Construction Of Nanocellulose Based Fluorescent Smart Tag And Its Application In The Detection Of Biogenic Amine

As a group of organic basic compounds containing nitrogen,biogenic amines（BAs）are generated from food spoilage and considered as important indicators for monitoring food freshness.BAs play essential roles in several processes such as gene expression,cell growth,and tissue repair.But excessive intake of foods containing BAs may produce toxicological effects and even lead to death.Therefore,it is of great significance to develop a simple,fast and efficient detection method of BAs to ensure food quality and human health.Fluorescent smart tags have attracted widespread attention for on-site,real time and visual monitoring of BAs.By using the good fluorescence properties of carbon dots（N,S-CDs）,Cd Te quantum dots（Cd Te QDs）and Rodamine B（Rb）,nanocellulose based fluorescent smart tags based on Rb@N,S-CDs and N,S-CDs@Cd Te QDs were successfully prepared for monitoring the freshness of shrimp.The work is mainly divided into three aspects as follows:（1）KMn O₄ oxidation method was developed to prepare carboxymethylated cellu-lose nanocrystals（CNCs-COOH）under mild conditions（5 wt%H₂SO₄ solution,room temperature,3 h）,with the yield of 49.63%.The KMn O₄ oxidation method was modified by introducing Na₂H₂P₂O₇ which could produce CNCs-COOH with a higher yield of 72.88%in less time（2.5 h）.The obtained CNCs-COOH was characterized by X-ray powder diffraction（XRD）,Scanning electron microscope（SEM）,Fourier transform infrared spectrometer（FT-IR）,Thermogravimetric analysis（TGA）,X-ray photoelectron spectroscopy（XPS）,Solid state NMR and Zeta potential.This study offered a kind of high efficiency and low-cost method for industrial preparation of CNCs-COOH.（2）A p H-sensitive blue emission carbon dots was synthesized by one-step solvothermal treatment of citric acid and N-acetyl-L-cysteine.Herein,a ratiometric fluorescent sensor for eight kinds of biogenic amines was established by facile mixing carbon dots and Rhodamine B with the advantages of rapid response（10 s）,low limits of detection（0.733–3.943μM）and wide linear ranges（0–150μM）.Nanocellulose based fluorescent smart tags based on Rb@N,S-CDs were prepared by simple immersing the nanocellulose membrane into the mixture of Rb and N,S-CDs.The obtained fluorescent smart tags could realize on-site and visual detection of the freshness of shrimp,showing an obvious color change from red to blue.The obtained fluorescent smart tags has broad prospects in food safety monitoring.（3）Herein,the p H-reponsive Cd Te quantum dots with yellow emission was synthesized via a reflux method by using cadmium chloride and sodium tellurite as precursor.The p H-insensitive blue emission carbon dots was synthesized via the solvothermal treatment using citric acid as carbon source.A novel fluorescent sensor for biogenic amines with the advantages of simplicity,low cost and high sensitivity was developed by simple mixing the above two fluorescent materials.Furthermore,color-tunable fluorescent smart tags were constructed,showing a distinguishable fluorescent color variation from blue to green during the corruption of shrimp samples.The smart tags provided a method for visually monitoring the freshness of food samples.