Synthesis of pure alginate-nano silver biocomposites via solution plasma process and their potentials as antimicrobial agents

Abstract

In this study, pure and safe biocomposites were synthesized via solution plasma process (SPP) that employed Ag electrodes as the precursor for AgNPs, which replaced AgNO3 and tungsten electrodes studied previously. In order to synthesize pure and medical grade biocomposites with AgNPs, Ag electrode was used. Plasma was discharged in 0.5% (w/v) or 0.75% (w/v) alginate solution at 800 voltages, 30 kHz for 2–7 min using a unipolar power supply and a reactor equipped with Ag electrodes. UV–Vis spectroscopy of the biocomposites showed a unique peak at 405.5 - 411 nm, indicating the synthesis of AgNPs. FTIR analysis indicated no change in the chemical bonds of alginate during the plasma discharge. SEM/TEM analyses showed that the biocomposites had micro-porous and micro-fibril structures with spherical AgNPs well dispersed in the alginate matrix. The average sizes of AgNPs were 12.5 ± 9.9 - 14.5 ± 6.9 nm and the size range of 2–41 nm. Dispersion stability of the biocomposites (0.75%, w/v, alginate) was excellent with zeta-potential values of −72.86 to −75.78 mV. Among them, 0.75% (w/v) alginate/AgNP discharged for 5 min showed the highest antimicrobial activity. The MICs of AgNPs in the biocomposites were 12.5–25.0 μg mL-1 for Gram-negative bacteria (E.coli, P.aeruginosa, V.vulnificus), 30.0–35.0 μg mL-1 for Gram-positive bacteria (S.aureus, B.cereus), and 265.0 μg mL-1 for C. albicans. The biocomposite did not exhibited significant toxicity against the HEK293 cells up to 300 μg/ml with LC50 of 419.2 ± 29.9 μg mL-1. Therefore, SPP using Ag electrodes is an improved and efficient way to produce pure and safe antimicrobial agents.