Polyethyleneimine and quaternized ammonium polyethyleneimine: the versatile materials for combating bacteria and biofilms.

Bacterial infection has become a serious clinical concern due to the emergence of drug-resistance and biofilm formation. Therefore, it is in great demand to develop efficient antimicrobial agents to treat bacterial infection without using antibiotics. Herein, we successfully prepared four quaternized ammonium PEI (QPEI: PEI1200-C2, PEI1200-C4, PEI1200-C6 and PEI1200-C8) using the commercial available PEI1200. Both PEI and four QPEI presented broad-spectrum antimicrobial activity against Gram-negative bacteria (E. coli, and P. aeruginosa) and Gram-positive bacteria (B. amyloliquefaciens and S. aureus), especially PEI1200-C6 showed the strongest antimicrobial activity with good biocompatibility at the MIC concentrations. Besides, PEI1200-C6 showed 4-16-fold better antibacterial effect than PEI1200, and fluorescent microscope imaging demonstrated that both of them could efficiently eradicate biofilms formed by four bacterial strains in vitro. As the accessible broad-spectrum antibacterial agents, PEI1200 and PEI1200-C6 are significant candidates to treat bacterial infections or eradicate biofilms on indwelling medical devices.

Assembly of pi-functionalized quaternary ammonium compounds with graphene hydrogel for efficient water disinfection.

Graphene hydrogels hold great potential for the disinfection of bacteria-contaminated water. However, the intrinsic antibacterial activity of graphene hydrogels is not satisfactory, and the incorporation of other antibacterial agents often results in their unwanted releases. Here, we present a new strategy to improve the antibacterial activities of graphene hydrogels. We first synthesized a new pi-conjugated molecule containing five aromatic rings and two side-linked quaternary ammonium (QA) groups, denoted as piQA. Next, we fabricated composite gravity filters by assembling piQA with reduced graphene oxide (rGO) hydrogel. The rGO hydrogel helps to form a sponge-like physical sieve, contributes to the overall antibacterial activity, and provides abundant pi-rich surfaces. The large aromatic cores of piQA allow the formation of collectively strong pi-pi interactions with rGO, resulting in a high piQA mass loading of ∼31 wt%. Due to the sieving effect of rGO hydrogel and the synergistic antibacterial activity of rGO and piQA, the filters prepared based on piQA-rGO assemblies can remove over 99.5% of Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) cells with a high-water treatment capacity of 10 L g-1. Furthermore, the piQA-rGO assemblies show low toxicity towards two different mammalian cell lines (L929 and macrophages), and the release of piQA is also negligible. Overall, the new piQA-rGO assembly demonstrates high potential for water disinfection applications.