Construction Of Rare Earth Upconversion Composite Nanoparticles For Fluorescence Sensing And Biological Antioxidant Study

Reactive oxygen species are produced by the partial reduction of oxygen to singlet oxygen such as hydrogen peroxide,hydrogen peroxide is both a type of reactive oxygen species and an important source of other types of reactive oxygen species.Reactive oxygen species cause oxidative damage to biological macromolecules and lead to many diseases.Plants contain a variety of natural antioxidant molecules that are important for their biological and free radical scavenging activities,therefore,the detection of hydrogen peroxide,the detection of antioxidants and the assessment of antioxidant power have received a lot of attention.Stains,quantum dots,etc.are often used as fluorescent detection materials,which are prone to photobleaching or have high biotoxicity,and some new materials have been studied for only one type of antioxidant.In addition,conventional antioxidant power assessment methods usually have long reaction times and cumbersome steps.Therefore,the development of methods that can detect both hydrogen peroxide and antioxidants and evaluate antioxidant power can greatly reduce the time and cost.Fluorescence detection based on upconversion nanoparticles（UCNPs）has the advantages of high stability and ease of operation.The internal filtration effect（IFE）sensing strategy involves only the transfer of radiant energy and is not limited by distance,which making the design of IFE-based sensing strategies simpler.The unique spectral overlap makes IFE sensing well selective and suitable for the detection field.The ratio fluorescence technique uses the change in intensity of two or more emission bands caused by the analyte to become an effective internal standard with the advantages of improved sensitivity and accuracy at low analyte concentrations and built-in correction for environmental effects.Therefore,based on the IFE between UCNPs and iron squareate(SA-Fe^III),an oxidation-reduction bidirectional assay system was designed to characterize and detect common oxidation and antioxidant reactions occurring in organisms by changing the conversion between Fe^III and Fe^IIthrough redox reactions.The assay consists of three experiments:the determination of ascorbic acid using the reduction of antioxidants,the evaluation of total antioxidant power,and the determination of hydrogen peroxide using the oxidation of Fenton reaction.1.Construction of ratio fluorescence sensing of ascorbic acid based on UCNPs.The upconversion nanomaterials were prepared based on the high-temperature dissolution method,their morphological structure and elemental distribution and composition were characterized by TEM and EDS.The fluorescence sensing method was studied and identified as IFE sensing.The assay results showed that the antioxidant was unstable at room temperature and the reaction required a short time（6 min）,which was beneficial to study the true antioxidant capacity of the samples.The response to ascorbic acid in fruits and vegetables was good with a detection limit of 0.1μmol L^-1and the linearity was good in the range of 0-1.0 mmol L^-1.2.Construction of a method to assess the total antioxidant power based on UCNPs.In this study,the antioxidants with high content and high contribution to the total antioxidant power in fruits and vegetables were selected.Since the reducing power of different antioxidants is different and there may be antagonistic or promoting effects between them,seven antioxidants including anthocyanins,glutathione and polyphenols were tested for the fluorescence response of single and mixed solutions,and the total antioxidant power of 11 common fruits and vegetables were evaluated and compared with the FARP assay.3.Construction of ratio fluorescence sensing of hydrogen peroxide based on UCNPs.This part of the study mainly utilizes the reverse reaction of ascorbic acid detection mentioned above,i.e.,H₂O₂ in acidic environment can react with Fe^II in Fenton reaction to produce reactive oxygen species with Fe^III,thus enhancing IFE.By modulating the doping ratio of UCNPs in experiment 1,UCNPs with better luminescence intensity were obtained,still using photoluminescence at 800 nm as the internal reference and 451 nm.The detection limit of H₂O₂ was 85 nmol L^-1,and the linearity was good in the range of 0-40μmol L^-1.