Review Article - Journal of Chemical Technology and Applications (2021) Volume 4, Issue 1
Review on green synthesis of positively charged biocompatible gold nanoparticles in water: use of ascorbic acid as reducing agent.
Well-monodispersed AuNPs were prepared by the reduction of KAuCl4 using sodium borohydride and ascorbic acid as reducing agents. Due to using different reducing agent power, we obtained different results for AuNPs that were functionalised with same ligands. The effect of two different reducing agents on size and stability of the colloidal cationic phosphonium AuNPs was investigated. Their formation and stability was monitored by using UV−Vis absorption spectroscopy, Transmission Electron Microscopy (TEM) and dynamic light scattering (DLS). Small sizes with higher stability during a period of time were generated when NaBH4 was used as reducing agent. AuNPs functionalised by tri(phenyl)phosphoniopropylthiosulfate (4C) (3-thioactylpropyl)- triphenylphosphonium bromide (5) and tri(p-tolyl)phosphoniopropyl- thiosulfate (4) zwitterion via using NaBH4 as reducing agent in H2O / DMSO as solvent, the maximum absorption bands centred at 519, 519 and 529 nm respectively. While, when the ascorbic acid is used as reducing agent, the maximum absorption of AuNPs functionalised by these ligands were centred at 542, 575 and 557 nm respectively. For (6-thioacetylhexyl)tris(2,4,6-trimethoxyphenyl)-phosphonium bromide (8B) showed little difference between two methods, whereas the absorbance centred at 522 nm in the case of NaBH4 and at 528 nm in the case using ascorbic acid as a reducing agent. ATR-FTIR, NMR, ESI-MS techniques can be employed to identify the kinds of functionality of ligands attached to the AuNPs. In this research, we proposed the bio-reducing agent, ascorbic acid, to synthesise the AuNPs, when compared to AuNPs fabricated by using NaBH4 as reducing agent. We studied the relationship between the reducing agents and the stability / sizes of AuNPs. It was found that, various sizes with different stabilities occurred based on various reducing agent used in this Chapter, where AuNPs of different sizes are known to produce contradictory results sometimes in vivo and in vitro bio application 00. All these results in this Chapter, confirmed that KAuCl4 could be reduced during the green synthesis of AuNPs through ascorbic acid, and the same protect ligands used in the case of NaBH4. KAuCl4 – NaBH4 system produced small sizes with small mean deviation and indicated spherical shape. However, they were nearly poly-dispersed and poly-shaped for most process conditions when KAuCl4 – ascorbic acid system was used as reducing agent. Different sizes of AuNPs usually have different bio-applications. Development of more environmentally friendly and biocompatible synthetic ways is one of the main aims to allow their use in biomedical applications. Ascorbic acid has been used as a benign naturally available reducing agent to synthesise AuNPs, due to its high water solubility, low toxicity, and biodegradability. In this review, a green synthesis methodology used in order to produce positively charged biocompatible AuNPs for possibility biomedical applications is outlined.Author(s): A.Mohamed Sikkander*