Synthesis of carbon dots from Combretum erythrophyllum leaves: Its optical, photothermal and antibacterial properties against dental caries causative organism

Dental caries is a disease caused by sugar-fermenting, acidogenic bacteria that affects millions of people globally. Antibiotics have been used to combat this disease; however, overuse has led to antibiotic-resistant strains. To combat these resistant strains, carbon dots (CDs) have gained attention as a promising material. CDs have been synthesised using plant-based materials; however, this study proposes the use of Combretum erythrophyllum (CE), as a new material for the synthesis of CDs, as it is cheap, renewable, and widely available. In this study, CDs were synthesised via hydrothermal and microwave methods using Combretum erythrophyllum leaf extract, which was extracted using water, water: ethanol at a 1:1 ratio, and ethanol as a solvent. The CDs were characterised using ultraviolet–visible spectroscopy (UV–Vis), photoluminescence spectroscopy (PL), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and X-ray diffraction analysis (XRD). The CDs synthesised via the microwave method emitted at 665–675 nm, whereas those synthesised via the hydrothermal method emitted at 425–428 nm. Photothermal analysis showed that CDs synthesised using a mixture of ethanol and water showed the highest heat-generating capacity. The PCE of CDs synthesised using the hydrothermal method with the mixture and deionised water as solvents were 22.5 and 9.6%, respectively. The PCE of CDs synthesised using the microwave method with the mixture and ethanol as solvents were 13.5 and 4.4%, respectively. The antibacterial activity was investigated using the microdilution method to determine the minimum inhibitory concentration (MIC). All as-synthesised carbon dots showed antibacterial potential, and the CDs synthesised by microwave using ethanol inhibited Streptococcus mutans (ATCC 25175) and Lactobacillus acidophilus (ATCC 4356) at 0.375 mg/mL. These results suggest that carbon dots synthesised from C. erythrophyllum may be explored in antibiotic therapy against pathogenic microorganisms.