One-pot fabrication of Ag @Ag2O core–shell nanostructures for biosafe antimicrobial and antibiofilm applications

Microbial contamination is one of the major dreadful problems that raises hospitalization, morbidity and mortality rates globally, which subsequently obstructs socio-economic progress. The continuous misuse and overutilization of antibiotics participate mainly in the emergence of microbial resistance. To circumvent such a multidrug-resistance phenomenon, well-defined nanocomposite structures have recently been employed. In the current study, a facile, novel and cost-effective approach was applied to synthesize Ag@Ag2O core–shell nanocomposites (NCs) via chemical method. Several techniques were used to determine the structural, morphological, and optical characteristics of the as-prepared NCs. XRD, Raman, FTIR, XPS and SAED analysis revealed a crystalline hybrid structure of Ag core and Ag2O shell. Besides, SEM and HRTEM micrographs depicted spherical nanoparticles with size range of 19–60 nm. Additionally, zeta potential and fluorescence spectra illustrated aggregated nature of Ag@Ag2O NCs by − 5.34 mV with fluorescence emission peak at 498 nm. Ag@Ag2O NCs exhibited higher antimicrobial, antibiofilm, and algicidal activity in dose-dependent behavior. Interestingly, a remarkable mycocidal potency by 50 μg of Ag@Ag2O NCs against Candida albican; implying promising activity against COVID-19 white fungal post-infections. Through assessing cytotoxicity, Ag@Ag2O NCs exhibited higher safety against Vero cells than bulk silver nitrate by more than 100-fold.


Characterization methods. The structural, composition and morphological properties of the (Ag@Ag 2 O)
NCs composite powder were investigated using X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), zeta potential and Fluorescence spectra. X-ray diffraction measurement was performed using Shimadzu 7000 XRD, with CuKα radiation (λ = 1.54 Å) generated at 30 mA and 30 kV with a scanning rate of 4° min −1 and 2θ values ranged between 25° and 80°. Raman spectrum was obtained at an excitation wavelength of 532 nm using Raman spectroscopy (Senterra, Germany). For the determination of the chemical bonds formed during the preparation process, Fourier Transform Infrared Spectrophotometer (FTIR, Bruker Corporation, Ettlingen, Germany) is used. The powder product morphology was investigated using Scanning Electron Microscopy [SEM, JEOL (JSM 5300)]. However, high resolution transmission electron microscope TEM (HR-TEM, JEOL-2100, Japan) was employed to examine morphology, high resolution d-spacing of the different structures, electron diffraction and mapping of silver and oxygen elements. X-Ray photospectroscopy (XPS) measurement was carried out using PHI 5000 Versa Probe III Scanning XPS Microprobe with Monochromatic Al source ranged from 0-1486.6 eV. Electrostatic potential was determined by the DLS technique using Zetasizer Nano ZS (Malvern Instruments, Worcestershire, UK) and the data were analyzed by Zetasizer software 6. Finally, the fluorescence spectrum was recorded at an excitation wavelength of 250 nm on fluorescence spectrophotometer (Agilent, G9800A, USA). Candidaalbicans (ATCC − 10,231) via well diffusion assay. The sterile agar plate sets (Müller-Hinton agar for bacteria and yeast extract peptone dextrose agar (YPD) for yeast) were swabbed homogeneously using sterile cotton-tipped applicators with 100 μL of 10 6 CFU/mL of each examined organism. A sterile cork-borer (5 mm) was used to make the wells. Different concentrations (5, 10, 25, 50 and100 µg/mL) of Ag@/Ag 2 ONCs and AgNO 3 were loaded separately in each well. The bacterially inoculated plate sets were incubated at 37 °C for 24 h. For yeast, the plates were incubated at 25 °C ± 2 °C for 2-3 days. The plates were examined after incubation for the presence of a zone of inhibition (ZOI), which were measured and expressed in millimetres (mm). It was calculated by subtracting the well diameter from the total inhibition zone diameter 10 .
Evaluation of the as-prepared Ag@Ag 2 ONCs as anti-bio-film agent. The inhibitory effect of Ag@ Ag 2 ONCs and AgNO 3 (5, 10, 25, 50 and100 µg/mL) against P. aeruginosa and S. aureus biofilms were assessed using tissue culture plate method. A sterile polystyrene 96-well microplate was seeded by 100 μL of tryptone soy broth (TSB) containing 10 8 CFU/mL of each tested strain. Simultaneously, two controls were run in parallel; positive control wells (medium containing a bacterial culture) and negative control wells (sterile TSB only). After 24 h of static incubation at 37 °C, washing, fixation and staining of the remained biofilm were carried out by 95% ethanol and 0.25% crystal violet, respectively. The absorbencies of adhered cells were measured spectrophotometrically at 595 nm. All the experiments were carried out in triplicate and the results are expressed as mean ± SD 11 . The following equation was employed to calculate inhibition percentage of biofilm formation where A represents the absorbance of the positive control wells and A 0 reveals the absorbance of the treated wells containing an antimicrobial agent.
Biofilm disintegrating assay. The potential of Ag@Ag 2 ONCs to degrade the already formed biofilms by P. aeruginosa and S. aureus were examined in comparison to AgNO 3 . Firstly, the bacterial lawn (10 8 CFU/mL) was inoculated into 96-well microplates and incubated statically at 37 °C for 24 h to permit biofilm formation. Secondly, the well contents were discarded aseptically. The diluted Ag@Ag 2 ONCs and AgNO 3 to concentrations (5, 10, 25, 50 and100 µg/mL) were added to each well. The incubation, processing, quantification and disintegration percentage of the biofilms were performed as previously described. All the experiments were carried out in triplicate and the results are expressed as mean ± SD. As stated by Cremonini et al. 12 the biofilm was deemed strong, medium and low at optical density (OD) ˃ 2, 1 ˂ OD ˂ 2 and 0.5 ˂ OD ˂1, respectively.

Results and discussions
Structural analysis and chemical bonds formation. X-ray diffraction (XRD). The X-ray diffraction (XRD) spectrum of nano-composite (Ag@Ag 2 O)NCsis given in Fig. 2a 16 .On the other hand, the close overlap between Ag and Ag 2 O diffraction peaks and the difficulty to distinguish between the Ag + and Ag 0 peaks at the diffraction angle of 38.1° inferred a formation of a hybrid structure 17,18 . Sajjad Ullah et al. 18    in the samples. The structure could possibly have an Ag 2 O shell with Ag as the core with a decreasing gradient of oxygen from the surface to the core 6 . Despite the simplicity of preparation method, the silver element needs a special medium during its preparation. The individual crystallite size (t) was calculated using Scherrer's formula 19 given by Eq. (2).
where k is the Scherrer's constant (0.89-0.9), λ is the X-ray wavelength, β is the full width at half maximum (FWHM) and θ is the Bragg angle 19 . According to Eq. (2), the sample crystallite size for the plan (111) is calculated and is found to be approximately 18.6 nm.
Raman analysis. The molecular structure and phase identification of the Ag@Ag 2 Ocore shell are explored using Raman spectra. Figure 2b shows the Raman spectrum for the prepared nanopowder in a range from 0 to 4500 cm −1 . Two major peaks are clearly detected; the first one at 74.1 cm −1 with an intensity of 7900 cps for Ag 0 (Ag lattice vibrational mode) and the other one at 1046.7 cm −1 with an intensity of 583 cps for Ag 2 O (Ag-O stretching/bending modes) 20 .
Fourier-transform infrared spectroscopy (FTIR):. FTIR analysis reveals the functional groups of the Ag@/Ag 2 O nanocomposite synthesized using alkali chemical treatment (Fig. 2c).The broad band at3400 cm -1 indicates the O-H stretching vibrations of the hydroxyl groups 21 corresponding to H-bonded alcohols and also to intramolecular H bonds which are most probably from water molecules 22 . The peaks at 2357 cm −1 and 1655 cm −1 prove the existence of O-H carboxylic acids 23 and OH bending, respectively 24 . The band at 1387 cm −1 assigned to O-H bend of carboxylate 25 . The absorption band on 675 cm −1 is due to Ag-O stretching mode, which corresponds to Ag-O vibration in Ag 2 O.Furthermore, the appearance of follower peak at 868.68 cm −1 corresponds to the metaloxygen vibrations for the formation of (Ag@Ag 2 O) NCs 15 ; thus, synchronizing with the aforementioned XRD results; confirming the formation of (Ag@Ag 2 O) NCs.
(2) t = k. /β. cos θ www.nature.com/scientificreports/ X-ray photoelectron spectroscopy (XPS). The XPS data for the chemically prepared Ag@Ag 2 O NCs is illustrated in Fig. 3. Figure 3a shows the general survey analysis of the nanopowder, which exhibits a major detected peak of the Ag3d at a binding energy of 368.34 eV with an atomic ratio of 48.5%. Also, O1s peak is detected at a binding energy of 530.81 eV with an atomic ratio of 29.75% and K2p peak is observed at a binding energy of 293.5 eV with an atomic ratio of 2.18%. Finally, C1s peak is measured at a binding energy of 285.21 eV with an atomic ratio of 19.56%. In Fig. 3b, the high resolution of the Ag3d spectrum displays two main strong bands. Such two bands can be further de-convoluted into two pairs of sub-peaks. The peaks at 367.98 eV with an atomic ratio of 44.01% and 373.96 eV with an atomic ratio of 28.75% are respectively assigned to Ag 0 (3d5/2 and 3d3/2). The other set of bands is detected at 367.38 eV with an atomic ratio of 10.48% and 373.6 eV with an atomic ratio of 10.36% are attributed to Ag + (3d5/2 and 3d3/2, respectively) in the nanocomposite. Figure 3c confirms the oxidation of the silver nanoparticles through the existence of the O1s spectrum at 529.39 eV with an atomic ratio of 47.64%, at 530.77 eV with an atomic ratio of 25.32% and at 531.4 eV with an atomic ratio of 23.19%. Finally, the results confirm that there are two different configurations of silver species, namely Ag 2 O and Ag, which is consistent with many published reports [26][27][28] . The detected elemental carbon in the main survey analysis may have originated from the ambient atmosphere itself. The adsorption of hydrocarbons from the surrounding atmosphere, which results in the creation of a thin carbon layer on surfaces, is most likely the source of the carbon contamination 29 .
Morphological analysis. Scanning electron microscope (SEM). Figure 4a and b illustrates the scanning electron microscope (SEM) surface morphological image of the nano-composite (Ag@Ag 2 O) at different magnifications. The Ag 2 O exhibited bundles of nearly spherical nanoparticles ranged from 19 to 59 nm and this result is nearly consistent with the result from XRD patterns in Fig. 2a. The silver oxide may have formed in as a solution mixture containing potassium hydroxide and n-propanol which have high oxidation potential 30 . Also, the time spent since the beginning of the reaction, i.e. when adding silver nitrate to the oxidized mixture and until the end of the reaction is not enough to produce the silver oxide in its final form. Thus, it is an incomplete reaction that results in the precipitation of the silver nanopowders. This step entails the formation of a layer of silver oxide on the surface of the silver powder nanoparticles as a result of remaining in the oxidizing solution for a longer time 31 . Thus, it is logical to form an Ag/Ag 2 O core shell compound of a spherical nature as a result of the lattice mismatch between silver metal and silver oxide 6 . However, the aggregation is more likely to occur due to too small size as shown in Fig. 4a and b. Generally, the smaller particle size is usually more beneficial for www.nature.com/scientificreports/ the antibacterial activity. Because the particle size is smaller, many more particles will be easily adsorbed on the surface of the bacterial cell membrane, and then successfully attack the cell, ultimately destroying the physiological functional groups of the cell 32 .
Transmission electron microscopy (TEM). TEM has been employed to characterize the size, shape, morphology and crystallinity of the synthesized Ag@Ag 2 O NCs. Zeta potential. The surface charge of Ag@Ag 2 O core shell was determined from Zeta potential by applying voltage across a pair of electrodes at either end of a cell containing the particle dispersed. The charged particles are attracted to the oppositely charged electrode and assessing the Zeta-potential value by − 5.34 mV (Fig. 5a). The Ag@Ag 2 O NCs show slightly low surface charges which tend to form agglomerates 33 . Moreover, the low surface charges of Ag@Ag 2 O NCs reflect the urgent requirement of a capping agent to prevent such agglomeration and keep nanocomposites stable for a long time 34 . However, upon antimicrobial application and cytotoxicity evaluation, the examined NCs were freshly prepared and examined after a short time of preparation (within 48 h of preparation). Subsequently, the prepared NCs, within such time, didn't exhibit aggregation and were still stable. Additionally, several reports 35,36 synthesized AgNPs and other metal-NPs in the same range of zeta and also exhibited antimicrobial activity.
Fluorescence spectra. The fluorescence emission peak of Ag@Ag 2 O NCs was detected using an excitation wavelength of 250 nm and appeared at about 498 nm in the visible range as shown in Fig. 5b. This fluorescence emission peak may be attributed to the relaxation of the electronic motion of surface plasmons 37 . The sharpening behavior in the peak may be due to the core shell structure and coverage of Ag by Ag 2 O, which prevents the nanopowder from combining with any water molecules as well as continuing the oxidation process 38 .
The chemical mechanism. Based on the preceding experimental data, it is worth mentioning to explain the chemical mechanism of the nanocomposite (Ag@Ag 2 O) formation as demonstrated in Eq. (3). The reaction of silver nitrate with potassium hydroxide produces silver hydroxide via the following mechanism 24 : www.nature.com/scientificreports/ The intermediate AgOH is thermodynamically unstable, and the Ag 2 O is formed phase through many steps, as shown in the following Eqs. (4)-(7). Briefly, a part of AgOH may be reacting with the n-propanol, which acts as a wetting agent that decreases the recombination rate and the generation of silver propanoate (Ag-O 2 CCH 2 CH 3 ), as shown in Eq. (4), which is inferred from FTIR spectra as a sharp peak at 1655 cm −1 and 3400 cm −1 as shown in Fig. 2c 39 . Meanwhile, Ag-O 2 CCH 2 CH 3 is reacted with the hydroxyl group of KOH producing silver ions (Ag + ) in a continuous oxidation process [Eq. (5)]. The silver ion reacts with water and n-propanol in an alkaline medium via the presence of OHgroup to produce silver element (core); as shown in [Eq. (6a)]. Additionally, some of the silver ions re-interact with water and n-propanol for producing silver hydroxide as in [Eq. (6b)]. Therefore, the unstable silver hydroxide product (AgOH) is reduced to silver oxide (Ag 2 O shell) as shown in [Eq. (7)].

Antimicrobial efficiency of Ag@/Ag 2 O NCs against planktonic pathogens.
Considering the health problems associated with microbial contamination, it is vital to find out effective antimicrobial agents that are able to control their outbreak. Thus, the current study is concerned with the antimicrobial activity of Ag@ Ag 2 O NCs against some prokaryotic and eukaryotic pathogens. The sensitivity of the examined pathogens to different concentrations of Ag@Ag 2 O NCs is shown through agar diffusion assay. Figure 6a Fig. 7A-E respectively. Generally, Ag NPs displayed considerable effectiveness indicated by halo zones which exceeded 1 mm, where any antimicrobial agent was evaluated as "good" atan inhibition zone greater than 1 mm 40 . For all the examined pathogens, inhibition halos were directly proportional to the concentration of AgNPs. In addition, Gram-positive strains seemed to be more resistant than Gram-negative strains. That could be attributed to the lipophilicity of Ag NPs according to different cell wall polarity and compositional variations 41 .
As revealed by Pazos-Ortiz et al. 42 the thickness of the cell wall increases the resistance of bacteria to the exposed NPs. The thick peptidoglycan layer of the Gram-positive bacteria's wall, which is composed of teicoic acids and lipoteicoic acids, restricts the diffusion of NPs. Moreover, the tolerance response of each microbe depends on its metabolic properties. However, the cell wall of the Gram-negative bacteria is composed of thinner peptidoglycan layer together with lipoprotein and lipopolysaccharide, which together represent 25% of its mass. It is noteworthy to mention that the nosocomial infections and enteric fever are associated with P. aeruginosa, E. coli and S. typhi, respectively. Therefore, their inhibition is a pivotal issue. In agreement with our results 42,43 reported low reduction in S. aureus count (CFU/mL) and also halo zone in comparison to Gram-negative bacteria upon treatment by Ag@Ag 2 O NPCs. Besides, Ag@Ag 2 O NPCs biosynthesized by aqueous leaf extract of Eupatorium odoratum (EO) exhibited antagonistic performance coincident with the obtained results of current study 41 . In the  www.nature.com/scientificreports/ same sense, D'Lima et al. 6 reported that Ag/Ag 2 O hybrid nanoparticles showed a considerable zone of inhibition against P. aeruginosa; declaring the enhancement of antibacterial activity upon combination with carbenicillin. In contrast, other studies reported higher susceptibility of Gram-positive bacteria for NPs treatment than Gram-negative one 11,44 . Remarkably, a considerable halo of mycostasis was noticed against C. albicans. Despite the oligodynamic nature of silver ions, which is due to their higher activity at minute concentrations, a potent antifungal efficiency of 50 μg of Ag@Ag 2 ONCs exhibited upon comparing with its precursor (Fig. 6); implying effectiveness in the treatment of COVID-19 post infections. Such fungal infections appeared recently in the second wave in India, in particular in patients who were put on mechanical ventilation in intensive-care units.
The fungicidal property of Ag@Ag 2 ONCs could be assigned to the damage of the glycoprotein-glucan-chitin cross-linkage of fungi cell wall followed by sever alterations in cellular biochemistry 11,45 . In addition, it has been suggested that Ag nanoparticles interact with the proteins of the plasma membrane, which is responsible for keeping trans-membrane electrochemical potential gradient such as H + ATPase protein. Such interaction leads to alterations of normal protein conformations and malfunctioning by blocking the regulation of H + transport across the membrane, which ultimately hindering growth, restraining respiration and ending with death [46][47][48] .
In coincidence with our results, Mallmann et al. 49  Evaluation of the as-prepared Ag@Ag 2 ONCs against biofilm formation, biofilm disintegration and algal growth. Biofilms are multicellular sessile microbial communities embedded in a self-produced extracellular polymeric matrix (EPS) (e.g. DNA, proteins and polysaccharides) and attached toa living or inert substratum or interface. Actually, the viscoelastic nature of the EPS represents a serious concern, especially in water pipes, water purification systems and also in medical devices. Where, the biofilms have the capability to withstand different stress factors by the virtue of such feature. Hence, nanotechnology invasion has provided a significant tool to eradicate such problem at both environmental and medical levels 50 . The inhibitory effect of different concentrations of as-synthesized Ag@Ag 2 ONCs and their precursor salt on biofilm formation/ disintegration of both Gram-positive and Gram-negative bacteria was illustrated in Table 1. As noticed, P. aeruginosa biofilm was less susceptible for both treatments and under formation/ disintegration conditions, in comparison to S. aureus biofilm. As revealed by Hoseini -Alfatemi et al. 51 , P. aeruginosa and S. aureus biofilms were inhibited by 10 and 1 mg/mL of AgNPs, respectively; which makes our study characteristic. Where, 100 µg/mL suppressed (98.7% and 87.5%) and (93.1 and 74.8%) of S. aureus and P. aeruginosa biofilm synthesis and disintegration, respectively. Interestingly, Gram-negative biofilms were comparatively more resistant to antibiofilm treatments than Gram-positive as reported in several studies 42,51,52 . Generally, Ag@Ag 2 O NCs exhibited antibiofilm activity via several routes including, destruction of initial planktonic phase, damage of aggregated/sessile phase, disruption of EPS matrix, increasing of hydrophobicity of EPS and inhibition of quorum sensing system 53 .
What is more, the inhibitory effect of Ag@Ag 2 ONCs against algal growth of C. vulgaris was studied. C. vulgaris is involved among other algal genera which are responsible for various environmental issues such as eutrophication and biofouling, especially in the availability of high concentrations of contaminants and in association with direct sunlight 53 . As illustrated in Table 1, Ag@Ag 2 O NCs exhibited a drastic algicidal effect on the proliferation and viability of algae with 98.4% growth inhibition. Severe damage of chloroplasts could be proposed due to yellowish to pale green color of algal growth in the presence of Ag@Ag 2 ONCs. Meanwhile, the control culture (without Ag@Ag 2 ONCs) appeared green and flourished during 7 daysof incubation as shown in Fig. 7D and E. Disintegration of algal cell organelles, thylakoid disorder and plasmolysis are common features associated with the destructive effect of Ag@Ag 2 ONCs on algal cell as stated by Duong et al. 54 . Therefore, the employment of Ag@ Ag 2 ONCs in restriction the algal blooms could result in constraining of their environmentally adverse influence.
As general observations, Ag@Ag 2 ONCs exhibited greater inhibitory activity than its precursor against all examined microbial forms. That could be assigned to the small size of nanoparticles and in relation to surface area. As pointed out by 55 , the antagonistic activity of NPs derived from their penetration ability which depends on www.nature.com/scientificreports/ sizes that are less than 100 nm. In addition, the biocide activity of Ag@Ag 2 ONCs uplifted linearly with increasing in Ag@Ag 2 O NCs concentration, which implies dose-dependent manner. However, NPs type, concentration, size, aggregation state, surface charge, synthesis conditions and tested microbe consider being governing parameters influencing of the effective doses 51 . Broadly, several strategies could be ascribed for NPs to display their toxicity against different microbial forms. The first strategy begins from puncturing and perforating the first protective barrier of the cell, which is cell wall, by interacting with its anionic components such as neuraminic acid, N-acetylmuramic acid, and sialic acid. However, as long as the NPs are smaller than 80 nm, their passage to cell membrane and later inside the cell is facile; causing phospholipid peroxidation, polysaccharides depolymerization and subsequently membrane detachment and integrity destruction 10,56 . At this stage, cell permeability increases followed by intracellular components leakage and proton motive force dissipation. Once NPs occupies intracellularly, more destructive features were exerted concerning metabolism and biochemical activities 10 . AgNPs showed higher affinity for binding with thiol group of amino acids; forming extra -S-S-bonds. By such way, deformation of protein configuration occurs, leading to proteins denaturation and ribosomes inactivation 56,57 . Further, NPs bind with nucleic acids such genomic and plasmid DNA; causing blockage of DNA replication and repair processes. With continuous release of Ag + ions and their oxide from Ag@Ag 2 O NCs, set of reactions (e.g., Fenton and Haber-Weiss reactions) are continuously and intensively generating Reactive Oxygen Species (ROS) such as hydroxyl radicals (OH − ), superoxide radicals (O 2 − ) and singlet oxygen ( 1 O 2 ). Under such oxidative stress, massive damage to the cell takes place and eventually lead to cell death. Tee et al. 58 and Pazos-Ortiz et al. 42 referred to the complexity of the mechanisms by which NPs exhibit their antagonistic influence. Figure 1b represents schematic illustration on the destructive effect of Ag@Ag 2 O NCs against different microbial forms.

Cytotoxicity assessment.
After 72 h of incubation of the Ag/Ag 2 O NPs and silver nitrate precursor with normal renal epithelial Vero cells, it was found that their estimated safe doses on cell viability were 13.43 ± 1.63 µg/mL and 0.075 ± 0.001 µg/mL, respectively. This indicates that Ag/Ag 2 O NPs ismore safe than silver nitrate source. However, at 100 µg/mL of Ag/Ag 2 O NPs or silver nitrate caused death in Vero cells by 79.69% and 91.09%, respectively, as it is shown in Fig. 8a. Moreover, severe collapse in the normal spindle shape of silver nitrate-treated cells, at 25 µg/mL, confirmed its cytotoxicity in comparison to the normal morphology of Ag/Ag 2 O NPs-treated cells and untreated control healthy cells (Fig. 8b) 14 . The lower cytotoxicity of the prepared NPs, at < 13 µg/mL, may be related to their particle size (≥ 40 nm), negatively particle charge and high agglomeration potential (Fig. 4a,b) which results in increasing their size thus decreasing their cellular uptake and diminishes ROS generation 59 .
In support of this issue, Liu et al. 60 found that Ag NPs with size of 55 nm generated less ROS than 15 nm Ag NPs. Moreover, silver NPs' tendency to agglomeration increases in culture medium 61 . Besides, based on the previous finding, corona formation which is mediated by adsorption of fetal bovine serum (FBS), from culture medium, on silver NPs, mainly limits their cytotoxicity via reducing their cellular uptake 59,62 . All these factors contribute to minimize the cytotoxicity effect of Ag/Ag 2 O NCs on normal cells. This higher safety of Ag/Ag 2 O NPs on human normal cells (Fig. 1c) lends credibility to their biomedical applications compared to bulk silver nitrate.

Conclusion
Due to the globally identified antibiotic resistance among clinical pathogens, novel antimicrobial materials are needed to circumvent drug resistance. In this study, we have demonstrated a facile chemical method to fabricate Ag@Ag 2 O core-shell nanocomposites and their antibacterial, antifungal and antibiofilm activities against a wide range of microbial pathogens were examined. Structural, morphological and optical properties were studied using different techniques. XRD, Raman, FTIR, XPS and SAED indicated the formation of a hybrid NC structure with a crystalline nature. SEM and HRTEM showed the evidence of Ag@Ag 2 O with a spherical core-shell structure and its particle size ranging from 19 to 60 nm.
Furthermore, the antagonistic properties of Ag@Ag 2 O core-shell and its precursor AgNO 3 were compared in the range of 5-100 μg/mL. The image data declared the sensitivity order of pathogens versus examined Ag@ Ag 2 O as follows: S. typhi ˃ P. aeruginosa ˃ E. coli ˃ B. cereus ˃ S. aureus. Besides, a noticeable antifungal potency of Ag@Ag 2 O was observed at 50 μg/mL. Additionally, its antibiofilm activity and disintegration capability were increased with elevation of concentration. Generally, a dose-dependent behavior could describe the inhibition of examined pathogens by Ag@Ag 2 O. Eventually, the cytotoxicity of the NC was analyzed by Vero cells and its effective safe concentration value was estimated to be about 36.31 ± 1.53 µg/ml. The promising structural features and biocidal activity of Ag@Ag 2 O opens up employment in various technological sectors.