Study On Rapid Colorimetric Food Analysis Based On The Activity Modulation Of Nanozymes

Due to the high catalytic activity and high specificity of natural enzymes,the enzyme-catalyzed reaction has important practical value in the field of food analysis.Based on the enzyme-catalyzed detection methods,the endogenous enzyme activity of foods can be determined,as well as various food components that can act as enzyme substrates or activators?inhibitors?,which can be used to indicate the biochemical status of foods.Moreover,enzyme-catalyzed detection methods can also be combined with other analytical techniques such as immunological technique to monitor many risk factors of food safety.However,natural enzymes suffer from limitations such as poor stability,limited sources,and low availability.In recent years,with the rapid development of nanoscience and nanotechnology,the progresses and applications of inorganic nanomaterial based artificial enzymes?nanozymes?have received more and more attention.The surface and interface of nanozymes are one of the key factors influencing its enzyme-like activity.Therefore,the study on the interface properties and the strategies of activity regulation of nanozymes would provide an important theoretical basis for the replacement of nanozymes to natural enzymes.This thesis systematically studied the regulating effects of several environmental factors(including sulfate anion(SO₄^2-),DNA single-stranded?ss DNA?,and mercury ions(Hg²⁺))on the activities of promising nanozymes such as nanoceria?CeO₂?,manganese cobalt oxide?MnCo₂O₄?submicrospheres and chitosan-modified molybdenum diselenide nanosheets?CS-MoSe₂ nanosheets?.The role,efficience,and mechanism of the three regulators on the corresponding nanozyme have been investigated to explore effective activity-modulating strategies for nanozymes and eventually to achieve more sensitive,reliable,and portable food detection methods.The main achievements of this study are as follows:1.Glutathione?GSH?with a broad-spectrum detoxification effect has been widely used in functional foods for anti-aging,enhancing immunity,and anti-tumor effects.Therefore,it is important to establish a sensitive and rapid detection method for glutathione.Thus,we studied the strategy of the facet-selective modification of SO₄^2-activator molecules to up-regulate the oxidase activity of CeO₂,in order to construct a highly sensitive detection platform for the colorimetric analysis of GSH in functional beverages.Our study reveals that CeO₂ nanozymes exhibite a morphology-dependent oxidase-like catalytic activity.As an activator molecule of CeO₂ oxidase mimics,sulfate ion preferentially binds to CeO₂ nanorods?NRs?,activating the catalysis of{110}plane of CeO₂ NRs.This phenomenon is attributed to the selective adsorption of sulfate ions,resulting in the surface charge change,electron transfer acceleration,and Ce³⁺content increase of CeO₂ NRs.Based on the truth that GSH can inhibit the catalysis of nanozymes,we finally proposed a colorimetric detection platform for GSH based on SO₄^2-/CeO₂ nanozymes.Results show that the detection limit of GSH has been improved to as low as 32 nM in this assay,demonstrating the assay that relies on the activity regulation of CeO₂ is potential to analyze GSH in actual functional beverages.2.The contamination of highly toxic mycotoxins in foods has been a problem that has plagued food safety researchers.In order to broaden the application of nanozymes in the detection of mycotoxins in foods,we systematically studied the oxidase-like activity of spinel MnCo₂O₄ and the mechanism of their ssDNA-inhibited activity,which eventually enabled a successful colorimetric detection method of mycotoxins in maize samples.As is concluded,the robust oxidase-mimicking activity of MnCo₂O₄may be due to the coexistence of Co^3+/Co²⁺and Mn³⁺/Mn²⁺redox cycles in their spinel structure.The reversible regulation of MnCo₂O₄ nanozyme activity was achieved by the attachment/detachment of the ssDNA strand on MnCo₂O₄ surface,which provided an efficient channel for biomolecular recognition.Based on this principle,we established a colorimetric method for the detection of ochratoxin A,achieving a detection limit as low as 0.08 nM.Our method was comparable to many commonly-used methods in view of the detection limit and specificity,and also showed good applicability in real maize sample analysis.3.Mercury ingested into the human body through food or drinking water poses a serious threat to human health.Therefore,the prevention and control of mercury poisoning has become an important problem faced by all countries worldwide.To establish a simple,rapid,sensitive and specific method for mercury ion(Hg²⁺)detection,we explored the activation of peroxidase?POD?and oxidase?OD?mimicking activity of CS-MoSe₂ nanosheets by mercury ions,and established a rapid and sensitive colorimetric probe based on CS-MoSe₂ for detecting Hg²⁺in drinking water samples.Studies have shown that even trace amounts of Hg²⁺can effectively improve the POD-like and OD-like activity of CS-MoSe₂.The main cause is that some mercury ions are in-situ reduced into Hg⁰on the surface of CS-MoSe2,which promotes the transfer of electrons between the nanozyme and the substrate.Further,using CS-MoSe₂ as the colorimetric probe for Hg²⁺,we can achieve a limit of detection as low as 3.5 nM?UV-vis spectrum?or 100 nM?naked eyes?while ensuring high selectivity.In addition,our method can also obtain reliable detection results in the actual water and serum samples.Our work has pioneered the precedent of non-noble metal nanozymes as Hg²⁺colorimetric sensor,greatly reducing the cost of such sensors and providing a simpler,cheaper,faster,and more reliable method for Hg²⁺detection.