Ultra small carbon dots from Crocus cancellatus as a highly fluorescence probe for synthetic Ponceau 4R dye sensing in food samples

In this work, for the first time, natural Crocus cancellatus was adopted for the green, low-cost, and simple synthesis of highly fluorescent ultra-small carbon dots (CDs) with well-distributed size using a one-pot hydrothermal treatment. As-synthesized CDs are used as fluorescence sensing probe for quantitative analysis of Ponceau 4R (E124) synthetic food dye, which is widely used. However, excessive consumption of Ponceau 4R poses potential health risks. To obtain better-quality performance of as-synthesized CDs, the time and temperature of the hydrothermal carbonization reaction of crocus were optimized simply. The as-prepared carbon dots exhibit exceptional advantages including excellent fluorescence, satisfactory chemical stability, low toxicity, and excellent biocompatibility. It produced a strong blue fluorescence when irradiated with UV light at 365 nm, which was subsequently effectively employed for Ponceau 4R sensing based on the quenching of fluorescence. The as-prepared CDs was characterized by EDX, XRD, FTIR, SEM, HRTEM, UV-Visible absorption spectrophotometry, and fluorescence. The effects of carbon dots fluorescence emission wavelength, CDs quantity, pH value, and reaction time were investigated to detect Ponceau 4R under optimum conditions. The synthesized carbon dot's fluorescence intensity allowed quantitative determination of Ponceau 4R in the linear range of 60-6000 nM with a detection limit of 40 nM that is lower than all previously published methods. Several soft drink samples were used to validate the potential use of this new fluorescent probe for P4R detection in actual samples with good precision and accuracy.