Fluorescent Sensing Visualization Of Milk Quality And Safety Indicators Based On Multicolor Carbon Quantum Dots Composites

Milk as the ideal food is rich in various nutrients required by the human body Its quality and safety directly affects the health and safety of consumers.The traditional methods for detection of food quality and safety is reliable,but it has the disadvantages of complicated or time-consuming operation.Fluorescence sensing technology has attracted much attention because it can rapidly and accurately detect the quality and safety of milk.Carbon quantum dots(CQDs)with excellent fluorescent properties and good biocompatibility are expected to be used to construct fluorescent sensors for detecting milk quality and safety indicators.This study combined multicolor fluorescent carbon quantum dots with other functional materials to construct fluorescent sensors for milk acidity,E.coli,tetracycline and mercury ions.The image processing platform was fabricated for automatic and simultaneous visual detection of the four milk quality and safety indicators.The main research contents are as follows(1)Fluorescent detection of milk acidity based on yellow carbon quantum dots(YCQDs).Carbon quantum dots with an optimal emission wavelength of 567 nm were synthesized by microwave heating p-phenylenediamine and acetamide.A fluorescence method for detecting the acidity of milk is established according to the linear relationship between the fluorescence intensity and the milk acidity.In order to verify the practicability,this study continuously monitored the change of milk acidity during storage.It is found that the detection results of the fluorescence method and the standard method were consistent(P>0.05).In summary,the fluorescence method can be used to detect the acidity of milk,and it can provide a sensitive,rapid,accurate and reliable method for milk freshness detection(2)Green magnetic carbon quantum dots(GCQD-MNPs)prepared for sensitive and selective assay of(E.coli):GCQDs were synthesized from orange peel as a carbon source via a microwave-assisted method.The GCQDs displayed strong green fluorescence with emission wavelength of 522 nm.A fluorescent sensor(CQDs-MNPs)for E.coli was fabricated based on CQDs labeled with aptamer(aptamer-CQDs)and magnetic nanoparticles labeled with complementary DNA(cDNA-MNPs).Fluorescent intensity of the CQDs-MNPs was decreased with addition of E.coli.The linearity between fluorescent intensity and E.coli concentration was used for developing a fluorescent method with detecting range of 500-106 CFU/mL and detection limit of 487 CFU/mL.Milk samples contaminated by E.coli were analyzed by this method,and the results agree with that achieved by plate-counting methods.This fluorescent sensor exhibits great potential in guaranteeing food quality and safety(3)Fluorescent and electrochemical dual-mode aptasensor for tetracycline detection using aptamer-modified carbon quantum dot@silver nanocomposites(Apta-BCQD@AgNP):Apta-BCQDs specifically binding to Tc were used as templates to synthesize apta-BCQD@AgNPs nanocomposites.The presence of Tc led to fluorescent recovery of apta-BCQD@AgNPs and a decrease in electrical conductivity of apta-BCQD@AgNPs-modified electrodes.Fluorescent and electrochemical methods were established through excellent linear relationship(R2=0.987 and 0.993)between response signal and Tc concentration with wide detection range(10"7-10"2 M and 10-9-10-4 M)and low limit of detection(15.2 nM and 0.258 nM).In addition,satisfied recoveries of Tc in milk samples were obtained by the developed fluorescent and electrochemical methods which were comparable to high performance liquid chromatography(HPLC)method.All results indicate that the apta-BCQD@AgNPs can be used as a dual-mode aptasensor for fluorescent and electrochemical detection of Tc in complex samples with high sensitivity and selectivity(4)A dual-emission fluorescent sensor for detection of mercury ions in milk based on europium-functionalized carbon quantum dots(CQDs@Ad-Eu-DPA):The lanthanide coordination polymer(Ad-Eu-DPA)was synthesized by solvothermal method using adenine(Ad),pyridinedicarboxylic acid(DPA)and nitric acid as raw materials.Then the Ad-Eu-DPA combined with carbon quantum dots(CQDs)formed CQDs@Ad-Eu-DPA with emission wavelength at 443 nm and 617 nm According to the fluorescence enhance of the sensor,a fluorescence method was constructed for the detection of mercury ions with a linear range of 1-20 nM and a detection limit of 0.2 nM.Finally,the fluorescence method was used to detect mercury-containing milk samples,and the detection recovery rate was 98.9-107.4%The results show that this sensor has high accuracy and good selectivity,which provides a new direction for trace detection of mercury ions in milk(5)Visual detection of four quality and safety indicators(milk acidity,E.coli,tetracycline,and mercury ions)based on multicolor CQDs composites:Fluorescent colorimetric cards of four indicators was fabricated by collecting images of the reaction system combined with the smart phone image processing platform.This method can realize simultaneous visualization detection of milk acidity of 11.6?34.2°T,E.coli at 500?106 CFU/mL,tetracycline at 10-7?10-2 M and mercury ion in the range of 5?20 nM.The four quality and safety indicators of milk samples were detected by the visual method and standard method.As a result,the detection results of the two were consistent.The results show that the simultaneous visualization method can be used for the automatic and simultaneous visual detection of four indicators,and provides a scientific basis for the simultaneous detection of multiple milk quality and safety indicators.