Synthesis of Zinc Oxide Nanoparticles (ZnO NPs) from Leaf Extract of Carthamus oxycantha and its In Vitro Biological Applications

Research Article

Austin J Anal Pharm Chem. 2023; 10(2): 1159.

Synthesis of Zinc Oxide Nanoparticles (ZnO NPs) from Leaf Extract of Carthamus oxycantha and its In Vitro Biological Applications

Abdul Wahab1; Muhammad Waqas¹; Sidra Urooj²; Hasnat Tariq¹; Zeeshan Younas Abbasi³; Mohammad Ali4; Christophe Hano5; Bilal Haider Abbasi1*

1Department of Biotechnology, Quaid-i-Azam University, Pakistan

2Atta-U-Rehman School of Applied Biosciences (ASAB), National University of Science and Technology, Pakistan

3Department of Biological sciences, International Islamic University, Pakistan

4Centre for Biotechnology and Microbiology, University of Swat, Pakistan

5Institut de Chimie Organique et Analytique, Université d’Orléans, CNRS, France

*Corresponding author: Bilal Haider Abbasi Department of Biotechnology, Quaid-i-Azam University, Islamabad 45320, Pakistan. Tel: +92-51-90644121 Email: bhabbasi@qau.edu.pk

Received: August 17, 2023 Accepted: October 02, 2023 Published: October 09, 2023

Abstract

Nanotechnology and nanosciences are emerging as new fast-growing fields due to their unique characteristics and phenomenal properties. In this study, we synthesized zinc oxide nanoparticles (ZnO NPs) by using leaf extract of Carthamus oxycantha. The morphological features of synthesized nanoparticles were evaluated by standard characterization techniques. The synthesized nanoparticles were irregular and hexagonal, and their average size was 11nm, as revealed by Scanning Electron Microscopy (SEM) and X-ray crystallography (XRD). Flavonoids and other phytochemicals were found to be capping metabolites for the nanoparticles. The synthesized nanoparticles showed significant inhibition of bacterial and fungal strains. The cytotoxicity assay showed 80% mortality of the marine larvae Artemia salina at a sample concentration of 40μg/ml. The crystallized ZnO NPs exhibited toxicity against MFC-7 breast cancer cells and displayed higher antioxidants profile i.e. free radical scavenging activity (76.824±1.22%), total reducing power (90.21±1.12μgAAE/mg), total antioxidant potential (72.936±0.93 μgAAE/mg). Quantity of 80 μg/ml of ZnO NPs resulted in 11.69±0.41% hemolysis against human red blood cells. Due to their potent biological activities, ZnO NPs synthesized from the leaf extract of Carthamus oxycantha could be used efficiently in transdisciplinary research in the future.

Keywords: Carthamus oxycantha; Zinc oxide nanoparticles; Green synthesis; Biological applications; Antioxidant activity; Anticancer activity

Introduction

Nanoscience and nanotechnology are rising as new emerging and fast-growing fields of science with diverse areas of applications in the manufacturing of various materials at the nanoscale [1]. Because of their phenomenal properties and unique characteristics, NPs have gained importance in various fields of sciences recently in a couple of year’s i.e., energy sectors, health care fields, agriculture, environmental sciences, etc [2]. The green synthesis of NPs using bacteria [3], fungi [4], or other diverse varieties of plant [5-7] in recent years have emerged as a feasible and alternative methodology to more expensive and intricate procedures of chemical synthesis. Presently, metal nanoparticle synthesis has become the major site of attention in the research area of nanotechnology, and its combination with biological sciences provides new opportunities for the researchers to utilize it because of its remarkable applications in the areas of medicine, biomedical research, pharmaceuticals, drug delivery tools, and photocatalytic activities [8,9].

ZnO NPs acquire unique properties and astounding applications as compared to other metal NPs, such as in the field of medicine to manufacture sunscreen lotions (UV filters), anti-inflammatory, utilized for the detection of biomolecules [9], diagnosis [10], inhibition of microbial growth [11], catalytic activity [12] and carrier of antibiotics [12], healing of wounds, drug delivery techniques, transparent electronics, UV light emitters, piezoelectric devices and chemical sensors [13-17]. Therefore, regarding the background information of nanoparticles, a green synthesis approach is employed for the formation of ZnO NPs by using an aqueous extract of the Carthamus oxycantha plant due to its cost effectiveness, environmental friendliness and biocompatibility.

Plants are considered a key source for the synthesis of stable nanoparticles on a large scale. [18]. Phytochemicals present in different parts of the diverse plants' flora, i.e. roots, stems, and leaves, help in the biosynthesis of NPs by acting as stabilizing and reducing agents; which gives a unique surface property to the NPs with a specific structure to enhance their practical applications [18,19]. Aqueous extract of plants contains natural biodegradable materials, which are eco-friendly and help in the development of non-toxic and cost-effective drugs at the nanoscale level [20].

Carthamus oxycantha (wild safflower, pohli) belongs to one of the largest flowering plant families “Asteraceae” which has1000 genera and about 10,000 species, spread over different areas in the world [21]. C. oxycantha is a bushy and annually grown medium-sized weed which has traditionally been used for medicinal purposes against a variety of diseases i.e. cough, typhoid, disorders related to the throat and heart, menstrual disorders, swelling, inflammation, anticoagulant, and cancer [22,23].

This study was aimed to design a plant-mediated eco-friendly and simple synthetic method for ZnO NPs by utilizing leaf extract of Carthamus oxycantha and to evaluate biological activities of the synthesized nanoparticles. To the best of our knowledge, this is the first study to synthesize ZnO NPs using the aqueous extract of Carthamus oxycantha leaves and their potent biological activities.

Materials and Methods

Collection of Plant

Fresh plants of C. oxycantha were collected from the south dessert area of Lakkimarwat, Khyber Pakhtunkhwa Province, Pakistan

Preparation of Carthamus oxycantha Leaves Extract

Leaves of Carthamus oxycantha were washed properly using distilled water, dried under shade and chopped up to a fine powder. Quantity of 10g of Carthamus oxycantha leaf powder was mixed with 60ml of distilled water. The mixture was retained in the water bath at 80°C for 30 minutes. The mixture was kept on a magnetic stirrer after boiling for 30 minutes. The extract obtained was then filtered through Whatman No.1 filter paper.

Formation of Biosynthesized ZnO NPs

A solution of 2 mM zinc acetate was mixed with plant extract with a 4:1 ratio by following Thema et al. with slight modification [24]. The solution mixture was kept on a magnetic stirrer for 6 hours at 70°C. The solution turned dark brown when the reaction was completed. The reaction mixture was centrifuged at 10,000 rpm for 15 minutes after 6hours of stirring to collect the precipitate/pellet. The resulting pellet was washed 3-4 times to remove the impurities. Later the pellet was dried out by pouring it on the Petri plate and incubated in a dry oven for 24 hours at 37°C. When the ZnO NPs were finally made, they were ground up into a fine powder and stored for further analysis and characterization.

Characterization of Biosynthesized ZnO NPs

The optical properties of biosynthesized ZnO NPs were determined using a Perkin-Elmer lambda spectrophotometer. Reflectance spectra of prepared samples were obtained at room temperature at a range of wavelength 360-380nm. The crystalline structure of ZnO NPs was confirmed through X-Ray Diffraction (XRD) analysis in the 20 range of 10°- 40°. PAN analytical Emprean Diffractrometer using CuKa radiation (λ=1.5406Å) and Bragg-Brentano 0-0 configuration. Morphology and elemental composition of biosynthesized ZnO NPs were determined by using a scanning electron microscope (SEM, NovaSEM450 operated at 20Kv) with Energy Dispersive X-ray (EDX) spectroscopy (IT100LA). Different chemical bonds present in biosynthesized ZnO NPs were identified by Fourier-Transform Infra-Red (FTIR) analysis within the 4000-515cm-1 range.

Biological Activities

Antioxidant Assay

DPPH Free Radical Scavenging Activity (FRSA)

DPPH free-radical scavenging activity was done as reported by [20]. Firstly, 3.2mg of 2,2-Diphenyl-1-Picryl Hydrazyl (DPPH) reagent was mixed with 100 mL of methanol. Sample concentrations of 20μg/ml, 40μg/ml, 60μg/ml, and 80μg/ml were mixed in 180μl of DPPH reagent solution. The mixture was thoroughly mixed before being incubated in the dark for an hour. Ascorbic acid served as a positive standard. Later, the absorbance of activity was taken using a spectrophotometer in a range of 514 nm.

The sample activity was analyzed by the following percentage formula,

Free Radical scavenging activity (%) = [( Ac – As )/ Ac ] × 100

Where Ac is the absorbance of control and As is the absorbance of sample.

Total Reduction Potential (TRP)

The reducing power of ZnO NPs was investigated as previously mentioned in the literature [25]. 100μl of the sample was mixed with dH2O to prepare a stock solution. Four different concentrations (20μg/ml, 40μg/ml, 60μg/ml, and 80μg/ml) were mixed in 200μl of Phosphate buffer (0.2M, pH=6.6) respectively and later 250μl of 1% potassium ferric cyanide was added. After proper mixing, the mixture was incubated in the water bath for 20 minutes at 50°C. 200μl of 10% Trichloro-Acetic acid (TCA) was added to acidify the mixture. Later, centrifugation was done to separate the supernatant. 150μl of supernatant from the sample was mixed with 50μl of ferric chloride. Ascorbic acid was used as a positive control. The absorbance peak for the sample activity was analyzed by a microplate reader at 680nm.

Total Antioxidant Capacity Assay (TAC)

The total antioxidant activity (TAC) of ZnO NPs was analyzed by the following method [26]. Four different concentrations (20μg/ml, 40μg/ml, 60μg/ml, and 80μg/ml) of NP samples were prepared from the stock solution. 100μl of the sample was collected from the stock solution of each and mixed with 900μl of reagent TCA, which consists of 0.6M of sulfuric acid, 4mM ammonium molybdate, and 28mM sodium phosphate. After proper mixing of the solution, incubation was done at 95°C for 90 minutes in the water bath. Later, the sample was cooled down at room temperature. The activity analysis was done at 695nm using a microplate reader. DMSO was taken as a negative and ascorbic acid was used as a positive control for curve calibration.

Total Flavonoid Content (TFC) Determination

For the determination of the TFC of ZnO NPs, the aluminum calorimetric method was followed according to [27] with a few modifications. The stock solution was made by mixing 10% aluminum chloride and 1M potassium acetate in distilled water. Four different concentrations (20μg/ml, 40μg/ml, 60μg/ml, and 80μg/ml) of the NP sample were prepared. After that, 20μl of samples from respective concentrations were poured into a 96 well plate, to which 10μl of aluminum chloride, 10μl of potassium acetate, and 160μl of distilled water were added. The samples were then incubated for 30minutes at room temperature. Positive control was employed by taking 20μl of quercetin as a standard and 20μl of methanol as a negative control. The absorbance analysis of activity was measured by a microplate reader at 415nm.

Total Phenolic Content (TPC) Determination

For the determination of TPC of biosynthesized ZnO NPs, the procedure of [27] with slight changes was followed. The stock solution was made by mixing 4mg of ZnO NPs in 1ml of DMSO. 20μl of the sample was taken from stock and poured into a 96-well plate. Later, 90μl of Folin-Ciocalteu reagent and 90μl of sodium carbonate were added to respective wells containing test samples. The microplate was then incubated for 1 hr at room temperature and a reading was taken at 630nm using microplate reader. 20μl of Gallic acid, 90μl Fc reagent, 90 μl NaCO3 as positive, and 20μl of DMSO as the negative standard were used.

Antibacterial Activity

The antibacterial activity of biosynthesized ZnO NPs was tested against four strains of bacteria by the disc diffusion method [28]. Two strains of gram-positive bacteria (Klebsiella pneumonia and Staphylococcus aureus) and two gram-negative bacterial strains (Escherichia coli and Pseudomonas aeruginosa) were studied. In this method, 4mg/ml of ZnO NPs were prepared in 1 ml of DMSO. After that, a sterile paper disk was soaked with a solution and was placed on the surface of agar plates on which pathogenic bacteria were inoculated. The plates were then incubated for 24hrs at 37°C. The diameters of the inhibition zones around the disks were measured as antibacterial activity. Positive and negative controls, Cefixime, and DMSO were used.

Antifungal Activity

Antifungal activity was tested against two fungal strains, including Candida albicans and Aspergillus niger, using the well diffusion technique following the protocol of [29]. The concentration of 4mg/ml of ZnO NPs sample wasutilized. Spores of fungal strains (0.1ml of each) were spread on a Sabouraud agar medium. Thereafter, 100μl of NP sample was transferred to a well plate. The plates were subsequently incubated at 37°C for 24hours and 32°C for 3 days. Biosynthesized ZnONPs samples were evaluated for their antifungal activity by measuring the zones of inhibition. Nilstat and DMSO were used as a positive and negative control, respectively.

Biocompatibility

The hemolytic activity assay RBCs-NPs interaction was conducted to evaluate the toxic nature of biosynthesized ZnO NPs using freshly obtained human blood. Approximately 1cc of blood was collected from volunteers (students) who had no other health issues. To prevent coagulation, blood was collected in an EDTA tube [30]. Blood was centrifuged at 14000rpm for 5 minutes to obtain fresh RBCs and separate plasma. RBCs were obtained in a pellet after 2-3 times centrifugation. Later, 9.8ml PBS (phosphate buffer saline) was added to 200μl of freshly obtained pellet erythrocytes. The solution in PBS was then thoroughly mixed by shaking it. NPs samples of four different concentrations (20μg/ml, 40μg/ml, 60μg/ml, and 80μg/ml, respectively) were added to suspended erythrocytes in a 1.5ml eppendorf tube. Then the mixture was incubated at 35°C for 1hr. Then, afterward, the centrifugation of incubated sample was carried out at 10,000 rpm for 10 minutes. The supernatant was obtained, of which 100μl of it was poured into a 96-well plate. The absorbance of the obtained supernatant was measured at 541nm using a spectrophotometer. Triton X-10 was used as a standard positive control and DMSO as a negative control. The percentage hemolytic activity of RBCs is determined by the following formula,

Anticancer Activity

The anticancer activity of biosynthesized ZnO nanoparticles was tested against the breast cancer cell line MCF-7. The evaluation of cytotoxicity was done by MTT assay.

MTT Assay

Double serial dilutions of sample nanoparticles were made up to the 9th column of 96 well plates. The 10th column had cells+DMSO. The 11th column contained only cells, while DMSO was added to the 12th column. After incubation of cells with nanoparticles, 100μl of MTT dye was added to each well and incubated for 4hrs at 37\0Cwith 5% CO2. Viable cells reduced the MTT dye to form crystals. After the incubation time, the media was removed carefully from each well without damaging the crystals. 100μl of DMSO was added to each well to solubilize the crystals. Then, the plate was placed in an incubator for 15 minutes at 37o. Plates were read at 520nm using a plate reader. The percentage of cell viability was calculated by using the following formula:

The Evaluation of ZnO Nanoparticles Activity Against Dengue Virus on Vero Cells Cell Line

Vero cell line (CCL-81, ATCC) was used in this study. Vero cells are anchorage-dependent (adherent) and susceptible to a wide range of viral infections. Vero cell line is a proven model for Dengue virus experimentation [31]. The effect of biosynthesized ZnO nanoparticles on dengue virus is being explored in this study.

Co-Exposure Treatment

The co-treatment assay was performed to evaluate the function of nanoparticles in inhibiting viral binding. Vero cells were grown in a 96-well microliter plate with a flat bottom at 5000 cells/well. After the formation of a monolayer, the media was removed from all wells and 100μl of 100 TCID 50/ml viral suspension and different concentrations of nanoparticles (500ug, 250ug, 125ug, and 62.5ug) were added simultaneously to the cells in triplicate and incubated for 1h at 37°C. The virus and cell controls were also included in this assay. After incubation of 1h, the solution was discarded from the cells carefully. Then, the cells were washed three times with PBS. In each well, fresh complete medium was added. The plate was incubated for another 48hrs at 37°C with 5% CO2

Post-Exposure Treatment

In each well, 5000 cells were inoculated and allowed to grow until a monolayer was obtained. A flat-bottom 96-well plate was used for this purpose. The confluent monolayer of Vero cells was incubated with 100μl of 100 TCID50/mL dengue virus (serotype 2) suspensions for 1 hour at 37°C in a CO2 incubator with 5% humidity. Then, the virus inoculum was removed from the wells and the cells were washed three times with PBS to remove unattached viruses. Different concentrations of ZnO nanoparticles suspended in a growth medium were then added in triplicate to the wells and the plate was further incubated for 48hrs at 37°C with 5% CO2. The virus control (virus + DMEM + cells) and the cell control (uninfected cells in DMEM) were also included in this experiment. In both co-exposure and post-exposure treatments, the morphology of cells was observed after 48hrs for each concentration of nanoparticles and compared to the level of efficacy of both treatments.

Brine Shrimp Lethality Assay

To test the mortality of ZnO nanoparticles, a 96-well microplate was used to perform the brine shrimp lethality assay. To hatch, the eggs of the test organism, Artemia salina, were incubated at 30–32°C for 24–48h in simulated seawater (38g/l supplemented with 6mg/l dried yeast), which was pre-saturated with oxygen. For this purpose, a specially designed tank with two compartments with a porous wall in between was used. In the bigger compartment, eggs were placed and covered with aluminum foil, and the smaller one was kept under constant illumination with the help of a lamp (the hatched nauplii (shrimp larvae) moved photo tropically to the other side through the pores). The Pasteur pipette was then used to harvest the nauplii and transferred to a small beaker (50ml) separately. From the beaker, the shrimp larvae (10 in number) were transferred to the 96 well microplates containing the samples in serial dilutions, and the volume was made up with seawater in such a way that the DMSO concentration remained less than 1%. The sample of ZnO NPs was tested at a concentration of 40μg/ml. The solutions of doxorubicin (4mg/ml DMSO) and DMSO served as positive and negative controls, respectively. After a period of 24hrs, the degree of lethality induced by each extract was quantified by taking into account the number of surviving larvae. The median Lethal Concentration (LC50) of the test samples with =50% mortality was calculated using graph pad prism software.

Results and Discussion

UV-Vis Spectrophotometer Analysis

The reduction of zinc by leaf extract of the Carthamus oxycantha to form ZnO NPs was confirmed through spectroscopy. Electrons in the conduction bands oscillated due to the effect of Surface Plasmon Resonance. A SPR peak was obtained in a range between 360nm - 380nm and showed confirmation of ZnO NPs formation after 24hrs of incubation (Figure 2) [18]. The bioactive compounds contained an extract of the Carthamus oxycantha plant, which reduced the Zn+2 to a zinc zero-valent Zn atom initially. The zero-valent Zn atom initiates the reduction of the remaining Zn+2 into ZnO and, finally, a cluster structure is obtained. ZnO NPs formation occurred by the reduction of zinc ions by the phytochemicals present in Carthamus oxycantha extract. These phytochemicals act as capping and stabilizing agents for stable ZnO NPs formation. The optical band-gap was calculated using Tauc`s equation