Direct-write patterning of bacterial cells by dip-pen nanolithography.

The ability of dip-pen nanolithography (DPN) to generate nano- or microarrays of soft or hard materials (e.g., small molecules, DNA, proteins, nanoparticles, sols, and polymers) in a direct-write manner has been widely demonstrated. The transporting of large-sized ink materials such as bacteria, however, remains a significant challenge with this technique. The size limitation of the water meniscus formed between the DPN tip and the solid surface becomes a bottleneck in such diffusion-based molecular transport experiments. Herein, we report a straightforward "stamp-on" DPN method that uses a nanostructured poly(2-methyl-2-oxazoline) hydrogel-coated tip and carrier agents to generate patterns of micrometer-sized Escherichia coli JM 109 bacterial cells. We demonstrate that this approach enables the deposition of a single bacterial cell array on a solid surface or arrays of layers of multiple cells by modulating the viscosity of the "ink" solution. Fluorescence microscopy images indicated that the deposited bacterial cells were kept alive on Luria-Bertani-agar layered solid surfaces after DPN patterning.

Dual functions of highly potent graphene derivative-poly-L-lysine composites to inhibit bacteria and support human cells.

Dual-function poly(L-lysine) (PLL) composites that function as antibacterial agents and promote the growth of human cell culture have been sought by researchers for a long period. In this paper, we report the preparation of new graphene derivative-PLL composites via electrostatic interactions and covalent bonding between graphene derivatives and PLL. The resulting composites were characterized by infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The novel dual function of PLL composites, specifically antibacterial activity and biocompatibility with human cells [human adipose-derived stem cells and non-small-cell lung carcinoma cells (A549)], was carefully investigated. Graphene-DS-PLL composites composed of 4-carboxylic acid benzene diazonium salt (DS) generated more anionic carboxylic acid groups to bind to cationic PLLs, forming the most potent antibacterial agent among PLL and PLL composites with high biocompatibility with human cell culture. This dual functionality can be used to inhibit bacterial growth while enhancing human cell growth.