Exploration Of Novel Nanozymes With Applications In Biosensors

Nanozymes,the term defined for nanomaterials with enzyme-like properties have attracted significant research attention owing to their simple preparation,storage,and separation,as well as the low-cost compared with natural enzymes.With the fast development of nanomaterials in recently years,a variety of nanocomposites have been extensively explored to possess the similar catalytic activities of natural enzymes,such as oxidase,peroxidase,and catalase.Because of the high stability and easy surface modification,nanozymes have been emerging alternatives to natural enzymes in the field of biosensing and immunoassay with respect to analytical chemistry.Herein,we have developed seveval kinds of peroxidase mimics to fabricate different colorimetric glucose biosensors.The nanomaterials range from metal,metal oxide to graphene nanocomposite;they possesse the catalytic activities range from one kind of enzyme mimetic activity,dual-enzyme mimetic activity to triple-enzyme mimetic activity.Futhermore,we have fabricated an artificial enzyme system for tandem catalysis via a co-precipitation method,achieving one-step analysis of glucose.More details are listed as follows:1.A novel one-pot strategy is proposed to fabricate 3D porous graphene?3D GN?decorated with Fe₃O₄ nanoparticles?Fe₃O₄ NPs?by using hemin as iron source.During the process,graphene oxide was simultaneously reduced and self-assembled to form 3D graphene hydrogel while Fe₃O₄ NPs synthetized from hemin distributed uniformly on 3D GN.The preparation process is simple,facile,economical and green.The obtained freeze-dried product?3D GH-5?exhibits outstanding peroxidase-like activity.Compared to the traditional 2D graphene-based nanocomposites,the introduced 3D porous structure dramatically improved the catalytic activity,as well as the catalysis velocity and its affinity for substrate.The high catalytic activity could be ascribed to the forming Fe₃O₄ NPs and 3D porous graphene structures.Based on its peroxidase-like activity,3D GH-5 was used for colorimetric determination of glucose with a low detection limit of 0.8?M.2.Porous Co₃O₄ nanoplates were synthesized via a soft template method.By using amphiphilic block copolymer F127 colloids as the pore producer,porous Co?OH?₂ nanoplates were prepared.After the procedure of annealing,the obtained Co₃O₄ reserved the hexagonal shape and similar size to the Co?OH?₂ precursor.The as-prepared porous Co₃O₄ nanoplates named Co₃O₄-F simultaneously possessed peroxidase and catalase mimetic activity.Interestingly,these two kinds of mimetic enzyme activities could be switched by modulating the temperature and pH,accompanied with the changes of each kind of catalytic ability.Moreover,Co₃O₄-F exhibited good peroxidase-like catalytic activity even in the neutral pH system,providing a new strategy for one-step analysis of glucose.Then,a novel one-step colorimetric glucose biosensor was fabricated based on the Co₃O₄-F nanozyme,making the operation of detection simpler and easier.3.We demonstrate that nickel-palladium hollow nanoparticles?NiPd hNPs?exhibit triple-enzyme mimetic activity:oxidase-like activity,peroxidase-like activity and catalase-like activity.As peroxidase mimetics,the catalytic activity of NiPd hNPs was investigated in detail.On this basis,a simple glucose biosensor with a wide linear range and low detection limit was developed.4.This work reports a facile approach to fabricate an artificial enzyme system for tandem catalysis.NiPd hollow nanoparticles and glucose oxidase?GOx?were simultaneously immobilized on the zeolitic imidazolate framework 8?ZIF-8?via a co-precipitation method.The as-prepared GOx@ZIF-8?NiPd?nanoflower not only exhibited the peroxidase-like activity of NiPd hollow nanoparticles but also maintained the enzymatic activity of GOx.A colorimetric sensor for rapid detection of glucose was fabricated through the GOx@ZIF-8?NiPd?based multi-enzyme system and the cascade reaction for the visual detection of glucose was successfully combined into one step.Moreover,the GOx@ZIF-8?NiPd?modified electrode showed good bioactivity of GOx and high electrocatalytic activity for the oxygen reduction reaction,which could also be used for electrochemical detection of glucose.The proposed strategy for the fabrication of artificial multi-enzyme system builds a potential bridge of cooperation between nanozyme and natural enzyme,combining together their properties and functionalities,as well making efforts to multi-catalysis and tandem reactions.