Cobalt Manganese Mixed Metal Oxides Colorimetric Determination Of Sulfites In Food

Sulfites(SO₃^2-)are one of the most common food additives and widely used as bleaching and preservatives in many foods.SO₃^2-inhibit the activity of phenoloxidase and prevent enzymatic browning of food.At the same time,the active components on the surface of microorganisms can be hydrolyzed,so that the normal physiological activities of microorganisms and the life activities of fruits.A large amount of SO₃^2-in food will not only destroy the nutrients in food,but also cause harm to human body.The common SO₃^2-detection methods have some problems,such as strict requirements on samples,expensive equipments and complicated operation.Colorimetric analysis method has the advantages of high sensitivity,short response time and excellent selectivity.Especially,colorimetric analysis based on nanoenzyme has become an important tool because of its advantages of better stability and lower cost than natural enzyme.In this paper,based on Co Mn MMOs nanomimetic enzyme,colorimetric detect SO₃^2-in food without hydrogen peroxide.At the same time,gel kits are prepared to achieve a simpler and faster visual detection of SO₃^2-in the field.The main results are as follows:Co-manganese mixed metal oxide（Co Mn MMOs）nanorods with oxidation-like activity are prepared by hydrothermal method and calcination method.Co Mn₂O₄was uniformlydispersedbetweenCo₃O₄bycalcinationof Co₆（CO₃）₂（OH）₈·H₂O@Co Mn₂O₄nanorods in air.The co-introduction of Co Mn₂O₄promoted electron transfer in Co₃O₄,which not only solves the aggregation problem of Co₃O₄,but also increases the active site of the nano-enzyme,and the catalytic activity of the Co Mn MMOs nanoenzyme is enhanced.The prepared nanoenzyme catalyzed the oxidation of color substrate 3,3,5,5-tetramethylbenzidine（TMB）to blue ox TMB with Michaelis-Menten constant（K_m）of 0.042 m M and V_maxof 0.85*10^-8M s^-1.Co Mn MMOs catalyzes decomposition of dissolved oxygen to generate·O₂^-.on the surface of Co Mn MMOs oxidizes TMB to ox TMB,and the solution changes to blue.The addition of SO₃^2-causes blue ox TMB to be reduced to colorless TMB,resulting in discoloration of the solution.Based on the inhibitory effect of SO₃^2-on Co Mn MMOs-TMB system,the linear range of SO₃^2-was 1.56～15.58μM and the limit of detection（LOD）was 62.38 n M under the optimal conditions（temperature40℃,concentration of TMB and Co Mn MMOs 67μM,p H 4.0）.Combined with smart phone APP（Color Picker）,a portable disposable agarose hydrogel detection kit was designed.The recoveries were in the range of 93.50%～111.47%,and the relative standard deviations（RSD）are in the range of 0.98%～8.76%.The semi-quantitative visual detection of SO₃^2-in food samples was realized.A hollow and porous N-doped core-shell core-manganese mixed metal oxide（Co Mn MMOs/NHCS）nanocomposite with oxidase-like activity is synthesized by semi-sacrificial template method.With the co-introduction of NHCS,the oxidase-like catalytic activity of Co Mn MMOs/NHCS is greatly improved,the pore structure is more open,and the specific surface area is larger.Its Michaelis-Menten constant is0.0125 m M and V_maxis 7.90*10^-8M s^-1.Co Mn MMOs/NHCS has higher enzymatic activity than Co Mn MMOs and Co Mn MMOs/HCS.The Co Mn MMOs/NHCS nanoenzyme showes excellent performance in the detection of SO₃^2-in food.The linear concentration range is 1.56～25.56μM,and the limit of detection（LOD）is42.72 n M.The colorimetric detection of SO₃^2-by agarose based hydrogel membrane is established based on the excellent performance of nanoenzyme.This work provides a new strategy for the controllable construction of novel NHCS hybrid materials,and opens up a new approach for the detection of Co Mn MMOs nanomaterials as efficient nanomases.In summary,two novel nanomimetic enzymes（Co Mn MMOs and Co Mn MMOs/NHCS）are synthesized in this study,and their catalytic performance is discussed.Co Mn MMOs,composed of Co Mn₂O₄modified Co₃O₄,formed a heterostructure to increase the active site,accelerate the electron transfer in the catalytic reaction,and solve the accumulation problem.NHCS,as a hard template,can assist the generation of Co Mn MMOs nanosheets on its surface.The Si O₂spheres used as sacrificial templates are dissolved in this process.Nitrogen doping can change the polarity of carbon matrix and change the electron distribution of carbon material.Nitrogen doping in carbon material can improve the catalytic activity of analog enzyme.On this basis,a colorimetric detection platform for SO₃^2-is constructed and successfully applied to the analysis SO₃^2-of food samples.This work opens up a new way for the application of novel colorimetric sensor in food safety field.