Carbon Materials Based Biosensors Used For The Detection Of Fe²⁺ And Glucose

Food nutrition and safety are related to the national economy and the people's livelihood.Some shortcomings of the traditional detection methods including the need of expensive equipment,high cost,time cosuming,specialized training of operators,and complicated experimental steps,which restrict its extensive use.Carbon nanomaterials were getting more and more attention for biosensing,as they havelarge ratio of surface to volume,good biocompatibility,easy to modification and the raw materials are easy to acquire.Based on the functional materials?composited with carbon materials and natural enzymes/mimic enzymes?,colorimetric methods to sensitively detect Fe²⁺and glucose were established.The details are as follows:?1?CNT-HRP composite material was synthesized through covalently conjugating horseradish peroxidase?HRP?on the carboxyl group functionalized CNT.H₂O₂ was decreased as a result of the Fenton reaction between Fe²⁺and H₂O₂.With increasing the amounts of Fe²⁺in the reaction solution,the concentration of H₂O₂ is decreased,and the oxidization extent of TMB is also decreased,consequently.By this means,the concentration of Fe²⁺can be determined.The optimal reaction conditions were:the concentration of HRP was 50?g/mL when synthesis CNT-HRP hybrid material;the reaction pH was 6.3;the reaction time between Fe²⁺and H₂O₂ was 2 min;and the concentration of H₂O₂ was 60?M.Under this optimal reaction conditions,the limit of detection was 0.22?M.the linear detection range of Fe²⁺was 0.8-100?M.the selectivity of this method is satifactory:other metal ions have no interference on the detection of Fe²⁺.Especially,this method can discriminate Fe²⁺with Fe³⁺.Due to the advantage of high sensitivity,high specificity,low cost and simple operation,the biosensor is possible to be utilized for Fe²⁺detection in food testing.?2?The CNT-HRP-GOD composite material was synthesized by the reaction between carboxyl on the surface of CNT and amino groups of HRP and glucose oxidase?GOD?.Glucose can be oxidized by GOD with the production of H₂O₂.Meanwhile,the TMB can be oxidized by the produced H₂O₂.Through this way,the rapid detection of glucose can be realized.The composite material is able to increase the active reaction sites to increase the amounts of immobilized enzyme molecules on the surface of biosensor.The electron transmission among different species is accelerated by the immobilized enzyme,and the diffusion of H₂O₂ is decreased.The limit of detection was 0.3?M,and the linear detection range of glucose was 1-100?M,the spiked glucose recovery ratio in serum was 90.97%-110%.Glucose analogues and metal ions did not interfere with the detection of glucose.Therefore,this method can be used to detect glucose in serum.This method may be used to detect real samples and is helpful for the fabrication of other biosensors.?3?ZnFe₂O₄/CNT composite material was synthesized by one-step solvothermal approach.GOD binds to the surface of ZnFe₂O₄/CNT composite material through amide covalent bonds and ZnFe₂O₄/CNT-GOD ternary composite material was produced.This composite material was used to detect glucose.When glucose present in the reaction solution,GOD is able to catalyze glucose and produce H₂O₂.ZnFe₂O₄as the HRP mimic species is able to catalyze H₂O₂ to oxidize TMB.The color of the solution increased with increasing the concentration of glucose.The limit of detection was 0.58?M,the linear detection range of glucose was 0.8-250?M.Compared with the clinical test result,the spiked glucose recovery rate in serum were 100%-107%.The advantages of this method are as follows:the preparation of ZnFe₂O₄/CNT is simple;the cascade reaction between ZnFe₂O₄/CNT-GOD and glucose limited the diffusion of intermediate H₂O₂ and accelerate the electron transferring rate and reaction rate;carbon nanotube with large surface to volume can combine many ZnFe₂O₄ and GOD.Compared with the ZnFe₂O₄ and Fe₃O₄,the catalytic ability of ZnFe₂O₄/CNT is significantly enhanced.This method has good selectivity and stability.It is helpful for the development of other biosensors.