Urea gemini surfactant capped silver nanoparticles: physical properties and structure-dependent antimicrobial activity

For decades, silver nanoparticles (AgNPs) continue to act as the object of interest of scientific community as well as industry, creating a variety of application opportunities in different areas such as pharmacy and medicine, catalysis, textile industry, sensors, and many others. Due to their strong antimicrobial and cytotoxic effect they form a broad basis for applications in medicine and healthcare. The present study describes the synthesis and functionalization of AgNPs by a series of cationic gemini surfactants with variable length of polymethylene spacer and the presence of urea groups in each of their alkyl chains. Investigations of physical parameters of functionalized AgNPs are represented by the UV-VIS spectral analysis, the determination of particle size and shape using dynamic light scattering and scanning electron microscopy, and the zeta potential measurements as a function of urea gemini surfactant structure. The biological function of functionalized AgNPs is represented by their antimicrobial activity determination against various types of pathogens. The presence of urea groups in surfactant molecular structure alters the physical parameters as well as biological activity of surfactant capped AgNPs due to their non-covalent bonding ability and flexibility control of the surfactant capping layer. As the results indicate, AgNPs functionalized with urea gemini surfactants showed the size in the range 58 – 144 nm and a positive zeta potential from +41 to +64 mV due to the presence of positive charge of surface-active cations on AgNPs surface. Investigations of AgNPs antimicrobial effect against Gram-negative, Gram-positive pathogens and yeast showed a complex behavior which depends on the urea gemini surfactant spacer length. The study provides a good basis for the development of silver nanoparticle systems with potent antibacterial properties.