Antibacterial and Antitumor Application of Carbon Dots Based on Natural Products for Photodynamic/Photothermal...

This work presents an easy one-pot synthesis to prepare carbon dots (CDs) from natural products, and their successful application as photosensitizers (PS) and photothermal agents (PA) to combat bacteria and cancerous cells. Despite some differences may appear in the natural extracts due to the obtaining process, it was possible to obtain antibacterial/antitumor photoactivated nanomedicine from common carbon sources as annatto, cinnamon and curcumin.

Water dispersions of Bixa Orellana L. (annatto), Cinnamomum verum J. Presl (cinnamon), Curcuma longa L. (turmeric or curcumin), and sucrose were used as precursors to prepare CDs1, CDs2, CDs3, and CDs4, correspondingly. The microwave-assisted route was selected to synthesize CDs since it is a simple-timesaving procedure that allows harnessing eco-friendly precursors. The shape, size, and chemical composition of CDs were determined by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform infrared (FTIR) and Raman spectroscopies, respectively. In addition, photodynamic, photothermal, luminescence, cytotoxicity, antimicrobial and antitumor analyses were carried out and assessed.

This research synthesized irregular shaped CDs, in the range of 2.3 to 3.7 nm, from natural sources. Regarding, their photodynamic and photothermal properties, it was demonstrated that after irradiation CDs generated ¹O₂ species and the temperature can raise in the range to 40-50 °C, respectively. The antimicrobial capacity of the CDs was tested against microorganism methicillin-resistant S. aureus (MRSA) and Extended-Spectrum β-Lactamase (ESBL)-producing E. coli. CDs1, CDs2, and CDs3 showed excellent antibacterial effects since complete inhibitions were observed after irradiation with blue light (450 nm; 40 mW·cm^-2). In addition, the positive antitumor effect was also evidenced against T47D cells. Therefore, it has been demonstrated that the CDs synthesized from green carbon sources such as annatto, cinnamon and curcumin have potential applications as antibacterial and antitumor nanomaterials.