Cytotoxic Effects of Phytomediated Silver and Gold Nanoparticles Synthesised from Rooibos (Aspalathus linearis), and Aspalathin

Abstract

The green chemistry approach has continuously been applied for the synthesis of functional nanomaterials to reduce waste, environmental hazards, and the use of toxic chemicals among other reasons. Bioactive natural compounds have been found great potential in this regard and are used to improve the stability, activity, and biodistribution of metal nanoparticles (MNPs). Aspalathin (ASP) from Aspalathus linearis (rooibos) has a well-defined pharmacological profile and functional groups capable of both reducing and capping agents in the synthesis of metallic nanoparticles (NP). This study provides the first report of the phytomediated synthesis of gold and silver nanoparticles (AuNPs/AgNPs) via ASP and the green rooibos (GR) extract. The study demonstrated a green chemistry approach to the biosynthesis of nanoparticles of GR-AuNPs, ASP-AuNPs, GR-AgNPs, and ASP-AgNPs. The results showed that GR and ASP could act both as reducing and stabilising agents in the formation of crystalline, with different shapes and dispersity of NPs in the ranges of 1.6–6.7 nm for AgNPs and 7.5–12.5 nm for the AuNPs. However, the ASP NPs were less stable in selected biogenic media compared to GR NPs and were later stabilised with polyethene glycol. The cytotoxicity studies showed that GR-AgNPs were the most cytotoxic against SH-SY5Y and HepG2 with IC50 108.8 and 183.4 μg/mL, respectively. The cellular uptake analysis showed a high uptake of AuNPs and indicated that AgNPs of rooibos at a lower dose (1.3–1.5 μg/mL) is favourable for its anticancer potential. This study is a contribution to plant-mediated metallic nanoparticles using a pure single compound that can be further developed for targeted drug delivery for cancer cells treatments in the coming years.

Phyto-Metallic Nanoparticles: Biosynthesis, Mechanism, Therapeutics, and Cytotoxicity

“…Akinfenwa et al reported a procedure in which optimum concentration (10 mL of aqueous 5% each) of green rooibos extract, and aspalathin compound were added to a 90 mL of 1 mM heated solution of respective gold and silver precursors while stirring at 70°C. A similar procedure for zinc oxide nanoparticles where 25 mL of aqueous 1% mango seed extract was added to 75 mL of 10 mM zinc nitrate solution maintained at 30°C in an orbital shaker was described by Rajeshkumar et al [35,36]. Contrarily, different concentrations of the metal precursor are added to a predetermined concentration of phytochemicals.…”

“…Also, Elbagory et al previously reported a method, for large-scale screening of plants with microtitre-plate. Through this method, the authors determined the optimum concentration for the biosynthesis of gold nanoparticles for further scale-up [36][37][38]. PM-NPs can also be synthesized by mixing plant extract clear solution with a predetermined concentration of the metal solution and boiling the above mixture at desired time and temperature while mixing.…”

“…The continuous reduction and nucleation of ions result in the growth and accumulation of stabilized NPs. In the final stage, accumulated NPs are capped by plant phytochemicals which leads to the growth termination of NPs [24,36,41,42]. Beyond the mechanism, researchers are also concerned about the size, shape, distribution of NPs, and time required in the synthesis.…”

Biosynthesis of Gold and Silver Nanoparticles Using Phytochemical Compounds

“…Nowadays, AuNPs and AgNPs have been widely studied due to their low toxicity to normal cells compared to other metal nanoparticles [ 7 ]. Their anticancer properties have been tested in vitro toward various types of cancer cells, such as breast cancer [ 70 , 71 ], lung cancer [ 64 , 76 ], liver cancer [ 66 , 86 ], cervical cancer [ 64 ], colon cancer [ 62 , 87 ], and human neuroblastoma cells [ 86 ]. Several studies have proven that plant-based AuNPs and AgNPs have anticancer biological activity, as shown in Table 3 .…”

A Review of the Green Synthesis of ZnO Nanoparticles Utilising Southern African Indigenous Medicinal Plants

“…There were no reports on the use of the synthesised ZnO NPs for any applications; therefore, further studies can also include the application of synthesised ZnO NPs. In addition to being used for the synthesis of ZnO NPs, A. linearis has been documented in the synthesis of various NPs, including Co 3 O 4 NPs [96], Au NPs [98], Eu 2 O 3 [100], Ag NPs [101] Pd NPs, PdO NPs [102], Rh NPs [103], RuO 2 NPs [104], SnO 2 NPs [105], and NiO NPs, [106]. The synthesised NPs were assessed for applications in photodegradation of dyes, water splitting and biological application.…”