Insights into the feature size required for the death of Pseudomonas fluorescens on nanostructured silicon fabricated by block copolymer lithography

It has been established that nanostructured surfaces can cause cell death for Gram-negative species; however, the exact mode of action has not yet been determined from among several agreed-upon possibilities. Herein, silicon nanospike arrays were fabricated via a combination of block copolymer lithography and plasma etching. Patterns were first developed on silicon substrates using tetrahydrofuran, chloroform, or acetic acid as annealing solvents with two different molecular weight block copolymers. Three silicon surface types (NSS, NSM and NSL) were fabricated after a hard mask development and plasma etching. These samples were designed to be "small, medium and large" versions of nanospike arrays regarding their height, diameter and pitch; maintaining the same approximate proportionality, while changing in size. NSS had structures of 28 nm in height, and 16 nm in base diameter, with a pitch of 36 nm. NSM structures were 140 nm in height, and 31 nm in diameter, with a pitch of 63 nm. NSL surface structures had a height of 272 nm, a diameter of 47 nm and a pitch of 99 nm. When suspensions of gentamicin-resistant P. fluorescens cells were interfaced with the arrays for 24 h, it was shown that the NSS had similar to 76% less cell death than both NSM and NSL. To the best of our knowledge, this is the first study that etched silicon patterned using block copolymer lithography has been used to fabricate surfaces with antibacterial activity.