The Electrochemical Biosensors Based On Novel Semiconductor Metal Nano-materials

Nanomaterials have many unique properties, such as the large surface area, highcatalytic efficiency, strong adsorption ability and so on, for this advantages it has beenwildly applied in the field of sensing and biological analysis. The electrochemicalbiosensors base on nanomaterials not only effectively solve the problem ofimmobilization and regeneration for the sensitive materials, but also greatly improvethe detection performance of the sensor. Furthermore, it makes the sensor easily tominiaturization and more function. In this paper, we synthesized three novelnano-particles and constructed the electrochemical biosensor base-on nanometerinterface. The prepared biosensor were application for the analytes in EscherichiaColi DNA sequences, Listeria DNA sequences and biological activity reductant ofgallic acid and obtained the satisfactory results. Main contents are as follows:(1) In this work, three CdS materials with different shapes (i. e., irregular, rod-like,and elongated hexagonal-pyramid) were hydrothermally synthesized throughcontrolling the molar ratio of Cd2+and thiourea. Then the products were characterizedby X-ray diffraction and scanning electron microscope, and the possible growthmechanism was also proposed. Electrochemical characterization experiments showedthat the elongated hexagonal-pyramid CdS (eh-CdS) had the higher electricconductivity than the other two forms because its polyhedron structure provided muchmore electrocatalytical sites. Therefore the eh-CdS was selected as anelectron-transfer medium to modify a glassy carbon electrode (GCE), which wasfollowed by in-situ electro-polymerization of a poly-isonicotinic acid (PIA) film toenhance the stability and functionality of the interface. The layer-by-layermodification process was characterized by atomic force microscopy andelectrochemistry. Then a new DNA biosensor was successfully constructed bycovalent coupling of5’-amino modified probe DNA of Listeria with the carboxylicgroups on PIA-eh-CdS composite film, and the hybridization performance of thebiosensor was evaluated using methylene blue as redox indicator. The results showed that the peak currents of methylene blue varied with target concentrations in a widelinear range from1.0×1014M to1.0×109M (r2=0.995). The detection limit wasestimated to be as low as3.9×1015M based on3σ. This biosensor also showed highstability and good discrimination ability to the one-base, three-base mismatched andnon-complementary sequence.(2) In this work, fern leaf-like α-Fe2O3nanoparticles were synthesized via a faciletemplate-free hydrothermal method and their morphologies, structures and elementcomponents were characterized by X-ray diffraction, energy dispersive spectrometry,scanning electron microscope and transmission electron microscope. Then thenanocomposite containing Fe2O3and chitosan (CS) was coated on the surface ofglassy carbon electrode. Electrochemical characterization showed that the modifiedelectrode possess large accessible surface area and high electrical conductivity. Therich amines on chitosan had an efficient reaction with aldehyde reagent. Then a DNAbiosensor was fabricated through covalent immobilization of5’-amino modifiedListeria specific DNA on CS-Fe2O3nanocomposite modified electrode usingterephthalaldehyde (TPA) as a bifunctional arm linker. The hybridization capacity ofthe developed biosensor was monitored with electrochemical impedance spectroscopy(EIS) using [Fe(CN)6]3/4as an indicating probe, and the experimental results showedthat the biosensor had fast hybridization rate and low background response. A widedynamic detection range (1.0×1014-1.0×109M) and a low detection limit (5.6×10-15M) were achieved for the complementary sequence. Moreover, the biosensor showedthe advantages of high selectivity to non-complementary DNA sequence,base-mismatched DNAsequence, and good stability.(3) A novel fishbone-like iron oxide (fFe2O3) nanoparticles were synthesized byhydrothermal method, and a highly sensitive and selective electrochemical sensor forgallic acid (GA) had been fabricated on the basis of modification of a glassy carbonelectrode (GCE) with the hybrid material of chitosan (CS)-fFe2O3-electrochemicallyreduced to graphene oxide (ERGO). Due to the synergistic of the three material, themodified electrode (CS-fFe2O3-ERGO/GCE) shows multiple advantages, such as largesurface area, excellent electrical conductivity and high stability during determination of GA. The electrochemical experiment shows that the modified electrode（CS-fFe2O3-ERGO/GCE）had a good electrocatalysis activity towards to GA in theacid conditions. Under the optical conditions, the oxidation peak currents (Ipa)presented a good linear relationship with the GA concentration over the rang from1.0×10-6to1.0×10-4M. Base on signal-to-noise characteristic, the detection limit wasestimated to1.3×10-7M. The proposed sensor has also been successfully applied forthe determination of GA in real samples of red wine, white wine and green teaextracts, and the results were satisfactory.