Synthesis and characterization of carbon dots derived from compounds containing thioureas and thiazole rings

Synthesizing carbon dots (CDs) using therapeutic compounds as precursors is a new trend in the applications of CDs in drug delivery and disease treatment by leveraging the advantages of nanoparticles and therapeutic molecules simultaneously, without the need of further modifications. Compounds containing thioureas and thiazole rings have been extensively studied in biological applications such as antidiabetic, anticancer, antimicrobial, antiviral and antifungal activities. However, the research using such compounds as precursors to synthesize CDs has not been reported. In this study, four types of CDs derived from 1-(benzo[d]thiazol-2-yl)− 3-phenylthiourea (H2PhT), N-ethyl-N′-(4′-methylthiazol-2′-yl) thiourea (H2EMT), N-phenyl-N′-(4′-methylthiazol-2′-yl)thiourea (H2PhMT) or N-methyl-N′-(4′-methylthiazol-2′-yl)thiourea (H2MMT) were successfully prepared and characterized. The UV–vis absorption, fluorescence, and Fourier-transform infrared (FTIR) spectroscopies, atomic force microscopy (AFM), zeta potential measurements and thermogravimetric analysis (TGA) suggested that these four families of CDs are all less than 10 nm. H2PhT-CDs, H2EMT-CDs, and H2PhMT-CDs possess excitation-independent PL emission at around 440 nm, while H2MMT-CDs exhibit excitation-dependent PL emission property. The structural properties of CDs indicate the presence of certain moieties that may be associated with the therapeutic effects of H2PhT, H2EMT, H2PhMT and H2MMT in the corresponding H2PhT-CDs, H2EMT-CDs, H2PhMT-CDs and H2MMT-CDs. Moreover, all four families of CDs possess a slightly positive or negative charge, which benefits their affinities to cells. The results in this study could provide the knowledge in understanding the potential applications of these CDs in the treatment of diabetes, cancer, and infections in future research.