Study of Molecular Interactions, Optical, and Structural Properties through the Green Synthesis of Selenium Oxide Nanoparticles from Hibiscus sabdarriffal: Biocompatibility for Biophysics

Abstract

Background:

Recently, the green synthesis process has been utilized to manufacture a large quantity of metal nanocrystallites due to its low cost and the availability of numerous natural resources and the find the activity of bacteria and viruses that in the body of humans.

Aims and Objectives:

In this study, nanocrystallites of selenium oxide were produced utilizing Hibiscus sabdariffa. Researchers have analyzed the antibacterial properties and nanostructure characteristics of selenium oxide nanocrystallites using various techniques methods, such as imaging microscopy, scanning electron microscopy, ultraviolet‒visible spectroscopy (UV‒VIS), transmission electron microscopy, atomic force microscopy, and X-ray diffraction (XRD) spectroscopy.

Results:

According to the results, the films are discovered to have a nanocrystalline structure in a cubic spinel configuration. The crystallites are semispherical in shape and are both uniform and easily distributed. The XRD data were recorded on card number 22-1314, and the 2 θ (hkl) value was 38.351 (311). The UV‒VIS spectrum of the material exhibited a plasmon resonance peak at 272 nm, confirming the presence here of selenium oxide. This study also investigated the response of four distinct strains of pathogenic bacteria to biosynthesized selenium oxide nanoparticles (NPs). The data indicate that the biosynthesized selenium oxide NPs were highly effective against Klebsiella spp. and had the lowest effectiveness against Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli.

Conclusions:

The utilization of selenium oxide nanocrystals as antibacterial agents has yielded diverse outcomes, demonstrating their remarkable efficacy in combatting Klebsiella spp.

INTRODUCTION

Selenium oxide plays a vital role in multiple human biological processes, yet it can become harmful when consumed within a specified dosage range.[1] Selenium oxide can naturally exist in several polymorphic shapes, such as crystalline and amorphous forms. Monoclinic selenium oxide (m-Se) exists in three different crystalline forms, each composed of eight selenium oxide rings organized in diverse patterns, resulting in brilliant red monoclinic structures. Selenium oxide, also referred to as trigonal selenium (t-Se) or black t-Se, is the most stable crystalline form of selenium at normal room temperature.[2] Selenium oxide exists in several nanocrystalline forms, including vitreous, red amorphous (a-Se), and black amorphous.[3] Furthermore, nanoparticles (NPs) can be employed to create biodegradable composites that exhibit outstanding biocompatibility. These characteristics render them crucial in several industries, such as electrical, food packaging, medicinal, and photocatalytic sectors.[4,5,6,7] selenium oxide NPs (Se NPs) possess noteworthy antioxidant and antibacterial properties, exhibit minimal toxicity, and demonstrate exceptional absorption capabilities.[8] There has been deliberation over the utilization of plant extracts as a prospective means for producing metallic NPs.[9] Recently, there has been increasing interest in finding environmentally acceptable techniques for producing NPs.[10]

Se NPs can be synthesized using many techniques, such as chemical, biological, and physical processes.[11,12] Nevertheless, a significant number of these techniques necessitate intricate and time-intensive protocols that are not viable over an extended period. Utilizing botanical extracts in the process of synthesis is a method that is both ecologically sustainable and economically advantageous. This streamlines the procedure, minimizes the requirement for solvents, and decreases the duration of the reaction.

Controlling the quantity of metal salts, selecting suitable reducing agents, maintaining specific temperature and pH conditions, and managing the duration of the reaction are crucial for obtaining Se NPs that are both pure and have a high yield.[13] Additional techniques for producing selenium NPs (Se NPs) include the use of ascorbic acid[14] or plant-derived polyphenols,[15] as reducing agents. The Se NPs generated using this method have certain limitations, such as their diminished stability. Stabilizing agents are therefore mandatory in the synthesis to get the best results possible. Previous works have focused on the stability of whole NPs[1,16,17,18,19] and the advantageous features of natural polysaccharide-modified Se NPs. Having performed multiple investigations, scientists managed run through different plant extract bioactive compounds suitable for the production and stabilization of Se NPs. Consequently, empirical models have been developed to estimate the optimal synthetic conditions of SeNPs by response surface methodology (RSM).[20,21] The results indicated that RSM was the best statistical method for optimizing the synthesis conditions.[8] This minimizes the number of tests that are required and allows testing of interactions between independent factors and response variables. Significant enhancements in carrier mobility and current flux are observed on the smoother surface of the sample.

MATERIALS AND METHODS

Green synthesis method

An aqueous solution was prepared by combining 4 g of Hibiscus sabdariffa with 100 ml of distilled water. The mixture was agitated for 30 min at 60°C using a magnetic stirrer in the presence of additional water. Subsequently, filtration paper was used to eliminate any residual plant matter. The next stage is the implementation of green synthesis. The physical characteristics of a solution of selenium oxide sulfide (SeS₂), derived from selenium (Se) with a molecular weight of 143.09 g/mol and a concentration of 0.15 mol are presented in Table 1. Next, the solution was dissolved in 100 ml of acetone, and the liquid was thoroughly combined using a magnetic stirrer at 50°C. To expedite the dissolution process, 10 ml of hydrofluoric acid was incorporated. Subsequently, 80 ml of plant extract was gradually introduced utilizing the droppers. Subsequently, during the heating process of the mixture to a temperature of 30°C, 10 ml of sodium hydroxide was gradually introduced using a magnetic stirrer. As soon as the hue shifts from a brilliant red to a verdant red, you should stop. The process of making selenium oxide is shown in Figure 1.

Table 1.

Physical properties of Se[12]

Chemical formula	Selenium (Se)
Phase at STP	Solid
Melting point	494 K (221°C, 430°F)
Boiling point	958 K (685°C, 1265°F)
Density (near room temperature)	Gray: 4.81 g/cm3, alpha: 4.39 g/cm3, vitreous: 4.28 g/cm3
When liquid (at melting point)	3.99 g/cm3
Critical point	1766 K, 27.2 MPa
Heat of fusion	Gray: 6.69 kJ/mol
Heat of vaporization	95.48 kJ/mol

STP: Sewage treatment plants

Figure 1.

Selenium oxide synthesis mechanism

Synthesis of a thin film of SeO₂

The glass substrates were carefully coated with a nanoselenium oxide solution using drop casting, and then precisely heated to a temperature of 70°C ± 10°C. Specifically, using appropriate instrumentation, a digital thermocouple (SC-3, Omega, Stamford, CT), and an electrical heating system, 3 drops of solution were very accurately squeezed on glass slides to verify correct precipitation. The samples were characterized by a number of scientific techniques, such as X-ray diffraction (XRD), ultraviolet–visible (UV-visible) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). It was confirmed by comparing with the JCPDS card that the particles were particles and the material was material. In Figure 2 the drop-casting technique is shown being used to deposit the impended.

Figure 2.

The drop-casting process

RESULTS AND DISCUSSIONS

XRD is a method to determine the structural features and crystalline phases of thin films. To make the nanostructure of SeO2, a thin layer containing NPs uniformly dispersed on a glass substrate that was previously heated at 70°C through drop-casting was prepared [Figure 3]. The XRD pattern is given in [Figure 3] that confirmed no amorphous structure of the prepared films as well as it was proven the polycrystalline structure with hexagonal and cubical phases. The primary peak (hkl = 311) at 2 θ = 38.351° on card no. 22-1314 indicates the presence of the crystallite phase.

Figure 3.

X-ray diffraction pattern of the SeO₂ NP film

Three dimensional (3D) atomic force microscopy images of the selenium oxide NPs were acquired by employing an environmentally friendly manufacturing method. The current crystallites are horizontally aligned, with their peaks inclined upward. The average value, measured in nanometers, was 4.91 nm on a scale ranging from 4 to 14, with a high value of 13.56 nm as clear in Table 2 for all values. The surface roughness root mean square value was 1.18 nm, which is the calculated average. Figure 4 shows that the 3D scans reveal a uniform distribution of grains across the scanning area of 1 µm × 1 µm. The grains have a semispherical shape, good dispersibility, homogeneity, and vertical alignment.

Table 2.

Atomic force microscopy data for the SeO₂ nanostructure

Samples	Average grain size (nm)	Roughness average (nm)	Root mean square (nm)
SeO2	4.91	13.56	1.18

Figure 4.

Three-dimensional atomic force microscopy SeO₂ images of the nanoparticles

FE-SEM was used to analyze morphological features of the NPs. Figure 5 displays field-emission scanning electron micrographs of selenium oxide thin films that were generated biologically and produced on a glass substrate using a drop-casting procedure. The photographs are magnified 330,000 times. Selenium oxide has nanoscale dimensions, with a particle size of approximately 15 nm, resulting in the formation of a nanostructure. These photographs provide irrefutable evidence that larger objects, which are composed of tiny NPs, indeed exist.

Figure 5.

FE-SEM image of the SeO₂ nanoparticles in the film

Figure 6 displays the FTIR spectrum of selenium oxide (NP_S) generated using a green synthesis method. From the data, it is evident that the OH vibrational overtone is associated with a peak at 3420 cm⁻¹. The peaks at approximately 2800–2900 cm⁻¹ are attributed to vibrations in the overtone band of CH. The peak corresponding to the CO band vibration is detected at 1740 cm⁻¹. The prominent peak observed at 1610 cm⁻¹ is ascribed to the oscillations of C₂. The peak observed at a wavenumber of 1400 cm⁻¹ is ascribed to the vibrational modes of the CH2 group. The CO band vibration peak is detected at a frequency of 1120 cm⁻¹. Figure 6 shows that the FTIR spectrum provides evidence of the presence of hydroxide, selenium oxide, and methylene, all of which are organic substances. The success of this green synthesis process is apparent.

Figure 6.

Spectrum obtained (Fourier-transform infrared spectroscopy) spectroscopy for the compound selenium oxide

The composite material clearly exhibited discernible selenium oxide NPs according to the TEM images showing in Figure 7. Nanocrystals generally have dimensions within the range of 35-55 nm.

Figure 7.

Transmission electron microscopy image of the SeO₂ film

Figure 8 displays the UV‒visible spectra of selenium oxide NPs produced by an environmentally friendly method. Spectral analysis revealed that selenium oxide has a plasmon resonance peak at a wavelength of 272 nm. The maximum point of the selenium oxide curve is observed at a wavelength of 210 nm. As the wavelength increases, it becomes less steep. Starting at a wavelength of 380 nm, the absorption curve decreases rapidly before eventually stabilizing. There is minimal absorption at 600 nm. Figure 8 shows that no absorption peaks are observed at wavelengths equal to or >750 nm. To determine the absorption coefficient, a, at the fundamental absorption edge, absorption measurements can be obtained through the following equation:[12]

Figure 8.

Optical band gap energy and ultraviolet‒visible spectroscopy spectrum of SeO₂

First, the thickness was measured at 0.9 µm. In addition, we have the absorption, denoted as “a.” For example, the selenium oxide NPs were approximated using Tauc’s equation[20].

The variable “hv” represents the energy of a photon, whereas “A” denotes a constant value. By graphing the square of the product of the Planck constant and the frequency (ahv)2 against the frequency (hv), we can determine the band gap of the selenium oxide NPs and their corresponding optical energy gap. The direct optical energy gap was 4.2 eV.

ANTIBACTERIAL ACTIVITIES OF SELENIUM OXIDE: BIOMEDICAL EFFECTS

This study investigated the antibacterial effects of biosynthesized selenium oxide utilizing the agar well diffusion method. Several pathogenic bacteria were subjected to testing to assess the efficacy of this procedure in eradicating them within a 24-h timeframe. The mentioned pathogens include Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Klebsiella spp. This study employed a scientific methodology to assess the efficacy of the antibiotic. Researchers have investigated the effectiveness of bioengineered selenium oxide NPs against four distinct types of pathogenic bacteria. Based on the data, the plate exhibited a zone of inhibition (ZOI) as a result of the concentration of the selenium oxide NPs, which effectively halted bacterial growth. The antimicrobial activities of the compounds [Figure 9] support these findings. Furthermore, ZOI analysis demonstrated that the biosynthesized selenium oxide NPs exhibited greater efficacy against Klebsiella spp. than against S. aureus and S. epidermidisa, with E. coli displaying the lowest level of effectiveness [Table 3]. Differences in cell wall architecture, composition, thickness, and interlayer distance among multiwalled positive/negative Gram bacteria may cause differences in the susceptibility of different bacteria to metal oxide NPs. Alternatively, this could be attributed to differences in bacterial reactions to metal oxide NPs. The interactions between NPs and bacteria exhibit variability based on the specific species and the type of metal oxide present. NPs, because of their unique chemical composition, physical properties, and capacity to liberate metal ions, have a vital function in facilitating electron transport across cell membranes, oxidizing and penetrating cellular structures, and generating reactive oxygen species. These characteristics contribute to their strong antibacterial capabilities. The antibacterial efficacy of NPs can be modulated by several factors, such as the size of the NPs, the viscosity of the growth medium, and the concentration of the medium.

Figure 9.

Selenium oxide nanoparticles demonstrated antibacterial efficacy against (a) Escherichia coli, (b) Staphylococcus aureus, (c) Staphylococcus epidermidis, and (d) Klebsiella pneumoniae at 38°C for 24 hours

Table 3.

The zone of inhibition (measured in millimeters) of selenium oxide nanoparticles, which were generated by biological means, against specific bacterial infections

Test pathogens	Selenium oxide NPs (mm)
Staphylococcus aureus	13
Staphylococcus epidermidis	13
Escherichia coli	10
Klebsiella sp.	15

NPs: Nanoparticles

CONCLUSIONS

This study successfully demonstrated the production of selenium oxide nanocrystals by environmentally friendly synthesis methods. Furthermore, the XRD pattern was corroborated by the UV‒visible spectrum and the FTIR spectrum, providing additional confirmation of the existence of selenium oxide nanocrystallites. The FTIR spectrum also verified the existence of organic constituents, including hydroxide, carbon dioxide, and methylene, indicating successful green synthesis. The UV‒visible spectra exhibited a prominent peak at 272 nm, which suggests the existence of selenium oxide. Scanning electron micrographs can be used to observe the presence of nanocrystallites of selenium oxide. The size of these crystallites is approximately 15 nm, and they have a semispherical shape. The utilization of selenium oxide nanocrystals as antibacterial agents has yielded diverse outcomes, demonstrating their remarkable efficacy in combatting Klebsiella species.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.