MOHAMAD AMANI - MSc OF Biomaterials, Amirkabir University Of Technology, Tehran, Iran

Introduction: Silver nanoparticles (AgNP) have been widely applied in household and industries. It was reported that commercial products containing AgNPs accounts for more than 23% of all nanotechnology based commercial products worldwide. PHMB is a positively charged polymer having polymeric biguanide units in the backbone of its structure. Keeping in view the widespread antimicrobial applications of PHMB, it set out to coat it on silver nanoparticles to develop a hybrid product with enhanced antimicrobial properties. AgNP can be synthesized using Tollens’ method, which reduces ionic silver into the elemental form using reducing agents such as mono- or di- saccharides.Methods: The silver colloid particles were prepared by the chemical reduction of silver nitrate in the presence of ammonia, forming a complex with silver ions of [Ag (NH3)2] + composition according to the Tollens’ method. PHMB added dropwise to the solution as a stabilizer. The synthesized silver nanoparticles were characterized by a dynamic light scattering (DLS) using a Zeta Plus analyzer. The average values of the particle size and polydispersity, defined as a relative width of the size distribution, were determined from the DLS measurements. The evaluation of silver particles was performed with a Microscopic transmission electron microscope (TEM). UV-VIS absorption spectra of the silver colloids were acquired by using a spectrophotometer.In order to study the effect of PHMB-stabilized Ag NPs on bacterial growth, E. coli strain was grown on an agar plate, and its fresh colony was transferred with the help of a sterilized loop into a shake flask which was then incubated in an incubator shaker for 12 h at 37°C at a shaking speed of 150 rpm under aerobic conditions. Different concentrations of clean PHMB-coated Ag NPs were added in triplicate into shake flasks.Results: The reduction of silver ions was visibly evident from the color changes associated with it. As a result of UV-VIS spectrophotometer, the silver nitrate solution showed a peak at about 300 nm, which gradually underwent red shift with appearance of a hump at 400 nm consistent with formation of silver nanoparticles. The sharp peak at 400 nm can be attributed to a narrow size distribution of the particles formed in the solution. The particles showed hardly any change in the absorption spectra even after three months, consistent with the highly stable nature of the nanoparticles. The TEM results suggest that the particles were found to be spherical or polyhedral in shape, having a mean size about 10–15 nm. The DLS data give clear evidence for the complete suppression of the aggregation process as documented by nearly the same size of the particles, suggesting that most of the particles conformed to the size range of 10–15 nm. PHMB, as an effective polymer stabilizer, enhanced the antimicrobial activity of the silver NPs in a significant extent. This positive influence can be attributed to the ability of the polymer to stabilize the NPs against aggregation and the inherent antimicrobial properties of PHMB. Conclusion: The uniformly sized silver NPs were synthesized by the modified Tollens’ process using maltose as a reducing agent and consequently modified by PHMB in order to achieve the enhancement of their stability and antimicrobial activity. A cationic biocide (PHMB) was used for the synthesis of fairly uniform silver nanoparticles. The cationic silver particles thus formed showed much higher antimicrobial activity than the previous reports.

PHMB, Wound Managment, Silver nanoparticles