A multifunctional guanosine-based carbon dots for dead microbial imaging and synergistic broad-spectrum antimicrobial therapy

Pathogenic microbial infection poses serious threats to human lives and antibiotic abuse leads to bacterial resistance. The development of alternative antibacterial agents and strategies with reduced resistance risk is urgently demanded. Heteroatom doping is a feasible method for adjusting the electronic and optical properties of carbon dots (CDs) to improve their bioimaging performance and light-mediated therapeutic efficiency. Herein, we synthesized a series of guanosine-derived CDs from guanosine (G), guanosine monophosphate (GMP), guanosine diphosphate (GDP), and guanosine triphosphate (GTP) as respective precursors. G-CDs, prepared by guanosine with strong surface negative charge and suitable size, can successfully differentiate and stain dead microbial cells (bacteria and fungi). G-CDs with a high N content exhibited the highest antibacterial activity in vitro and in vivo among the four guanosine-derived CDs, owing to triple synergistic antibacterial actions - the intrinsic antibacterial mechanism, bacterial photodynamic and photothermal inactivation against bacteria and fungi. In this paper, we present a promising new method to prepare CDs using natural biomolecules from living systems as precursors for multifunctional dead microbial cells imaging and broad-spectrum theranostic applications.