Abstract
In this study, a ‘green chemistry’ approach was introduced to synthesize silk sericin (SS)-capped silver nanoparticles (AgNPs) under an alkaline condition (pH 11) using SS as a reducing and stabilizing agent instead of toxic chemicals. The SS-capped AgNPs were successfully synthesized at various concentrations of SS and AgNO3, but the yields were different. A higher yield of SS-capped AgNPs was obtained when the concentrations of SS and AgNO3 were increased. The SS-capped AgNPs showed a round shape and uniform size with diameter at around 48 to 117 nm. The Fourier transform infrared (FT-IR) spectroscopy result proved that the carboxylate groups obtained from alkaline degradation of SS would be a reducing agent for the generation of AgNPs while COO− and NH2 + groups stabilized the AgNPs and prevented their precipitation or aggregation. Furthermore, the SS-capped AgNPs showed potent anti-bacterial activity against various gram-positive bacteria (minimal inhibitory concentration (MIC) 0.008 mM) and gram-negative bacteria (MIC ranging from 0.001 to 0.004 mM). Therefore, the SS-capped AgNPs would be a safe candidate for anti-bacterial applications.
Highlights
Over the last decades, silver nanoparticles (AgNPs) have been widely used in catalytic, optic, electronic, and other applications due to their unique size-dependent properties and high surface-to-volume ratio, which are significantly different from those of the corresponding bulk materials [1]
At pH 11, all concentrations of silk sericin (SS) (5 and 10 mg/mL) and AgNO3 (1, 5, and 10 mM) formed SS-capped AgNPs with different yields. This is because the functional groups with reducing potential of SS could be obtained from the alkaline degradation [29,30,31]
They found that degraded intermediates with reducing potential of starch are concomitantly generated when the alkaline concentration is greater than 0.025 M and the in situ generated species could completely reduce platinum ions (20 mM) and sufficiently stabilize the obtained platinum nanoparticles (5 mM) of uniform particle size (2 to 4 nm)
Summary
Silver nanoparticles (AgNPs) have been widely used in catalytic, optic, electronic, and other applications due to their unique size-dependent properties and high surface-to-volume ratio, which are significantly different from those of the corresponding bulk materials [1]. There has been a great deal of interest in the effective anti-bacterial/anti-fungal activity of AgNPs [2,3,4,5]. Das et al showed that AgNPs with a 12-nm size could be used as effective growth inhibitors against Bacillus subtilis, Staphylococcus aureus, and Pseudomonas aeruginosa [3]. Kim et al reported that yeast and E. coli were inhibited at the low concentration of AgNPs [7]. Silver exhibits low toxicity and minimal risk in the human body [8]
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