Rapid Green Synthesis of Silver Nanoparticles and Alginate-Silver Nanocomposite Beads Using Mashmoom (Ocimum basilicum), a Bahraini Household Medicinal Herb

Jude Alhaddad ^†, Hawra Alkhadad ^†, Fatima AlHannan , Fryad Henari , G. Roshan Deen ^*

1. Materials for Medicine Research Group, School of Medicine, Royal College of Surgeons in Ireland, Medical University of Bahrain, Busaiteen 228, Kingdom of Bahrain

† These authors contributed equally to this work.

* Correspondence: G. Roshan Deen

Academic Editor: Paschalis Alexandridis

Special Issue: Synthesis, Properties and Applications of Nanocomposite Materials

Received: June 16, 2025 | Accepted: November 10, 2025 | Published: November 17, 2025

Recent Progress in Materials 2025, Volume 7, Issue 4, doi:10.21926/rpm.2504017

Recommended citation: Alhaddad J, Alkhadad H, AlHannan F, Henari F, Deen GR. Rapid Green Synthesis of Silver Nanoparticles and Alginate-Silver Nanocomposite Beads Using Mashmoom (Ocimum basilicum), a Bahraini Household Medicinal Herb. Recent Progress in Materials 2025; 7(4): 017; doi:10.21926/rpm.2504017.

© 2025 by the authors. This is an open access article distributed under the conditions of the Creative Commons by Attribution License, which permits unrestricted use, distribution, and reproduction in any medium or format, provided the original work is correctly cited.

1. Introduction

Nanotechnology is an interdisciplinary science that deals with the synthesis and structural manipulation of particles at the length scale of nanometers (typically 1-100 nm). The nanoparticles are synthesized either by scaling up from single groups of atoms (bottom-up approach) or by reducing materials (top-down approach). This technology is now widely used in translational research, such as the development of drug delivery systems, diagnostic tools, water decontamination, and communication technologies [1,2,3,4]. Physical and chemical methods are widely used in the synthesis of various types of nanoparticles. However, the use of hazardous chemicals, high temperature and extreme pH conditions in these methods limits the biological and clinical applications of the nanoparticles.

Green nanotechnology (or green method) has gained much research attention in recent years due to sustainability, reduced waste generation, use of non-toxic substances, and environmentally friendly protocols. This technology uses extracts from biological materials like plants, microorganisms, and biopolymers (polysaccharides and proteins) to develop nanomaterials. The metal nanoparticles synthesized using green nanotechnology have drawn immense interest such as therapeutic drug delivery systems, antimicrobial agents, and anticancer agents due to their exceptional physicochemical properties, biocompatibility, cost-effectiveness and eco-friendliness [4,5,6,7,8,9,10].

The synthesis of AgNPs by green methods has attracted extensive attention due to their wide range of applications in cancer diagnosis and therapy, chemical sensors, catalysis, and antimicrobial coatings for medical devices [6,7,8,9,10]. This method offers an alternative approach to the conventional physical and chemical methods. A wide variety of plants have been used in the green synthesis of AgNPs [5]. The plant extracts contain a range of phytochemicals or metabolites such as polyphenols, saponins, terpenoids, flavonoids, tannins, and proteins. They act as chemical reducing agents, reducing metal salts (e.g., silver nitrate) to metallic (silver) nanoparticles. In addition, these phytochemicals form a coating around the nanoparticles, stabilizing them against aggregation. The ease of synthesis and stabilization with phytochemicals allows the synthesis of nanoparticles with high yields and unique shapes [11].

Ocimum basilicum, commonly known as sweet basil and known as mashmoom in the Gulf region, is a standard household medicine in Bahrain. It is used to treat microbial infections, headache, flatulence, indigestion, and stomach cramps [12]. Many varieties of basil have been widely used in traditional medicine systems like Ayurveda, Siddha, and traditional Chinese medicine [13]. All these varieties contain varying amounts of polyphenols, flavonoids, and essential oils like eugenol, linalool, rosmarinic acid, and methyl chavicol. Many of these compounds have been shown to possess antioxidant, antimicrobial and anticancer properties [13,14].

In line with our research interest in green nanotechnology for medical applications, we have explored the green synthesis of AgNPs and their nanocomposites in the form of polymer beads using the extract of mashmoom leaves. This report evaluates the morphology and optical properties of AgNPs, as well as the catalytic and antibacterial properties of their nanocomposites. The results indicate that these materials have massive potential for optoelectronics, antimicrobial and catalytic applications.

2. Experimental Section

2.1 Materials

Mashmoom leaves (Ocimum basilicum L) were purchased from a grocery store in Bahrain. Silver nitrate (AgNO₃), sodium hydroxide (NaOH), sodium alginate (NaC₆H₇O₆), sodium borohydride (NaBH₄), calcium chloride (CaCl₂), and methylene blue (MB) were purchased from Sigma-Aldrich (USA) and were used as supplied. All materials were of analytical grade with purities >98%. All aqueous samples were prepared using Milli-Q water, obtained from the Milli-Q system (Elix Technology), with a conductivity of 18.2 Ω cm^-1.

2.2 Preparation of Mashmoom Leaves Extract

Mashmoom leaves were washed and dried in the drying oven at 60°C for 1 day. Approximately 8.0 g of dried leaves were weighed and boiled in 150 mL of water for 30 min. The mixture was centrifuged for 10 min at 4200 rpm to remove suspended particulates and filtered using Whatman No.1 filter paper. The extract was diluted by 1/5 (extract/water) before use.

2.3 Synthesis of AgNPs

AgNPs were synthesized by mixing an equal volume of mashmoom extract with an equal volume of silver nitrate solution of different concentrations. The synthesis of sample M-1Ag is described as follows: mashmoom extract (5 ml) was added to silver nitrate solution (5 ml, 1 mM) in a clean glass vial under gentle stirring. To this solution, sodium hydroxide (100 µL, 1 M) was added and the mixture was stirred vigorously for 10 min. The addition of sodium hydroxide was necessary to increase the pH of the reaction mixture to basic (pH 10), and to favor the deprotonation of the polyphenols present in the mashmoom extract. The solution turning from colorless to pale yellow indicated the formation of nanoparticles. The nanoparticles were isolated by repeated centrifugation, washed, and lyophilized. Samples containing different concentrations of silver nitrate were prepared similarly, and the compositions are presented in Table 1. The synthesis scheme is illustrated in Figure 1.

Table 1 Materials for mushroom-mediated green synthesis of AgNPs.

Figure 1 Schematic illustration of mashmoom mediated green synthesis of AgNPs. Created in BioRender. Bahrain team 2, R. (2025) https://BioRender.com/np8kom6.

2.4 Synthesis of Alg-AgNc Beads

Alg-AgNc beads were prepared by in-situ loading of AgNPs onto the alginate beads by ionotropic crosslinking as described below. Sodium alginate solution (2 wt.%) containing 4 mM AgNO₃ was first prepared by dissolving the appropriate amounts of materials in water at 65°C. To this solution, 10 ml of mashmoom extract and 500 µL of 1 M NaOH were added dropwise under mild stirring to reduce silver nitrate to AgNPs in solution. Using a plastic syringe (20 ml), the alginate solution containing the AgNPs was added dropwise into a beaker containing calcium chloride solution (2 wt.%) under gentle magnetic stirring. The formed alginate silver nanocomposite beads were allowed to react in calcium chloride solution for a further 2 h, followed by filtration using a plastic sieve. The beads were washed repeatedly with water and dried in an oven at 60°C until a constant weight was recorded. Digital images of wet and swollen Alg-AgNc beads are shown in Figure 2.

Figure 2 Digital photos of Alg-AgNc beads (A) wet, (B) dry.

2.5 UV-Vis Spectroscopy

The UV-Vis absorption spectra of the synthesized nanoparticles were recorded on a double-beam Shimadzu UV-1800 spectrophotometer. Samples were placed in a quartz cuvette (Helma) with a path length of 1 mm and the spectrum was recorded in the wavelength range 250 nm to 900 nm with 1 mm resolution.

2.6 Electron Microscopy and Energy Dispersive X-Ray (EDS) Spectroscopy

The size and shape of the AgNPs were imaged on FEI Morgagni 268 Transmission Electron Microscope (TEM) operating at an accelerating voltage of 80 kV. The samples were prepared by depositing a drop of colloidal nanoparticles onto a carbon-support copper grid. The grids were air-dried and transferred to the microscope for bright-field imaging. The surface morphology and elemental distribution of Alg-AgNc beads were investigated using a Field Emission Scanning Electron Microscope (FE-SEM, Quattro S, Thermo Scientific, USA), equipped with an UltraDry EDS detector (Thermo Scientific, USA) with an energy resolution of 129 eV. The SEM imaging was performed at an accelerating voltage of 15 kV. The samples were imaged in both low vacuum mode using the secondary electron detector to examine the surface topography, and in high vacuum mode using backscattered electron detectors to enhance the compositional contrast.

2.7 Dye Degradation

The catalytic property of the Alg-AgNc beads was studied by following the degradation of methylene blue in the presence of sodium borohydride. The dye solution (2.5 ml, 1 mM), and sodium borohydride (0.5 ml, 0.1 M) were placed in a quartz cuvette (pathlength 1 cm) and the absorbance of the solution was recorded. In this cuvette, 10 nanocomposite beads were placed, and the absorbance change was recorded every 2 minutes.

2.8 Anti-Bacterial Studies

The anti-bacterial property of the alginate silver nanocomposite beads against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was studied by the incubation method. The beads were sterilized using UV irradiation at a wavelength of 256 nm for 20 min before this study to eliminate any contaminants. Into the tubes containing the sterilized beads (2, 5, 10 and 20 beads), the bacterial culture (0.5 ml) was introduced and the tubes were incubated at 37°C for 24 h. After this period, the solution was streaked on agar plates under sterile conditions and the plates were incubated at 37°C for 24 h. Based on the formation of bacterial colonies on the agar plates, the antibacterial property of the beads was evaluated.

3. Results and Discussion

3.1 Mashmoom Mediated Green Synthesis of AgNPs

Green synthesis of metallic nanoparticles using plant extracts and products has gained significant attention in recent years owing to its environmentally friendly protocol. The synthesis of metallic nanoparticles using plant extracts under non-toxic conditions is of paramount importance for biomedical applications. The mashmoom extract contains a wide variety of phytochemicals, of which phenolic concentration is about 80 mg/g [14,15]. The phenolic components are rosmarinic acid, lithospermic acid, vanillic acid, p-coumaric acid, hydroxybenzoic acid, syringic acid, caffeic acid, ferulic acid, cinnamic acid, dihydroxyphenyl lactic acid, and sinapic acid. The most abundant components of mashmoom leaves are rosmarinic acid and flavonoids such as luteolin, apigenin, orientin, vicenin, and isoeugenol [12]. These phytochemicals are responsible for reducing the silver ions (Ag⁺) to AgNPs (Ag⁰) and further stabilizing them against aggregation by forming a stable coating around the nanoparticles. It is believed that the liberation of reactive hydrogen in rosmarinic acid or luteolin during the conversion from keto to enol form [12,16] is involved in the reduction process, as illustrated in Figure 3.

Figure 3 Mechanism of reduction of silver nitrate to AgNPs by metabolites in mashmoom extract.

3.2 UV-Vis Absorption Spectroscopy

The formation of AgNPs as a function of silver nitrate concentration (0.5 mM, 2.0 mM, and 4.0 mM) with a fixed volume of Mashmoom extract (5 ml) was studied using UV-Vis absorption spectroscopy, and the results are shown in Figure 4(A). A well-defined surface plasmon resonance (SPR) peak is observed at 380 nm, which is characteristic of colloidal AgNPs. In general, the characteristic absorption peak for colloidal AgNPs is detected in the range 350-450 nm, depending on the size of the nanoparticles. The SPR peak arises from the collective oscillations of free electrons at the surface conduction band when the incident light frequency matches the natural frequency of the electron oscillation [17].

Figure 4 (A) UV-Vis absorption spectra of AgNPs, (B) Digital images of colloidal AgNPs, (C) spectra of mashmoom extract.

The SPR peak of the solution increases from 0.297 (sample M-0.5Ag) to 0.374 (sample M-4.0Ag) with an increase in concentration of AgNPs. In general, an increase in the concentration of the precursor silver nitrate upon reduction increases the concentration of AgNPs in solutions. A visible change from colorless to pale and dark yellow of the solutions as a function of silver nitrate concentration was observed, confirming the above observation as shown in Figure 4(B). The absorption spectrum of mashmoom extract is also shown in Figure 4(C). The extract does not exhibit an absorption peak in the 350-400 nm range, which further confirms that the peak at 380 nm is due to AgNPs. The spectra of the sample M-4.0Ag show an offset starting at 800 nm due to an increase in turbidity of the solution arising from the high concentration of AgNPs. The turbidity (τ) of the solutions at 700 nm was determined using the following expression [18],

\[ \tau=\frac{2.303\times Abs^{700\,nm}}{l\,(cm)} \tag{1} \]

where Abs is the absorbance of the solution at wavelength of 600 nm, and l is the pathlength of the cuvette (0.1 cm). The following turbidity values (cm^-1) were obtained: 0.458 (M-0.5Ag), 0.550 (M-2.0Ag), and 1.35 (M-4.0Ag). The turbidity thus increases with an increase in the concentration of AgNPs in solution.

The attenuation of light intensity as it passes through a substance is given by the optical absorption coefficient (α). The optical absorption coefficient of the AgNPs was calculated from absorbance using the following equation [19],

\[ \alpha(\lambda)=\frac{Abs}{d}\times2.303 \tag{2} \]

where λ is the wavelength of light, and d is the sample thickness (0.1 cm). The variation of the absorption coefficient with wavelength of light for the AgNPs is shown in Figure 5. The absorption coefficient peaks at 380 nm, with an absorption edge close to the UV region, and shows a similar behavior to that of AgNPs synthesized using the green method.

Figure 5 Variation of the absorption coefficient for AgNPs with wavelength.

3.3 Bandgap and Urbach Energy of AgNPs

The optical bandgap of the AgNPs was estimated by fitting the absorption spectra to a power-law Tauc equation [20] as given below,

\[ (\alpha h\nu)^{1/n}=A(h\nu-E_g) \tag{3} \]

where α is the wavelength dependent absorption coefficient, h is the Planck’s constant, E_g is the optical bandgap of the nanoparticle, ν is the frequency, A is a proportionality constant, and n is the Tauc exponent. The optical band gap (eV) for the nanoparticles is given in Table 2, and the Tauc plots for the samples are shown in Figure 6. The calculated bandgap values are within the range of optical bandgap values (2.09-3.61 eV) that have been reported for the green synthesis of AgNPs [21,22].

Table 2 Average size and optical properties of AgNPs.

Figure 6 Tauc plot for colloidal AgNPs synthesized using mashmoom extract at 23°C and pH 10.

When a photon strikes the nanoparticle, an electron from the valence band is excited through the energy gap to the bottom of the conduction band. During the transition, the presence of any disorder in the nanoparticle (localized tail states) makes the density of electronic states to the tail through the energy difference between the valence and conduction bands. The tail of the density of electronic states that extends through the bandgap energy is referred to as the Urbach tail, which is an exponential correlation between the photon energy and absorption coefficient [23]. The defect states in the nanoparticles are created by oxygen vacancies, which distort the band structure. As electrons in an excited state are irradiated, these defects tend to trap the electrons, preventing them from direct transition to the conduction band, thereby creating an absorption tail (Urbach tail) in the absorption spectra. The Urbach energy for the AgNPs was calculated using the following expression [24],

\[ \ln(\varepsilon)=\ln(\varepsilon_0)+\frac{1}{E_U}h\nu \tag{4} \]

where ε is the absorption coefficient, hν is the energy of photon, and E_u is the Urbach energy. The Urbach energy for the mashmoom mediated synthesis of AgNPs was obtained from the inverse of the slope of a plot of ln(ε) versus hν (Plot not shown). The calculated values for the AgNPs are given in Table 2.

The Urbach energy values of AgNPs synthesized using Mashmoom extract are in the range of 0.76-0.96 eV, and these values are high in comparison to pure AgNPs (0.15-0.40 eV). This is attributed to a more disordered structure and to the presence of phytochemicals on the nanoparticles' surfaces. The Urbach energy values can vary depending on the type of plants used and the synthesis conditions in the synthesis of nanoparticles [19,25].

3.4 Size and Morphology of AgNPs

The size and morphology of the AgNPs were studied using TEM and the micrographs are shown in Figure 7.

Figure 7 Transmission electron micrographs of AgNPs, (A) M-0.5Ag, (B) M-2.0Ag, (C) M-4.0Ag, (D) Selected area electron diffraction pattern (SAED) for M-0.5Ag.

The nanoparticles are predominantly spherical, with the following average sizes: M-0.5Ag = 32.3 ± 1.5 nm, M-2.0Ag = 38 ± 1.5 nm, and M-4.0Ag = 45.6 ± 2.0 nm. The average size of the nanoparticles increases with an increase in the concentration of the precursor salt, silver nitrate in the reaction solution. This leads to the formation of a large number of nanoparticles in the solution, which could undergo agglomeration, as clearly observed for sample M-4.0Ag. This observation also correlates with the increase in turbidity of the solution as discussed earlier. However, in all three samples, the average size did not exceed 50 nm, which further indicates that the nanoparticles are stabilized by the phytochemicals present in the mashmoom extract.

The dark contrast on the surface of the nanoparticles is due to the coating of the organic components (phytochemicals) from the mashmoom extract. This surface capping is known to provide steric stabilization of the nanoparticles against aggregation. The nanoparticles were polycrystalline in nature, with a face-centered cubic (fcc) structure and distinct Miller indices of 111, 200, 220, 222, and 311 as observed in the SAED pattern. The SAED pattern of sample M-0.5Ag is shown as a representative example in Figure 7(D).

3.5 Average Number of Silver Atoms

The average number of silver atoms per nanoparticle was determined using the equation [26],

\[ N_{A\nu}=\frac{\pi\rho D^3}{6M}\times N_A \tag{5} \]

where, π = 3.14, ρ is the density of face-centered cubic structure (for silver = 10.5 g/cm³), D is the average diameter of nanoparticles (determined from TEM), M is the atomic mass of silver = 107.87 g, and N_A is Avogadro’s number = 6.023 × 10²³ atoms.

Based on the size of nanoparticles and assuming 100% conversion of all silver ions to AgNPs, the average number of silver atoms per silver nanoparticle was determined to be 1.03 × 10⁶ atoms (M1-0.5Ag), 1.72 × 10⁶ atoms (M1-2.0Ag), and 2.90 × 10⁶ atoms (M1-4.0Ag). It is observed that the number of silver atoms increases with an increase in the average size of the AgNPs, which is to be expected since larger nanoparticles accommodate more atoms.

The number of surface atoms (N_s) on a single silver nanoparticle was calculated using the equation [1],

\[ N_s=4N_{A\nu}^{2/3} \tag{6} \]

The number of surface atoms were calculated to be 40.8 × 10³ atoms (M1-0.5Ag), 57.4 × 10³ atoms (M1-2.0Ag), and 81.0 × 10³ atoms (M1-4.0Ag).

3.6 Morphology of Alginate-Silver Nanocomposite Beads

The morphology of nanocomposite beads was studied using scanning electron microscopy, and the results are shown in Figure 8. The beads are close to spherical shape with a rugged surface morphology. The average size of the nanocomposite beads is in the range 1.0-1.5 mm (Figure 8(A)). The surface morphology is rugged, porous, and contains a non-uniform distribution of AgNPs/clusters in the size range 500 nm to 1 µm (Figure 8(B)). The average amount of AgNPs/clusters present on the surface of the nanocomposite beads was estimated to be 3.9 wt.%, using energy dispersive X-ray spectroscopy (EDX). The EDX map indicating the presence of AgNPs/clusters on the nanocomposite bead is shown in Figure 8(C). Interestingly, the AgNPs exist as nanoclusters on the surface of the beads.

Figure 8 Scanning electron micrographs and EDX map of alginate-silver nanocomposite beads. (A) Surface of the bead, (B) Surface of the bead showing the nanoparticles, (C) EDX mapping of AgNPs on the surface of the bead.

3.7 Catalytic Property of the Nanocomposite Beads

The catalytic property of the nanocomposite beads was studied by following the degradation of a model cationic dye, methylene blue. The change in absorbance of the methylene blue solution (1 mM) in the presence of 10 silver nanocomposite beads and sodium borohydride (0.1 M) was recorded. The change in absorption at 660 nm was recorded and the results are shown in Figure 9(A). The initial absorption intensity of 3.1 decreased steadily to 0.25 over about 60 min, indicating the discoloration of methylene blue due to its degradation into various products. The electrons from the reducing agent (BH₄^-) react with the aromatic groups of the dye molecules. As electron conjugation is lost, the dye decolorizes [27]. The percentage degradation of the dye was calculated using the following equation [28],

\[ \text{Degradation }(\%)=\frac{A_0-A_t}{A_0}\times100 \tag{7} \]

where A₀ and A_t are the absorbance at time zero and absorbance at time t, respectively. The degradation kinetics are shown in Figure 9(B), and 92% degradation is observed after about 90 min of reaction. The degradation data was fitted with a sigmoidal-Boltzmann model and two distinct regions can be identified in the graph. A 20% degradation is observed during the first 38 min of reaction. Beyond this time and for 90 minutes of reaction, the degradation is fast and reaches 92%. The degradation of the dye reaches 50% at 54 min. The results can be explained as follows: The initial slow degradation is due to the slow swelling of the nanocomposite bead in the reaction medium and the adsorption of the dye on the surface of the bead. Due to the low number of silver nanoclusters on the bead surface, the dye degradation is relatively low (~20%) until 38 min into the reaction. Beyond 38 min, the nanocomposite bead becomes fully swollen and allows faster diffusion of dye molecules into the matrix, thereby favoring a faster degradation process of 92%. It must be mentioned that the distribution of silver nanoclusters in the beads is random, which also explains the observed trend in the degradation process.

Figure 9 (A) Change in absorbance for methylene blue in the presence of nanocomposite beads and NaBH₄ as a function of time, (B) Plot of degradation (%) versus time (Red line is the sigmoidal-Boltzmann fit), (C) Reaction kinetic plot for degradation process (Red line is the linear regression fit).

The degradation time could be further improved by increasing the porosity and the proportion of beads with high silver nanocluster concentrations. This would provide faster diffusion of the dye molecules into the beads for reaction with the active proton species. Interestingly, in the absence of the nanocomposite beads the degradation was significantly slow and it took about a few days to observe a slight change in absorbance of the sample. This confirms the catalytic role of silver nanoclusters in the degradation of the dye, methylene blue.

The catalytic degradation kinetics for methylene blue were evaluated using the Langmuir-Hinshelwood model which is appropriate for solid-liquid interactions as [29],

\[ ln\frac{C_t}{C_0}=ln\frac{A_t}{A_0}=-k\times t \tag{8} \]

where C₀ and C_t are the initial concentration, and concentration at time t, A₀ and A_t are the initial absorbance and at time t, respectively and k is the rate constant.

From the slope of a plot of ln(A_t/A₀) versus time (Figure 9(C)), the rate constant for the degradation process was determined. The degradation follows pseudo-first order kinetics as the concentration of sodium borohydride was much higher (10 mM) than that of methylene blue (1 mM) [30].

Two distinct regions corresponding to two rate constants are observed in Figure 9(C), which correlates with the degradation curve in Figure 9(B). The first-rate constant, k_a of 0.0063 min^-1 for the first 38 min of the reaction, is attributed to swelling of the bead and surface adsorption of the dye. The second-rate constant k_b of 0.033 min^-1 is attributed to the diffusion and degradation of the dye. The five-fold increase in the rate of reaction signifies a faster degradation process after 38 min of reaction. The presence of two distinct rate constants demonstrates that MB degradation using the beads is a complex process due to limitations in mass transfer [31,32].

3.8 Antibacterial Property

The silver nanocomposite beads exhibited dose-dependent antibacterial properties against E. coli (Gram-negative), but not towards S. aureus (Gram-positive). Different numbers of nanocomposite beads (2, 5, 10, and 20) were immersed in bacterial broth for 24 h, and the broth was then streaked onto fresh agar medium. The formation of bacterial colonies after incubation for 24 h at 37°C was indicative of the antibacterial property of the nanocomposite bead. The bacterial agar plates after the broth treatment with different numbers of nanocomposite beads (2, 5, 10 and 20) are shown in Figure 10.

Figure 10 Images of agar plates showing the formation of bacterial colonies of (A) S. aureus, and (B) E. coli after treatment with silver nanocomposite beads in broth.

No antibacterial activity against S. aureus is observed even for 20 beads, while a dose-dependent effect is observed for E. coli. This could be due to a low concentration of AgNPs on the beads, which is insufficient to kill the bacterial cells. Increasing the concentration of AgNPs on the surface and interior of the beads could improve antibacterial activity.

The mechanism of interaction of AgNPs with bacteria is mainly ionic [33,34]. The AgNPs and silver ions (released from the nanoparticles) can accumulate in the pits of the cell wall, leading to denaturation of the cell membrane. In addition, the AgNPs could penetrate the cell membrane, leading to denaturation and rupture of organelles resulting in lysis. Further, the AgNPs can disrupt bacterial signal transduction, leading to cell apoptosis and the termination of bacterial cell multiplication.

4. Conclusions

The successful synthesis of stable AgNPs in the size range of 32 to 45 nm and Alg-AgNc beads using the aqueous extract of mashmoom (Ocimum basilicum), a household medicinal herb in Bahrain, was demonstrated in this work. The nanoparticles were spherical and crystalline. The Alg-AgNc beads containing silver nanoclusters exhibited a catalytic activity and effectively reduced 92% of the organic dye, MB, in 90 min. The Alg-AgNc beads exhibited dose-dependent antibacterial activity against Escherichia coli. These results highlight the potential application of these composite materials in catalytic degradation of organic waste, hospital wastewater, and point-of-contact water decontamination. Further, the sustainable development of advanced materials using household herbs has also been demonstrated in this work.

Author Contributions

JA: experimental work, data analysis, & writing; HA: experimental work, data analysis, & writing; FA: experimental work, & data analysis; FH: characterization of materials; GRD: project development, supervision, writing, & revision.

Competing Interests

The authors have declared that no competing interests exist.