Glucose-reduced silver nanoparticles prepared with amylose-sodium palmitate inclusion complexes and their dry storage and reconstitution

Authors: Felker, Frederick; Fanta, George; Peterson, Steven - Steve

Submitted to: Starch/Starke
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2018
Publication Date: 5/2/2019
Citation: Felker, F.C., Fanta, G.F., Peterson, S.C. 2019. Glucose-reduced silver nanoparticles prepared with amylose-sodium palmitate inclusion complexes and their dry storage and reconstitution. Starch. https://doi.org/10.1002/star.201800238.
DOI: https://doi.org/10.1002/star.201800238

Interpretive Summary: The use of silver nanoparticles as an anti-microbial technology has rapidly expanded in response to the growing problem of acquired resistance to antibiotics. They are most often produced by converting silver nitrate to metallic silver with a reducing agent in the presence of a stabilizing polymer. Currently starch is the preferred stabilizer and glucose is a widely used "green" reducing agent. We have previously shown that jet-cooked corn starch combined with a vegetable oil derivative to produce starch complexes can produce smaller and thus more effective silver nanoparticles by providing a slow release of silver ions to the glucose. In this study, it was found that gently treating these nanoparticle dispersions with dilute acid causes the starch complexes to form a gel, and that this gel can be freeze-dried and later reconstituted in water. The reconstituted gel fragments were shown by transmission electron microscopy to contain silver nanoparticles as small as those present in the preparations before forming the gel. Since the freeze-dried nanoparticle gel can be stored indefinitely, this new technology provides a way to easily obtain a marketable form of very small silver nanoparticles without having to establish the conditions and stringent requirements to produce the small nanoparticles from the starting materials. This will facilitate the incorporation of silver nanoparticles into a variety of consumer products such as fabrics, packaging films, and medical products.

Technical Abstract: Methods for producing silver nanoparticles for antimicrobial and other applications using green chemistry approaches have been shown to have many variables that affect their properties. We have previously shown that using amylose-sodium palmitate complexes produced by steam jet-cooking as a capping agent enables exchange of silver ions with the sodium of the complexes leading to sustained production of much smaller nanoparticles than with soluble starch. In this study, silver nitrate was added to reconstituted complexes with glucose and sodium hydroxide to generate silver nanoparticles with average diameters of 3.04 to 4.66 nm. When waxy starch was used, which contains no amylose, the reduction reactions were not sustained beyond 1 hour, more insoluble material was produced, and nanoparticles were larger (13.8-15.8 nm). Reducing the pH of final reaction mixtures prepared with amylose complexes resulted in gel formation, and the silver nanoparticles precipitated with the gel fragments upon centrifugation. When these gel fragments were freeze-dried and reconstituted, TEM revealed small nanoparticles averaging 4.83 nm within the hydrated gel fragments. This enables the storage of silver nanoparticles in a dry state and later reconstituting in water to form silver nanoparticles of with known characteristics, making de novo synthesis of silver nanoparticles from the starting materials unnecessary. This novel approach would facilitate the incorporation of silver nanoparticles into a variety of products.