We have utilized GHz burst mode femtosecond (fs) laser that delivers a series of pulse trains with a high repetition rate, featuring pulse intervals of several hundred picoseconds (ps), for formation of laser-induced periodic surface structures (LIPSS). Linearly polarized GHz burst mode can create distinct lattice-like LIPSS, unlike the well-known stripe-patterned LIPSS formed with the conventional irradiation scheme of fs laser pulses (single-pulse mode). Meanwhile, circular polarized GHz burst can fabricate rock-surface or tetrapod-like LIPSS depending on the number of intra-pulses, that also differ from the dot-patterned LIPSS created by the single-pulse mode. These unique 2D LIPSS are expected to provide different surface functionalities compared to those produced by the single-pulse mode. In this study, we investigate the potential of suppressing microbial growth on LIPSS, without relying on the conventional biochemistry method.

In the experiment, we evaluated microbial colony growth to investigate the physical effect of LIPSS on microbial growth. To exclude biochemical effect of a metal substrate, we transferred positive patterns of LIPSS fabricated by fs laser pulses on titanium (Ti) to PDMS specimen areas by the two-step molding technique. Then, we observed the growth of a colony of microbes (S. aureus) sandwiched between the agar medium and structured PDMS specimens. Consequently, the size of S. aureus colony in the area covered by PDMS with LIPSS patterns was significantly smaller than that in the area of flat PDMS. Interestingly, the PDMS with 2D LIPSS formed using linearly polarized GHz burst mode exhibited greater inhibitory effects than the other LIPSS.