Antibacterial photodynamic inactivation with elicited Andrographis paniculata (Burm. f.) Wall. ex Nees plant extract derived carbonaceous nanoparticle

Conversion of phytoproducts into nanoparticles for antimicrobial intervention is common but employing elicitation to the plant to achieve dual and more potent chemical and photodynamic effects is seldom researched or achieved. Antimicrobial photodynamic inactivation using nanotized plant extracts of Andrographis paniculata in the form of a carbonaceous nanoparticle is established here through the fabrication of a Carbon Dot (CD). Leaves extracts of Plant growth promoting bacteria (PGPR) elicited plants are transformed to CD to induce unique photophysical properties without any surface modification and passivation to achieve the enhanced antimicrobial activity. CD with diameter ∼20 nm synthesized through hydrothermal pyrolysis of elicited A. paniculata leaf extracts. The nanoscale dimensions and photophysical characteristics of the CD were confirmed by Transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Ultraviolet-visible (UV-vis), Fluorescence, and Fourier transform infrared spectroscopy (FTIR) characterizations. Antibacterial activity in both gram-positive and gram-negative bacteria was evaluated to determine the combined effect of the dark activity and visible light-induced photosensitization. Secondary metabolites are elicited by microbial inoculation to form nanotized phytoproducts in the present study, which does not rely on any polymeric or lipidic nanocarriers. In vitro, studies showed that the antibacterial effects of CDs against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) under the irradiation of visible light depend on the bioactive components, their concentrations, and duration of light irradiation. The CD itself sustainably acts as a photo-antibiotic as well as produces reactive oxygen species (ROS). This study showed that PGPR elicited leaf extracts of A. paniculata-derived CDs used as antibiotic therapy, due to its effectiveness in eliminating synthetic drug-resistant microbes through reactive oxygen species (ROS) via photodynamic inactivation. In comparison to the unelicited phyto substrate, it served as a more effective option for “Natural-Antibiotic-Antibacterial Photodynamic Therapy” (APDT) applications.