Fabrications And Applications Of Carbon Nanotubes Electrode

Direct electron transfer (DET) of proteins (enzymes) has received much attentionfor the development of reagentless biosensors.These studies can help us understandthe structure and electron transfer mechanism of proteins.However,the DET betweenproteins and electrode is difficult realized due to the deeply embedded redox-activecenter of potein molecules.The attempts for improving protein bioactivity,andrealizing the direct protein electrochemistry have been reported recently,such as usingnanoparticles,carbon nanotubes.Since the discovery of carbon nanotubes,they have attracted enormous interestbecause of their unique mechanical,electronic and chemical properties.Because oftheir unique structural,extraordinary physical and mechanical properties and goodconductance,carbon nanotubes are attractive for a diverse range of applications inprobe of microscope,panel displays,supercapacitor,chromatographic separation andsensors.Moreover,the surface effect of carbon nanotubes such as high surfaceactivity makes high electron transfer when used as electrode and has been wellapplied in electro-catalysis and electro-chemistry,such as direct electron transfer ofproteins and electrochemical biosensors.In this paper,we have fabricated two types of multiwalled carbon nanotubesmodified electrodes by combining the excellent physical,chemical,electro-catalyticproperties and good biocompatibility of carbon nanotubes,with the small size andlarge specific surface area effects of nanoparticles.Hemoglobin on the carbonnanotubes based electrodes has well-defined redox reaction.The biosensors showedgood electrocatalytic activities to the reduction of H₂O₂.Aligned carbon nanotubesarray (ACNTs) have been prepared in this dissertation by chemical vapor deposition. The ACNTs electrode was fabricated and then hemoglobin and glucose oxidase wereimmobilized on its surface using different methods.The ACNTs based biosensorsexhibited high sensitivity,low detection limit and faster response time.The details aregiven as follows:Chapter One:PrefaceDiscovery and applications of carbon nanotube were introduced in the first part,including the classification,properties,preparation methods,functionalizations andapplications of carbon nanotubes.After that,the direct electron transfer of proteins(enzymes) was introduced,including the significance and progress of research and theapplications of nanomaterials in the protein (enzyme) biosensors.Chapter Two:Electrochemistry and Electrocatalysis of Hemoglobin on1-Pyrenebutanoic acid Succinimidyl ester/Multiwalled Carbon Nanotube and AuNanoparticle modified ElectrodeA biocompatible nanocomposite film was fabricated for hemoglobin (Hb)molecules immobilization.This film consists of multiwalled carbon nanotubes(MWNTs),1-pyrenebutanoic acid,succinimidyl ester (PASE),hemoglobin (Hb) andAu nanoparticles (AuNPs).Herein,PASE molecules physically adsorbed ontoMWNTs,and its groups then covalently bond with Hb.AuNPs were then linked withHb/PASE/MWNTs via electrostatic adsorption force.UV-visible adsorption spectra,Fourier transform infrared spectra,scanning electron microscope and electrochemicalimpedance spectroscopy have characterized the film.Cyclic voltammetry (CV) scansshowed that in the film Hb has well-defined redox reaction,with the formal potential(E⁰) at about-0.27V (vs.Ag/AgCl).Herein,differential pulse voltammetry (DPV) wasemployed to electrochemically detect the Hb in the film with a detection limit of9.3×10^-8 M.The proposed method was also succeeded for Hb detection in clinicalblood samples.Furthermore,the Hb in the film showed good electrocatalytic activitiesto the reduction of H₂O₂,TCA,NaNO₂ and O₂. Chapter Three:Electrochemistry and Electrocatalysis of Hemoglobin onMWNTs/Au and SiO₂ sol-gel Assembly modified ElectrodeA protein electrochemical biosensor was fabricated by immobilizing Hb onMWNTs/Au and SiO₂ sol-gel assembly modified electrode.First of all,a certainamount of MWNTs and AuNPs were mixed together,and then the MWNTs/Aumixture was dropped on the GCE.Subsequently,Hb molecues with altematelayer-by-layer assemble of SiO₂ sol-gel,provide {SiO₂/Hb}_n film modifiedMWNTs/Au/GCE.Different Pulse Voltammetry (DPV) was used to monitor thelayer-by-layer assembling procedure.At two layered assembly,the redox peakcurrents of Hb achieved the highest.It is showed that the Hb on the{SiO₂/Hb}₂/MWNTs/Au/GC electrode had well-defined redox peaks,and the{SiO₂/Hb}₂/MWNTs/Au/GC electrode displayed good electrocatalytic activity toH₂O₂ reduction.Chapter Four:Direct electrochemistry study of glucose oxidase on Ptnanoparticle-modified aligned carbon nanotubes electrode by the assistance ofchitosan-CdS and its biosensoring for glucoseThe Aligned carbon nanotubes (ACNTs) were fabricated on quartz substrate using athermal chemical vapor deposition system followed by sputtering a thin-layer Au film,then removed from quartz substrate with HF as ACNTs electrode.The FESEMshowed that the electrode was tip-opened,purified and vertically aligned.The ACNTselectrode has been developed for the direct protein electrochemistry andenzyme-biosensor study involving two types of nanoparticles.Pt nanoparticles (Pt_nano)were electro-modified on the ACNTs' each tube,greatly increasing the electrodesurface area for locating protein and also its electronic transfer ability.Glucoseoxidase (GOD) with chitosan (CS) and CdS nanoparticles electrochemically coated oneach tube of ACNTs-Pt_nano by the electrodeposition reaction of CS when pH valuepassing its pKa.The CdS nanoparticles between ACNTs electrode and GOD havestimulated the GOD's direct electron transfer during its redox reaction of FAD/FADH₂.The CS-GOD-CdS/ACNTs-Pt_nano electrode also offer sensitive response to the substrate of glucose with detection limit of 46.8μM (S/N=3) and apparentMichaelis-Menten constant of 11.86 mM.Chapter Five:Direct Electrochemistry and Electrocatalysis of the HemoglobinImmobilized on Diazonium-Functionalized Aligned Carbon Nanotubes ElectrodeA simple and efficient electrochemical method is utilized to functionalize alignedcarbon nanotubes (ACNTs) by the electrochemical reduction of 4-carboxyphenyldiazonium salt.Thus hemoglobin (Hb) molecules were covalently immobilized on thediazonium-ACNTs surface via carbodiimide chemistry.Direct electrochemistry andbioelectrocatalytic activity of the immobilized Hb were then investigated by cyclicvoltammetry (CV) and amperometry techniques.It is showed that the Hb film on thediazonium-ACNTs electrode had well-defined redox peaks with a formal potential (E⁰)at-312 mV (vs.Ag/AgCl),and the Hb-ACNTs electrode displayed goodelectrocatalytic activity to H₂O₂ reduction.Owing to the high Hb covering on theACNTs surface (Γ^*=2.7×10^-9 mol/cm^-2),the catalytic current were significantlyimproved when compared to the current measured at an Hb-tangled carbon nanotubeselectrode.The Hb-ACNTs electrode exhibited high sensitivity,long-term stability andwide concentration range from 40μM to 3mM for the amperometric detection of H₂O₂.The heterogeneous reaction rate constant (ks) was 0.95±0.05 s^-1 and the apparentMichaelis-Menten constant (K_m^app) was 0.15 mM.Chapter Six:Direct Electrochemistry and Eleetrocatalysis of the HemoglobinImmobilized with Au nanoparticles and SiO₂ sol-gel onto Aligned CarbonNanotubes ElectrodeThe Aligned carbon nanotubes (ACNTs) electrode was used as an efficient matrixfor immobilization hemoglobin (Hb) by the assistance of Au nanoparticles (AuNPs)and SiO₂ sol-gel.The SiO₂/Hb-AuNPs/ACNTs electrode showed well-defined redoxpeaks at-0.221 and-0.323 V.The biosensor showed an excellent electrocatalyticactivity towards H₂O₂ with a linear range from 40μM to 4 mM,and the detectionlimit was 22μM at 3σ.The apparent Michaelis-Menten constant of the immobilized hemoglobin was calculated to be 0.44 mM.