Modification of Silver Nanoplates with Cell-Binding Subunit of Bacterial Toxin and Their Antimicrobial Activity against Intracellular Bacteria

Intracellular bacteria are able to survive and grow in host cells and often cause serious infectious diseases. The B subunit of the subtilase cytotoxin (SubB) found in enterohemorrhagic Escherichia coli O113:H21 recognizes sialoglycans on cell surfaces and triggers the uptake of cytotoxin by the cells, meaning that Sub B is a ligand molecule that is expected to be useful for drug delivery into cells. In this study, we conjugated SubB to silver nanoplates (AgNPLs) for use as an antibacterial drug and examined their antimicrobial activity against intracellularly infecting Salmonella typhimurium (S. typhimurium). The modification of AgNPLs with SubB improved their dispersion stability and antibacterial activity against planktonic S. typhimurium. The SubB modification enhanced the cellular uptake of AgNPLs, and intracellularly infecting S. typhimurium were killed at low concentrations of AgNPLs. Interestingly, larger amounts of SubB-modified AgNPLs were taken up by infected cells compared with uninfected cells. These results suggest that the S. typhimurium infection activated the uptake of the nanoparticles into the cells. SubB-modified AgNPLs are expected to be useful bactericidal systems for intracellularly infecting bacteria.

Tailored Structure and Antibacterial Properties of Silica-Coated Silver Nanoplates by Pulsed Laser Irradiation

We coated triangular-shaped silver nanoparticles, a type of anisotropic nanoplate (NPL), with silica (i.e., prepared Ag@SiO₂ NPLs). When we irradiated Ag@SiO₂ NPLs with nanosecond-pulsed laser light for 10 s, the triangular shape changed to spherical because of the photothermal effect. A high laser power exposed the silver core, and the particles exhibited strong antimicrobial activity. In contrast, at a moderate laser power, the silica layer crystallized, and the particles' antimicrobial activity decreased. Thus, a combination of Ag@SiO₂ NPLs and an appropriately tuned power of pulsed laser irradiation facilitated a decreased or an increased antimicrobial activity.

Facile Synthesis of Zn-Doped Bi2O3 Nanoparticles and Their Selective Cytotoxicity toward Cancer Cells

Bismuth (III) oxide nanoparticles (Bi2O3 NPs) have shown great potential for biomedical applications because of their tunable physicochemical properties. In this work, pure and Zn-doped (1 and 3 mol %) Bi2O3 NPs were synthesized by a facile chemical route and their cytotoxicity was examined in cancer cells and normal cells. The X-ray diffraction results show that the tetragonal phase of β-Bi2O3 remains unchanged after Zn-doping. Transmission electron microscopy and scanning electron microscopy images depicted that prepared particles were spherical with smooth surfaces and the homogeneous distribution of Zn in Bi2O3 with high-quality lattice fringes without distortion. Photoluminescence spectra revealed that intensity of Bi2O3 NPs decreases with increasing level of Zn-doping. Biological data showed that Zn-doped Bi2O3 NPs induce higher cytotoxicity to human lung (A549) and liver (HepG2) cancer cells as compared to pure Bi2O3 NPs, and cytotoxic intensity increases with increasing concentration of Zn-doping. Mechanistic data indicated that Zn-doped Bi2O3 NPs induce cytotoxicity in both types of cancer cells through the generation of reactive oxygen species and caspase-3 activation. On the other hand, biocompatibility of Zn-doped Bi2O3 NPs in normal cells (primary rat hepatocytes) was greater than that of pure Bi2O3 NPs and biocompatibility improves with increasing level of Zn-doping. Altogether, this is the first report highlighting the role of Zn-doping in the anticancer activity of Bi2O3 NPs. This study warrants further research on the antitumor activity of Zn-doped Bi2O3 NPs in suitable in vivo models.

Preparing Alumina-Supported Gold Nanowires for Alcohol Oxidation

The development of shape-controlled noble metal nanocrystals such as nanowires (NWs) is progressing steadily owing to their potentially novel catalytic properties and the ease with which they can be prepared by reducing the metal ions in a particular solution as capping agents. Recently, many reports have been presented on the preparation of shape-controlled Au nanocrystals, such as nanostars and nanoflowers, by a one-pot method using 2-[4-(2-hydroxyethyl)-1-piperazinyl] ethanesulfonic acid (HEPES) as capping and reducing agents. The catalytic activity is depressed due to the adsorption of the capping agent onto a Au surface. Since HEPES has low binding affinities on the Au surface, shape-controlled nanocrystals obtained using HEPES are effective for application as nanocatalysts because HEPES was easily removed from the Au surface. In this study, we report the preparation of AuNWs, with an average diameter of 7.7 nm and lengths of a few hundred nanometers, in an aqueous solution containing HEPES and sodium borohydride. A γ-Al2O3-supported AuNW (AuNW/γ-Al2O3) catalyst was obtained using catalytic supporters and a water extraction method that removed HEPES from the Au surface without morphological changes. AuNW/γ-Al2O3 was then utilized to catalyze the oxidation of 1-phenylethyl alcohol to acetophenone. The formation rate of acetophenone over AuNW/γ-Al2O3 was 3.2 times that over γ-Al2O3-supported spherical Au nanoparticles (AuNP/γ-Al2O3) with almost the same diameter.

Pyramid-Shaped PEG-PCL-PEG Polymeric-Based Model Systems for Site-Specific Drug Delivery of Vancomycin with Enhance Antibacterial Efficacy

Antibacterial resistance remains a major global problem due to frequent prescriptions, leading to significant toxicities. To overcome the limitations of antibiotic therapy, it is highly desirable to provide site-specific delivery of drugs with controlled release. Inspired by the biocompatible, biodegradable, and site-specific mimicking behavior of poly(ethylene glycol) (PEG) and poly(caprolactone) (PCL), we developed vancomycin-PEG-PCL-PEG conjugates to maximize the pharmacological effects and minimize the side effects. Drug-loaded vancomycin-PEG-PCL-PEG conjugates are influenced by size, shape, surface area, encapsulation efficiency, in vitro drug release, hemolysis assay, cytotoxicity, and antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and bacterial kill kinetics. The results demonstrated that vancomycin (VCM) release from PEG-PCL-PEG triblock revealed a biphasic manner. Hemolysis assay showed the nonprescription nature of VCM-PEG-PCL-PEG. Cytotoxicity studies confirmed the biocompatibility of VCM-PEG-PCL-PEG. The in vitro antibacterial results showed enhance activity with minimum inhibitory concentration compared to bare VCM. Molecular dynamics simulation study revealed that binding between VCM and PEG-PCL-PEG by hydrophobic interactions offers molecular encapsulation and steric barrier to drug degradation. This newly developed therapeutic delivery system can offer to enhance activity and delivery VCM against MRSA.

Effect of NaOH concentration on antibacterial activities of Cu nanoparticles and the antibacterial mechanism

A series of Cu nanoparticles (NPs) have been prepared by a facile hydrothermal method at 180 °C using different concentrations of NaOH solutions and characterized by XRD, SEM, TEM and FT-IR spectra. Their antibacterial activities were assessed by means of Gram-positive S. aureus and Gram-negative E. coli bacteria, where various dosages (3, 5, 7, 10 mg) of the antibacterial agents were applied, and compared with that of the commercial CuSO₄ salt. The antibacterial mechanism was explored based on series of control experiments. The results show that the NaOH concentration affects the crystallinity, crystal size and surface hydroxyl content of the Cu NPs, which significantly influence the antibacterial activities. Compared to the commercial CuSO₄ salt, the four Cu samples prepared using no <4 mol L^-1 of NaOH display excellent antibacterial activities with low concentrations of copper leachates, which is great beneficial to the practical applications. The experimental results support that the highly reactive and soluble copper species in the antibacterial system of the Cu NPs is a Cu (II)-peptide complex, but not free Cu²⁺ ions.