Correlation notice on the electrochemical dealloying and antibacterial properties of gold-silver alloy nanoparticles

Bacterial synthesis of anisotropic gold nanoparticles

Pseudomonas aeruginosa was used to synthesize anisotropic gold nanoparticles from the unusually reducible aryldiazonium gold (III) salt of the chemical formula [HOOC-4-C6H4N≡N]AuCl4 (abbreviated as DS-AuCl4). We investigated the effect of bacterial cell density, temperature, and pH on the AuNP synthesis. The bacterial cell density of 6.0 × 108 CFU/mL successfully reduced 0.5 mM DS-AuCl4 salt to AuNPs after incubation at 37 °C (24 h), 42 °C (24 h), and 25 °C (48 h). Transmission electron microscopy (TEM) images revealed the formation of spherical, triangle, star, hexagon, and truncated triangular morphologies for the AuNPs synthesized using P. aeruginosa bacteria. The average size of AuNPs synthesized at 25 °C (48 h), 37 °C (24 h), and 42 °C (24 h) was 39.0 ± 9.1 nm, 26.0 ± 8.1 nm, and 36.7 ± 7.7 nm, respectively. The average size of AuNPs synthesized at pH 3.7, 7.0, and 12.7 was 36.7 ± 7.7 nm, 14.7 ± 3.8 nm, and 7.3 ± 2.5 nm, respectively, with the average size decreasing at a pH of 12.7. The reduction of the DS-AuCl4 salt was confirmed using X-ray photoelectron spectroscopy (XPS). The significant peaks for C1s, Au4f doublet, N1s, and O1s are centered at 285, 84-88, 400, and 532 eV. The ability of inactivated bacteria (autoclave-dead and mechanically lysed bacteria), peptidoglycan, and lipopolysaccharides to reduce the DS-AuCl4 salt to AuNPs was also investigated. Anisotropic AuNPs were synthesized using inactivated bacteria and peptidoglycan but not using lipopolysaccharides. The AuNPs demonstrated biocompatibility with human RBCs and were safe, with no antibacterial activities against Escherichia coli and Staphylococcus aureus. This is the first report demonstrating the synthesis of AuNPs using aryldiazonium gold(III) salts with P. aeruginosa. These AuNPs are promising candidates for exploring potential applications in nanomedicine and drug delivery. KEY POINTS: • Anisotropic AuNPs were synthesized using P. aeruginosa bacteria. • Dead and lysed bacterial residues synthesized anisotropic AuNPs. • AuNPs are hemocompatible.

Surface Modification of Magnetite with Carboxyl Arylated Gold Nanoparticles for Capture and Removal of Bacteria

This study presents a novel synthesis method for fabricating magnetic-plasmonic Fe3O4@CS-AuNPs nanocomposite utilizing aryldiazonium gold(III) salts. The low reduction potential of aryldiazonium gold salts enables their spontaneous reduction on the surface of Fe3O4 NPs stabilized with chitosan (CS), as CS facilitates the electron transfer process. The Fe3O4@CS-AuNPs nanocomposite exhibited gold plasmon peaks at 525 nm in UV-vis spectra and demonstrated long shelf life in an aqueous solution, with a ζ-potential of -42.8 mV. XPS revealed the complete reduction of gold(III) supported by the Au 4f peak for Fe3O4@CS-AuNPs. The increased Fe(II) ratio in XPS suggests a green reduction, where chitosan reduced Au(III) to Au(0). HR-TEM images demonstrated that Fe3O4@CS-AuNPs have an average nanoparticle size of 17.0 ± 3.8 nm. The high surface area of 55.15 m2/g for Fe3O4@CS-AuNPs supports their enhanced adsorption and removal of E. coli bacteria. Fe3O4@CS-AuNPs exhibited superior removal efficiencies of 100%, 99%, and 97%, outperforming Fe3O4@CS bacteria removal of 3%, 21%, and 40%. Surface modification with arylated AuNPs enhanced the adsorption and bacterial binding, enabling Fe3O4@CS-AuNPs to demonstrate high capture efficiency and bactericidal activity, eliminating viable bacteria at a minimum inhibitory concentration (MIC) of 50%. These findings highlight the potential of Fe3O4@CS-AuNPs for enhanced microbial removal.

The roles of templates consisting of amino acids in the synthesis and application of gold nanoclusters

Gold nanoclusters (AuNCs) with low toxicity, high photostability, and facile synthesis have attracted great attention. The ligand is of great significance in stabilizing AuNCs and regulating their properties. Ligands consisting of amino acids (proteins and peptides) are an ideal template for synthesizing applicative AuNCs due to their inherent bioactivity, biocompatibility, and accessibility. In this review, we summarize the correlation of the template consisting of amino acids with the properties of AuNCs by analyzing different peptide sequences. The selection of amino acids can regulate the fluorescence excitation/emission and intensity, size, cell uptake, and light absorption. By analyzing the role played by AuNCs stabilized by proteins and peptides in the application, universal rules and detailed performances of sensors, antibacterial agents, therapeutic reagents, and light absorbers are reviewed. This review can guide the template design and application of AuNCs when selecting proteins and peptides as ligands.

Design and preparation of Ti-xFe antibacterial titanium alloys based on micro-area potential difference

Fe was selected as an alloying element for the first time to prepare a new antibacterial titanium alloy based on micro-area potential difference (MAPD) antibacterial mechanism. The microstructure, the corrosion resistance, the mechanical properties, the antibacterial properties and the cell biocompatibility have been investigated in detail by optical microscopy, scanning electron microscopy, electrochemical testing, mechanical property test, plate count method and cell toxicity measurement. It was demonstrated that heat treatment had a significant on the compressive mechanical properties and the antibacterial properties. Ti-xFe (x = 3,5 and 9) alloys after 850 °C/3 h + 550 °C/62 h heat treatment exhibited strong antimicrobial properties with an antibacterial rate of more than 90% due to the MAPD caused by the redistribution of Fe element during the aging process. In addition, the Fe content and the heat treatment process had a significant influence on the mechanical properties of Ti-xFe alloy but had nearly no effect on the corrosion resistance. All Ti-xFe alloys showed non-toxicity to the MC3T3 cell line in comparison with cp-Ti, indicating that the microzone potential difference had no adverse effect on the corrosion resistance, cell proliferation, adhesion, and spreading. Strong antibacterial properties, good cell compatibility and good corrosion resistance demonstrated that Ti-xFe alloy might be a candidate titanium alloy for medical applications.