Abstract
The present article reports the development of soft nanohybrids comprising of single walled carbon nanotube (SWCNT) included silver nanoparticles (AgNPs) having superior antibacterial property. In this regard aqueous dispersing agent of carbon nanotube (CNT) containing a silver ion reducing unit was synthesised by the inclusion of tryptophan and tyrosine within the backbone of the amphiphile. The dispersions were characterized spectroscopically and microscopically using TEM, AFM and Raman spectroscopy. The nanotube-nanoparticle conjugates were prepared by the in situ photoreduction of AgNO3. The phenolate residue and the indole moieties of tyrosine and tryptophan, respectively reduces the sliver ion as well as acts as stabilizing agents for the synthesized AgNPs. The nanohybrids were characterized using TEM and AFM. The antibacterial activity of the nanohybrids was studied against Gram-positive (Bacillus subtilis and Micrococcus luteus) and Gram-negative bacteria (Escherichia coli and Klebsiella aerogenes). The SWCNT dispersions showed moderate killing ability (40–60%) against Gram-positive bacteria however no antibacterial activity was observed against the Gram negative ones. Interestingly, the developed SWCNT-amphiphile-AgNP nanohybrids exhibited significant killing ability (∼90%) against all bacteria. Importantly, the cell viability of these newly developed self-assemblies was checked towards chinese hamster ovarian cells and high cell viability was observed after 24 h of incubation. This specific killing of bacterial cells may have been achieved due to the presence of higher –SH containing proteins in the cell walls of the bacteria. The developed nanohybrids were subsequently infused into tissue engineering scaffold agar-gelatin films and the films similarly showed bactericidal activity towards both kinds of bacterial strains while allowing normal growth of eukaryotic cells on the surface of the films.
Highlights
Over the decades, the development of novel antimicrobial agents has undergone a continuous process of evolution and still remains an important domain of research [1,2,3,4,5,6,7,8,9,10,11,12,13]
The first step towards developing biocompatible antibacterial dispersion of carbon nanotube (CNT) is to design dispersing agents that would facilitate the exfoliation of CNTs in water
To this end recently we reported the formation of electrostatically bound composite material of single walled carbon nanotube (SWCNT) and gold nanoparticles where the nanotubes were dispersed in water using cationic amphiphile and the nanoparticles were capped with anionic surfactants [60]
Summary
The development of novel antimicrobial agents has undergone a continuous process of evolution and still remains an important domain of research [1,2,3,4,5,6,7,8,9,10,11,12,13]. The growing resistance of microbes against the conventional antibiotics necessitated the restructuring of the antibiotic design and newer formulations have emerged with time. This drug resistance mostly arises as a natural process of adaptation and random selection through mutation. To this end, in addition to the conventionally known antibiotics, nanomaterials like silver nanoparticles (AgNPs) have emerged as a class of alternative antibiotics possessing a different mechanism of bacteria killing [14,15,16,17,18,19]. Recently gold and silver nanoparticles were shown to have specific antibacterial and anticancer activities and AgNP is being used to incorporate antimicrobial activity in paints and biomedical implants [20,25,26,27]
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