Studies Of The Third-generation Electrochemical Biosensor Based On Different Dimension Nanomaterials

Direct electrochemistry of redox proteins has attracted considerablerecent attention since it provides fundamental knowledge of redox behavior ofproteins or enzymes in a biological system and serves as a model system to aidin the understanding of electrontransfer mechanisms, and also provides afoundation for the construction of third-generation biosensors.Nanotechnology provides a new way to construct the third-generationbiosensor. Nanomaterials have unique optical, electrical and catalyticproperties and large surface area, good biocompatibility, which can greatlyenhance the direct electron transfer of proteins and promote the biosensorperformance. The object of this dissertation is to explore different dimernsionsnanomaterials for fabrication the third-generation biosensors. More details aresummarized below:1.1-D nanomaterial, MnO₂nanorods, was prepared and shown to be apromising matrix with biocompatible polyquaternium (QY) for Mb immobilization. The structure and morphology of the MnO₂nanorods werecharacterized by X-ray diffraction (XRD) and scanning electron microscopy(SEM). Fourier transform infrared (FTIR) spectra revealed that Mbimmobilized in the MnO₂-QY nanocomposite film retained its native structure.Compared with Mb-MnO₂/GC electrode, the prepared Mb-MnO₂-QY/GCelectrode displayed wider linear range0.5-120μmol·L^-1, a lower detectionlimit of0.3μmol·L^-1, better stability, interference immunity andreproducibility.2.2-D nanomaterial, TiO₂nanosheets, was applied to assemble(Mb/TiO₂)nfilms by layer-by-layer technology. Electrochemical impedancespectroscopy (EIS) and UV-Vis spectra were used to monitor thelayer-by-layer process. The morphology of films was characterized by SEMand Atomic force microscope (AFM). The thickness of film was much smallerthan the films assembled by other nanomaterials. The prepared electrodeexhibited high catalytic efficiency to H₂O₂. On the basis of MnO₂nanosheetsand Mb, Nafion was added to successfully assemble the(Mb/Nafion/Mb/MnO₂)nmultilayer films. The composite film not onlyprovided a favorable microenvironment for Mb but also kept the stability dueto the rigid structure of nanosheet.3.2-D nanomaterial, commercial conductive graphite nanosheet KS6,was designed for the immobilization of Hb to construct biosensors for thedetection of NaNO₂. The FTIR and UV-Vis spectra revealed that Hb retained its native secondary structure in the KS6-based composite film. TheHb-KS6-Nafion/GC electrode exhibited fast direct electron transfer andshowed a good electrocatalytic performance to NaNO₂with wide linear rangeof8-460μmol·L^-1and460-2300μmol·L^-1, stability and interference immunity.4.3-D nanomaterial, nanosheet-based TiO₂microspheres with a hollowcore-shell structure, have been synthesized and employed to immobilize HRPin order to fabricate a mediator-free biosensor. The morphology and structureof the TiO₂microspheres were characterized by XRD, SEM and TEM. Apossible growth mechanism has been proposed. Spectroscopic andelectrochemical measurements revealed that the TiO₂microspheres are animmobilization support with biocompatibility for enzymes, affording goodenzyme stability and bioactivity. Due to the nanosheet-based hollow core-shellstructure of the TiO₂microspheres, the direct electron transfer of HRP isfacilitated and the resulting biosensor displayed good performance for thedetection of H₂O₂, with both a low detection limit of0.05μmol·L^-1and a widelinear range from0.4to140μmol·L^-1.5.3-D nanomaterial, interlaced nanosheet-based Co(OH)₂porous film, havebeen successfully fabricated by one-step cathodic electrodeposition method.Hb was successfully immobilized on a GC electrode modified by interlacednanosheet-based3-D acroporous Co(OH)₂films. The nanosheet-likemorphologies of Co(OH)₂were observed by SEM. UV-Vis spectra reveal thatHb immobilized on the Co(OH)₂film almost retains its native structure. A fast direct electron transfer is achieved between Hb and underlying electrode withan average electron transfer rate of8.34s1. The resulting biosensor exhibitsgood performance for the detection of H₂O₂, with a wide linear range from0.4to200μM,low detection limit of0.2μM, high sensitivity of743.67μA mM-1cm-2, excellent stability and reproducibility.