Construction Of Ratiometric Fluorescent Sensor And Its Application For Detection Of Melamine In Milk

Excessive intake of melamine-containing foods not only causes kidney stones and other diseases,but also causes malnutrition due to inadequate protein intake.Melamine cannot be used as food additive and is forbidened to be added to food and animal feed.The use of melamine in dairy products and other foods must be strictly controlled.However,the incident of "Milk Powder Tainted with Melamine" caused great panic.To solve the problem of melamine pollution and illegal addition,here,a ratio fluorescence sensor was constructed,which can rapid and sensitive detect melamine in milk samples.Copper nanoclusters with red fluorescence were synthesized with Poly-T DNA as template.The excitation wavelength and emission wavelength were 346 nm and 630 nm,respectively.Because the binding ability of melamine to DNA is stronger than that between DNA and copper nanoclusters,the target analyte melamine can quench the fluorescence of copper nanoclusters.On the other hand melamine and thymidine bases bind to form double-stranded DNA structure through T-M-T.When the double-stranded DNA fluorescent dye Picogreen is added to the system,the fluorescence value at 535 nm is obviously enhanced.Finally,a ratio fluorescence sensor was constructed with the emission wavelength ratio of copper nanoclusters and Picogreen fluorescent dyes(F535/F630)as the detection signal.Under the optimal experimental conditions,the linear range of detection for melamine was found in the range of 0.0-5.0 ?M,and the correlation coefficient R2 was 0.992.According to the principle of 3?(standard deviation slope),the detection limit for melamine was calculated to be 57 nM.Meanwhile,the constructed ratio sensor did not respond to the structural analogues of melamine and the other interfering substances in milk samples,indicating that this method has good specificity for the detection of melamine.The recovery rate of melamine was 98%-111%by adding actual milk samples.Furthermore,the visual detection of melamine was realized considering the purpose of rapid detection.The constructed ratio fluorescence sensor has the advantages of low cost,short detection time,high sensitiveity and specificity.It has great potential application in real sample detection.