pH-Responsive carbon dots with red emission for real-time and visual detection of amines

Biogenic amines (BAs) from rotten food cause serious harm to sensitive people. Therefore, the development of a smart label that can intuitively monitor the degree of food decay in real-time is of great significance in food safety. Herein, we report the synthesis of pH-responsive carbon dots with red emission (R-CDs) by the solvothermal treatment of citric acid and urea. The fluorescence intensity of R-CDs gradually increased as the pH of the solution increased from 1 to 12. We studied the mechanisms of pH response and found that H-aggregation occurred when R-CDs were in acidic solution and caused quenching; when they were distributed in alkaline solution, the Fermi level shift caused reduced self-absorption and enhanced red fluorescence emission. The intense red emission of R-CDs is beneficial for the visual detection of alkaline organic amines and BAs derived from rotten shrimp to achieve food safety detection. Moreover, the R-CDs can be used as a promising pH-sensitive fluorescent ink, which has broad prospects and significance in anticounterfeiting and information encryption. The pH-responsive emission of R-CDs with H-aggregation and Fermi level shift has been applied in the real-time and visual detection of amines.