| Based on the special properties of large surface area, high catalytic efficiency andmultiple active sites of graphene oxide and graphene, a series of graphene oxide andgraphene-based modified electrodes were prepared and used for the determination ofdopamine （DA） and oligonucleotides. Some new types of electrochemical sensors wereconstructed. The main contents are as follows:（1） A graphene oxide （GO） modified glassy carbon electrode （GCE）, namely GO/GCEwas prepared by covalent coupling method, which was characterized by atomic forcemicroscope （AFM）, cyclic voltammetry （CV） and electrochemical impedance spectra （EIS）.When the electrode was applied to determine the biological molecules of dopamine （DA） andascorbic acid （AA）, it is found that DA shows great enhancement, while the electrochemicalresponse of AA is completely precluded, showing that GO has completely different impact onthe electrochemical response of DA and AA. The electrochemical parameters such as thecatalytical rate constant, diffusion coefficient, and electron/proton transfer number of DA onGO/GCE were comprehensively studied, and the possible mechanism to cause the differentresponse variation of DA and AA on GO/GCE was proposed. Furthermore, the modifiedelectrode was applied as a biosensor for the determination of DA. The results show that in theco-exist solution of DA and AA, only the redox signal of DA can be detected, showing thatthe presence of AA has not interference for the electrochemistry of DA. The oxidation peakcurrents of DA present a good linear relationship with the concentrations of DA in the rangefrom1.0×10-6mol/L to1.5×10-5mol/L with a detection limit of2.7×10-7mol/L based on3S/N characteristic.（2） L-cysteine （L-cys） was self-assembled on the electrode surface according to the Au-Sbond. Then graphene oxide, which was preactivated by1-（3-Dimethylanminopropyl）-3-ethylcarbodiimide hydrochloride （EDC） and N-Hydroxy succinimide （NHS）, wascovalently grafted to L-cys/Au surface. Then the amino modified probe DNA was covalentlygrafted on GO/L-cys/Au by a carboxyl-amino condensation reaction to construct a novelDNA biosensor. Through using methylene blue （MB） as the electroactive hybridizationindicator, the electrochemical sensing properties of sensors are investigated by CV anddifferential pulse voltammetry （DPV）. The results show that the biosensor can quantitativelydetect target DNA in the range from1.0×10-15mol/L to1.0×10-9mol/L. The detection limit was estimated to be of5.0×10-17mol/L. The selectivity experiments show that the sensingsystem can accurately discriminate single base mismatch, complementary sequence, threebase mismatch and non complementary sequences. The biosensor has good recognitionability, and high selectivity.（3） An inorganic-organic nanocomposite （GR-CD） containing graphene （GR） andβ-cyclodextrin （CD） was obtained by "one-pot" method. The characterication results fromscanning electron microscope （SEM）, transmission electron microscopy （TEM） and FT-IRspectra confirmed that CD had been effectively functionalized on the surface of graphene.The functional composite was firstly coated on glassy carbon electrode （GR-CD/GCE）. Then2,4,6-trichloro-1,3,5-triazine （TCT） was applied as a linker to graft the5’-anmino modifiedprobe DNA. Thus, a new electrochemical DNA biosensor based on CD functionalizedgraphene sheets was constructed. Through using [Ru（NH3）6]<sup>3+as indicator, the surfacedensity of probe DNA was measured as6.5×1013molucules/cm2. The analysis performanceof the biosensor was investigated by EIS, and the results showed that the electron transferresistance presents a good linear relationship with the concentrations the complementarysequences in the range from1.0×10-16mol/L to1.0×10-12mol/L with a detection limit of3.4×10-17mol/L. The sensor also displayed good selectivity for complementary sequence,base mismatch and non complementary sequences（4） Thioglycolic acid （TGA） and graphene oxide （GO） were immobilized on a goldelectrode in turn by self-assemble and covalent method. The graphene modified electrode（GR/TGA/Au） was obtained by electrochemistry redution, and then1-Pyrene butyric acid（PBA） was functionalized on the suface of GR/TGA/Au through π-π accumulation effect. Anovel electrochemical DNA biosensor was construced by choosing PBA as covalent platformof probe DNA.[Ru（NH3）6]3+was used as the electroactive indicato to monitor analyticalperformance of the biosensor. The experimental results showed that the biosensor canquantitatively detect target DNA in the range from1.0×10-18mol/L to1.0×10-13mol/L with adetection limit of3.6×10-19mol/L. The specificity experiments show that the sensing systemcan accurately discriminate complementary sequence from single base mismatch, three basemismatch and non complementary sequences. |
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