Highly Stable Core-Shell Nanocolloids: Synergy between Nano-Silver and Natural Polymers to Prevent Biofilm Formation

Abstract

Active investment in research time in the development and study of novel unconventional antimicrobials is trending for several reasons. First, it is one of the ways which might help to fight antimicrobial resistance and bacterial contamination due to uncontrolled biofilm growth. Second, minimizing harmful environmental outcomes due to the overuse of toxic chemicals is one of the highest priorities nowadays. We propose the application of two common natural compounds, chitosan and tannic acid, for the creation of a highly crosslinked polymer blend with not only intrinsic antimicrobial properties but also reducing and stabilizing powers. Thus, the fast and green synthesis of fine spherically shaped Ag nanoparticles and further study of the composition and properties of the colloids took place. A positively charged core-shell nanocomposition, with an average size in terms of the metal core of 17 ± 4 nm, was developed. Nanoantimicrobials were characterized by several spectroscopic (UV-vis and FTIR) and microscopic (transmission and scanning electron microscopies) techniques. The use of AgNPs as a core and an organic polymer blend as a shell potentially enable a synergistic long-lasting antipathogen effect. The antibiofilm potential was studied against the food-borne pathogens Salmonella enterica and Listeria monocytogenes. The antibiofilm protocol efficiency was evaluated by performing crystal violet assay and optical density measurements, direct visualization by confocal laser scanning microscopy and morphological studies by SEM. It was found that the complex nanocomposite has the ability to prevent the growth of biofilm. Further investigation for the potential application of this stable composition in food packaging will be carried out.

Self-Standing Bioinspired Polymer Films Doped with Ultrafine Silver Nanoparticles as Innovative Antimicrobial Material

“…In contrast with the uneven distribution within the layers observed for the F2Ag sample, the polymer matrix of the GA-containing sample F3Ag presents evenly distributed nanophases without visible aggregates ( Figure 5 ). Dispersion of small particles is detected, which is in accordance with the expectations: for colloidal solutions of the same nature, the size of the metal core was found to be around 20 nm [ 12 ]. From the images presented in Figure 5 c,d, it can be gathered that AgNPs are tightly and homogeneously immobilized within the layers of the polymer blend.…”

“…Scheme 1 shows the main steps of the synthesis of the core–shell nanocolloids. The process has been described in detail elsewhere and is briefly described in Section 3.1 [ 12 ]. Briefly, CS and polymer blends of different compositions—with addition of crosslinkers TA and glutaraldehyde (GA)—were used as reducing and stabilizing components during the chemical synthesis of AgNPs.…”

“…Given the notable differences in the distribution of nanosilver between the two samples shown in Figure 4 and Figure 5 , it is important to understand and discuss possible explanations for the observed phenomena. In the previous study with core–shell nanocolloids, SEM analysis was performed on the colloidal solutions deposited on the solid substrate: no thin silver layer was observed on the upper part of the films for any of the tested samples [ 12 ]. These colloidal solutions, with compositions CS/TA/AgNPs and CS/GA/TA/AgNPs used as precursors for solid material, were thermally treated and resulted in the development of the self-standing films F2Ag and F3Ag, respectively.…”

“…Previously, we studied the antibiofilm effectiveness of spherical colloidal nanoantimicrobials (NAMs), with an average size of around 20 nm, with fine silver nanoparticles (AgNPs) as a core and a chitosan-based polymer blend as a shell [ 12 ]. Chitosan (CS), a natural polymer with several attractive physical, chemical and biological properties, has been used for some time as a reducing and stabilizing agent in the chemical synthesis of metal nanoparticles, including silver [ 13 ].…”

“…In this context, the presence of AgNPs in a homogeneous manner should provide prolonged antimicrobial activity. Keeping in mind several potential antimicrobial modes of action at the molecular level, we set out to create a robust solid system to prevent biofilm formation and kill bacterial cells upon direct interaction, avoiding resistance development [ 12 ]. Diverse key properties of the material, which could potentially be used in food packaging, were assessed through spectroscopic, microscopic, and other characterization methods.…”