Application Of Multifunctional Iron-based Nanozymes In Visual Biosensor Detection

Natural enzymes is a kind of protein molecule,exhibiting excellent catalytic activities.However,they are easily affected by external environment conditions(e.g.temperature,acidity)and lose their catalytic activities,as well as limited by the low content in biological body,the unstability and the high costs of purification and storage.Nanozymes,as a kind of nanomaterials with enzyme-like activity,have been extensively applied in the fields of drug delivery,nano-diagnosis and biosensing due to their unique properties and convenient purification and storage.However,nanozymes still face numerous challenges and difficulties,such as,the relative low efficiency of most nanozymes and their unclear physical and chemical properities.Therefore,it is of significance in biomedical field for synthesis of nanomaterials with adjustable surface properties,excellent catalytic performance,and good structural stability.Based on novel iron oxide-based nanozymes with different nanostructures,we explored their applications in visualization detection of biological small molecules and utilized DNA to precise regulate the catalytic activities of inorganic nanozymes.Chapter one:The research progress of nanozymes was introduced,including the classification and application.The three major categories of oxide nanomaterials,noble metal nanomaterials,and carbon-based nanomaterials were introduced.Various applications of nanozymes have been summarized,which focused on detection of H₂O₂ and glucose,sensing of cell and bacteria,detection of nucleotides,and bioimaging.Chapter two:A novel multifunctional yolk-shell nanostructured Fe₃O₄@C MNPs(Fe₃O₄@C YSNs)was synthesized by a simple and facile method.Based on the peroxidase activity,a visual and label-free detection of H₂O₂ and glucose with high sensitivity and selectivity was achieved.Owing to its unique nanostructure,the nanomaterial showed a much higher peroxidase-like activity than the similar nanozymes and natural enzymes(e.g.HRP).Also,it was found that the catalytic mechanism followed typical Michaelis-Menten model.The typical H₂O₂concentration with a wide dynamic range from 1?M to 2000?M has been detected with a low detection limit of 0.39?M.Meanwhile,the linear range for glucose sensing is from 1?M to 200?M and a detection limit of 1.12?M could be achieved,as well as the good selectivity to other three glucose analogues.Based on this proposed method,the preliminary detection of human serum samples were completed,and the analytical result were quite close to the provided value from the hospital,which is of great significance in the future application on point-of-care diagnosis and on-site test.Chapter three:We presented a facile and one-pot method to prepare Fe₃O₄@C/Ni hollow nanotubes(Fe₃O₄@C/Ni NT).Due to the synergistic effect of nickel nanoparticles and iron oxide nanoparticles,the nanomaterial exhibits excellent catalytic activity and magnetic properties.Based on its peroxidase activity,a method for detection of H₂O₂ and cholesterol was established.Under the optimized experimental conditions,the typical H₂O₂ concentration with a wide dynamic range from 1?M to 2000?M has been detected and the limit of detection is as low as 0.18?M.Meanwhile,the linear range for cholesterol sensing is from 1?M to 1000?M and a detection limit of 2.90?M could be achieved.The proposed sensor also showed good selectivity even the concentration of the interferences as high as 20 times than that of cholesterol.The average recovery of human serum cholesterol detection is ranged from 88%to 105%,which is basically consistent with the provided value from the hospital.It is promising to be applied in point-of care test of serum cholesterol in the future.Chapter four:Through the interface engineering between different structured DNA ligands and inorganic nanoenzymes,the high-precise and controllable regulation of the catalytic activity of inorganic nanoenzymes bas been realized.Currently,the catalytic activities of nanozymes were commonly regulated by complicated synthesis procedure or surface modification,which were sophisticated,time-consuming and laborious.Here,four different structured DNA,including single-stranded DNA(ss DNA),short double-stranded DNA(ds DNA),hairpin DNA(H-DNA),and long double-stranded DNA of hybridization chain reaction(HCR)were used to realize the precise regulation of the catalytic activities of inorganic nanozymes.As a result,rigid ds DNA-treated nanoparticles only showed a negligible enhancement in catalysis.The absorption of both random coil-like ss DNA and stem-loop hairpin DNA on nanoparticles led to a moderate enhancement of the catalytic activity of nanozymes.HCR product-treated nanoparticles exhibited the highest enhancement of the catalysis of nanozymes.Moreover,we studied the impact of various parameters on the catalytic activity of nanozymes in detail,and the mechanism of different structured DNA and NPs was preliminarily proposed through adsorption and desorption experiments.Based on HCR amplification and iron oxide(Fe₃O₄ NPs),we develop a simple,fast,label-free,and sensitive colorimetric strategy for sensing of Yersinia pestis relevant DNA sequence,which provide a useful strategy in the test against biological terrorism attacks in the future.Chapter five:Conclusion.