Construction Of Near-infrared Fluorescent Probes For Amino Semicyanines And Their Applications In Food Detection And Bioimaging

Food is the fundamental of people's livelihood.Food safety issues are closely related to the development of food enterprises and personal health.With the rapid development of modern food enterprises,the variety of food products and processing technologies have been developed.However,the illegal addition of food additives,pesticide residues and food deterioration factors are not monitored properly,making food safety problems appear one after another.Traditional detection techniques are usually not highly sensitive,complex and have long response times.Therefore,it is important to adopt new rapid,simple and highly sensitive analytical techniques to control food quality and safety.Based on this,this thesis focuses on the development of three novel NIR optical probes for rapid detection of food safety related substances and bioimaging applications.The unique long wavelength emission in the near-infrared region of the NIR fluorescence probe gives the optical probes strong background interference resistance,strong tissue permeability,low damage to the actual sample,and superior spatiotemporal sampling ability,so it is beneficial to realize the rapid and nondestructive detection and imaging analysis of various food quality and safety factors in living bodies or actual food samples.In this study,we synthesized AXPI,a semicarbocyanine skeleton with amino group,mainly from IR-780,a semicarbocyanine fluorescent dye with stable structure and stable NIR fluorescence signal.Based on above,we designed and synthesized three novel NIR fluorescent probes by introducing different recognition groups through the linker arm,which were applied to detect tyrosinase,formaldehyde and sodium bisulfite,respectively,and performed detailed structural characterization and performance characterization of the probes,and finally applied them to the detection of target substances in actual food samples and bioimaging applications.The main work includes the following three aspects.(1)Tyrosinase,a bicopper monophenolic oxidase among polyphenol oxidases,is closely associated with browning in fruits and vegetables and melanoma-related diseases.The first work developed a near-infrared fluorescent probe for the detection of tyrosinase by introducing a carbamate bond coupled to 3-hydroxybenzyl alcohol with high resistance to ROS interference,using the amino-semicarbazone backbone AXPI as a near-infrared fluorophore.The probe has a low detection limit of 0.36 U mL-1 for tyrosinase.The probe was firstly applied to the real-time monitoring of tyrosinase during browning of apple slices and the spiked recovery detection of tyrosinase from actual food samples,and finally,it was successfully applied to the real-time monitoring of endogenous tyrosinase in B16 cells.(2)Formaldehyde has good solubility in water and easily combines with proteins and other substances to change its properties,which has the effect of preserving"freshness"in food and is often illegally added as a food preservative and preservative.In this thesis,two NIR fluorescent probes were developed for the highly sensitive detection of formaldehyde in food based on the formation of methylene amine and the condensation of hydrazine with the near-infrared fluorescent dye IR-780.The detection limits of the two probes for formaldehyde were 1.87 ?M and 0.68 ?M,respectively,and they have the advantages of simple detection operation steps,fast detection speed and high spatio-temporal sampling ability.Herein,this study attempted to construct a method for the rapid detection of formaldehyde by paper chips in the near-infrared region,which is expected to be used for the rapid detection of formaldehyde residues in food.Finally,it was successfully applied to the imaging analysis of endogenous formaldehyde in mice,which is expected to provide a feasible sensing tool for the study of the pathogenic mechanism related to formaldehyde transition expression.(3)Sodium bisulfite(Na2S2O4)is a common food additive with the functions of flour whitening and bean sprout bleaching.In the third work,an "OFF-ON" NIR fluorescent probe for Na2S2O4 detection was designed by linking the semicarbonylamino backbone fluorophore AXPI and N,N-2(2-chloroethyl)-1,4-phenylenediamine through an azo bond.The probe showed good spectral performance in the in vitro detection of Na2S2O4,and the spike-recovery of Na2S2O4 in actual flour samples was good and met the detection requirements.The probe can achieve highly sensitive and selective detection of Na2S2O4 with rapid response to cleavage of the azo bond and release of a strong near-infrared fluorescence signal.