David Omar Oseguera-Galindo

Silver Nanoparticles (AgNPs) were synthesized in a brown sugar solution at three different temperatures (23 °C, 40 °C and 60 °C) with a concentration of 2.5 mM of AgNO3 and 0.02 g·mL-1 of brown sugar. The sample prepared at 60 °C exhibited the highest nanoparticle yield, with an average diameter of 22 nm, as determined by analyses of micrographs. The bactericidal effect of these nanoparticles was evaluated against Escherichia coli American Type Culture Collection (ATCC) 25922 using the microdilution method, monitoring bacterial growth via absorbance at 600 nm. After 24 hours, nanoparticles formed at 60 °C demonstrated a significant inhibitory effect on E. coli growth when used at volumes of 300 µL and 400 µL in the assay.

A high rate of silver nanoparticle formation, effective against the Escherichia coli (E. coli) bacterium, was obtained for the first time by means of a simple, eco-friendly, and low-cost green method in a solution of agave inulin. The study was carried out using the traditional method, in which the effects of the concentration of agave inulin, AgNO₃, temperature, and pH on the synthesis were analyzed by UV-Vis spectroscopy and transmission electron microscopy (TEM). Most of the nanoparticles produced were spherical with a size less than 10 nm. In a sample with 20 mg/mL of agave inulin, 1 mM of AgNO₃, T = 23°C, and pH = 12, the highest percentage of Ag⁺ ions available in the solution were reduced for the formation of nanoparticles in less than 40 min, whereas a sample prepared with 60 mg/mL of agave inulin, 10 mM of AgNO₃, T = 23°C, pH = 12, and a storage time of 40 min showed a significant bactericidal effect on the E. coli strain. Agave inulin is a good biological compound for the formation of small, spherical silver nanoparticles. A pH of 12 favors a higher production speed of the silver nanoparticles and better use of the available Ag⁺ ions. In addition to this, the concentration of AgNO₃ is a determining factor for increased formation of the nanoparticles necessary to bactericidal effect.

A simple, low-cost, and ecofriendly method of obtaining silver nanoparticles was obtained from AgNO₃ in dilution for the first time with a habanero pepper infusion. Two sets of experiments were carried out. The samples obtained in the first experiment were analyzed by SEM and TEM. Results showed that the samples prepared using 0.001 M and 0.005 M of AgNO₃ and particles with an average size of 19.3 and 26.4 nm were obtained. Furthermore, the nanoparticles prepared with 0.005 M showed an absorption peak shifted toward a larger wavelength, and according to its distribution, it also exhibited larger particle sizes. In the second experiment, different concentrations of habanero pepper (10, 50, and 100 mL) were explored and the pH and oxidation reduction potential were monitored. The sample with 100 mL concentration showed the most intense absorption peak and the highest decrease in pH, which is explained by biomolecules deprotonation.

Laser ablation of a silver target confined in distilled water allowed us to obtain silver nanoparticles. However, to have knowledge of their production by this method, common instruments for measurement of the silver concentration in a colloidal solution are employed, this is due to laser ablation and is usually considered a top-down physical approach in the synthesis of nanoparticles. In consequence, this research has suggested an alternative to know the silver nanoparticles production through theoretical considerations, which depends on laser parameters and intrinsic properties of a silver target. Theoretically, this result has given us a silver concentration around 0.029 mg ml^−  1 and from of transmission electron micrographs were obtained a size distribution, where it was fitted with one Gaussian peak, being the smaller sizes the most frequent. The mean peak was centered at 12 nm, having a nanoparticle mass of 7 × 10^−  18 g, and regarding a relation with the silver concentration, the nanoparticles production was around 4 × 10¹² nanoparticles ml^−  1.