Investigation On The Electrochemical Behavior Of Cobalt-Based Core-Shell Nanocomposite In Hydrogen Peroxide Sensor

Hydrogen peroxide（H₂O₂）is one of the most important reactive oxygen species（ROS）in organisms.It performs important biological functions in a dynamic equilibrium state.Excessive H₂O₂ can cause harmful oxidation of biomolecules and results in aging,Alzheimer’s disease,and cancer,etc.Therefore,real-time monitoring of H₂O₂ is helpful to understand its physiology and pathology processes.However,it is difficult to achieve quantitative detection of H₂O₂ in the complex bioenvironment due to the low level and rapid diffusion of H₂O₂.Among H₂O₂ detection methods,the electrochemical method is one of the most attractive ones because of its continuous monitoring and easy operation.Normally,H₂O₂ electrochemical sensor realizes the quantitative detection by introducing the biological enzyme on the electrode surface to catalyze the decomposition of H₂O₂.The sensing performance of this kind of H₂O₂ sensor mainly depends on the expensive biological enzymes,which are easily affected by temperature,p H,and other factors,so the application of the biological enzyme-based electrochemical sensors is greatly limited.In recent years,various nanomaterials with enzyme-like activity（nano-enzyme）have been synthesized and used to construct nano-enzyme H₂O₂ electrochemical sensors with good stability,high sensitivity,and good selectivity.Cobalt-based materials have demonstrated their huge practical application potential in sensing due to the unique 3d electronic structure,adjustable valence,stable physical and chemical properties.With the rapid development of nanomaterials synthesis and characterization techniques,the controllable synthesis of cobalt-based materials with excellent properties has become a research hotspot.In this work,four new cobalt-based nanocomposites with enzyme-like activity are synthesized by simple green synthesis methods,aiming to improving the stability and loading of active sites,introducing cocatalysts,increasing electron transport channels,and compounding new active centers.Their electrochemical catalytic behavior was further studied,and the practical application was verified by detecting H₂O₂ released from cells.The detailed research contents of this work are as follows:1.In the presence of AA,two-dimensional graphene self-assembles to form hydrophilic 3D graphene aerogel（3DG）under hydrothermal condition.Co²⁺was then uniformly adsorbed on the 3DG through electrostatic adsorption,followed by annealing in the mixture of hydrogen and argon to produce C@Co/3DG.The resulted C@Co/3DG nano-enzyme is further modified on the glassy carbon electrode（GCE）to construct electrochemical H₂O₂sensor.This developed sensor shows excellent electrocatalytic performance for H₂O₂ with a linear range of 0.3μM-100.1μM,a limit of detection（LOD）of 0.03μM,and sensitivity of 113.3μA·m M^-1·cm^-2.In the C@Co/3DG nanocomposite,cobalt nanoparticles provide active sites for electrocatalytic reactions,the unique Co and C layer structure is beneficial to improve the electrocatalytic activity of the composite material for H₂O₂.Specifically:The C layer formed by annealing can improve the stability of cobalt nanoparticles and reduce the corrosion of cobalt nanoparticles;The hydrophilic 3DG can effectively increase the loading of cobalt nanoparticles and improve the charge transfer efficiency of materials.2.Au@Co₃O₄/CeO₂ yolk-shell nanoparticle（YSN）,synthesized by a two-step method of self-assembly and cation exchange,was modified on GCE to construct an electrochemical H₂O₂sensor.A linear range of 5.0 n M-5.4μM,a LOD at 2.74 n M,and sensitivity at 35.67μA·μM^-1·cm^-2 have been achieved with the developed electrochemical H2O2 sensor.H₂O₂ released by the human umbilical vein endothelial cells（HUVEC）and human cervical cancer cells（He La）has also been quantitatively detected,demonstrating its good potential for practical application.In the Au@Co3O4/Ce O2 YSN,Co₃O₄ provides an electrochemical active center for catalyzing H₂O₂.Ce O₂ as a cocatalyst,embedded in Co₃O₄,not only can enhance the oxygen defect content of the material and improve the adsorb of H₂O₂,but also can reduce the high background current caused by Co₃O₄.Au provides good support for self-assembly of the precursor Au@Co₃O₄core-shell nanoparticle（CSN）and helps to enhance the electron transfer rate.The three complements synergistically improve the H₂O₂detection performance through enhancing the electron transmission rate,reducing the background current,and enhancing the H₂O₂ adsorption.3.Prussian blue（PB）is synthesized by the hydrothermal method.By modifying the cationic adsorbent sodium polystyrene sulfonate（PSS）,a large hydrated shell was formed on the surface of PB to make it have enough space to form the outer shell.Cobalt ion(Co²⁺)is introduced to the surface of PB by electrostatic adsorption,then 2D/3D-Co-MOF is self-assembled on PB surface by adding different concentrations of 2-methylimidazole（2-Me IM）.Finally,2D/3D-Co-MOF coated PB is used to develop H₂O₂electrochemical sensors.Experimental results show that the electrochemical detection of H₂O₂ based on PB@2D-Co-MOF has a very low detection limit（0.11 n M）and good selectivity.And the mechanism of PB@2D-Co-MOF-based H₂O₂detection was also investigated by cyclic voltammetry.In this design,PB has a good catalytical ability to H₂O₂reduction,the porous 2D-Co-MOF is beneficial to increase the specific surface area and provide channels for the adsorption,transport,and electron transfer of H₂O₂.In addition,the effect of O-Linked N-Acetylglucosamine hydrolase（OGA）inhibitor Thiamet G on cell proliferation was studied by investigation of H₂O₂.4.ZIF-67 prussian blue analogue（ZIF-67 PBA）with cube structure is synthesized by self-assembly.ZIF-67/Co-Fe PBA nano-enzyme is prepared by the cation exchange method using ZIF-67 PBA as a template and potassium ferricyanide as an iron source.The catalytic mechanism of ZIF-67/Co-Fe PBA in electrochemical and colorimetric H₂O₂detection is also discussed.In ZIF-67/Co-Fe PBA,porous ZIF-67 PBA not only provides a synthesis template but also increases the specific surface area.The Co-Fe PBA shell effectively solves the problem that the easy collapse of the ZIF-67 PBA structure and increases the active sites and electron transfer rate.These two components synergistically enhance the catalytic activity of ZIF-67/Co-Fe PBA nanocomposite for H₂O₂.Furthermore,H₂O₂ released from prostate normal cells（RWPE-1）and prostate cancer cells（DU145）is electrochemically and colorimetrically detected based on the ZIF-67/Co-Fe PBA nano-zymes,confirming its great potential practical application.In summary,four novel cobalt-based nanomaterials are successfully synthesized by using simple and green controllable methods and used as nano-enzymes to construct H₂O₂electrochemical sensors,overcoming the shortcomings of traditional biological enzymes such as expensive and easy to be affected by environmental and effectively solving the problems of low sensitivity and poor LOD.The catalytic behavior of these nano-enzymes on H₂O₂is also studied from different angles.And the advantages of the cobalt-based composite nano-enzymes are analyzed and discussed from the aspects of material structure,active sites,electron transmission,and background signal suppression.This thesis not only provides a more effective method for sensitive and quantitative detection of H₂O₂ but also provides new directions and strategies for the development of new nano-enzymes.