The role of deep eutectic solvents and carrageenan in synthesizing biocompatible anisotropic metal nanoparticles

Abstract

Plasmonic metal nanoparticles are widely used for many applications due to their unique optical and chemical properties. Over the past decade, anisotropic metal nanoparticles have been explored for imaging, sensing, and diagnostic applications. The variations and flexibility of tuning the size and shape of the metal nanoparticles at the nanoscale made them promising candidates for biomedical applications such as therapeutics, diagnostics, and drug delivery. However, safety and risk assessment of the nanomaterials for clinical purposes are yet to be made owing to their cytotoxicity. The toxicity concern is primarily due to the conventional synthesis route that involves surfactants as a structure-directing agent and as a capping agent for nanoparticles. Wet chemical methods employ toxic auxiliary chemicals. However, the approach yields monodispersed nanoparticles, an essential criterion for their intended application and a limitation of the green synthesis of nanoparticles using plant extracts. Several biocompatible counterparts such as polymers, lipids, and chitosan-based nanoparticles have been successfully used in the synthesis of safe nanomaterials, but there were issues regarding reproducibility and yield. Enzymatic degradation was one of the factors responsible for limiting the efficacy. Hence, it is necessary to develop a safer and nontoxic route towards synthesizing biocompatible nanomaterials while retaining morphology, high yield, and monodispersity. In this regard, deep eutectic solvents (DESs) and carrageenan as capping agent for nanoparticles can ensure the safety. Carrageenan has the potential to act as antibacterial and antiviral agent, and adds enhanced stability to the nanoparticles. This leads to a multidimensional approach for utilizing safe nanomaterials for advanced biomedical and clinical applications.

Keywords: anisotropic nanoparticles; carrageenan; cytotoxicity; eutectic solvents; surfactants.

Figure 1

Number of publications over the last five years on the synthesis of nanoparticles (NPs)/nanomaterials (NMs) using carrageenan and a deep eutectic solvent (DES). The numbers have been obtained from SCOPUS-indexed journals using PubMed.

Figure 2

Cytotoxicity of anisotropic gold metal nanoparticles in vitro and in vivo.

Figure 3

Synthesis of gold nanoparticles of different shapes using the seed-mediated approach. Chitosan was used for post functionalization of (A) gold nanospheres, (B) nanorods and (C) nanostars. Adapted from [54], © 2019 Y. J. Lee et al., distributed under the terms of the Creative Commons Attribution 4.0 International Licence, http://creativecommons.org/licenses/by/4.0/.

Figure 4

A deep eutectic solvent as green solvent in the synthesis of anisotropic nanoparticles (flower shape). All micrographs are adapted from [27], H. G. Liao et al., “Shape-Controlled Synthesis of Gold Nanoparticles in Deep Eutectic Solvents for Studies of Structure-Functionality Relationships in Electrocatalysis”, Angew. Chem. Int. Ed., with permission from John Wiley and Sons. Copyright © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. This content is not subject to CC BY 4.0.

Figure 5

Carrageenan as capping and reducing agent for gold nanoparticle synthesis. (A) Histogram for the size distribution of nanoparticles. (B), (C) and (D) show TEM micrographs of the nanoparticles at different magnifications. (E) and (F) show the antitumor activity against MDA-MB-231 and HCT-116. Adapted from [32], © 2018 X. Chen et al., distributed under the terms of the Creative Commons Attribution 4.0 International Licence, http://creativecommons.org/licenses/by/4.0/.

Figure 6

(A) A κ-carrageenan-stabilized hydroxyapatite rod-shaped nanocomposite. (B) Antibacterial study using E. coli, S. aureus, B. subtilis, P. aeruginosa showing the bactericidal properties of the nanocomposite. (C) The nanocomposite shows osteoblast cytotoxicity tests in cell lines (L02 and L929). Adapted from [116], J. I. González Ocampo et al., “Evaluation of cytotoxicity and antimicrobial activity of an injectable bone substitute of carrageenan and nano hydroxyapatite”, J. Biomed. Mater. Res. A., with permission from John Wiley and Sons. Copyright © 2018 Wiley Periodicals, Inc. This content is not subject to CC BY 4.0.