Functionalised Anodised Aluminium Oxide as a Biocidal Agent

Abstract

In this article, we describe the antimicrobial properties of a new composite based on anodic aluminium oxide (AAO) membranes containing propyl-copper-phosphonate units arranged at a predetermined density inside the AAO channels. The samples were prepared with four concentrations of copper ions and tested as antimicrobial drug on four different strains of Escherichia coli (K12, R2, R3 and R4). For comparison, the same strains were tested with three types of antibiotics using the minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests. Moreover, DNA was isolated from the analysed bacteria which was additionally digested with formamidopyrimidine-DNA glycosylase (Fpg) protein from the group of repair glycosases. These enzymes are markers of modified oxidised bases in nucleic acids produced during oxidative stress in cells. Preliminary cellular studies, MIC and MBC tests and digestion with Fpg protein after modification of bacterial DNA suggest that these compounds may have greater potential as antibacterial agents than antibiotics such as ciprofloxacin, bleomycin and cloxacillin. The described composites are highly specific for the analysed model Escherichia coli strains and may be used in the future as new substitutes for commonly used antibiotics in clinical and nosocomial infections in the progressing pandemic era. The results show much stronger antibacterial properties of the functionalised membranes on the action of bacterial membranes in comparison to the antibiotics in the Fpg digestion experiment. This is most likely due to the strong induction of oxidative stress in the cell through the breakdown of the analysed bacterial DNA. We have also observed that the intermolecular distances between the functional units play an important role for the antimicrobial properties of the used material. Hence, we utilised the idea of the 2D solvent to tailor them.

Aluminium(III) Oxide—The Silent Killer of Bacteria

“…In reference to our previous work related to the analysis of functionalised anodised aluminum oxide [11], we observed a clear effect of their action on selected bacterial strains. On the other hand, compared to the analysed nonfunctionalised anodised aluminum oxide, we found similar but lower values for the model bacterial slippers.…”

“…Self-organised nanoporous materials, in general, have great potential to be used in a broad range of applications [5] with functionalisation [2,6,7] or additional coatings [8] giving rise to new possibilities. One of the impressive applications of such nanocomposites is the new-generation biocidal materials which may be applied as disinfecting surfaces in both public spaces and medical facilities [9][10][11][12]. Such action in times of the SARS-CoV-2 pandemic and hospital-acquired infections seems to be highly justified [13][14][15][16].…”

“…The procedure for the fabrication of AAO Cl+Cr can be found in our previous work on the antibacterial properties of AAO membranes with chemically attached functional groups [11]. In short, aluminium foil (99%, SmartMembranes, Halle, Germany) was cut into 3 cm × 3 cm squares and heated at 550 • C for 12 h in a nitrogen atmosphere.…”