Ecofriendly synthesis of silver nanoparticles using metallic solution-based goji berry extract for their antibacterial properties

From the last decade to date, the use of metallic nanoparticles (MNPs) has been widely studied in the fields of materials science, optoelectronics, tissue engineering, catalysts, biosensors, nanomedicine, and antimicrobials.¹ MNPs, more specifically Ag-NPs, have been extensively researched as they show very good antimicrobial properties. Such properties include fast-acting, low cytotoxicity, and great antimicrobial performance.² Several techniques have been developed so far for the synthesis of Ag-NPs, which include chemical vapor deposition (CVD), physical vapor deposition (PVD), electrochemical deposition, and photochemical techniques.³ Besides all these techniques, green nanotechnology using biological sources⁴ is mostly preferred as it is a simple and straightforward technique that consumes less energy, eliminates the use of expensive chemicals, and requires no inertness during synthesis.⁵ Moreover, it is biologically compatible, sustainable, non-toxic, eco-friendly, and cost-effective. In the bio-nanotechnology route, Ag-NPs are synthesized by using a source of fungi, bacteria, or yeasts.^2,4,6,7 However, these methods are relatively more complex and take longer. At this stage, Ag-NPs synthesis using fruit or leaf extract is mostly preferred and highly recommended, as these synthesis routes are faster to process and are eco-friendly, non-toxic, non-hazardous, sustainable, clean, biologically compatible, and easy to synthesize. Green bio-nanotechnology using fruit and/or leaf extract can also produce polydisperse MNPs.^5,8,9 To date, various MNPs have been synthesized by using green bio-nanotechnology that include gold,¹⁰ silver,¹¹ copper,¹² zirconium oxide,¹³ platinum,¹⁴ zinc oxide,¹⁵ etc. Among various metals, Ag-NPs are the material of choice of researchers due to their remarkable properties such as chemical stability, broad-spectrum, antimicrobial activity, surface-enhanced Raman scattering, and nonlinear optical goji behavior.¹⁶ A broader spectrum of fungicidal and bactericidal activity of Ag-NPs has made them an extremely popular component in the fields of medicine, agriculture, food preservation, and consumer products.¹⁷ Hence, it is very important to explore the synthesis methodologies for Ag-NPs to avoid toxic chemicals that are more reactive. Therefore, green synthesis using biological sources has received remarkable consideration because of its simple and straightforward preparation, which is less time-consuming, high stability, and cheap.¹⁸ Fruit extracts for the synthesis of Ag-NPs, such as black pepper palm and Sesbania grandiflora leaf Piper nigrum, have been used for several years.¹⁹ 

This research article demonstrates the synthesis of silver nanoparticles using green bio-nanotechnology, where a biodegradable Goji Berry fruit extract as a source has been used. The applications of such NPs are remarkable for instance, in food packaging, medical industries, coating, textile, and several other energy applications. These NPs have prime importance due to their stability, resistance to bacteria, and more specifically, antimicrobial agents.²⁰ Moreover, Ag-NPs are considered a good conductor and give a faster response with lower detection limits.²¹ The antimicrobial activity of such Ag-NPs has been analyzed through disk methods, which can be used for food preservation applications.²² 

Silver nitrate (AgNO₃) used in this study was purchased from Sigma-Aldrich, Germany, and is in pure form with analytical grade (99.9%). Goji Berry was purchased from a local market.

Goji berries were collected, washed thoroughly with distilled water (DW), and dried. The dried material was chopped and ground finely. A 5 g of Goji berries dried powder was then mixed with distilled water at a speed of 1000 rpm at 80 °C on a magnetic stirrer for 120 min. The solution was then filtered several times to obtain extract and stored in the fridge at 6 °C. A complete process flow of goji berries extraction is shown in Fig. 1.

The prime requirement for the synthesis of Ag-NPs is the metallic ion solution of silver as a reducing agent and plant extract.²³ In most cases, reducing agents or other constituents present in the fruit extract act as stabilizing and capping agents, so there is no need to add capping and stabilizing agents from outside.²⁴ 

The Ag-NPs have been successfully synthesized using fruit extract (goji berry). Locally available Goji Berry Fruits have been arranged in the form of bundles. The bundle dimensions are 10 cm in length by 4 cm broad with rounded tips. The locally collected Goji Berry leaves were then washed carefully with distilled water several times to remove the dirt and dust particles from the samples, and then the samples were dried at ambient temperature. The dried samples were then ground into fine powders, and 5 g of powder was stirred with 100 ml of distilled water at 100 °C for 10 min. The obtained extract was stored at 6 °C and used as a reducing agent. 5 ml of the extract was mixed with 1 mM solution of AgNO₃. The Ag⁺ ions are obtained from the reduction reaction of an aqueous AgNO₃ solution, which is then responsible for the formation of Ag-NPs²⁵ as shown in Fig. 2. These NPs were monitored visually by their color²⁶ from yellow to black. The synthesized Ag-NPs were then centrifuged at a constant speed of 12000 rpm for 30 min and then washed and stored at 6 °C for further characterization.

The crystalline nature and crystal symmetry of Ag-NPs were determined using an Xpert Pro XRD (Cu Ka = 1.540 60 Å radiation). However, the powder size (D) was calculated using the Scherer equation through XRD peak broadening.²⁷ 

The absorption spectrum of Ag-NPs concerning incubation was determined using UV–Vis spectroscopy (Perkin Lambda 365), with absorption peak wavelengths ranging from 250 to 800 nm.

The prepared Ag-NPs were collected from centrifugation, washed in distilled water to remove macromolecules from Ag-NPs, and sent for functional group analysis through FT-IR. The FT-IR spectrum for dried samples of fruit extract and Ag-NPs was monitored with the help of FT-IR (PerkinElmer Spectrum-3) spectroscopy with the wavelength range of 4400–400 cm⁻¹.

The microstructural analysis of prepared Ag-NPs was done using high-resolution mode in Transmission Electron Microscope (TEM) and Selected Area Electron Diffraction Pattern (SAEDP) in JEOL (JEM-2100) equipment. An operating source as the cathode of LaB₆ is provided, which works at a voltage of 200 kV.

The loaded Ag-NPs scaffolds of gelatin and Goji Berry fruit extract were tested against antimicrobials through a gram-positive (Staphylococcus aureus) bacterial strain, which showed zones of inhibition. After several experimentations, it is concluded that the Ag-NPs showed good antibacterial activity against a gram-positive (Staphylococcus aureus) bacterial strain. Furthermore, these Ag-NPs also have very good antimicrobial properties as compared with other doses. Because of its high surface area, it also provides good contact with the cell wall of micro-organisms, thus causing the rupture of microbes.

The crystallinity of Ag-NPs has been determined by XRD. As shown in Fig. 3, almost five peaks of diffraction patterns at different angles such as 38.2°, 44.50°, 54.1°, 64.51°, and 77.40° have been observed corresponding to 111, 200, 220, 142, and 311 planes of FCC of Ag crystals (JCPDS Number 04-0783).²⁸ The average particle size of Ag-NPs was calculated using the Scherer equation through XRD peak broadening is ∼22 nm. Moreover, the diffraction peaks show two peaks that belong to the Goji Berry fruit extract. This is because very small and few particles from the extract have been incorporated with Ag-NPs, but there is no negative effect found on the antimicrobial activities.²⁹ 

The absorption peaks of Ag-NPs concerning incubation time were analyzed by UV–Vis spectrometers. As shown in Fig. 4, the characteristic absorption peak of Ag-NPs for all incubation times (2–36 h) is at around 430 nm, which is evidence of the successfully synthesized Ag-NPs. This is because of the Surface Plasmon Resonance (SPR) of metallic NPs, where the collective oscillation of outermost electrons in metallic NPs has taken place. These oscillations of electrons mainly depend on the size, shape, and the surrounding environmental interactions of Ag-NPs.³⁰ As shown in Fig. 4, when a 2 h incubation time has been provided, the absorption peak is short at a wavelength of around 430 nm due to the formation of Ag-NPs being very less. In contrast to that, when the incubation time is going to be increased up to 36 h, the concentrations and size distribution of Ag-NPs have also been increased. This leads to increased absorption peak intensity and peak boarding concerning incubation time.³¹ Furthermore, the phenomenon of the formation of Ag-NPs over incubation time has also been observed by a color change from transparent white (2 h) to dark black (36 h).³² 

The optimized reaction condition of samples was analyzed using the absorbance peak graph concerning incubation time. As shown in Fig. 5, it shows the direct relation with time. At 0 h, the absorbance peak was very small, and as we increased the reaction time up to 2 h, the absorption peaks also increased. However, it has been observed from several reaction times that 36 h is the ideal condition for Ag-NPs formation. If go beyond 36 h, a decrease in the absorption peak has been observed due to a change in the size and shape of Ag-NPs.³³ 

The structural properties and bonds of Ag-NPs nanoparticles were analyzed by FT-IR. The bioactive molecules of the hydroxyl functional group of the samples were observed during FT-IR analysis. As shown in Fig. 6, the FT-IR spectrum of Goji Berry fruit extract showed bands at 3287.40, 2928.85, 1590.8, and 1391.7 cm⁻¹, while for Ag-NPs, peaks were slightly shifted, indicating that the presence of bonds of C–H, O–H, C=O, and –C–H is attributing to the water-soluble phenolic content of the extract. The appearance of Ag-NPs can be concluded from the above statements.³⁴ 

A well-dispersed and spherical shape of silver nanoparticles (having a diameter around 10–50 nm) has been observed by HR-TEM as shown in Fig. 7, while irregularities in the shape of very few Ag-NPs and an ultra-thin film of capping agents on the surface of Ag-NPs were also observed during TEM analysis shown in Figs. 7(a)–7(c). Figure 7(d) shows NPs size (10 nm) marked in yellow dashed circles. The diffraction pattern by SAED mode in TEM of Ag-NPs is shown in Fig. 7(e), which corresponds to bright circular rings that correspond to the lattice plane of NPs and, therefore, confirm that NPs are crystalline and have FCC structure.³⁵ 

The antimicrobial activities were tested against gram-positive (Staphylococcus aureus) bacterial strains using the disk diffusion method, which shows the zones of inhibition (Fig. 8). From several experiments, it has been observed that Ag-NPs show the best antimicrobial activity against gram-positive (Staphylococcus aureus). Due to its large surface area, it makes better contact with the micro-organism cell walls, thus causing a rupture in microbes.³⁶ 

The gram-positive (Staphylococcus aureus) bacteria strain values of the inhibition zone having different Ag-NPs (μg/ml) concentrations are shown in Table I.

In this research article, silver nanoparticles were successfully synthesized using Goji berry fruit extract through a green nanotechnology approach based on antimicrobial response without any chemical changes at room temperature. Such metallic NPs were then characterized by using advanced analytical methods. The diffraction pattern of XRD showed that NPs have FCC crystal structure and have ∼22 nm diameter. The optimum absorption peak of Ag-NPs at the wavelength of 430 nm for 36 h incubation time was analyzed by UV–Vis. The presence of bonds and hydrocarbon groups between Ag-NPs and extract was justified by FT-IR. TEM investigations show the ultrafine particle size of Ag-NPs with an ultra-thin film of capping agents. Hence it is concluded that green biosynthesis is a straightforward, cost-effective, and eco-friendly route for the antimicrobial performance of the Ag-NPs-impregnated scaffold that can be used for food packaging.

The authors sincerely appreciate funding from Researchers Supporting Project No. RSP2025R58, King Saud University, Riyadh, Saudi Arabia. The authors would also like to acknowledge the Department of Materials Engineering, NED University Karachi for providing the necessary facilities.

The authors have no conflicts to disclose.

Abdul Rauf Jamali: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Resources (equal); Writing – original draft (equal). Waseem Khan: Conceptualization (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Project administration (equal); Supervision (equal); Writing – original draft (equal); Writing – review & editing (equal). Salahuddin Khan: Conceptualization (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Project administration (equal); Resources (equal); Writing – original draft (equal); Writing – review & editing (equal). Ahmed Ahmed Ibrahim: Conceptualization (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Project administration (equal); Supervision (equal); Validation (equal); Writing – review & editing (equal). Kamran Alam: Conceptualization (equal); Formal analysis (equal); Methodology (equal); Software (equal); Validation (equal); Writing – review & editing (equal).

The data that support the findings of this study are available within the article.