Antimicrobial Studies of Black Silicon and Black Diamond Using Gram-Positive Bacteria

Herein, it is investigated if black diamond is useful in a bactericidal surface. Black diamond is derived from black silicon, a silicon surface structured into nanosized needles. Black diamond is obtained by coating black silicon with a thin diamond film, rendering the nanostructures more robust. The bactericidal and antibacterial properties of fluorine-terminated and hydrogen-terminated black diamonds with those of black silicon and for flat surfaces of diamond (on silicon) with the same terminations are studied. The ability to repel and kill Gram-positive Staphylococcus aureus and Staphylococcus epidermidis is evaluated, which have a thicker cell wall and are more mechanically robust than the bacteria that are studied before. The initial adhesion as well as long-term 24 h biofilm formation is studied. The number of bacteria that initially adhere to the fluorine-terminated black diamond surface is reduced and has the highest dead bacterial ratio. Biofilm formation after 24 h shows that while all surfaces outperform glass over the long term, diamond-coated surfaces with both fluorine and hydrogen termination have a significant inhibiting biofilm formation effect. In conclusion, fluorinated and hydrogenated diamond-coated surfaces with and without nanoneedles have repelling, bactericidal, and biofilm-inhibiting effects on Gram-positive bacterial strains and are promising antimicrobial surfaces.