Fluorescent Ink and Chemical Sensing Towards Tartrazine Based on Nitrogen-Doped Carbon Dots Derived from Durian Seed Waste

Background Nitrogen-doped carbon dots (N-CDs) have wide interest owing to their unique fluorescence and electronic characteristics. Materials and methods In this work, novel NCDs were synthesized by a facile hydrothermal treatment method utilizing durian seed waste (DS) and glutamine (Gln) as carbon and nitrogen sources, respectively. The as prepared NCDs were utilized as a fluorescent ink and a chemical sensor toward tartrazine. Results The optical properties of N-DS-CDs possessed a bright blue emission color under UV-light radiation and a strong emission peak at 432 nm excited at 340 nm with the excitation-dependent emission behavior and fluorescent quantum yield (FL-QY) of 17.24±0.13%. Interestingly, the dilution factors of N-DS-CDs solution with different absorbance values at 340/350 nm wavelength can distinguish the energy transitions of the samples. These CDs exhibited high water solubility and good optical stability towards several environmental conditions, such as ionic strength, light radiation, and heating temperature. The pH change of the solution possed high fluorescence intensity at pH 4-5. For structural characteristics, the TEM image showed that the average size of the N-DS-CDs was 2.2 nm. Raman analysis confirmed the graphitic nature of the N-DS-CDs. FTIR analysis confirmed the successful doping of nitrogen moiety over the CDs. In addition, N-DS-CDs showed high colloidal stability from zeta analysis. Based on their meaningful characteristics, the N-DS-CDs were applied as invisible fluorescent ink and homogenously mixed with commercial pen ink to draw the letters. The N-DS-CDs were also applied as a fluorescent sensor toward tartrazine dye with a LOD of 0.059 μM. Conclusion Thus, the biowaste from durian seeds was successfully converted to functional nanomaterials and applied in important applications. Graphic Abstract