Abstract
The mycelium-free supernatant (MFS) of a five-day-old culture medium of Fusarium oxysporum was used to synthesize gold nanoparticles (AuNPs). The experimental design of the study was to answer the question: can this production process of AuNPs be controllable like classical chemical or physical approaches? The process of producing AuNPs from 1 mM tetrachloroauric (III) acid trihydrate in MFS was monitored visually by color change at different pH values and quantified spectroscopically. The produced AuNPs were analyzed by transmission electron microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The presence of capping agents was confirmed by Fourier transform infrared spectroscopy (FTIR). Two AuNP samples with acidic and alkaline pH were selected and adjusted with the pH gradient and analyzed. Finally, the size and zeta potential of all samples were determined. The results confirmed the presence of the proteins as capping agents on the surface of the AuNPs and confirmed the production of AuNPs at all pH values. All AuNP samples exhibited negative zeta potential, and this potential was higher at natural to alkaline pH values. The size distribution analysis showed that the size of AuNPs produced at alkaline pH was smaller than that at acidic pH. Since all samples had negative charge, we suspect that there were other molecules besides proteins that acted as capping agents on the surface of the AuNPs. We conclude that although the biological method of nanoparticle production is safe, green, and inexpensive, the ability to manipulate the nanoparticles to obtain both positive and negative charges is limited, curtailing their application in the medical field.
Highlights
There are many different types of nanoparticles (NPs) used in science and technology
In this study, AuNPs were prepared using the biological method at different pH values to understand the relationship between the ambient pH and the size, shape, agglomeration, and zeta potential of AuNPs, all of which are directly triggered by the nanoparticle capping agents
3.1. pH Adjustment before AuNPs Production After the pH of the mycelium-free supernatant was adjusted to pH 2, 4, 6, 8, and 10 and incubation was performed, color changes were observed in all experimental flasks except the control
Summary
There are many different types of nanoparticles (NPs) used in science and technology. A high percentage of NP production utilizes physical and chemical methods, there has recently been an increased focus on using biological processes or their products in NP production This is due to the improved properties of NPs in terms of biocompatibility and an environmentally friendly means of production [13,15]. F. oxysporum was acquired from the Culture Collection of Fungi of Charles University (CCF 3732, isolated from waste bags in Bohemia, Czech Republic) It was cultured in Sabouraud Dextrose Broth (SDB) at 30 ◦C for 5 days with shaking (150 rpm) to release its enzymes and extracellular material [26]. To analyze the effects of pH variation on the size and zeta potential of AuNPs, the mycelium-free supernatant vials were adjusted to final pH values of 2, 4, 6, 8, and 10 with 1 molar solution of HCl and/or NaOH. A flask containing fresh SDB medium containing 1 mM HAuCl4 was incubated in parallel and used as a control
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