Electrochemical Sensors Based On The Carboxylic Graphene And Aptamer For The Detection Of Bacterial

The study in this paper can be divided in two parts:(1)An electrochemical aptasensor based on the carboxylic graphene oxide(CFGO)/single-walled carbon nanotubes(SWCNTs)modified electrode was fabricated and applied in the detection of E.coli in water;(2)The carboxylic reduced graphene oxid(CFrGO)was employed in the construction of the electrochemical aptasensor for detecting E.coli and the aptasensor was applied in the meat and the milk.The detailed work was as follows:In chapter 2,the graphene oxide was firstly carboxylated to CFGO with a high amount of the carboxylic group by HBr and oxalic acid.The scanning electron microscope(SEM),the transmission electron microscope(TEM)and X-ray photoelectron spectroscope(XPS)were employed for the characterization of CFGO.Secondly SWCNTs was dropped to the surface of the glassy carbon electrode(GCE)to obtain SWCNTs/GCE,which SWCNTs can enhance the electron-transfer ability.And then CFGO was added on SWCNTs/GCE to get CFGO/SWCNTs/GCE.The amino-aptamer was immobilization onto the CFGO/SWCNTs/GCE through the amide bond by EDC(1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride)and NHS(N-hydroxysuccinimide).The effect factors on the construction process of aptasensor were studied,such as dropping times of SWCNTs,the activation time of the carboxylic group and the binding time of the aptamer.Moreover,the adhesion of bacteria on the surface of the aptasensor was also discussed.Electrochemical impedance spectroscopy(EIS)was employed to characterize the construction of aptasensor and to detect E.coli.The results showed that CFGO contained more-COOH groups than GO and could be used for the immobilization of the aptamer.The aptamer-CFGO/SWCNTs/GCE showed the good specific recognition of the target bacterial(E.coli KCTC 2571)with the wider concentration range(10~2-10~7 CFU/mL)and the lower detect limit(2.7 CFU/mL,S/N=3).The aptamer-CFGO/SWCNTs/GCE was successfully used in the detection of E.coli in the lake water.In chapter 3,firstly the oxygen–containing groups except the carboxylic group on the CFGO were reduced by thiourea dioxide(TUD).Secondly the cyanide was introduced on the graphene by 2,2'-azobis(2-methylpropionitrile)(AIBN)and then changed to the carboxylic group through the hydrolysis reaction.The CFrGO with20%carboxylic group was obtained.CFrGO was added to the surface of GCE to obtain CFrGO/GCE and the amino-aptamer was immobilized on the surface of CFrGO/GCE by EDC.The effects of activation time of-COOH and the binding time of aptamer on the construction of aptasensor was discussed.Meanwhile,the adhesion time of E.coli on the surface of aptasensor was also studied.Under the optimal conditions,the detection of E.coli at different concentrations was studied by EIS.The results showed that CFrGO not only could bind to the aptamer by condensation reaction,but also had the excellent ability of electron-tranfer.Furthermore,the electrochemical aptasensor showed good linear response in range of 10~1-10~7 CFU/mL.The modified electrode was also successfully applied in the analysis of real samples,such as meat and milk.