Background: The extensive application of silver compounds especially in nanomedicine, has increased the need to develop environmental friendly and cost effective route to synthesizing silver nanoparticles (AgNPs). Methods: Water, diethyl ether, and ethanol were used in the extraction of Waltheria americana root. Silver nanoparticles (AgNPs) were synthesized by reacting 0.001 M AgNO 3 solution with the different crude extracts of W. americana root in the ratio of 10:1. The synthesized AgNPs were analyzed using UV-visible spectrophotometer, X-ray diffraction (XRD), scanning electron microscope (SEM), and FTIR techniques. The different crude extracts and their synthesized colloidal AgNPs were tested against Proteus species, Streptococcus species, Klebsiella species, Staphylococcus aureus, and ciprofloxacin (control). Results: UV-vis results showed surface plasmon resonance (SPR) at 415, 435, and 425 nm for synthesized colloidal AgNPs from water, diethyl ether, and ethanol extracts, respectively. When screened against all test organisms, the synthesized colloidal AgNPs from diethyl ether extract of W. americana root (WARDEEP) showed more improved antimicrobial efficacy than other crude extracts and their synthesized AgNPs. The strongest antimicrobial activity of WARDEEP against all test organisms were at 400, 100, and 200 mg/mL concentrations for Proteus species and Staphylococcus aureus, Klebsiella species, and Streptococcus species, respectively. From minimum inhibitory concentration (MIC) results, it was observed that WARDEEP exhibited a strong antibiotic activity against Proteus and Streptococcus species at a least value of 12.5 mg/ mL concentration. Minimum bactericidal concentration (MBC) results showed that WARDEEP exhibited a minimum antibiotic activity at 25 mg/mL concentration against Proteus and Streptococcus species. Conclusions: Therefore, silver nanoparticles were sucessfully synthesized from all the crude extracts. The synthesized silver nanoparticles could comparatively provide better alternative treatment to both gram-positive and gram-negative bacteria than the crude plant extracts.

Silver nanoparticles (AgNPs) antibacterial and antimicrobial properties have made them useful in the fields of medicine, for health care, consumer products, industrial purposes and more specifically food packaging industries. Though AgNPs can be synthesized by various methods, the more environmentally friendly option was adopted. Available literature shows that AgNPs can be infused into plastic and polyethylene containers and used for packaging foods and drinks to shield them from fungal or bacterial decay thereby extending their shelf lives. Tests to ascertain the concentration and rate of migration of the AgNPs from the packaging to the food are deemed necessary. In this research Ocimum gratissimum (Og) and Vernonia amygdalina (Va) silver nanoparticles were biosynthesized, and were of varied sizes with some agglomeration with mean sizes 41 nm and 28 nm, respectively. Their Surface Plasmon Resonance (SPR) occurred in the range 432 nm - 442 nm. Electrodeposition of these nanoparticles on a gold substrate from an acidic medium was done and AFM images show that the Va-silver nanoparticles had small grains and provided a better surface coverage than the larger round flakes of the Og-silver nanoparticles. The nanoparticles were found to have diffusion coefficient values which tallied with their sizes. Thus for the smaller Va-silver nanoparticles it was 1.76 X 10^{-7} \ cm^2/s, while for the Og silver nanoparticles it was 3.94 \times 10^{-7}  cm^2/s showing that the migration rate of the Og- silver nanoparticles was higher than that of the Va-silver nanoparticles. Hence for faster nanoparticle migration, the Og-nanoparticles is ideal but for a uniform, and even surface coverage, the Va-silver nanoparticles should be employed.