Constructions Of Biosensors Based On Various Nanomaterials With Investigations On Electrochemistry And Electrocatalytic Performances

Detection,identification and testing for specific targets has been acted as a significant and essential key in many fields such as environmental sciences,medical treatment,food security and agricultural development.Biosensors exhibit highly sensitive,strongly target locating,easily performed,less required for determination steps and low cost which have been gaining much attentions nowadays.Nanomaterialspossesspropertiesincludingbigspecificarea,excellent biocompatibility,strong biomolecules adsorbability and good stability inside or outside the chemical micro-environment,play an important role in modification,construction and transduction processes of biosensors.This study focuses on the synthesis of multi-nanomaterials,their morphological,spectroscopic,electrochemical characterizations,and investigations on electrochemistry and electrocatalytic performances.Various nanomaterials involved in this study are graphene quantum dots related nanomaterials,gold particles related nanomaterials,noble metal and metallic oxide immobilized on three dimensional graphene related nanomaterials,and metallic oxdie.This thesis mainly includes the following six parts:1.Boron-doped graphene quantum dots?B-GQDs?fixed on carbon ionic liquid electrode?CILE?was constructed for the immobilization of hemoglobin?Hb?.Spectroscopy explained that the original structure in Hb molecules was unchanged and its biostructure was retained in Nafion/Hb/B-GQDs composite film.Compare Nafion/Hb/GDQs/CILE,Nafion/Hb/N-GQDs/CILE and Nafion/Hb/B-GQDs/CILE with each other by cyclic voltammetry in pH 4.0 PBS,and there all appeared a couple of redox peaks on cyclic voltammograms,but when modified with B-GQDs,the redox peak were more symmetrical and sharper,illustrating the positive effects due to the introduction of B-GQDs for electron communication and loading capability of Hb on the electrode surface were improved which ascribed to its high conductivity and big specific area.Electrocatalysis of Hb towards various substrates such as trichloroacetic acid?TCA?,sodium nitrite?NaNO₂?and hydrogen peroxide?H₂O₂?were checked in detail by cyclic voltammetry and differenetial pulse voltammetry,exhibiting the advantages such as good linear relationships,high sensitivit,low detection limit and detectability,which can be found in wide applications in the field of food safety and medical sample determination.2.Co₃O₄ nanoparticles?NPs?and horseradish peroxidase?HRP?were decorated on CILE surface to fabricate an electrochemical biosensor for the detection of TCA,sodium nitrite NaNO₂ and H₂O₂.Many material characterization methods such as scanning electron microscope,transmission electron microscope,Raman and X-ray photoelectron spectroscopy were employed to observe the structural,morphological features in Co₃O₄ NPs.Spectroscopic results testified that there was no denaturation takingplaceinHRPmolecules.Electrochemicalperformancesof Nafion/HRP/Co₃O₄/CILE were performed in pH 3.0 PBS,indicating electron communication was realized because of the appearance of one pair of well-distinct and sharp peaks.Co₃O₄ NPs were treated to connect the gaps between electron transport of electrochemical active sites in HRP and the electrode surface.The apparent heterogeneous electron transfer rate constant?k_s?was got as 0.94 s^-1.Low detection limits,wide linear ranges and strong enzyme loading capacity were obtained in electrocatalytic investigations towards different substrates including TCA,NaNO₂and H₂O₂ and the apparent Michaelis-Menten constant(K_M^app)was calculated as 88.15mmol·L^-1,0.201 mmol·L^-11 and 17.54 mmol·L^-1,respectively.real samples detection were successfully achieved.3.Gold nanotriangles?AuNTs?have become one kind of the most popular nano structures for biosensing.Direct electrochemistry and electrocatalysis of HRP on AuNTs which was immobilized on CILE as a biosensor for TCA and NaNO₂detection.The presence of AuNTs was aimed at bridging the gaps between electrochemical active sites of HRP and substrate interfaces,and further improved the loading capacity of HRP.The morphology and nanostructure of AuNTs was observed by transmission electron microscopy.UV-Vis results testified that no denaturation occurred in HRP molecules.Electrochemical behaviors of Nafion/HRP/AuNTs/CILE were checked in pH 3.0 PBS at the scan rate of 0.1 V·s^-1.Kinetic effect was investigated,and k_s and the charge transfer coefficient???were gained as 1.01 s^-11 and0.49.Detection limits from electrocatalysis for TCA and NaNO₂.were 0.33 mmol·L^-1and 0.53 mmol·L^-1,respectively.4.We designed a new electrochemical biosensor by immobilizing myoglobin?Mb?and TiO₂-three dimensional graphene?3DGR?on the CILE surface and utilized Nafion as the cover.Preparing Nafion/Mb/TiO₂-3DGR/CILE was aimed at investigating the electrochemistry in Mb molecules and electrocatalytic performance toward TCA,NaNO₂ and H₂O₂.Scanning electron microscope showed that 3DGR was present as a three-D hollow structure like a spider web and TiO₂ NPs were successfully loaded on and beneath the surface of 3DGR.UV-Vis and FT-IR illuminated that Mb kept the enzyme-like structure and remained stable for enzymatic reaction and amplifying signals.The impact of PBS pH and scan rate on electrochemical performance was checked in detail.Chose pH 4.0 PBS to be the electrolyte solution with the scan rate swept at 100 mV·s^-1.K_M^apppp towards TCA,NaNO₂ and H₂O₂ were calculated as 107.12 mmol·L^-1,31.53 mmol·L^-11 and 34.23mmol·L^-11 with wide linear range and low limits of detection.5.We emphasized the preparation of Nafion/Mb/Pt-Au-GR/CILE and investigation on electrochemistry and electrocatalysis in this section.The experimental synthesized Pt-Au-GR was characterized by scanning electron microscope and transmission electron microscope,which demonstrated that there were many 3D hollow structures in 3DGR and Pt-Au NPs were successfully fixed like small spiders hanging on and beneath the 3DGR surface.Excellent conductivity and adsorption capacity of Pt-Au-GR made electron transfer in Mb ferroporphyrins easily achieve.UV-Vis and FT-IR data exhibited that Mb-Pt-Au-GR in pH 3.0 PBS can still keep its original enzyme-like structure and be functional for electrochemical reactions.Checked the scan rate impact and electrochemical impedance spectroscopy and realized the direct electrochemistry in Mb.K_M^apppp towards TCA and NaNO₂ were computed as 15.97 mmol·L^-11 and 9.51 mmol·L^-11 with wide linear range as 1.0mmol·L^-130.0 mmol·L^-11 and 0.05 mmol·L^-10.55 mmol·L^-1,and low limits of detection were calculated as 0.33 mmol·L^-11 and 0.01 mmol·L^-1,respectively.