Rapid Preparation Of Novel Graphene-gold Composite Sensing Materials And Their Application In Electroanalysis

Due to the excellent catalytic activity,conductivity,biocompatibility,plasma properties and easy modification of gold nanoparticles（AuNPs）,they are widely used in the catalysis,optics,medical treatment and electrochemical sensing.However,AuNPs prepared by the existing technology are easy to agglomerate and have unstable three-dimensional network structure,which limits the further application of AuNPs.In recent years,the composite of AuNPs and graphene-based materials has become a research hotspot.The gold-graphene composite provides a more stable three-dimensional structure and higher catalytic activity.However,the lack of strong interaction between AuNPs and graphene results in poor dispersion of gold-graphene composite,which limits the the prominent improvement of electrochemical sensing performance.Therefore,it is of great practical significance to carry out the rapid preparation of AuNPs and combine AuNPs with graphene.This paper focuses on enhancing the catalytic activity of gold-graphene composite,and carries out research work of increasing the exposure of high-index facets,rapid and efficient preparation and construction of nano/microstructure.The mulberry fruit-like gold nanocrystals（MF-Au）with more exposed high-index facets were synthesized by mixed shape inducers.Under the induction of CTAC,KBr and KI,trioctahedron-like gold seeds were obtained by reducing HAuCl₄ with ascorbic acid.Then,the seeds continued to evolve asymmetrically to turn into MF-Auwith the help of L-cysteine（L-cys）.The results show that MF-Auwas a core-shell structure composed of gold nanocrystals of about 200 nm as the core and many irregular gold nanoparticles of about 30 nm as the shell,with more exposed high-index facets.Based on multiple graphene aerogel and DNA cycle amplification,MF-Au-based electrochemical aptasensor was developed and successfully applied to the detection of carbendazim in cucumber.The linear range was from 1.0×10^-16 to1.0×10^-11 mol/L,and the detection of limit（LOD）was 4.4×10^-17 mol/L（S/N=3）.The electrochemical aptasensor had good sensitivity and selectivity compared with the methods reported in the literature.The aspartic acid-functionalized graphene quantum dot-gold composite（Asp-GQD-Au）was rapidly and efficiently prepared by reducing HAuCl₄ with aspartic acid-functionalized graphene quantum dot（Asp-GQD）,which was as reducing agent and stabilizer.The results show that Asp-GQD-Aucould be prepared in a few minutes.Moreover,Asp-GQD with functional groups increased the water dispersion of gold nanoparticles.In addition,Asp-GQD was closely combined with AuNPs through chemical bonds,which significantly improved the electrochemical sensing performance of Asp-GQD-Au.An electrochemical biosensor based on Asp-GQD-Auwas constructed for the determination of chlorpyrifos,carbendazim and acetamiprid in apple.The linear ranges of chlorpyrifos,carbendazim and acetamiprid were1.0×10^-11-1.0×10^-4 mol/L,1.0×10^-10-1.0×10^-4 mol/L and 1.0×10^-9-1×10^-5 mol/L respectively.And the LODs were 3.3×10^-11 mol/L,3.3×10^-10 mol/L and 3.3×10^-9 mol/L separately.Only changing the aptamer of pesticides,this method can be used for the detection of other pesticides.The hybrid of arginine and aspartic acid-functionalized graphene quantum dot（Arg/Asp-GQD）and gold nanoparticles（Arg/Asp-GQD-Au）was synthesized via reduction of HAuCl₄with Arg/Asp-GQD which was as reductant and morphology inducer.As a result,the formed Arg/Asp-GQD-Auwith a pomegranate-like nano/microstructure had excellent structural stability,electronic/ionic conductivity and catalytic activity.Based on Arg/Asp-GQD-Auand double target-induced DNA cycle amplification,an electrochemical aptasensor was constructed to simultaneously determine omethoate and acetamiprid in vegetables and fruits.It was found that the linear range of omethoate was from 5×10^-14 to 5×10^-10 mol/L,and the LOD was 1.7×10^-14 mol/L（S/N=3）.And the linear range was from 5×10^-14 to 5×10^-10 mol/L with a LOD of3.3×10^-15 mol/L（S/N=3）for acetamiprid.The electrochemical aptasensor had better sensitivity and selectivity compared with other methods.