Nanomaterials synthesized by biosurfactants

Currently, the application of biosurfactants in the syntheses of nanomaterials is an emerging technology that reduces environmental impact, minimizes waste and increases energy efficiency by using renewable substrates. The biosurfactant-mediated synthesis is preferable to the methods of bacterial- or fungal-mediated nanoparticle synthesis, since biosurfactants reduce the formation of aggregates (formed due to the electrostatic forces of attraction) and facilitate a uniform morphology of the nanoparticles (NPs). For the purpose, this chapter describes the use of different kind of biosurfactants such as glycolipids, lipopeptides and lipoproteins, in the process of metal NPs or microemulsion-based NPs production as a green route of synthesis. Biosurfactants, also known as microbial surfactants, are generally composed of sugars, lipids, and proteins, converting them into a biocompatible, nontoxic and ecofriendly component for NPs formulations in comparison to the synthetic surfactants. Biosurfactants not only can act as capping, stabilizing and dispersing agents in the NPs-synthesis process, but also function as coating and reducing agents. Furthermore, due to the multifunctional properties of biosurfactants, the nanomaterials synthesized with these surface-active compounds present also some bioactivities; for instance, additional antimicrobial properties. Based on their chemical composition and microbial origin, it is remarkable that glycolipid biosurfactants are the most used in the syntheses of nanoparticles, followed by lipopeptide biosurfactants. Amongst the glycolipids, rhamnolipids are by far the most employed in the production of silver, nickel oxide or zinc sulphide nanoparticles as a template, providing particles with small size (1–300 nm) and great stability. Amongst the lipopeptides, surfactin has been the most studied as a coating agent of NPs, giving spherical structures of 3–160 nm. Also, they can act as template to synthetize metallic nanoparticles (Ag-NP, Au-NP, Cd-NP, among others) with high stability and biological activity. However, the applications of glycolipopeptides, glycopeptides, and glycoproteins in making nanomaterials are still in the development stage.