Deposition of Silver Nanoparticles on Multiwalled Carbon Nanotubes Grafted with Hyperbranched Poly(amidoamine) and Their Antimicrobial Effects

A nanohybrid comprising silver nanoparticles within third-generation dendritic poly(amidoamine) (PAMAM) grafted onto multiwalled carbon nanotubes (MWNTs) was applied as an antimicrobial agent in solution. The high abundance of amine groups on the dendrimer-modified MWNTs (d-MWNTs) provided sites for reduction and precipitation of silver nanoparticles from silver acetate aqueous solution, resulting in carbon nanotubes/Ag nanohybrids (d-MWNTs/Ag). The content of PAMAM grafted on d-MWNTs determined by using a thermal gravimetric analyzer (TGA) was about 45%. The silver nanoparticles produced were determined to be face-centered cubic silver nanocrystals by X-ray powder diffraction (XRD). The nanohybrids were investigated with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray energy dispersive spectroscopy (EDS). The antimicrobial properties of acid-treated MWNTs (MWNTs-COOH), d-MWNTs, and d-MWNTs/Ag were investigated against Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Pseudomonas aeruginosa (P. aeruginosa). Against E. coli and P. aeruginosa which are Gram-negative, d-MWNTs and d-MWNTs/Ag which are equally effective were found to have a stronger antimicrobial effect than MWNTs-COOH Against S. aureus (Gram-positive), d-MWNTs/Ag showed a stronger antimicrobial effect than d-MWNTs (92.3% kill versus 71.6% kill), while MWNTs-COOH only killed 15.4% of this bacteria. Possible mechanisms are proposed to explain the higher antimicrobial activity by d-MWNTs/Ag nanohybrids. These findings suggest that PAMAM/Ag grafted onto insoluble MWNTs may be used as effective antimicrobial materials.