Pathogenic biofilms raise significant health and economic concerns, because these bacteria are persistent and can lead to long-term infections in vivo and surface contamination in healthcare and industrial facilities or devices. Compared with conventional antimicrobial strategies, photocatalysis holds promise for biofilm control because of its broad-spectrum effectiveness under ambient conditions, low cost, easy operation, and reduced maintenance. In this study, we investigated the performance and mechanism of Staphylococcus epidermidis biofilm control and eradication on the surface of an innovative photocatalyst, graphitic carbon nitride (g-C3N4), under visible-light irradiation, which overcame the need for ultraviolet light for many current photocatalysts (e.g., titanium dioxide (TiO2)). Optical coherence tomography and confocal laser scanning microscopy (CLSM) suggested that g-C3N4 coupons inhibited biofilm development and eradicated mature biofilms under the irradiation of white light-emitting diodes. Biofilm inactivation was observed occurring from the surface toward the center of the biofilms, suggesting that the diffusion of reactive species into the biofilms played a key role. By taking advantage of scanning electron microscopy, CLSM, and atomic force microscopy for biofilm morphology, composition, and mechanical property characterization, we demonstrated that photocatalysis destroyed the integrated and cohesive structure of biofilms and facilitated biofilm eradication by removing the extracellular polymeric substances. Moreover, reactive oxygen species generated during g-C3N4 photocatalysis were quantified via reactions with radical probes and 1O2 was believed to be responsible for biofilm control and removal. Our work highlights the promise of using g-C3N4 for a broad range of antimicrobial applications, especially for the eradication of persistent biofilms under visible-light irradiation, including photodynamic therapy, environmental remediation, food-industry applications, and self-cleaning surface development.
Keywords: biofilms; extracellular polymeric substances; graphitic carbon nitride; mechanical properties; visible light.