UCNPs Nanoprobes Constructed Based On IFE For Food Safety Detection

With the development of global food diversification,people’s understanding of food nutrition and safety is gradually improved,and the demand for traditional and emerging food quality and safety testing is also gradually rising.The traditional sensory evaluation method is inefficient and subjective.In order to respond to the high efficiency of food industry production,there is an urgent need to develop advanced food testing methods.In recent years,lanthanide-doped upconversion nanoparticles（UCNPs）with near infrared light as excitation source have been widely used in food detection because of their unique luminescence properties.The unique anti-Stokes displacement luminescence of UCNPs significantly reduces the interference of the food substrate background,simplifies the sample pretreatment phase,and provides the possibility for efficient detection methods.In addition,the luminescence of UCNPs can be regulated by changing the type and proportion of doping elements,which also provides more possibilities for the design of food detection probes.In this thesis,UCNPs was used as a signal probe,and based on the luminescence internal filtration effect（IFE）,the colorimetric and luminescence dual-signal sensitive detection of glucose oxidase（GOD）,alkaline phosphatase（ALP）,D-type amino acids（D-AAs）and organophosphorus pesticides（OPs）in food was constructed.The content of the article is summarized as follows.In the second chapter,we designed a method for the activity determination of GOD and ALP in milk by UCNPs nanoprobe.The redox properties of hydrogen peroxide（H₂O₂）and ascorbic acid（AA）changed the color and absorption spectrum of gallic acid-iron complex（GA-Fe）.The luminescence spectra of UCNPs were affected by the change of GA-Fe absorbance through IFE.When glucose and L-ascorbate-2-phosphate were used as substrates,H₂O₂and AA were catalytic products of GOD and ALP,respectively.The changes in absorption and luminescence signals were calculated as enzyme activity.The probe was able to achieve colorimetric and luminescence dual-signal detection of the two enzymes,and had good results in milk samples.In the third chapter,a method of emulsion self-assembly UCNPs（ES-UCNPs）for the detection of D-AAs in food was designed.Two dumbbell UCNPs were polymerized by emulsion self-assembly mediated by sodium dodecyl sulfate（SDS）.The ES-UCNPs formed by the polymerization had multiple emission peaks and good water solubility.Meanwhile,polyethyleneimine modified copper ferricyanide（PEI-Cu Fc）was synthesized,which has good peroxidase activity and high affinity for H₂O₂.D-AAs was specifically catalyzed to produce H₂O₂by D-type amino acid oxidase（DAAO）,and then 3,3’,5,5’-tetramethylbenzidine（TMB）was catalyzed by PEI-Cu Fc to achieve colorimetric detection of D-AAs.Colorimetric and luminescent dual signal detection of D-AAs were realized by IFE.In addition,SDS in ES-UCNPs enhanced the color development of TMB,shortened the reaction time and improved the sensitivity of detection.Finally,the probe showed good results in a variety of food samples.In the fourth chapter,ES-UCNPs were designed to detect OPs in food and a logic gate was constructed.The probe ES-UCNPs in the third chapter was used to prevent the reduction of cupric ferricyanide to cupric ferricyanide through the selective inhibition of acetylcholinesterase（ACh E）by OPs.The change of absorption spectrum of the system was correlated with the content of OPs.And because of IFE,the colorimetric and luminescent double signal detection of OPs were realized.In addition,the AND logic gate was constructed,which simplified show whether the OPs in the sample exceeds the standard,so that the probe could get rid of professional restrictions and had practical application significance.In conclusion,the detection method based on IFE has realized the sensitive detection of colorimetric and luminescence signals,which contributes to in the field of food detection.