Biogenic Synthesis of Bismuth Oxide Nanoparticles and its Antifungal Activity

Introduction

Despite bismuth’s proximity to other dangerous elements on the periodic table, the metal and its derivatives have been recognized to humans for thousands of years without causing any significant damage ¹. Compared to sodium chloride, several bismuth substances have a lower toxicity ². Because of this, bismuth is distinguished from other heavy metals and designated a “green element” ¹. For instance, bismuth subsalicylate is prescribed for those experiencing diarrhoea in addition to other symptoms (such as nausea, vomiting, and abdominal discomfort) ³. Bismuth oxychloride gives beauty products and toiletries a metallic silver lustre. The product is sold as BIRON powder and has significant clinical uses.

The oxide of bismuth most often used in industry is bismuth trioxide (Bi₂O₃). It’s used as a building block in the production of several chemical reagents and other bismuth-based products ⁴. Bi₂O₃ has a unique polymorphism, with four different solid phases: monoclinic (α-Bi₂O₃), tetragonal (β-Bi₂O₃), body-centered cubic (γ-Bi₂O₃), and triclinic (ω-Bi₂O₃) ⁵. The α-Bi₂O₃ is generally stable at ambient temperatures and has a low solubility in water due to the presence of a surface hydroxyl group ⁶. Since α-Bi₂O₃ is a basic oxide, the vast majority of its bonds are ionic in nature ⁷. As it is utilized in dentistry substances to make these more transparent to X-rays than the underlying teeth surface ⁸, it may find usage in biomedicine. AnuSol lotion, an astringent, an emollient, an antiseptic, and has Bi₂O₃ as one of its main ingredients ⁹. As a homeostatic topical application, it may be considered to be utilized in free soft tissue transplants for oral injuries ¹⁰. Further, it is tested as a possible drug for treating Helicobacter pylori diseases ¹¹. Non-DNA locations are where bismuth substances are bio-coordinated, which opens up new possibilities for the development of novel mechanisms of action in chemotherapeutic agents ¹².

While nanomaterials have a relatively high surface area, they are able to communicate with their biological targets more effectively. They can be used in the nanoformulations since they have different chemical and physical characteristics from the bulk versions. The fact that Bi₂O₃ nanoparticles are safe for human tissue ¹³ means that they may be employed for a wide variety of applications, including those involving the measurement of temperature, the combination of imaging modalities, and the administration of therapeutic agents ¹⁴. Anti-fungal, anti-bacterial, and anti-cancer properties of Bi₂O₃ nano-structures have been reported ^15-17. Multiple topologies are produced during the fabrication of Bi₂O₃ nanostructures using different chemical and physical approaches ¹⁸.

Extracts from plants may play a role in the creation of metals and metal oxide nanostructures by acting as reducing and capping agents. Using non-toxic chemical ingredients and moderate reaction conditions is the technique to construct a greener method ¹⁹. Because herbal phytochemicals facilitate the safest and also most cost-effective massive creation of biodegradable nanomaterials. Plants are able to produce a broad array of sophisticated nano-structures that equal the complexity of contemporary manufactured materials. Phytoconstituents that are water-soluble are accountable for the reduction ²⁰. These include catechins, phenolic compounds, terpenoids, flavonoids, and alkaloids. The use of a green approach in the production of nano-materials aids in reducing or removing the use of dangerous toxic pollutants.           

Efficient microbiological production of Bi₂O₃ nanoparticles through the phytopathogenic fungi Fusarium oxysporum has been reported by Uddin et al. ²¹. Employing tannic acid as a reductant, Aguirre et al. ²² produced β-Bi₂O₃. Despite being produced via environmentally friendly methods, all of these technologies involve intricate methods and extended incubation periods. But Karnan et al. ²³ had designed and synthesized Bi₂O₃ nanoparticles via a green approach, although with a lengthy incubation and higher calcination temperature. Thus, it is important to create a straightforward, speedy, and completely environmentally friendly method for synthesising stabilized α-Bi₂O₃ nanoparticles. The production of α-Bi₂O₃ from chenopodium album leaf extract is reported for the first time in this work. For the production of α-Bi₂O₃ nanoparticles, aqueous extract of the leaf of C. album is used as a reductant and a stabilizing agents. The procedure is straightforward, quick, and really environmentally benign; moreover, it is very scalable.

Materials and method

Chemicals

Nice and Loba chemicals were used for all of the material acquisition. The reactions took place in very pure solvents that required no additional processing.

Plant material collection

Chenopodium album was gathered from the marketplaces around the Trichirappalli region. The fresh leaves of plant was employed for the production of bismuth oxide Nps.

Plant extract preparation

Fresh leaves of the chenopodium album plant were used to produce the extract solution. Leaves of a newly harvested plant that have been thoroughly washed in de-ionized water and then chopped very finely. Finally, after boiling the plant leaves in 100 mL of distilled water at 100°C, the resulting liquid was filtered and stored at 4°C for advance usage in the experiments.

Synthesis of Bismuth oxide nanoparticles

Bismuth oxide nanoparticles were made by dissolving 0.1g of Bi(NO₃)₃.5H₂O in a sufficient volume of de ionised water and then combining that solution with 10mL of a leaf extract, while stirring at room temperature through a magnetic stirrer at 1000 rpm for 3 hours. The pH of the reaction medium was attuned via adding 1 mL of 10% NaOH solution. The solid that had been precipitated was drained and dried. It took 12 hours in the oven at 150 ° C to refine the raw material. After three hours of calcination at 500 ° C, the resulting material was ground into a fine powder utilising mortar and pestle.

Antifungal activity

The in-vitro antifungal activity of the synthesized Bi₂O₃ Nps and plant extract were evaluated by disc diffusion method. 100µl of extract and the synthesized Bismuth oxide NPs were tested against 4 fungal pathogens. All the test samples were loaded in the pre-prepared petri plates which is having the respective medium. After 32 hrs, the zone of the each sample measured by millimeter scale. ²⁴.

Results and discussion

UV-Visible

Bismuth oxide NPs are formed when a UV-visible absorption peak appears between 200 and 400 nm. The specific SPR band for smaller Bismuth oxide NPs is guided by the significant absorption peak seen at 234 nm in our study. The UV-vis spectra of fabricated Bi₂O₃ NPs are displayed in Fig. 1.

Figure 1: UV-Vis spectrum of Bi2O3 Nps. Click here to View Figure

FT-IR

FT-IR spectra measured between 400 and 4000 cm^-1. A broad band at 3400.00 cm^-1 is consistent with the NH moiety that could be present due to the presence of alcohol. Alkanes belonging to the C-H functional group are shown by the peaks at 2800-3000 cm^-1. The carbonyl moiety contributed the C-O and C=O bands at 1601 and 1396 cm^-1. Because of the presence of Bi-O-Bi linkage, a characteristic peak can be seen at 829 cm^-1. Band of intense absorption at 442 cm^-1 results from Bi–O mode. It squares with the information provided in the cited work. Bismuth oxide is responsible for the observable significant peaks at 442, 470, and 510 cm^-1. FT-IR testing verified that Bi₂O₃ NPs formed and also found evidence of functional groups in the capping agent. Bi₂O₃ NPs were produced, and their FT-IR spectra are shown in Fig. 2.

Figure 2: FT-IR spectrum of Bi2O3 Nps. Click here to View Figure

SEM and Mapping

SEM (scanning electron microscopy), was used in order to control the size and shape of the produced bismuth oxide nanoparticles (NPs). The spherical form of the generated Bismuth oxide NPs was verified by SEM as displayed in Fig. 3. Bismuth oxide NPs were uniform in size and shape after synthesis. Researchers used SEM mapping to confirm that the produced nanoparticle was really Bismuth oxide. Each red dot symbolizes a single atom of bismuth, and each green dot an individual atom of oxygen. SEM mapping experiments performed on Bismuth oxide Nps are shown in Fig. 4.

Figure 3: SEM image of Bi2O3 Nps. Click here to View Figure

Figure 4: SEM mapping of Bi2O3 Nps. Click here to View Figure

EDX

EDX examination verified the elemental makeup of the produced Bi₂O₃ NPs. Bismuth oxide nanoparticles (NPs) were proven to be the produced material due to the appearance of zinc and oxygen atoms in the EDX spectra (Fig. 5). Specifically, 7.42% of the atomic weight was attributed to bismuth, and 92.58% to oxygen. The presence of bioorganics or contaminants in the solutions could account for the occurrence of additional peaks in the spectrum. Table 1 shows the elemental make-up of a nanoparticle of bismuth oxide.

Figure 5: EDX spectra of Bi2O3 Nps. Click here to View Figure

Table 1: Elemental conformation of Bi₂O₃ Nps

Element	Atomic Number	Atom %	Weight %	Weight % Error
O	8	51.14	7.42	1.70
Bi	83	48.86	92.58	5.10
Total	–	100.00	100.00	–

 

XRD Analysis

Bismuth oxide NPs were produced, and their XRD pattern is shown in Figure 6. Pure monoclinic structure of Bismuth oxide NPs was identified by diffraction peaks at 2θ = 25.2°, 26.4°, 27.4°, 27.8°, 28.2°, 33.6°, 34.8°, 37.6°, 46.2°, 48.3°, 54.8°, and 67.3°, which were indexed to (102), (002), (-111), (120), (012), (211), (200), (-112), (223), (311), (241)  and (341) planes.  Bismuth oxide NPs, as expected, were found to have diffraction peaks that were consistent with those observed. All of the diffraction peaks correspond rather well with the typical arrangement for pure Bismuth oxide nanoparticles (JCPDS No. 01-076-1730). These prominent peaks are indicative of the highly crystalline character of the produced nanoparticles. The average crystallographic size may be determined from the observed primary diffracted peak by using the Scherer equation,

The average crystallite size of the produced Bi₂O₃ Nps was 79.99 nm.

Figure 6: XRD spectra of Bi2O3 Nps. Click here to View Figure

Antifungal activity

The antifungal efficacy of the manufactured Bi₂O₃ Nps and fresh leaf extract against four distinct fungus species was evaluated. Compared to Chenopodium album, the Bi₂O₃ Nps exhibits exceptional antifungal effectiveness. In tests with C. albicans and M. audouinii, two fungal species, Bi₂O₃ Nps exhibits strong antifungal activity. As compared to control clotrimale, which had a MIC value of 02 μg/mL, Bi₂O₃ Nps was much more active. In M. audouinii, Bi₂O₃ Nps with a MIC value of 02 μg/mL exhibits significant antifungal effect than clotrimale with a MIC value of 04 μg/mL. Table 2 provided a summary of the findings.

Table 2: Antifungal activity of chenopodium album leaf extract and Bi₂O₃ Nps

Compounds	MIC (μg/mL)#
	Aspergillus Niger	Candida albicans	Microsporum audouinii	Cryptococcus Neoformans
Plant extract	52	18	32	24
Bi2O3	46	01	02	18
Clotrimazole	01	02	04	05

#Values are the means of ±SD.

Conclusion

In conclusion, chenopodium album leaf extract was used for the first time to effectively produce Bi₂O₃ Nps in under 3 hours utilizing a straightforward, eco-friendly, and green technique. This methodology eliminates the drawbacks of the traditional procedures mentioned in the prior literature [25-28], such as lengthy incubation periods, extremely high temperature and pressure settings, complicated and costly apparatus, and time-consuming reactions. As a potential reducing and capping agent in nanoparticle production, chenopodium album leaf extract helps keep the synthesis process gentle. The synthesized Nps were assessed for antifungal activity towards various pathogenic fungi. Compared to chenopodium album leaf extract and clotimale, Bi₂O₃ Nps are a more effective fungicide.

Acknowledgments

All the Authors thank the management of Srinivasan College of Arts and Science, Perambalur District, Tamil Nadu, South India, Bishop Heber College, Tiruchirappalli District, Tamil Nadu, South India and St. Joseph’s Institute of Technology (Affiliated to Anna University), Chennai, Tamil Nadu, South India for their constant support and providing the lab facility to do the research work.

Conflict Of Interests

There is no conflict of interest

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