Synthesis and characterization of metallic and functionalized nanoparticles of copper, zinc, silver and iron and their polymer composites for biomedical applications

Abstract

Series of water in oil (w/o) microemulsions of cationic, anionic and nonionic surfactants were prepared in a wide range of compositions by varying different parameters related to the preparation of microemulsionsincluding nature and concentration of surfactant, water to surfactant molar ratio andamount and chain length of cosurfactant. The influence of these parameters on the formation of microemulsionsand the size of microemulsion droplets have been discussed in detail. The potentials of these microemulsion droplets as nanoreactors for reactions within restricted geometries have been explored. Themicroemulsions have been used for preparation of different metal and functionalized metal nanoparticlesand metal nano/polymer composites with controllable size. Efforts have been made to correlatedifferent parameters with the sizes of microemulsion droplets andalso the sizes of nanoparticles prepared in these systems.Special emphasis has been given onthe understanding of the template role of microemulsion droplets to control over the size of nanoparticles.Finally, the antibacterial activity of different metallic and functionalized nanoparticles and their polymer composites has been investigated. The size and size distributions of microemulsion droplets have been studied by dynamic light scattering (DLS) measurements. The size of the microemulsion droplets has been found to be dependent on the nature of the surfactant.The average size is affected by water to surfactant ratio and surfactant concentration. Addition of cosurfactant couldalso modulate the dimensions of microemulsion droplets. Increasing the amount and chain length of cosurfactant resulted in relatively smaller microemulsions. Four metallic nanoparticles, copper (Cu), zinc (Zn), silver(Ag) and iron(Fe)were synthesized by reduction of corresponding metal salts in different microemulsions.Nanoparticles with varyingsize could be synthesized by the manipulation of different components of microemulsions. DLS results showed that nanoparticles of varying size could be prepared in microemulsions of different surfactants with the same composition. The size of nanoparticles was governed by the hydrophilic–lipophilic balance(HLB) and rigidity of the surfactant. The average size of nanoparticles was affected by water to surfactant ratio and surfactant concentration. Cosurfactant acted as a key factor in regulating the dimensions of nanoparticles. Increasing the concentration and chain length of cosurfactant resulted in relatively smaller nanoparticles. In most of these cases there was a concomitant relation between the size of nanoparticles and microemulsion droplets. Antibacterial activity of the nanoparticles against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) were tested by zone of inhibition method. The nanoparticles showed antibacterial activity against E. coli and S. aureus at very low concentrations. Ag nanoparticles showed higher antibacterial activities compared to other nanoparticles. At high concentrations, Ag and Cu nanoparticles showed sensitivity comparable to conventional antibiotics against E. coli. However the concentration dependence on antibacterial activity has been less pronounced. Functionalized nanoparticles, Fe3O4@Ag were prepared by reducing silver nitrate on the surface of Fe3O4 nanoparticles inw/omicroemulsions. Two polymer composites, Ag/polyaniline (Ag/PAni) nanocomposite and Ag/poly(vinyl alcohol) (Ag/PVA) nanocomposite film were also successfully prepared using w/o microemulsion. For the preparation of Ag/PAninanocompositesin w/o microemulsion, chemical oxidative polymerization of aniline monomer by ammonium peroxydisulfate in preformed Ag nanoparticles (prepared by the reduction of metal salts in microemulsion) was carried out. For a comparative studypure PAni was also prepared by using w/o microemulsionand aqueous solution method.For the preparation of Ag/PVA nanocomposite film reduction of metal salt was carried out in the core of w/o microemulsion droplet containing PVA polymeric matrix. Ag/PVA nanocomposite film was then prepared by solution casting method after separation from the microemulsion. For a comparison Ag/PVA film was also prepared through in situ generation of Ag nanoparticles by chemical reduction process on PVA host without using microemulsion. For optical, structural and morphological characterization of these nanoparticles and composites UV-visible spectra, Fourier transform infrared spectra andscanning electron microscopic (SEM) images were taken.DLS measurements gave size and size distribution of nanoparticles. Thermogravimetric analysis was carried out to study the thermal stability of nanocomposites. Finally, the antibacterial activity of these functionalized nanoparticles and polymer composites was evaluated by zone of inhibition method. DLS showed that Fe3O4@Ag particles innanodimensionwas formed.SEM images revealed spherical morphology of the functionalized nanoparticles and showed uniform coating of Ag around Fe3O4. The antibacterial testresults showed pronounced antibacterial performance ofFe3O4@Ag nanoparticles against E. coli and S. aureus because of synergistic antibacterial effect of Fe3O4 and Ag nanoparticles. In w/o microemulsion it was possible to prepare PAninanoparticles which was smaller in size compared to that obtained from bulk.But thermal stability of thesePAni from microemulsionwas lower than PAni from bulk synthesis because of less conjugation in PAni chain prepared in microemulsion. In comparison with PAni from microemulsion,Ag/PAninanocomposites showed somewhat better thermal stability which is attributed to interactions of Ag nanoparticles with PAni chain. The antibacterial test resultsdemonstrated that Ag/PAninanocomposites have enhanced antibacterial efficiency compared to PAni generated in microemulsion which is more efficient than PAni from aqueous synthesis. Ag/PVA nanocomposite film with high concentration of Ag nanoparticles wassuccessfully prepared using w/omicroemulsion.In this approach the presence of polymeric matrix in the droplets of microemulsion ensured uniform and homogeneous distribution with smaller Ag nanoparticles which also prevented aggregation of nanoparticles even after separation from microemulsion. The uniform dispersity could be achieved at high Ag content whereas conventional in situgeneration of Ag nanoparticles by chemical reduction process on PVA host gave agglomerated particles. As prepared Ag/PVA nanocomposite film has higher thermal stability than that prepared from bulk synthesis. The antibacterial properties of Ag/PVA films against E. coli and S. aureus showed that the as synthesized Ag/PVA nanocomposite film has enhanced antibacterial efficacy compared to that generated through in situ synthesis without using microemulsion under the same test condition.This methodology is advantageous than in situapproach of Ag/PVA film formationwithout using microemulsionsince the template role of microemulsion in combination with PVA nanoreactor provide homogeneous and uniform distribution of Ag nanoparticles which enable controlled leaching of nanoparticles making the film effective bactericide. Thusitis possible to fine-tune the droplet-size in the microemulsionsby the proper selection of composition of microemulsionsand hencethismicroemulsion method iseffective and advantageous to synthesize metallic nanoparticles, functionalizednanoparticles and metal nano/polymer composites of precisely controlled sizefor efficiently use as antibacterial agents.