A facile synthesis of silver nanoparticle with SERS and antimicrobial activity usingBacillus subtilisexopolysaccharides

Abstract

In this study, we report a facile synthesis of silver nanoparticle having SERS and antimicrobial activity using bacterial exopolysaccharide (EPS). Bacillus subtilis (MTCC 2422) was grown in nutrient broth and the extracellular EPS secreted by the organism was extracted and purified. The purified EPS was used for the synthesis of silver nanoparticles. The kinetics of silver nanoparticle synthesis was deduced by varying the exposure time and the concentration of EPS. The rate constant (k) for the synthesis of silver nanoparticle was calculated from the slope of ln(A 1 À A t ) versus time plot. The k value was found to be 3.49 Â 10 À3 , 5.81 Â 10 À3 and 5.03 Â 10 À3 per min for particle synthesis using 2, 5 and 10 mg/mL EPS, respectively. The nanoparticles synthesised had an average particle size of 5.18 AE 1.49 nm, 1.96 AE 0.77 nm and 2.08 AE 0.88 nm for 2, 5 and 10 mg/mL EPS, respectively. The synthesised particles were characterised using UV-Vis absorbance spectroscopy, high-resolution transmission electron microscopy (HRTEM) attached to EDS (energy dispersive spectroscopy), Fourier transform infrared spectroscopy (FTIR), surface enhanced Raman spectroscopy (SERS) and zeta potential analyser. To our knowledge, this is the first study to report SERS activity of microbial Bacillus subtilis EPS-based synthesis of silver nanoparticle. HRTEM images showed silver nanoparticle entrapped in polysaccharide nanocages. Silver nanoparticle showed higher adherence towards the bacterial surface, with good bactericidal activity against Pseudomonas aeroginosa and Staphylococcus aureus.

Differently Environment Stable Bio-Silver Nanoparticles: Study on Their Optical Enhancing and Antibacterial Properties

“…In a recent study, effective anchoring of Ag NPs on E. coli cell surface was stated due to the adsorbed organic molecule on the NP surface from the guava leaf broth during synthesis, which aided in better interaction with the cell surface when compared to the chemically synthesized Ag NPs [33]. Polysaccharides (exopolysaccharide) surfaced Ag NPs are also reported for a higher adherence towards bacterial surface to provide an efficient bactericidal activity [34]. As stated in above literatures, the organic (phytochemicals) coat on A. indica Ag NPs and polysaccharide (pectin) coat on pectin Ag NPs might have been aided in their better interaction with the bacterial cell wall [33,34].…”

“…Polysaccharides (exopolysaccharide) surfaced Ag NPs are also reported for a higher adherence towards bacterial surface to provide an efficient bactericidal activity [34]. As stated in above literatures, the organic (phytochemicals) coat on A. indica Ag NPs and polysaccharide (pectin) coat on pectin Ag NPs might have been aided in their better interaction with the bacterial cell wall [33,34]. A good physical interaction between the NP and the bacterial cell wall is vital for the cell damage [35].…”

“…E. coli membrane is known to consist of lipopolysaccharids (LPS) in the outer membrane which serves as an effective permeability barrier [39,40]. The interaction of NPs with the membrane may affect the LPS and other membrane proteins, causing change in the membrane permeability (or degradation of membrane structure) (Figure 9) [13,33,34,41]. …”

Green synthesis of polysaccharide-based inorganic nanoparticles and biomedical aspects

“…AgNPs produced using the EPS secreted from B. subtilis has shown an effective inhibition against bacterial growth, with greater efficiency toward gram-negative than grampositive bacteria [61]. These types of AgNPs synthesized from bacteria secreted ESP have shown successful inhibition activity against microorganisms such as P. aeruginosa, S. aureus, B. cereus, E. coli, and P. vulgaris [62,63]. AgNPs synthesized using sulfated polysaccharide extracted from marine red algae (Porphyra vietnamensis) were also more effective to inhibit gram-negative bacteria, that is, E. coli compared to gram-positive bacteria (S. aureus).…”

“…Thus, the AgNPs might be a good alternative for MDR bacterial strains [65]. The majority of AgNPs reported spherical shape [15,65] varied in size, between 1.1 [62] and 65.1 nm [66]. Nevertheless, shapes such as polygonal, oval-shaped, face-centered-cubic [67], irregular shape [68], rod/oval-shaped structures [69], triangular [70], and uneven shape [71] have also been documented for AgNPs.…”