Study On The Preparation And Application Of Electrochemical Biosensor Based On Dnazyme And Graphene

With the rapid development of urbanization and industrialization, pollution raisedseriously, became one of the most concerned problems in public. Dihydroxybenzenewas widely used in the production of dyes, pesticides, rubber and other industrialfields. It is serious environmental pollutants because it is toxic to humans and difficultto degrade in the ecological environment. The harm of heavy metal ions has beenfamiliar to people, which difficult to degrade, and which can be accumulated in thehuman body through the air, water, food chain, leading a serious threat to people’shealth and life. Therefore, it is of great significance to establish a sensitive, fast,simple and convenient method to detect them as to the control of environmentalpollution and the protection of human health. Electrochemical biosensor exhibitsadvantages of low cost, high sensitivity, good selectivity and quick involved inpharmaceutical, environment detection analysis, food areas, indicating its broad spaceto develop and apply. In this dissertation, we developed the electrochemical Pb2+sensor based on DNAzyme labeled with electroactive and an electrochemical sensorfor determination of dihydroxybenzene based on graphene and titanium dioxidenanocomposite. The details are summarized as follows:(1) Electrochemical sensor for lead ion based on conformational change ofDNAzyme. In this chapter, We have developed an electrochemical biosensors basedon Pb2+- dependent DNAzyme occurs Specific fracture through ferrocene as thesignal expression. ferrocene covalently attached to DNAzyme 5’-end, the other endbonding on a gold electrode surface via thiol-Au interactions. Through thecomplementarily of bases, prompted the DNA terminal that labeled with ferrocene foldback to form a "hairpin" structure, then ferrocene close to the electrode surface andincreased the charge transport efficiency, the electrochemical signal enhancement.When the solution containing Pb2+, enzymes are activated, prompting the substratestrand fracture. The substrate strands along with the ferrocene was released tosolution from the Au electrode surface. The dissociation of Fc caused electrochemicalsignal change to detect Pb2+. The system exhibits a dynamic response range for thelogarithmic concentration of Pb2+from 0.5 to 5000 n M with a detection limit of 0.25 n M. The sensor has the advantages of simple preparation, good performance, highselectivity.(2) Electrochemical sensor for lead ion based on DNAzyme labeled withferrocene. We designed DNA probes for the construction of electrochemicalbiosensors. Which inducing hydrolysis of RNA by Pb2+caused electrochemical signalchange by electroactive group abscission. Ferrocene covalently attached to DNA25’-end according to the succinimide coupling method. The Ferrocene modifiedfragments are used as signaling probes to hybridize with the complementary DNA1 strands, enable DNA2 to upright partial, at the end of the soft T chain labeled withferrocene under the influence of the gravity and draping, brought ferrocene in closeproximity to the gold electrode surface, produce a detectable redox current, cancapture the strong electrochemical signal. In the present of Pb2+, hydrolytic cleavageof the ribonucleic acids, the cleaved pieces away from electrode surface, thisdiffusion resulted in the decrease of electrochemical signal. The differenceconcentration of Pb2+caused electrochemical signal change to detect Pb2+. The systemexhibits a dynamic response range for the logarithmic concentration of Pb2+from 0.2- 1000 n M with a detection limit of 0.11 n M. In addition, the sensor exhibits excellentcharacteristics, such as high sensitivity, wide linear range, lower detection limit andfast response time.(3) Electrochemical sensor for dihydroxybenzene based on graphene and titaniumdioxide nanoparticles nanocomposite. We developed graphene and titanium dioxidenanoparticles nanocomposite modified glass carbon electrode for simultaneousdetermination of catechol(CC) and hydroquinone(HQ). The application of Gr-Ti O2 nanocomposite in simultaneous determination of CC and HQ was investigated bycyclic voltammetry and differential pulse voltammetry. The results show that Gr-Ti O2 nanocomposites promote electron-transfer kinetics occurs which could be attributedto high electrical conductivity and larger surface area. A pair of well-defined redoxpeaks are observed in CV, the peak potential separation is large enough to separate thetwo components. The oxidation peak currents of CC and HQ were linear over therange of 0.5- 100 μM with the detection limits of 0.087 μM for CC and 0.082 μM forHQ, respectively. In addition, the modified sensor shows excellent reproducibility,stability anti-interference, and was successfully applied in real water samples.