Sustainable Synthesis of Ionic Liquid-Functionalized Zinc Oxide Nanosheets (IL@ZnO): Evaluation of Antibacterial Potential Activity for Biomedical Applications.

Zinc oxide (ZnO)-derived materials exhibit unique antibacterial, antifungal, and photochemical activities and are widely used in antibacterial formulations. In this work, ZnO nanosheets were prepared by green and cost-effective synthesis via a hydrothermal method, and the prepared ZnO nanosheets were further functionalized with an eco-friendly ionic liquid (IL). Thus, a sustainable approach was established to synthesize ZnO nanosheets. The functionalization of ZnO with the synthesized IL was fully characterized by advanced spectroscopic and microscopic techniques. The prepared ionic liquid-functionalized ZnO (IL@ZnO) showed self-organized layered-sheet arrangements caused by the intercalation of the IL onto the surface of ZnO nanosheets as revealed by scanning electron microscopy (SEM). The design of the IL comprised a carboxylic acid moiety for functionalization onto the surface of ZnO, whereas the hydrophobicity was tuned through the incorporation of a long alkyl chain. The developed IL@ZnO material was also tested against both Gram-positive and Gram-negative pathogenic bacteria for potential antibacterial activity by colony-forming unit (CFU) and minimum inhibitory concentration tests. The results revealed that the IL@ZnO exhibits significant antibacterial activity against tested strains. In particular, potent activity was observed against the Gram-positive skin-specific Staphylococcus aureus bacteria strain. The mechanism of bactericidal activity against bacteria was also explored along with the cytotoxicity toward mammalian cells, which reveals that the IL@ZnO is nontoxic in nature. To utilize the developed material owing to its bactericidal activity for practical applications, the IL@ZnO was fabricated onto the surface of cotton fabric, and its surface morphology was examined by SEM; the activity of IL@ZnO-treated cotton fabric was evaluated by the zone of inhibition assay. Additionally, the IL@ZnO-treated cotton fabric exhibited remarkable stability along with significant hydrophobicity and breathability and thus can be utilized as a biomaterial for biomedical applications, especially in medical masks, for reducing the risk of transmission of infectious diseases.

Ionic Liquid-Functionalized Multiwalled Carbon Nanotube-Based Hydrophobic Coatings for Robust Antibacterial Applications.

In recent years, the biomimetic superhydrophobic coatings have received tremendous attention, owing to their potential in fabricating self-cleaning surfaces, in environmental applications. Consequently, extensive research has been devoted to create a superhydrophobic surface using the oxidized derivatives of CNTs and graphene. Thus, the design and development of a self-cleaning/superhydrophobic surface with good biocompatibility are an effective approach to deal with the bacterial infections related to biomedical devices used in hospitals. In this context, herein, we have developed the material based on ionic liquid (IL)-functionalized multiwalled carbon nanotubes (MWCNTs) for hydrophobic coatings, which was fully characterized with various techniques such as Fourier transform infrared, powder X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. We have evaluated the synthesized ILs for their antibacterial potential against the pathogenic bacterial strains such as Gram-positive (Staphylococcus aureus and methicillin-resistant S. aureus) and Gram-negative (Escherichia coli) bacterial strains. Further, atomic force and scanning electron microscopic studies have been performed to investigate the morphological changes to unravel the mechanism of action, whereas DNA binding study indicates the binding of IL-1d@MWCNT with DNA (Ka = 2.390 × 104 M-1). Furthermore, the developed material (IL-1d@MWCNT) is coated onto the surface of polyvinyl chloride (PVC) and evaluated for hydrophobicity through water contact angle measurements and possesses long-term antibacterial efficiency against both under-investigating pathogenic strains. For the biocompatibility assay, the obtained coated PVC material has also been evaluated for its cytotoxicity, and results reveal no toxicity against viable cells. These all results are taken together, indicating that by coating with the developed material IL-1d@MWCNT, a robust self-sterilizing surface has achieved, which helps in maintaining a bacteria-free surface.

Formation of a Au/Au9Ga4 Alloy Nanoshell on a Bacterial Surface through Galvanic Displacement Reaction for High-Contrast Imaging.

The spontaneous electron transfer between GaAs and ionic gold through the galvanic displacement reaction results in the formation of gold nanoparticles and a Au9Ga4 alloy. We investigated this process for decorating Legionella pneumophila and Escherichia coli, aiming at enhanced imaging of these bacteria. The surface of bacteria was modified with gold ions through the electrostatic linkage of ionic liquids with phosphate units of the bacterial cell wall. The modified bacteria were further incubated with an antibody-functionalized GaAs substrate. Due to a large gap in the reduction potential of gold and gallium ions, the induced reaction involving bacteria resulted in a reduction of the gold ions to gold nanoparticles and oxidation of GaAs to Ga2O3 and a Au9Ga4 alloy. The bacteria covered with a Au/AuGa nanoshell, if excited at 377 nm, show a bright emission at 447 nm originating from Au/Au9Ga4. This approach offers a simple and potentially less expensive method for high-contrast imaging of bacteria in comparison to the conventional methods of staining with different dyes or by conjugating green fluorescent proteins.

Development of an Ionic Liquid@Metal-Based Nanocomposite-Loaded Hierarchical Hydrophobic Surface to the Aluminum Substrate for Antibacterial Properties.

Designing biomaterials and substrates possessing antibacterial properties is a growing field nowadays. In this context, we have developed benzimidazolium ionic liquids ILs-1(a-d)-based metal hybrid nanocomposites using various metals such as silver (Ag), gold (Au), and copper (Cu), which were fully characterized by various techniques. Their morphology, elemental composition, crystallinity, and size were studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, powder X-ray diffraction, and dynamic light scattering, respectively. Further, the prepared ionic liquids ILs-1(a-d) and ionic liquid@metal composites were screened for their antibacterial potential against Gram-positive and Gram-negative pathogenic microorganisms via the colony forming unit assay, and their minimum inhibitory concentrations (MICs) were also evaluated. The results obtained from preliminary antibacterial screening demonstrated that these ionic liquid@metal nanocomposites IL-1d@M (M = Ag, Cu, and Au) exhibited potent antibacterial activity in comparison to the ionic liquids ILs-1(a-d). In particular, the ionic liquid@silver nanocomposites (IL-1d@Ag) showed the most potent activity against both E. coli and S. aureus bacterial strains with MIC = 12 ± 2 and 08 ± 2 µg/mL, respectively. The mechanism of action for antibacterial activity of IL-1d@Ag nanocomposites was investigated through generation of 1O2 (ROS), whereas the morphology of treated pathogenic bacteria was examined through atomic force microscopy and SEM. Furthermore, to utilize this developed material IL-1d@Ag in biomedical applications, the prepared ionic liquid material was fabricated onto a microstructured aluminum (Al) substrate with hierarchically arranged functionalities, and the modified surface was characterized and also evaluated for antibacterial activity. Moreover, the hydrophobicity of the material coated onto the Al substrate was also measured by static water contact angle measurement, which reveals its improved hydrophobic character. Thus, the developed hierarchical hydrophobic coating material possessing long-term antibacterial activity on an Al substrate may minimize the wetting by biological secretions and also prevent the substrate from corrosion.