Use of a smartphone for visual detection of melamine in milk based on Au@Carbon quantum dots nanocomposites.

Gold nanoparticles@Carbon quantum dots nanocomposites (Au@CQDs) were designed for analyzing melamine in milk visually. Fluorescent emission of Au@CQDs enhanced with the increase of melamine concentration. A calibration curve (R2  = 0.9856) and fluorescence standard array were established for detection of melamine in the range of 1 μM-10 μM. Limit of quantification and limit of detection were 12 nM and 3.6 nM, respectively. The approximate concentration of melamine adulterated in milk samples were detected visually by the fluorescence standard array and smartphone. The accurate concentration was obtained by the calibration curve and portable fluorescence spectrometer with recoveries of 105.64%-102.75% and less than 2% of coefficient of variation (CV) (n = 18). This performance was consistent with that of the high-performance liquid chromatography (HPLC) method (recoveries of 105.56%-107.95% with 2.24%-3.56% of CVs). The Au@CQDs-based fluorescent method for visual and accurate detection of melamine in milk was presented and showed strong application potential.