Studies On Piceatannol Detection With Carbon Quantum Dots Probe Based Fluorescence Spectroscopy And Surface-enhanced Raman Spectroscopy

Piceatannol?Pic?is a natural polyphenolic stilbene,produced in response to biotic or abiotic stress,exhibits good biological activity.At present,the available detection methods for pic include liquid chromatography,gas chromatography,or combination of these approaches with mass spectrometry,nuclear magnetic resonance spectrometer and so on.But the mathods deliver some limitations such as they are time consuming,need a lot of reagents,require trained person and need expensive equipments.To combat with aforementioned issues researchers proposed some modalities.Carbon quantum dots?CDs?and surface enhanced Raman spectroscopy?SERS?are among the extensively used methods in both food and non food experimentations due to the advantages of simplicity,fast,accuracy and their reliability.The purpose of my disertaion is to ascertain Pic based on CDs probe and SERS,showed promising methods to detect and provide refrence for polyphenol from plant based sources.In our work we successfully prepared CDs with emission wavelengths of 570 nm in water and then CDs/Cu²⁺fluorescent probe was constructed and finally detection model for Pic was established.The proposed model showed good linerar range and low limit of detection?LOD?in blueberries and grape juice.Moreover,we also prepared silver-coated gold nanoparticles?Au@Ag NPs?and modified with 4-Aminothiophenol?ATP?for rapid detection Pic by SERS method,with the principle that pic enhances the Raman signal of ATP molecules significantly.The main contents and conclusions are as follows:1)Preparation of yellow-green CDs and characterize their properties.The CDs were synthesized by the o-phenylenediamine and ethanol,and were purifed by thin layer chromatography.For characterization of CDs,transmission electron microscopy?TEM?,fourier transform infrared spectroscopy?FTIR?,UV-vis absorption and fluorescence spectrophotometer was exploited.Moreover,the stability of the CDs to ultraviolet?UV?light,temperature,pH,and ionic strength was also investigated.The results showed better seperation of CDs on thin layer,when the volume ratio of methanol,dichloromethane and triethylamine was 1:25:0.39.Whereas,the optimal excitation wavelength for CDs was recorded at 385 nm,while the emission wavelength depends on the polarity of solvent,in water it was recorded at 570 nm and in ethanol it was observed at 540nm.The TEM imgaes confirmed particle size of CDs as 7.4±0.6 nm.The UV excitation tests?for 10 h?revealed that it exhibits excellent anti-photobleaching,and has negligible effect on temperature and ionic strength.Furthermore it also has stable fluorescence properties in the range of pH 5⁹.2)Construct CDs/Cu²⁺fluorescent probe for rapid detection of Pic.Firstly,the appropriate concentration of Cu²⁺was selected to construct CDs/Cu²⁺.Secondly,detection time and temperature were optimized and then the linear range and LOD of Pic were established by using different concentrations of Cu²⁺.The results showed that the linear ranges under 25,100,400mmol/L of Cu²⁺are 0.1²5mmol/L,0.75²5mmol/L,0.75⁵0mmol/L,and LOD were 0.04,0.01,0.03mmol/L,respectively.Subsequently,whether the high LOD concerned CDs was investigated.The results showed that 4 mol/L H₂O₂ caused 94.63%quenching of CDs.So,the high LOD was not related to CDs.Furthermore,using ethylenediaminetetraacetic acid disodium salt and butyl hydroxyanisole to study the detection mechanism.It releaved that Cu²⁺and reactive oxygen species?ROS?are very important to the method.The principle is that Pic and Cu²⁺generate ROS,which cause fluorescence quenching of CDs,thereby quantitatively determining Pic.Finally,the interference experiment and the spiked recovery experiment were carried out.The results showed that the selectivity of CDs/Cu²⁺to Pic was good and practical application was potential with the recoveries of 85%¹29%and the relative standard deviation?RSD?of 14%²0%.3)Detect Pic based on Au@Ag-ATP NPs by SERS technology.Firstly,Au@Ag NPs was successfully prepared,and then modified by ATP.The ATP modified nanoparticles was then employed as Raman active substrate for Pic detection.The TEM Images confirmed gold core with 32 nm and shell?silver?thickness of about 5 nm in diameter.The fitted equation was y?=?338?x-166 with the coefficient of determination?R²?of 0.993.Besides,the LOD of Pic detected by Au@Ag-ATP NPs substrate was calculated to be 0.62mmol/L with RSD of 4.14%.