Hydrogel-assisted synthesis of gold nanoparticles with potential to enhance bactericidal and in vivo wound healing

This study reports a hydrogel-based sunlight-assisted synthesis of gold nanoparticles (Au NPs) with enhanced antibacterial and wound healing potential.Au NPs were synthesized for the first time using hydrogels extracted from periwinkle seeds as reducing agent and capping agent.The synthesized Au NPs were characterized by average size, shape, surface functionalization, antibacterial and wound healing abilities.Cubic and rectangular Au NPs with an average edge length of 74 ± 4.57 nm depict a characteristic surface plasmon resonance band at 560 nm.The hydrogel-based gold nanoparticles inhibited the growth of microorganisms in an area with a diameter of 12 mm.In vitro experiments showed that the minimum inhibitory concentration of Au NPs (16 µg/mL) was sufficient to simulate 95% growth of pathogenic microorganisms within 24 hours.In vivo treatment of wounds with Au NPs in a mouse model showed that 99% of the wounds closed within 5 days.Quantitative PCR analysis performed to decipher the role of Au NPs in promoting wound healing revealed increased expression levels of NANOG and CD-34 proteins.
Despite the tremendous progress, the diverse applications of nanoparticles (NPs) still attract researchers around the world to develop new synthetic methods.Medical uses of NPs include, but are not limited to, eye drops, dental treatments, catheter coatings, wound dressings, antimicrobial filters, and sterilizing medical devices1,2.Compared to typical antifungal and antibacterial drugs, NPs have higher bactericidal properties because they more easily penetrate the cell membrane and cell wall of pathogens3,4.For example, the incorporation of gold and selenium-based NPs into nanofibers can significantly enhance the antibacterial properties of polymer-based wound dressings5,6.Likewise, Au-Se hybrid NPs implanted in cellulose-based polymer nanofiber wound dressings were reported to increase their antibacterial activity.Silver- and gold-based NPs have also been used as carriers for blackberry extracts to treat cisplatin-induced cardiotoxicity.Carvacrol-based nanoemulsions are effective in alleviating neurodegenerative diseases in diabetes, which is another example of the biomedical application of NPs9.
Recently, several chemical, physical and green methods have been reported for the synthesis of NPs10,11,12.Compared with other metallic NPs such as Ag and Pt, the nontoxic properties of Au NPs have been recognized.The most common method for the synthesis of Au NPs using citrate as a reducing agent was reported by Turkevich et al.Au NPs can also be synthesized by reducing Au(III) salts using gallic acid, hydrogen peroxide, and hydrazine as reducing agents.Some of these reducing agents such as citric acid, oleylamine, sodium borohydride (NaBH4), trioctylphosphine, cetyltrimethylammonium bromide and polyethylene glycol are considered toxic, flammable and environmentally hazardous 17,18.Therefore, there is an urgent need to develop clean, biocompatible and eco-friendly methods to synthesize NPs19.

Green methods for the synthesis of NPs using bacteria, fungi, actinomycetes, algae and plants are considered to be environmentally friendly and economical20,21.These methods, also known as biosynthesis, typically utilize natural products and hydrogels in living organisms as reducing and capping agents22.Availability, biodegradability, and biocompatibility are important features of hydrogels that have attracted the attention of scientists to use them as capping and reducing agents for the synthesis of NPs.Hydrogels have extensively cross-linked 3D hydrophilic structures and absorb large amounts of aqueous solutions due to the presence of certain functional groups such as -OH, -COOH, -SO3H, and -CONH223.
Hydrogels have been used to prepare Ag NPs, however, so far, there is no report on the preparation of Au NPs.The current study proposes a method for the green synthesis of Au NPs under sunlight using a hydrogel extracted from C. oblonga seeds, which acts as a stabilizer and a reducing agent.The as-prepared Au NPs were characterized using scanning electron microscopy (SEM), UV-Vis and Raman spectroscopy, energy dispersive X-ray (EDX) and dynamic light scattering (DLS).The antibacterial activities of the synthesized NPs against different bacterial (B. subtilis, B. simplex, S. aureus, P. aeruginosa, and E. coli) and fungal strains (P. notatum and A. niger) were evaluated.The formation of the zone of inhibition, the minimum inhibitory concentration (MIC) value, and the effect of Au NPs on wound healing in a mouse model were intensively studied.
Plant (C. oblonga) seeds were purchased from Punjab Seed Company, Pakistan and validated by the Department of Botany, University of Government College, Lahore, Pakistan.Wash the seeds and store at room temperature.The gold precursor hydrogen(III) tetrachloroaurate (HAuCl4, 99.98%) was purchased from Merck, Darmstadt, Germany.All solutions were prepared in deionized water.The CYBER green real-time PCR kit for quantitative analysis of wound-healing-related biomarkers was purchased from Thermo Fisher Scientific (USA).All experiments involving seeds (seed collection, identification and research use) followed the guidelines of the IUCN Council of Grande, Switzerland and CITES Geneva, Switzerland.
Hydrogels are widely used for green synthesis of nanoparticles.The hydrogel adsorbs large amounts of water and metal ions, which readily penetrate the polymer matrix of the hydrogel28.Initially, plant seeds (200 g) were soaked in 1.0 L of water for 20 minutes at room temperature.The hydrogels extracted from the seeds were isolated using a cotton muslin.The isolated hydrogels were dried in a hot air oven at 60-65°C for 4-5 hours and then ground to a fine powder.Prepare a hydrogel suspension (1.0% w/v) by suspending the hydrogel powder (1.0 g) in 100 mL of deionized water.A gold precursor solution (100 mmol) was prepared by dissolving 0.393 g HAuCl4 in deionized water (10.0 mL).The freshly prepared hydrogel suspension (10 mL) was then mixed with HAuCl4 solution (10 mL, 100 mmol) and stirred at room temperature.The progress of the reaction was monitored by the color change from yellow to reddish-brown and the localized surface plasmon resonance (LSPR) absorption band at 2 h using a UV-Vis spectrophotometer.

Post time: Oct-28-2022