Study On Nanozyme-based Optical Methods Of Inorganic Arsenic Detection In Rice

With development of modern industry and agriculture,irrigation water and soil are easily sufferring from pollution of inorganic arsenic.And rice grown in this environment easily has excessive levels of inorganic arsenic.The rice enters into the market,seriously threatening country's rice security and people's health.Hence,it is significant to accurately detect inorganic arsenic in rice,ensuring country's rice security and people's health.Traditional detection is extremely dependent on large instruments and professional operation,which is unable to meet the requirements of convenience testing.Nanozyme-based optical analytical methods have great application prospect in the filed of food analysis due to their low cost,easy operation,and high sensitivity.Hence,five nanozymes are prepared for inorganic arsenic detection in rice by using nanozyme catalysis-based optical analytical methods in this work.The detailed work is as follows:1.Colorimetric detection of inorganic arsenic in rice based on surfactant modified?-Fe OOH.Surfactant modified?-Fe OOH(Surfactant-?-Fe OOH)was prepared.Surfactant-?-Fe OOH shows peroxidase-like activity,catalyzing 3,3',5,5'-tetramethylbenzidine(TMB)chromogenic reaction to form blue product(TMBox)in the presence of H₂O₂.After addition of As(?),As(?)can rapidly inhibit the peroxidase-like activity of Surfactant-?-Fe OOH.Among them,the inhibition ratio of As(?)towards dodecyl trimethyl ammonium bromide modified?-Fe OOH(DTAB-?-Fe OOH)is the highest because modification of DTAB makes?-Fe OOH carry many positive charges,resulting in the rapid interaction between DTAB-?-Fe OOH and As(?).Based on this principle,As(?)ranging from 1.67 to 3333.33?g L?(-1) can be well detected by using DTAB-?-Fe OOH,with a LOD calculated as low as 0.84?g L?(-1).Finally,organic arsenic in rice was determined by using DTAB-?-Fe OOH,providing well recoveries ranging from 97.2?104.9%.In addition,the relative standard deviation(RSD)is less than 9.9%and the results detected by using DTAB-?-Fe OOH agreed with those obtained from inductively coupled plasma mass spectrometry(ICP-MS).These results indicate that DTAB-?-Fe OOH can be employed to accurately determine the inorganic arsenic in rice.2.Colorimetric detection of inorganic arsenic in rice based on L-arginine modified Fe OOH.L-arginine modified Fe OOH(x Arg@Fe OOH)was prepared by using L-arginine instead of DTAB,which simplified the synthesis process.x Arg@Fe OOH possesses peroxidase-like activity,which can catalyze the TMB chromogenic reaction in the presence of H₂O₂.After introduction of As(?),As(?)can remarkably inhibit the peroxidase-like activity of x Arg@Fe OOH.Among them,the inhibition ratio of As(?)towards 2Arg@Fe OOH(material ratio is 2:1)is the highest.Based on this principle,As(?)ranging from 0.67 to 3333.33?g L?(-1) can be well detected by using 2Arg@Fe OOH,with a LOD calculated as low as 0.42?g L?(-1).Finally,organic arsenic in rice was determined by using 2Arg@Fe OOH,providing well recoveries ranging from 98.6%to 103.8%.In addition,the RSD is less than 8.5%and the results detected by using 2Arg@Fe OOH agreed with those obtained from ICP-MS.These results indicate that 2Arg@Fe OOH can be employed to accurately determine the inorganic arsenic in rice.3.Ratiometric fluorescent detection of inorganic arsenic in rice based on acid phosphatase and hemin loaded Zn-based metal–organic framework.Ratiometric fluorescent detection strategy is employed to further improve the reliability of inorganic arsenic detection.Acid phosphatase and hemin loaded Zn-based metal–organic framework(ACP/hemin@Zn-MOF)was prepared by one-pot self-assembly.ACP/hemin@Zn-MOF possesses peroxidase-like activity,which can catalyze o-phenylenediamine(OPD)oxidation reaction to form fluorescent 2,3-diaminophenazine(DAP)(564 nm)in presence of H₂O₂.Also,ACP/hemin@Zn-MOF possesses a fluorescent signal at 452 nm.Due to fluorescent inner effect,the fluorescent signal of ACP/hemin@Zn-MOF decreases and the fluorescent signal of DAP nm increases.After addition of ascorbic acid 2-phosphate(AAP),AAP can be hydrolyzed by the loaded ACP to form ascorbic acid(AA),thereby competitively inhibiting the oxidation of OPD.This can lead to the decrease of DAP fluorescent signal and increase of ACP/hemin@Zn-MOF fluorescent signal.After addition of As(?),the activity of ACP was inhibited by As(?)and AAP cannot be hydrolyzed,resulting in the increase of DAP fluorescent signal and decrease of ACP/hemin@Zn-MOF fluorescent signal.Based on this ratiometric fluorescent principle,As(?)ranging from 3.33 to 300?g L?(-1) can be well detected by using ACP/hemin@Zn-MOF,with a LOD calculated as low as 1.05?g L?(-1).Finally,organic arsenic in rice was determined by using ACP/hemin@Zn-MOF,providing well recoveries ranging from 96.2%to 103.8%.In addition,the RSD is less than 7.2%and the results detected by using ACP/hemin@Zn-MOF agreed with those obtained from ICP-MS.These results indicate that ACP/hemin@Zn-MOF can be employed to accurately determine the inorganic arsenic in rice.4.Colorimetric detection of inorganic arsenic in rice based on three-dimensional flower-like iron alkoxide.Oxidase-like nanozyme was introduced to avoid the adverse effect of H₂O₂.Three-dimensional flower-like iron alkoxide was prepared,which exhibits oxidase-like activity,catalyzing the TMB chromogenic reaction in the presence of O₂.After addition of As(?),As(?)can significantly inhibit the oxidase-like activity of iron alkoxide by specifically interacting with iron alkoxide to form stable As-O bond.Based on this principle,As(?)ranging from 3.33 to 333.33?g L?(-1) can be well detected by using iron alkoxide,with a LOD calculated as low as 1.57?g L?(-1).Finally,organic arsenic in rice was determined by using iron alkoxide,providing well recoveries ranging from 95.7%to 104.8%.In addition,the RSD is less than 9.9%and the results detected by using iron alkoxide agreed with those obtained from ICP-MS.These results indicate that iron alkoxide can be employed to accurately determine the inorganic arsenic in rice.5.Colorimetric detection of inorganic arsenic in rice based on dithiothreitol-capped Pd.Inorganic arsenic(As(?)form)was decteted by oxidase-like dithiothreitol-capped Pd(Pd-DTT).Pd-DTT shows oxidase-like activity,catalyzing TMB chromogenic reaction in the presence of O₂.After addition of As(?),As(?)can chelate with Pd-DTT to lead the reassembly of Pd-DTT.Compared with the oxidase-like activity of original Pd-DTT,that of Pd-DTT after reassembly decreased,resulting in the catalytic ability decrease of TMB chromogenic reaction.Based on this principle,As(?)ranging from 3 ng L?(-1) to 333.3?g L?(-1) can be well detected by using Pd-DTT,with a LOD calculated as low as 35 ng L?(-1).Moreover,with assistance of EDTA,selective detection of As(?)can be achieved.Finally,inorganic arsenic in rice was determined by using Pd-DTT,providing well recoveries ranging from 95.4%to 105.0%.In addition,the RSD is less than 8.6%and the results detected by using Pd-DTT agreed with those obtained from ICP-MS.These results indicate that Pd-DTT can be employed to accurately determine the inorganic arsenic in rice.6.Comparison and combination of nanozyme catalysis-based optical analytical methods.The performances of five nanozyme catalysis-based optical analytical methods are compared.In addition,nanozyme catalysis-based optical analytical methods are combined to further enhance the detection performance.Among them,the combination of Pd-DTT and DTAB-?-Fe OOH-based colorimetric methods can further improve the inorganic arsenic detection range;the combination of iron alkoxide-based colorimetric methods and ACP/hemin@Zn-MOF ratiometric fluorescent methods can enhance the reliability of inorganic arsenic detection.In this work,nanozyme catalysis-based optical analytical methods were successfully applied to the inorganic arsenic detection in rice.And they possess many referential values to the subsequent research of food analysis.