Investigation Of Electrochemical Biosensor Based On Nanocomposite And Redox Protein

In general the direct electron transfer rate of redox protein with the electrode is slow.The reasons can be summarized as follow:most proteins have larger molecular weight and their electrical activity group or redox center was far from the electrode surface and usually deeply buried within the protein molecules;the orientation of the protein in the electrode surface is negative.So it is difficult for electron to transfer between proteins and electrode.Aslo the impurities in solution can be adsorbed on the electrode surface and hinder electron transfer between proteins and electrode.Nanomaterials have exhibited unique optical,electrical and catalytic properties with good biocompatibility,high activity and selectivity.When nano-materials are used as the modifier on the electrode,the specific physical and chemical properties of the nanomaterial itself with the large electrode surface area and good adsorption properties result in the increase the current response with low detection limit.In this paper different nanomaterial are used as modifiers to fabricate several kinds of proteins modified electrodes with the direct electrochemistry and electrocatalysis of proteins investigated in details.The thesis can be summarized as follows:1.CILE was constructed by mixing graphite powder with 1-hexylpyridinium hexafluorophosphate(HPPF6)thoroughly.Hb and Mb was immobilized on the surface of CILE with different composite material such as chitosan,Mg2Al-Cl layered double hydroxide,graphene and Mg2Al layered double hydroxide(LDH)functionalized with 1-carboxyl-methyl-3-methylimidazolium tetrafluoroborate(CMMIMBF4)by step-by-step method to prepare two different modified electrodes denoted as CTS/GR-LDH-Hb/CILE and CMMIMBF4-LDH-Mb/CILE,respectively.UV-vis and Fourier transform infrared spectra(FTIR)indicated that Hb and Mb retained original structure in the resulting GR-LDH-Hb and CMMIMBF4-LDH membrane.Cyclic voltammetric results indicated that a pair of well-defined and quasi-reversible electrochemical responses appeared in pH 3.0 phosphate buffer solution(PBS),indicating that direct electron transfer of Hb and Mb were realized in these modified electrodes.The formal potentials(E0’)were calculated as-0.196 V and-0.209 V(vs.SCE),respectively.These modified electrodes showed excellent electrocatalytic behaviors to the reduction of trichloroacetic acid(TCA)and the apparent Michaelis-Menten constants(KAPpp)was calculated as 8.48 mmol/L and 13.5 mmol/L,respectively.2.A novel,biocompatible sensing strategy based on graphene and titanium dioxide composite for immobilizing the Hb was firstly adopted.Direct electron transfer and bioelectrocatalytic activity of hemoglobin after incorporation into the composite film were investigated.UV-vis and FT-IR spectroscopy confirm that Hb retained its native structure in the composite.A pair of reversible redox waves of Hb appeared and Hb exhibited good electrocatalytic activity toward to the reduction of trichloroacetic acid(TCA).The apparent heterogeneous electron transfer rate constant was calculated as 0.65 s-1 indicating that graphene and titanium dioxide in the composite film could facilitate the electron transfer between matrix and the electroactive center of Hb.The biosensor displays high sensitivity,good reproducibility,and long-term stability.3.Horseradish peroxidase(HRP)was immobilized on the surface of CILE with graphene(GR)and double-stranded DNA(dsDNA)composite material to fabricate the modified electrodes.UV-vis and FT-IR spectroscopy confirmed that HRP intercalated into dsDNA-GR retained its native secondary structure.A pair of well-defined and quasi-reversible cyclic voltammetric peaks appeared,which indicated that the direct electrochemistry of HRP were realized.HRP exhibits excellent long-term bioelectrocatalytic activity towards TCA in the range from 1.0 to 21.0 mmol/L,with a detection limit of 0.133 mmol/L(at S/N=3).So the dsDNA-GR is expected to have widely potential applications for development of new biosensors and biocatalysis.