Research Of The Electrochemical DNA Biosensor Based On Graphene

Being a new kind of biosensor,the electrochemical DNA sensor plays an important role in the research of genetic diagnosis and medicine analysis.The electrochemical properties of electrode surface,the immobilization of probe DNA and the detection of electrochemical signals will directly affect the performance of the biosensor.Considering the good electrical conduction ability or the rich oxygen containing groups of graphene and its derivative materials,they are employed as the modified materials in this paper.DNA labeled at 5'-end using amino?NH₂-DNA?was immobilized on the electrode surface through covalent interaction between amino and carboxyl groups on the carboxyl functionalized graphene?or its derivative materials?.Based on the different electrochemical responses of[Fe?CN?₆]^3-/4-toward pDNA versus double-stranded DNA after hybridization,the hybridization process is recorded.During the preparation process,the surface electrochemical properties and the ability for DNA detection of carboxyl functionlizated graphene materials were researched as following:?I?In the first part,carboxyl functionalized graphene oxide?CFGO?was prepared with a novel carboxyl method.With the reasonable dispersion ability of CFGO,the increased amount of carboxyl groups could improve much more anchor for probe DNA immobilization.SWCNTs were employed to promote the electrical transfer and to amplify detectable electrochemical signals.With the electrochemical determination methods of cyclic voltammetry?CV?and differential pulse voltammetry?DPV?,the electrochemical properties of the CFGO and SWCNTs modified glassy carbon electrode were studied.The as-prepared composite film showed a reasonable detection limit and linear range.?II?With the increase of the oxygen groups,the electric transfer rate of CFGO decreaded greatly.Therefore,CFGO was further functionalized to improve its conduction ability.After the partly reduction of CFGO,addition reaction of cyan groups?–CN?and the hydrolysis reaction of–CN,carboxyl functionalized graphene?CFGR-COOH?was obtained with an increased electrical conduction ability and carboxyl groups.The content of oxygen-containing functional groups was estimated by X-ray photoelectron spectroscopy?XPS?,and CV,DPV were used to detect the electrochemical properties of the as-prepard biosensor.CFGR-COOH modified glassy carbon electrode?GCE?performed a good sensitivity and selectivity in the determination of oligonucleotide obtained from the tlh gene segment.?III?In the third section,we developed a new biosensor based on a CFGR-COOH and polyaniline?PANI?modified Platinum electrode?Pt?to detect the tlh gene sequences.The electrochemical performance of the as-prepared biosensor was studied by CV and DPV.All the experimental results showed that CFGR-COOH could not only combine with PANI very well to form a thin film with improved properties,but also performed a reasonable sensitivity and selectivity toward the detection of tlh gene sequences.At the same time,we also established a biosensor for the DNA determination,with a hairpin DNA as probe and the Horseradish peroxidase-Streptavidin?HRP-Streptavidin?as molecular beacon.The sensor showed reasonable electrochemical performance in catalyzing H₂O₂ hydrolysis,which contributed in the oxidation of hydroquinone,indicated that CFGR-COOH hold the ability to realize the amino modified probe immobilization with various base sequences or configuration.All the above experiments further illustrated that CFGR-COOH had feasibility and universality to be used as modified materials in the electrochemical sensing platform.