Bacterial biofilms formed on touchable surfaces such as displays of electronic devices not only reduce the product service life, but also cause human health issues. There is an urgent need to research into the biofilm formation mechanism and methodologies to prevent formation of the biofilms on human touchable surfaces. It has been reported that laser-induced graphene (LIG) helps resist biofilm growth, which has been attributed to the atomic composition and its sharp edges of graphene. However, LIG alone was not able to retard bacterial growth completely. It has been reported that LIG incorporated with silver (Ag) nanoparticles exhibited enhanced surface antibacterial activity. As a heavy metal, overdose of Ag is harmful to human health. Therefore, a new biocompatible antibacterial agent to replace or reduce the use of Ag is highly important.
In this study, we investigate and compare the effect of doping two types of nanocrystals, i.e., ZnO and silver (Ag) doped ZnO, into LIG on antibacterial actions. A 355 nm ultraviolet (UV) laser was studied to produce LIG on a watercolor paper substrate. Formation of few-layer graphene has been verified by Raman spectra. Escherichia coli (E. coli), the representative of Gram-negative bacteria and Staphylococcus aureus (S. aureus), the representative of Gram-positive bacteria were employed for the investigation of the anti-biofilm properties of the LIG paper substrate. Results show that with the incorporation of either the ZnO nanocrystals or the silver (Ag) doped ZnO into the LIG, the antibacterial effect became stronger. It is further shown that the Ag doped ZnO nanocrystals has superior antibacterial performance to that of the ZnO nanocrystals. The Ag doped ZnO nanocrystals is potentially an effective and biocompatible antibacterial agent and yet has a much reduced and acceptable level of Ag concentration.

laser-induced graphene (LIG), paper, Ag/ZnO, antibacterial