?based on the self-assembly method.The SBE-?-CD/PILs-rGO nanocomposites not only have the hydrophilicity of polymeric ionic liquids,the recognition of host-guest of?-cyclodextrin,but also have the advantages of ultra-high specific surface area of graphene materials.The composites were used for the cholesterol fluorescent sensing and exhibited good selectivity towards the substrate.The fluorescence quenching property of graphene improved the sensitivity of fluorescence detection.At the same time,SBE-?-CD/PILs-rGO nanocomposites were used to construct modified electrode for electrochemical detection of bisphenol A?BPA?.The experimental results showed that the modified electrode exhibited good electrochemical detection performance for BPA.2.The poly?vinyl-3-ethylimidazolium bromide?functioned reduced graphene oxide?Poly?ViEtIm⁺Br^-?-rGO?nanocomposites with good dispersion in water and positively charged were prepared via?-?interaction.The morphologies and properties of the nanocomposites were characterized by transmission electron microscopy?TEM?,infrared absorption spectroscopy?FT-IR?,ultraviolet-visible absorption spectroscopy?UV-vis?and zeta potential.By means of ion exchange property of the polymeric ionic liquids,the dispersity of the Poly?ViEtIm⁺Br^-?-rGO in aqueous solution can be regulated.Due to the positive charge on the surface of the nanocomposites,the negatively charged catalase?CAT?can be adsorbed onto the surfaceofthePoly?ViEtIm⁺Br^-?-rGOnanocompositestoform CAT/Poly?ViEtIm⁺Br^-?-rGO nanocomposites under electrostatic force.The preparation process of the nanocomposites was monitored by UV-vis and FT-IR.In addition,the electrochemical behavior of CAT/Poly?ViEtIm⁺Br^-?-rGO/GC modified electrode was also studied.The results showed that the modified electrode not only effectively promote the direct electron transfer of CAT on the electrode surface,but also displayed good electrocatalytic performance for H₂O₂.The experiment results demonstrated that Poly?ViEtIm⁺Br^-?-rGO composites could not only promote the direct electron transfer between the immobilized CAT and the surface of electrode,but also displayed excellent bioelectrocatalytic activity to the reduction of H₂O₂.3.A novel aspartame-reduced graphene oxide?APM-rGO?nanocomposites were prepared based on the self-assembly of aspartame?APM?and rGO.Due to the amphiphilicity of APM,the new nanocomposites have good dispersibility and biocompatibility.The prepared nanocomposites were characterized by TEM,FT-IR,UV-vis and Zeta potential.The nanocomposites not only dispersed well in water,but also exhibited negative charge properties.Under mild conditions,the positively charged horseradish peroxidase?HRP?was immobilized on the surface of APM-rGO nanocomposites by electrostatic adsorption,and the HRP/APM-rGO/GC modified electrode was constructed.Uv-vis and FTIR spectra confirmed that HRP immobilized onto the hybrid matrix maintained its native activity.Moreover,the nanocomposite facilitated the direct electron transfer for the HRP-Fe?III?/Fe?II?redox centre.The prepared modified electrode exhibited good catalytic activity for H₂O₂ and NaNO₂,respectively.Therefore,this work provided a practical platform for the commercial application of dipeptides in electrochemical?biological?sensing.4.In this chapter,a novel methylene blue-reduced graphene oxide?MB-rGO?nanocomposites were prepared by?-?interaction between methylene blue?MB?and rGO The nanocomposites were characterized by scanning electron microscopy?SEM?,TEM,X-ray diffraction?XRD?,Zeta potential,FT-IR,UV-vis and X-ray photoelectron spectroscopy?XPS?.UV-vis spectroscopy and electrochemical tests showed that the MB-rGO modified on the electrode exhibited glucose oxidase-mimetic catalytic activity towards glucose,and displayed good electrocatalytic performance for electrochemical detection of glucose with a wide linear range from 1.04 to 17.44 mmol L^-1,a low detection limit of 45.8?M and a large sensitivity of 13.08?A cm^-2 mM^-1.The proposed glucose sensor also showed high stability,reproducibility and good abilities of anti-interference to dopamine,ascorbic acid and uric acid.Moreover,the modified electrode was used to determine glucose concentration in human blood serum sample with satisfactory results.The research results exhibited that the polymeric ionic liquid had good conductivity and ion exchangeability,which made it an ideal non-covalent modification medium.The cyclodextrins immobilized on graphene by polymerized ionic liquids were well maintained their molecular recognition function.Their graphene nanocompostie showed good electrochemical and fluorescence sensing properties.The catalase immobilized on graphene by polymeric ionic liquids maintained high catalytic activity.In addition to polymeric ionic liquids,aspartame,the simple small molecules,were also good dispersants for graphene.As a medium,the biological enzymes could be immobilized on graphene by electrostatic interaction at a certain pH value.The methylene blue-graphene composites were simple in composition and apt to be prepared.As an electrode material,methylene blue-graphene complex had excellent catalytic activity of enzyme-mimetic.The preparation of these graphene-based composites provided new research platforms for the study of novel sensors.