Aconitic acid derived carbon dots: Conjugated interaction for the detection of folic acid and fluorescence targeted imaging of folate receptor overexpressed cancer cells

Herein, we utilized aconitic acid (AA) as the precursor for preparing carbon dots (AA-CDs) by a facile hydrothermal reaction, and the resulting AA-CDs exhibited bright blue fluorescence with an absolute quantum yield of 56.5% in aqueous solution. Preliminary experiments showed that the prepared AA-CDs without further surface passivation or modification could selectively interact with folic acid (FA), resulting in significant fluorescence quenching. Based on this, a sensitive method for FA analysis was developed with a detection limit of 40 nM (S/N = 3), which was then successfully applied for the detection of FA in food and pharmaceutical samples with the average recoveries of 95.0–105.3%. Furthermore, a weak fluorescent nanoprobe (FA-AA-CDs) was fabricated based on the conjugated interaction of FA and AA-CDs, and its feasibility was evaluated as a fluorescence turn-on nanoprobe for targeted imaging of cancer cells using Hela, SMMC-7721, and A549 cells as models that expressed different levels of folate receptors (FRs) on the cell surface. The results exhibited that the fluorescence intensity of these cells was in accordance with their FRs expression levels, testifying its potential of FA-AA-CDs for targeted imaging of cancer cells. Subsequently, the internalization mechanism of FA-AA-CDs into cells was elucidated via receptor-mediated endocytosis using control experiments.