Antimicrobial activity of CdS and Ag2S quantum dots immobilized on poly(amidoamine) grafted carbon nanotubes

Herein we report the design of antimicrobial nanohybrids, f-MWCNTs-CdS and f-MWCNTs-Ag2S developed by covalent grafting of cationic hyperbranched dendritic polyamidoamine (PAMAM) onto multiwalled carbon nanotubes (MWCNTs) and successive deposition of CdS and Ag2S quantum dots (QDs). The CdS and Ag2S QDs were in situ deposited on PAMAM grafted MWCNTs instead of anchoring the pre-synthesized QDs. The fourth generation, amine terminated hyperbranched PAMAM was grafted on MWCNTs, which was achieved through repetitive reactions of Michael addition of methylmethacrylate to the surface amino groups and amidation of terminal ester groups with ethylenediamine. The covalent grafting of PAMAM onto MWCNTs and the consecutive conjugation of CdS and Ag2S QDs were characterized using Fourier transform infrared spectroscopy, elemental analysis, powder X-ray diffraction, Raman spectroscopy, transmission electron microscopy and energy dispersive spectroscopy. The antibacterial activity of f-MWCNTs-CdS and f-MWCNTs-Ag2S nanohybrids was evaluated against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus and the results were compared with the activity of carboxylated MWCNTs, PAMAM grafted MWCNTs, PAMAM dendrimer, and CdS and Ag2S QDs. It was found that the germicidal action of MWCNTs was enhanced by grafting of PAMAM, which was further improved with immobilization of CdS and Ag2S QDs.