Structural and antimicrobial response of chitosan capped gold nanostructures employing two different synthetic routes

Abstract Sodium citrate and polyethylene glycol functionalized gold (Au) nanostructures are synthesized at low temperature by two different chemical routes. HR-TEM analysis confirmed that sodium citrate produces spherical shaped Au nanoparticles (AuNPs) and polyethylene glycol (PEG) functionalized AuNPs have highly branched dendritic structures. For antimicrobial activity analysis, AuNPs and AuNDs (Au nanodendrites) are capped with chitosan. Microscopic analysis shows that after chitosan capping, spherical shaped AuNPs turned into urchin-like AuNPs composite with average particle size 3.5 nm, while AuNDs changed into dragonfly-like nanocomposites with particle size 2.1 nm. Atomic force microscopy shows low surface roughness ~1.5 nm of AuNPs after chitosan capping, whereas AuNDs roughness increased up to 7.5 nm after chitosan capping. In Fourier Transform-Infrared spectrum the presence of 1634 cm−1 band revealed –NH bending along with C O vibrations after chitosan capping. It indicates AuNPs incorporation with chitosan species. For antimicrobial performance analysis, four different concentrations (0.1%, 0.5%, 0.7%, and 0.9%) of urchin-shaped C-AuNPs nanocomposite and dragonfly-shaped C-AuNDs nanocomposite are tested against gram-negative bacteria (Pseudomonas aeruginosa). The antimicrobial analysis confirmed that 0.7% C-AuNDs nanocomposite exhibits effective performance against Pseudomonas aeruginosa compared to C-AuNPs nanocomposite.