Silver Nanocoatings at Large Length Scales: Influence of the AgNPs Morphology and Capping Agents on the Coating Chemical Stability and Antimicrobial Effect

Abstract

We assessed at multiple length scales (nanometers to millimeters) the nanocoatings of silver nanoparticles (AgNPs) on model SiO 2 /Si substrates. The coatings from biogenic AgNPs (from yeasts Rhodotorula glutinis and Rhodotorula mucilaginosa) were compared to those formed from "synthetic" AgNPs capped with citrate and sodium dodecyl sulfate (SDS). With computational analysis of large-field (LF) X-ray images of the whole substrates (5 × 5 mm), we were able to assess the coatings homogeneity, relative amount of AgNPs, and their distribution as agglomerates. Surprisingly, by analyzing more than 100,000 elements (nanoparticles and agglomerates) in each sample, it was observed that the mentioned features have little dependence on the AgNPs morphology and capping agents. All silver nanocoatings resisted when immersed in phosphatebuffered saline medium by forming agglomerates of up to 10 μm 2 . However, coatings formed with synthetic AgNPs (capped with citrate and SDS) led to a higher antimicrobial efficiency against Staphylococcus aureus.Keywords: nanobiotechnology, image processing, confocal laser scanning microscopy, scanning electron microscopy, large-field X-ray imaging IntroductionSilver nanoparticles (AgNPs) have many technological applications as films and coatings over solid surfaces such as metals, ceramic, glasses and polymers, to prevent growth of bacteria and fungi. [1][2][3][4][5] For the AgNPs to be successfully attached, a suitable match between the solid surface and the nanoparticle physicochemical characteristics must occur. By synthesizing AgNPs with the mediation of bacteria and fungi extracts (biogenic AgNPs or bio-AgNPs), the resulting protein-stabilizing capping agent over the nanoparticle contains a variety of chemical groups bonded to the amino acids fragments. This latter aspect may lead to a myriad of possible chemical interactions (e.g. electrostatic, hydrophobic, hydrogen bonds and van der Waals) between the nanoparticles and solid surfaces. [6][7][8] Essentially, bio-AgNPs are formed from interaction mechanisms ruled by proteins present in the bacterial/ fungal extract or filtrate, which drive the bio-AgNPs' nucleation → growth → colloidal stabilization steps. 2,9,10 At the end of the kinetic process, a protein corona phase on the bio-AgNPs provides a long-term colloidal stability. In contrast, "synthetic" AgNPs are produced from the reduction of Ag + and commonly stabilized by small capping agents of low molecular complexity, such as citrate and sodium dodecyl sulfate (SDS). 11,12 Several insightful studies in the literature [13][14][15] reported the formation of coatings and films of AgNPs (both biogenic and synthetic) and their dependence on the chemical functionalization of the solid surfaces upon which they are attached. However, the characterization of these coatings are limited to small length scales (up to microns), commonly achieved through imaging techniques such as electron microscopy performed at high magnifications.1,2,4,16-25 A complete understanding of the Silver Nanocoating...

Morphological analysis of soil particles at multiple length-scale reveals nutrient stocks of Amazonian Anthrosols

“…A detailed description of the assembly process for generating the LF X-ray images was provided by our group in previous works (Noronha et al, 2017;N.C. Oliveira et al, 2015;Sousa et al, 2017). In addition, all image-processing steps used in this work are described in the Supporting Information.…”

“…As recently shown by our group, this can be currently achieved by large-field (LF) X-ray imaging in combination with image analysis algorithms (Noronha et al, 2017;N.C. Oliveira et al, 2015;Sousa et al, 2017). Thus, by applying this approach for soil samples, one can unveil direct or indirect fertility aspects, especially those related to the sustainability of fertility, i.e., the "storage" of elements, such as carbon, phosphorus, nitrogen and calcium, which are present as particles (Kern and Kämpf, 1989).…”

Vibrational Spectroscopy and Morphological Studies on Protein-Capped Biosynthesized Silver Nanoparticles

“…To use them, one just has to take the desired amount of the stored AgNPs, sonicate, and dilute; this takes only a few hours and large quantities can be prepared if necessary. Further details on the biogenic synthesis are given elsewhere. − A summary of the whole process is illustrated in Figure .…”

“…14,15 These microorganisms possess the capacity to carry out the reduction of metal ions to metallic nanoparticles due to the secretion of a large number of enzymes (generally proteins); the said protein layer generates compartments capable of providing structural, spatial, and chemical controls for the stabilization and generation of nanoparticles. 12,15 The AgNPs created by the fungi Rm and Rg are very stable (we have AgNPs in perfect conditions that have been stored for many months). When compared with other nontoxic alternative methods (e.g., plants and bacteria), Rm and Rg fungi-based methods generate a much larger amount of biomass.…”

“…After separating the fungus from the enzyme broth, silver nitrate is added to the broth and the stabilization of the nanoparticle is achieved by the formation of a thin layer of protein cover that involves the Ag nucleus in a mechanism that has been investigated for different fungi. , These microorganisms possess the capacity to carry out the reduction of metal ions to metallic nanoparticles due to the secretion of a large number of enzymes (generally proteins); the said protein layer generates compartments capable of providing structural, spatial, and chemical controls for the stabilization and generation of nanoparticles. , The AgNPs created by the fungi Rm and Rg are very stable (we have AgNPs in perfect conditions that have been stored for many months). When compared with other nontoxic alternative methods (e.g., plants and bacteria), Rm and Rg fungi-based methods generate a much larger amount of biomass. − Plants might be used, but this method requires a place (e.g., orchards) and a continuous maintenance; it occupies a larger space, and thus, it is more time-consuming; bacteria culture might not be healthy because many of them can be very dangerous for human beings. It should be noted that it is not a straightforward answer to say which method of green synthesis is the best; there are many variables involved that will depend more on the protocols, materials, resources, and biological organisms that we have at hand.…”