Construction Of Rapid Detection Methods For Nitrite Based On Coupling Of Nanozyme Catalysis And Diazotization

Nitrite（NO₂^-）,as a food additive,has been used for a long time.However,high levels of NO₂^-in food and drinking water pose a great threat to human health.Therefore,it is very important to develop reliable,convenient,and low-cost methods for NO₂^-detection.As a product of the rapid development of nanotechnology,nanozymes have attracted much attention in the field of biochemical sensing in recent years.Developing high-performance methods for NO₂^-rapid detection using nanozyme catalysis has great potential.In this thesis,to meet the needs of rapid analysis of NO₂^-in food and environmental matrices,several methods for rapid detection of NO₂^-were developed through the design and development of multi-functional nanozymes.By combining nanozyme catalysis and diazotization reaction,efficient detection of NO₂^-was realized.The details are as follows:（1）Traditional NO₂^-analytical methods are mostly based on single-signal detection,which is prone to interference during detection process.In order to address this issue,we constructed a ratiometric colorimetric detection method for nitrite based on coupling of nanozyme catalysis and diazotization.The developed hollow Mn Fe O material had excellent oxidase-like activity,which could effectively catalyze the oxidation of colorless 3,3’,5,5’-tetramethylbenzidine（TMB）to blue 3,3’,5,5’-tetramethylbenzidine oxide（TMBox）.The presence of NO₂^-could trigger the diazotization reaction of the blue product TMBox,leading to the formation of diazotized TMBox with a yellow color.The process resulted in a weakened UV-vis absorption signal at652 nm and an enhanced absorption signal at 445 nm.Based on the reverse change of the two signals induced by NO₂^-,we achieved the efficient detection of NO₂^-using a ratiometric colorimetric strategy.（2）Although dual-signal analytical methods have higher sensitivity and lower detection limit,single-mode detection based on target-induced changes often has the problem of limited application scenarios.To solve this problem,we constructed a dual-mode double-ratiometric colorimetric and electrochemical sensing strategy for nitrite based on coupling of nanozyme catalysis and diazotization.Mn₃O₄/C with good oxidase-like activity was prepared to catalyze the oxidation of colorless TMB to blue TMBox,and the latter would undergo a specific diazotization reaction with NO₂^-.This reaction,on the one hand,could induce a decrease in the UV-vis absorption signal at 652 nm and an increase in the signal at 445 nm,and on the other hand,triggered a decrease in the homogeneous electro-oxidation signal of TMB and an increase in the electro-oxidation signal of NO₂^-itself.Based on such a principle,a dual-ratiometric dual-mode detection method of NO₂^-in food and environmental matrices were implemented.（3）In our previous work,the double-ratiometric dual-mode method developed is based on the UV-vis signal and electrochemical signal inductions of the same species TMBox.Although it can realize mutual verification and self-correction of detection results,it cannot avoid the false results caused by TMBox’s own fluctuations.To address this problem,we constructed a ratiometric colorimetric/fluorometric dual-mode detection method for NO₂^-based on coupling of nanozyme catalysis and diazotization.The developed Mn-CDs material had both oxidase-like activity and tunable photoluminescence.It could effectively catalyze the oxidation of colorless TMB to generate blue TMB⁺,which further reacted specifically with NO₂^-to generate yellow diazotized TMB⁺,resulting in a significant change of solution color.Meanwhile,the fluorescence of Mn-CDs could be quenched by diazotized TMB⁺through internal filtration effect.Based on this strategy,efficient quantification of NO₂^-in complex matrices was realized.（4）In the last two studies,we developed bimodal nitrite detection methods.Although the application scope has been expanded,the detection often requires the use of different instruments and cannot be implemented in the same scene.To solve this issue,we constructed a naked-eye visible multicolor/multifluorescence dual-mode detection method for NO₂^-based on coupling of nanozyme catalysis and diazotization.The developed Mn-Si QDs featured both stable luminescence performance and excellent oxidase-mimetic catalytic activity.By utilizing the dual effects of diazotization of NO₂^-and TMB⁺on colorimetric and fluorescence properties,a portable paper-based sensor was developed,which combined Mn-Si QDs/[Ru（bpy）₃]²⁺modified paper strips,a smartphone with built-in color analysis and data processing App and a3D printing holder.With the portable sensor,visual multicolor/multifluorescence dual-mode on-site detection of NO₂^-was achieved.