Exploring the photodynamic antifungal efficacy and mechanism of red-emissive carbon dots

These red-emissive carbon dots (CDs) can localize the mitochondria of the fungi and generate abundant singlet oxygen ( 1 O 2 ) under 525nm LED irradiation, thereby disrupting the mitochondria of yeasts, and inhibiting their growth. This photodynamic anti-fungal method can bypass the potential risks of conventional anti-fungal drug therapy, such as increased resistance, and improve the inhibitory efficiency. Carbon dots (CDs), a rapidly emerging class of carbon-based nanomaterials with exceptional photophysical properties and excellent biocompatibility, have demonstrated significant potential in the biomedical field, particularly in photodynamic therapy (PDT). Given that fungi exhibit mitochondrial-dependent characteristics analogous to those of animal and plant cells, this work aimed to develop mitochondrial-localising CD-based photosensitisers for antifungal PDT. In this work, Rhodamine B and sulfanilic acid were selected as precursors, and a one-pot hydrothermal synthesis method was employed to fabricate a new type of red-fluorescent carbon dots (designated RS-CDs). The RS-CDs demonstrated mitochondrial localisation in Saccharomyces cerevisiae (S. cerevisiae) and efficiently produced singlet oxygen under appropriate excitation light (λ ex = 525 nm), thereby inducing damage to S. cerevisiae mitochondria and achieving a photodynamic antifungal effect. Experimental results showed clear antifungal activity of RS-CDs, with IC 50 values of 189.2 μg mL -1 against nonpathogenic S. cerevisiae and 387.9 μg mL -1 against pathogenic Candida albicans. Furthermore, RS-CDs also significantly inhibit bacteria without mitochondria, such as Staphylococcus aureus and Escherichia coli, suggesting potential broad-spectrum photodynamic antimicrobial activity. This work proposes a strategy for synthesising an effective photosensitiser for antifungal PDT and provides preliminary insights into its mechanism of action.