Introduction

Nanotechnology is the unique design of art and technology throughout the world, dealing with the materials at a special scale. Most of the researchers worldwide, appreciate the advantages it would cause to the intact community and economy [1,2,3].

Element develops its characteristics toward the nano-scale, so scientists tried to discover a method to obtain the secure application of the improved benefits of metal-based elements (Au NPs or Ag NPs), carbon-based materials (nano-tubes) or nano-composites (mixing nanoparticles with extraordinary and larger elements) [4,5,6].

The research on inorganic–polymer nano-materials has gained significant attention in current years because of the properties novelty that formed after the reaction between inorganic and polymer materials. After nanocomposites formation, all the researchers try to create different beneficial applications like in biological, medical and pharmaceutical purposes, also in photo-conductors and electrics [7, 8]. In the last few years, notable synthetic methods were performed on certain composites, and several modern techniques [9,10,11,12,13,14] were applied for the construction of unique nano-composites with desirable qualities and purposes like the sol–gel procedure, mixing means and so on without practicing the use of gamma rays in the synthesis process. To manage the generation of inorganic–polymer nano-materials, organic polymeric stabilizers such as PVP and PVA were combined for stabilization and capping process [15, 16].

A fast development in the microbial contamination was increased especially after the microbial resistance to the synthetic antibiotics [17]. Escherichia coli and Staphylococcus aureus are distinct kinds of bacteria obtained directly from the intestinal region of all individuals and several additional animals. E. coli was causing enteric infection and additional intestinal disorder such as UTI [18].

The bacterial biofilm is a complex of the multi-cellular field produced at the covers [19]. It gets the community in nearly all wet situations wherever a sufficient nutrient current is probable and the exteriors contact can be achieved [20]. Biofilms were adopted to maintain the microbial community from the environmental stresses. Accordingly, the maturation of the biofilm allows the microbes to manufacture resistance to various biocides, bacteriophages, the host defended replies and several medicines by the production of the extracellular polysaccharide substances (a shielding barrier) [19].

Metal nanostructures in different configurations, arrangements, sizes, and patterns drew exceptional attention because of their novel and improved photoelectric, catalytic, and visible characteristics [21,22,23,24,25]. Nanoparticles were received from various origins of liquid, gas, or substantial structures. They can be produced using several synthetic processes e.g. chemical, natural, biological, and physical organization [26,27,28,29,30,31,32]. Gamma rays were confirmed to be an accessible process for nanoparticles construction that requires an aqueous form and an ambient temperature [33,34,35].

Ag NPs were used for different goals like flat splashes, pharmaceutical materials, freezers, antimicrobial agents and cosmetics [6, 26, 36]. The antimicrobial effects of Ag NPs were examined, the mechanism needed and the cytotoxic results to the individual cells were not considered [26, 37].

In this respect, we selected for the initial time, PVP (protective polymer), as a model to represent an encouraging cost-effective and eco-friendly green construction and manufacture of silver boron nanoparticles (AgB NPs), as well as their capping after the impact of gamma irradiation. A full characterization and identification had been performed to achieve further developed data concerning size, crystallinity, distribution, and shape of the incorporated AgB NPs. Following that, the study of the antimicrobial and anti-biofilm activities of AgB NPs against bacteria and fungi causing UTI were examined.

Materials and Methods

Chemicals Used

Media ingredients were purchased from Oxoid. Chemicals (boric Acid, silver nitrate, PVP, and isopropanol) and reagents used in the next experiments and biological tests were obtained at the analytical standard form (Sigma-Aldrich) and allowed without further purification.

Radiation Source

The process of gamma irradiation was directed at the NCRRT, Cairo, Egypt. The irradiation source was 60Co-Gamma chamber 4000-A-India. Gamma rays were produced utilizing 60Co at a dose rate of 2.10 kGy/h at the time of the experiment. In this manner, 60Co gamma rays connect with elements in the solution typically via Compton scattering and photoelectric absorption to produce hydrated and free electrons from the radiolysis of water.

Synthesis of AgB NPs

AgB NPs were synthesized through PVP (as a stabilizing polymer) and gamma-rays (as reducing agent). The mixture includes 1.0 ml of 100 mM silver nitrate and 1.0 ml of 100 mM boric acid and filled to nearly 25.0 ml solution containing 4.0% PVP and 0.2% isopropanol solution. Next, the produced mixture was gamma irradiated at various doses such as 10.0, 15.0, 20.0, and 25.0 kGy. The most effective gamma dose was decided after measuring the Optical Density (O.D.) using UV–Vis. spectroscopy.

An experimental study (Table 1) was examining the influence of the concentration of silver nitrate and boric acid on AgB NPs synthesis after gamma irradiation at the chosen dose. The examined factorial study contained two variables in six levels; concentration of silver nitrate and boric acid. The principal purposes for factors selected from the current research that, they produce the multiple significant influences on AgB NPs construction [5, 38].

Table 1 Experimental factorial design for the optimization of AgB NPs production (diluted 15 times)
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Silver nitrate solution (at different conc. shown in Table 1) was mixed with the boric acid solution (at different conc.), 4.0% PVP solution and 0.2% isopropyl alcohol as a free radical scavenger. Mixtures were agitated at room temperature (24.0 ± 3 °C) and exhibited to the chosen gamma rays from the initial screening examination. UV–Vis. responses were considered the principal important parameters used for AgB NPs organization.

Characterization of AgB NPs

AgB NPs validation was completed by UV–Vis. spectrophotometer (JASCO V-560. UV–Vis Spectrophotometer) using a negative control (the irradiated samples) for autozero.

The common particle size and the size distribution of the synthesized AgB NPs were determined by Dynamic Light Scattering (DLS-PSS-NICOMP 380-USA). The size and shape of the synthesized AgB NPs were investigated by using High-Resolution Transmission Electron Microscope (HRTEM, JEM2100, Jeol, Japan).

X-ray Diffraction study was connected with the XRD-6000 lists, Shimadzu apparatus, SSI, Japan. XRD was used to determine crystallinity and crystallite size/lattice strain elements. The strength of the diffracted X-rays measured as a purpose of the diffracted angle 2θ.

FT-IR examination was a significant purpose that presents knowledge about chemical functional groups founded in PVP polymer. The tests were conducted by a JASCO FT-IR 3600 Infra-Red spectrometer by operating KBr Pellet method. It was shown at a wave number scale of 400–4000 cm−1. The surface morphology and the particle size distribution of the synthesized AgB NPs and PVP were examined by SEM, ZEISS, EVO-MA10, Germany. Finally, EDX (BRUKER, Nano GmbH, D-12489, 410-M, Germany) was applied to measure the elemental structure and mapping method for providing a full understanding of the purity and placement of the synthesized AgB NPs and PVP polymer.

Antimicrobial Activity of AgB NPs

The synthesized AgB NPs (25.0 µg/ml), Ag NPs (25.0 µg/ml), boric acid (25.0 mM), silver nitrate (25.0 µg/ml) and PVP (4.0%) were examined for their antimicrobial potential by applying the agar-disc diffusion method [30, 32, 39]. They were tested against different pathogenic bacteria and yeasts taken from the culture collections in Drug Microbiology Lab., Drug Radiation Research Dep., NCRRT, Cairo, Egypt. The tested pathogens were multidrug-resistant (MDR) causing UTI.

The tested bacteria were Gram-positive like Bacillus subtilis, and Staphylococcus aureus (MRSA), and Gram-negative like Escherichia coli, and Pseudomonas aeruginosa. The bacterial inoculums were established and fixed at 0.5 McFarland (1–4) × 108 CFU/ml (at 600 nm) [40]. The growth inhibition of all the examined bacteria was determined through the zone of inhibition (ZOI) after 24 h of incubation [28, 35, 36].

The examined MDR bacteria-causing UTI were tested by Vitek® two systems (bioMarieux, Marcy-LEtoile, France) [40]. Most of them were resistant to antibiotics like Cefapirin, Ciprofloxacin, Amikacin, Norfloxacin, Cefoxitin, Gentamicin, Ampicillin, and Cefotaxime.

Additionally, the antifungal activity of the synthesized AgB NPs, Ag NPs, boric acid, and PVP was examined against unicellular fungi-causing UTI (Candida albicans, and Candida tropicalis) following that, the yeast inoculums were fixed at 0.5 McFarland (1–4 × 108 CFU/ml) [40]. Amoxicillin/Clavulanic Acid (AMC; 20/10 μg/ml) and Nystatin (NS 100; 100 μg/ml); were examined as standard antibiotics (positive control).

The minimum inhibitory concentrations (MIC) determination was formed in Luria–Bertani (LB) broth containing serial dilutions [28, 32]. In these methods, a positive control (the microorganism and the nutrient), a negative control (the nutrient solely), and the examined AgB NPs (beginning with 250 μg/ml conc.) were applied. MIC was determined after 24 h at 37 °C. The bacterial inoculum was at 4–5 × 108 CFU/ml and 1–3 × 107 CFU/ml to Candida species [40]. MIC was defined by operating ELISA plate (at 600 nm).

Antibiofilm Activity of AgB NPs

A qualitative determination of the biofilm developing was determined according to Christensen et al. [41]. The visible investigation of the biofilm covering the tube wall in the absence and presence of AgB NPs was defined. The antibiofilm activity of the synthesized AgB NPs (at 25.0 µg/ml) was checked against the sensitive microbes causing UTI (bacteria and yeast showing sensitivity in the antibiogram test) and was examined with regard to the control one. Four ml of the nutrient broth was added within each tube, and an aliquot (0.5 McFarland (1–2.5) × 108 CFU/ml) of the tested bacteria and (1–4) × 107 CFU/ml for Candida sp. were inoculated then incubated for 24 h at 37 °C. The nutrient broth in the treated and control tubes were removed, and then treated with Phosphate Buffer Saline (PBS; pH 7) then dried [42].

The adherent bacterial and yeast layers were maintained by 3.0% sodium acetate (5.0 ml) for 10.0 min then washed with deionized water. Bacterial and yeast biofilms were stained with 0.1% Crystal Violet (CV) for 10.0 min and then rinsed with deionized water to discharge the excess of the stain. Finally, for dissolving the stain, 2.0 ml of the ethanol was added. The given biofilm was real if a prominent stained layer was identified on the walls and the bottom of the tube [42].

The bacterial and yeast biofilms were investigated by UV–Vis. spectrophotometer (at 570.0 nm). The inhibition percentage was measured using the following equation [41].

$${\text{Percentage}}\, {\text{of}}\, {\text{bacterial}}\, {\text{and}}\, {\text{yeast} }\,{\text{biofilms}}\, {\text{inhibition}} \left( \% \right) = \frac{{{\text{O}}.{\text{D}}. \, {\text{of}}\, {\text{control}}\, {\text{sample}} - {\text{O}}.{\text{D}}. \, {\text{of}}\, {\text{treated}}\, {\text{sample}} }}{{{\text{O}}.{\text{D}}. \, {\text{of}}\,{\text{control}}\, {\text{sample}}}} \times 100 .$$

Scanning Electron Microscopy and Elemental Analysis of the Tested Microbes

In summary, the chosen bacterial cells (from the biofilm activity result), were covered with PBS and maintained with 3.5% glutaraldehyde. The preserved bacterial samples were consequently washed regularly with PBS and rinsing with the ethanol for 10.0 min at 28 °C before draining. Finally, the bacterial cells were placed and fixed over the aluminum stubs for imaging [42]. The morphological and surface features of the treated bacteria with the synthesized AgB NPs and untreated cells were investigated using SEM (ZEISS). On the other hand, the total elemental analyses of the tested bacterial cells were carried out using Energy-Dispersive X-ray spectra (EDX).

Statistical Analysis

The statistical analysis of the results were implemented by applying the ONE WAY ANOVA (at P < 0.05), Duncan’s multiple ranges and the least significant difference summary (LSD) [43]. The results and data were examined and calculated by SPSS software version 15.

Results and Discussion

Synthesis of AgB NPs by PVP Polymer and Gamma Rays

Figure 1 and Table S1 reveal the common and effective gamma irradiation doses that accepted for AgB NPs synthesis. It was estimated by UV–Vis. spectroscopy and was reported to be at 20.0 kGy with the highest O.D. (0.7780; diluted 15 times) at the particular wavelength (420.0 nm).

Fig. 1
figure 1

UV–Vis. spectroscopy of AgB NPs synthesized by PVP polymer at different gamma irradiation doses

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After the optimization method, Table 1 established the synthesis of AgB NPs throughout the reduction of aqueous silver nitrate (2.0, 4.0, 6.0, 8.0, 10.0 and 12.0 mM) and boric acid (2.0, 4.0, 8.0, 12.0, 16.0 and 20.0 mM) solutions after stirring with 4.0% PVP solution and subjected to 20.0 kGy gamma rays through measuring the O.D. of all the tested samples.

The result recorded in Table 1 registered that run (5) was the choicest one applied for great yield (2.890; diluted 15 times) of AgB NPs (4.0 mM silver nitrate, and 16.0 mM boric acid) at 410 nm wavelength.

On the other hand, Fig. 2A illustrates the continuous O.D. developing with the first runs (runs 1–5) where the concentration of silver nitrate was fixed at 4.0 mM and the concentration of boric acid was varied from 2.0 to 16.0 mM and decreased in the run (6) when the boric acid concentration was at 20.0 mM. Additionally, Fig. 2B displays that there is constant increase in O.D with the second runs (runs 7–12) where the concentration of boric acid was fixed at 4.0 mM and the concentration of silver nitrate ranged from 2.0 to 12.0 mM.

Fig. 2
figure 2

UV–Vis. spectroscopy of AgB NPs optimization diluted 15 times where A at different boric acid concentration, and B at different silver nitrate concentrations as mentioned in Table 1

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It must be considered that both runs 11 and 12 are the same in O.D. but there are shifting in the wavelength in run 12 towards the high wavelength showing the large size in AgB NPs. So, we do not need to raise silver nitrate concentration to reach the greater yield (high O.D.).

Results in Table 1 and Fig. 2A and B shows that O.D. of AgB NPs increases the peak intensities with simultaneous shifts. This implies the synthesis of AgB NPs with small size and highest yield [44]. It is remarkably realized that AgB NPs solutions exhibit a deep brownish color because of the Surface Plasmon Resonance (SPR) [45, 46].

Proposed Reaction Mechanism of Gamma Rays and PVP-Assisted Nucleation and AgB NPs Construction

Kinetic studies of the reduction process described that AgB NPs synthesis starts after gamma radiation. This reduction is especially improved individually at 20.0 kGy, implying that radiation has a vital role in AgB NPs synthesis [5, 30].

Free radicals and electrons formed in water after gamma irradiation were e-aq, OH·, H·, H2O2 and H2 (Eq. 1). The benefit of gamma rays for AgB NPs synthesis was defined as a desired product of highly reducing power such as electrons were generated without the production of any useless byproducts [6, 36].

The overall reaction explains the use of possible electron as a reducing agent to Ag+ ions and PVP as a stabilizing polymer for AgB NPs growth. The effect began by the ionization of AgNO3 and boric acid to produce cations and anions such as Ag+, \({\text{B}}\left( {\text{OH}} \right)^{ - }_{4}\), H+ and NO3− (Eqs. 2 and 3) [5, 47].

Boric acid is known as a weak Lewis acid. The inadequate acidity was due to its ability to accept OH−. It dissolved and ionized in the liquid solution like water (Eq. 3) producing a balance concentration of the [B (OH)4]− anion [47, 48].

It must be noted that B(OH)3 and the base [B (OH)4]− that incorporated with it were the unique and significant boron kinds in a borate solution [47]. Additionally, B(OH)3 and [B (OH)4]− compressed borate classes to create complexes (at conc. more than 0.1 mol/l) and were named poly-borates [47]. The common major poly-borate kinds in aqueous solutions are the tri-borate mono-anion, [B3O3(OH)4]− [47, 49].

After that, the reduction of Ag+ may be produced by electron discharge from the hydrated electrons for Ag NPs production (probability; Eq. 4). Another probability can take place after the dissolved anion [B (OH)4]− was reacted with Ag+ to form the complex nanoparticles (Ag B(OH)4; Eq. 5) [50].

On the other hand OH· and H· radicals were able to remove hydrogen from the PVP creating a PVP radical (secondary radicals = \(({\text{C}}_{6} {\text{H}}_{8} {\text{NO}})_{\text{n}}^{ \cdot }\); Eq. 6). Following the reaction, PVP radical reacted with Ag+ to form stable and capped Ag NPs and constant PVP polymer (Eq. 7). Finally, the stable PVP can maintain Ag B(OH)4 or Ag NPs stable and react by the incorporation with them (Eq. 8).

$${\text{H}}_{2} {\text{O}}\mathop{\longrightarrow}\limits^{{\gamma {\text{-ray (Radiolysis)}}}}{\text{e}}^{ - }_{\text{aq}} + {\text{OH}}^{ \cdot } + {\text{H}}^{ \cdot } + {\text{H}}_{2} + {\text{H}}_{2} {\text{O}}_{2}$$
(1)
$${\text{AgNO}}_{3} + {\text{H}}_{2} {\text{O}}\mathop{\longrightarrow}\limits^{{{\text{Hydrolysis}} }}{\text{Ag}}^{ + } + {\text{NO}}_{3}^{ - }$$
(2)
$${\text{B}}\left( {\text{OH}} \right)_{3} + 2{\text{H}}_{2} {\text{O}}\mathop{\longrightarrow}\limits^{{{\text{Hydrolysis}} }}[{\text{B}}\left( {\text{OH}} \right)_{4} ]^{ - } + {\text{H}}_{3} {\text{O}}^{ + }$$
(3)
$${\text{Ag}}^{ + } + {\text{e}}^{ - }_{\text{aq}} \mathop{\longrightarrow}\limits^{{{\text{Reduction}} }}{\text{Ag}}^{ \cdot }$$
(4)
$$[{\text{B}}\left( {\text{OH}} \right)_{4} ]^{ - } + {\text{Ag}}^{ + } \to {\text{AgB}}\,({\text{OH}})_{4}$$
(5)
$$({\text{C}}_{6} {\text{H}}_{9} {\text{NO}})_{\text{n}} + {\text{OH}}^{ \cdot } \to ({\text{C}}_{6} {\text{H}}_{8} {\text{NO}})_{\text{n}}^{ \cdot } + {\text{H}}_{2} {\text{O}}$$
(6)
$$({\text{C}}_{6} {\text{H}}_{8} {\text{NO}})_{\text{n}}^{ \cdot } + {\text{Ag}}^{ + } + {\text{H}}_{2} {\text{O}}\mathop{\longrightarrow}\limits^{\text{Reduction}}\,{\text{Ag}}^{ \cdot } + ({\text{C}}_{6} {\text{H}}_{9} {\text{NO}})_{\text{n}} + {\text{H}}_{3} {\text{O}}^{ + }$$
(7)
$$({\text{C}}_{6} {\text{H}}_{9} {\text{NO}})_{\text{n}} + {\text{AgB}}\left( {\text{OH}} \right)_{4} \mathop{\longrightarrow}\limits^{{{{{\text{Stabilization}}\,{\text{ and}}\,{\text{ capping}}}} }}({\text{C}}_{6} {\text{H}}_{9} {\text{NO}})_{\text{n}} {\text{AgB}}\left( {\text{OH}} \right)_{4}$$
(8)

Characterization of AgB NPs

Scanning Electron Microscopy (SEM)

The uniform nano-composite appearance and the surface morphology of AgB NPs and PVP polymer are shown in Fig. 3A and B. It can be recognized that Ag and B NPs were dispersed regularly in the adjusted nanocomposite as displayed in Fig. 3A which presents as a bright particle. On the other hand, Fig. 3B describes the SEM image of PVP polymers that are utilized in AgB NPs assembly and stabilization which seems to be incorporated with the synthesized AgB NPs [51].

Fig. 3
figure 3

SEM images of the synthesized AgB NPs by PVP and gamma rays at 20.0 kGy where A the homogenous nanocomposite (Ag and B NPs) distribution, and B AgB NPs incorporated with PVP polymer

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Elemental Mapping Analysis and Energy Dispersive of X-ray (EDX) Spectroscopy

The elemental mapping models of AgB NPs are displayed in Fig. 4. The images are identified as Ag, B, N, O, and C for AgB NPs. From this figure, it is obvious that AgB NPs are similar in terms of the appearance of Ag and B atoms. Also, N, O, and C atoms were for PVP polymer.

Fig. 4
figure 4

SEM/EDX mapping images of the synthesized AgB NPs by PVP and gamma rays at 20.0 kGy

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EDX spectroscopy is an analytic method used for the elemental examination or chemical validations of the prepared samples [2, 3, 32, 39]. The EDX analysis show that the synthesized AgB NPs (Fig. 5) are stoichiometric and comparable with a regular arrangement.

Fig. 5
figure 5

EDX elemental analysis of the synthesized AgB NPs by PVP and gamma rays at 20.0 kGy

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The typical X-ray peaks of Ag, O, N, C and B atoms are visible in EDX of AgB NPs, additionally, O, N and C atoms are the main components of PVP polymer.

High Resolution Transmission Electron Microscopy (HRTEM), and Dynamic Light Scattering (DLS)

To check the common particle size and the appearance shape of the synthesized AgB NPs, TEM images were conducted, and its effects were compared with the DLS investigation [6, 52]. HRTEM image represented the diverse shapes of the synthesized AgB NPs such as hexagonal, pentagonal, oval and spherical in scale from 15.23 to 110.85 nm with the common average diameter about 85.25 nm as illustrated in Fig. 6A.

Fig. 6
figure 6

Size and shape determination of the synthesized AgB NPs by PVP and gamma rays at 20.0 kGy where A HRTEM image and B DLS analysis

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The average particle size distribution was defined by DLS technique and was determined as 25.46 nm in the AgB NPs synthesized by PVP and gamma radiation at 20.0 kGy as displayed in Fig. 6B.

Fourier Transform Infrared Analysis

Figure 7 explain the FTIR analysis of boric acid, silver nitrate, PVP, and AgB NPs. In the FTIR spectrum of boric acid, the broad band at 3193.53 cm−1 could be attributed to the O–H stretching which due to the moisture found at the boric acid surface.

Fig. 7
figure 7

FTIR spectrum analysis for A boric acid, B silver nitrate, C non-irradiated PVP and D the synthesized AgB NPs by PVP and gamma rays at 20.0 kGy

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The band at 1409.78 cm−1 was assigned to the stretching B–O while the band at 1187.50 cm−1 was corresponding to the stretching B–O–H as presented in Fig. 7A [53]. On the other hand, Fig. 7B demonstrated the FTIR analysis of silver nitrate and the peak at 1285.43 cm−1 was corresponding to the bond vibrations of [NO3]− anion in silver nitrate backbone [54].

FT-IR spectrum analysis and its assignments for PVP and AgB NPs which incorporated with PVP are exhibited in Table 2 which agreed with the literature reports [55,56,57,58,59,60,61,62,63]. FTIR spectrum (Fig. 7D) of AgB NPs incorporating PVP explained that there is a binding among PVP polymer and silver boron complex (AgB (OH)4; Eq. 8). PVP possesses C–N and C=O bonds (the functional groups) and these groups used for the attraction for silver ions and its complex [64]. It appears that the incorporation of PVP polymers into the metal colloidal complex (AgB (OH)4) depends on the size and the intensity of the colloidal NPs [54].

Table 2 FT-IR spectrum of non-irradiated PVP and AgB NPs synthesized by PVP and gamma rays at 20.0 kGy, and its corresponding assignment with literature references
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The C=O peak (at 1648.60 cm−1) in pure PVP (Fig. 7C) was changed to 1640.72 cm−1 including a small broadening in the AgB NPs/PVP composite. This shift was compatible among those described by Zhang et al. [65]. The reduction in the wave numbers for C=O peak may occur from link weakening and because of the reverse bonding by the incomplete contribution of the lone pair of electrons found in the oxygen of PVP to AgB nano-complex and recommended the incorporation of AgB nano-composite with PVP C=O functional group [65].

Our proposed reaction mechanism for AgB NPs incorporation with PVP was illustrated in Fig. 8A and B. It is necessary to mention that, the peak at 1492.05 cm−1 was matching to the C=N vibration (founded in the pyridine ring), and the drop in the wave number in AgB NPs/PVP FTIR spectrum (1423.38 cm−1), also, the presence of N–H (1540.0 cm−1) may occur from the ring break due to the entire oxidation of PVP by gamma rays as displayed in Fig. 8B [66] which may be corresponding to the continuous reduction of silver ions to form silver boron nano complex (Eqs. 4 and 5; Fig. 8A).

Fig. 8
figure 8

The proposed mechanism for AgB NPs synthesized where A formation of silver boron nano-complex incorporated with C=O group of PVP polymer B ring opening of PVP (formation of N–H bond) due to oxidation after gamma irradiation at 20.0 kGy that suggested the continuous reduction to form silver boron nano-complex

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X-ray Diffraction Analysis

XRD performs a true summary of the crystal structure and the combination of the recognized NPs because it gives crystal size and the state of the examined atoms [2, 39]. XRD designs were presented in Fig. 9A–D.

Fig. 9
figure 9

XRD analysis for A boric acid, B silver nitrate, C non-irradiated PVP and D the synthesized AgB NPs by PVP and gamma rays at 20.0 kGy

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Figure 9D displayed the XRD for the synthesized AgB NPs which do not possessed any peaks refers to the starting materials (boric acid and silver nitrate; Fig. 9A and B) except for PVP (Fig. 9C) that involved in the assembly and incorporation. The comparison of XRD for each element symbolizes the development of nano-complex in accordance with the results of FTIR investigation.

Figure 9A presents XRD diffraction properties of boric acid including 2θ degree like 14.67°, 28.00°, 40.24°, and 56.32° (ICDD card no. 30-0620) [67]. Also, Fig. 9B shows XRD diffractions of silver nitrate such as 21.88°, 35.75°, 49.31°, and 67.83° [67]. Additionally, Fig. 9C for XRD result of PVP polymer displayed two identical peaks about 12.28° and 21.74°, which are related to the amorphous type of PVP polymer [68].

XRD for the synthesized AgB NPs (Fig. 9D) exhibits the behavior diffraction features with 2θ like 38.09°, 44.61°, 64.36°, 77.00°, and 81.59° where those peaks represent the Bragg’s reflections (111), (200), (220), (311) and (422) respectively (JCPDS card no. 04-0783) [3, 5, 6, 27, 29, 38]. This means that the synthesized AgB NPs were crystalline nano-composite. It must be remarked that there is a small shifting in 2θ states which may be due to the development of the silver boron nano-composite [2, 39].

Finally, there are two amorphous peaks at 11.70° and 20.26° for the PVP polymers (Fig. 9C) that were included in the synthesis and stability of AgB nano-composite but they have intensity less than that present in pure PVP and the data was corresponding to the FTIR spectrum (Fig. 8C and D). The absence of peaks at 31.30°, 32.62°, and 33.68° indicates that, the synthesized AgB NPs are pure and free of AgO NPs [69].

Antimicrobial Activity of AgB NPs

It was tested using a disc agar diffusion method where AgB NPs showed an antibacterial activity against most of the tested microbes-causing UTI following 24.0 h of incubation. The test results revealed that AgB NPs displayed the greatest action against E. coli (18.0 mm ZOI) and S. aureus (16.0 mm ZOI), as listed in Table 3.

Table 3 Antibacterial and antifungal activities of AgB NPs, Ag NPs, boric acid, PVP and silver nitrate, against some MDR bacteria and unicellular fungi-causing UTI as ZOI (mm) and MIC for AgB NPs (μg/ml)
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Additionally, the synthesized AgB NPs were encouraging antifungal agent with great potency against C. albicans (20.0 mm ZOI; Table 3).

The tested Ag NPs that synthesized and published in our earlier research [3], had limited effect compared to the synthesized AgB NPs after adjusting the concentration of all the same (about 25.0 μg/ml), these describe the purpose of boron in the synthesized AgB nano-complex. All the precursors used for AgB NPs (boric acid, silver nitrate, and PVP) were examined towards the tested microbes-causing UTI. The results indicated that, the microorganisms showed resistance against all tested precursors and produced a weak activity against E. coli and S. aureus.

The 3D ZOI images containing AgB NPs discs (Fig. 10A–C) describes the division ability of the tested AgB NPs. The dark appearance represented the bulk of the examined bacteria and yeast, while the faint background evaluated the bactericidal and fungicidal impact of AgB NPs upon the pathogen.

Fig. 10
figure 10

Antimicrobial activity of the synthesized AgB NPs by PVP and gamma rays at 20.0 kGy against AEscherichia coli, BStaphylococcus aureus and CCandida albicans as ZOI

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The antimicrobial potency of the synthesized AgB NPs was compared with silver nitrate, PVP, boric acid, Ag NPs and standard antimicrobial agents (AMC and NS), and was determined to be the greatest. On the other hand, the synthesized AgB NPs were effective against Gram-negative bacteria more than Gram-positive one. Gram-negative cell wall consists primarily of lipopolysaccharide and peptidoglycan light layers, while Gram-positive includes a just full peptidoglycan building layer [70].

The benefits of inorganic NPs were their large surface-to-volume proportion, an encourage physical characters, and nano-scale spectrum, that exhibits prominently a great potential to connect with the living organisms like yeast and bacteria [5, 35, 36]. This is the vital difference between inorganic nano-composites and the natural and artificial antimicrobial factors that may reduce the chance of producing the antimicrobial defense [28, 30].

The MIC determinations of the synthesized AgB NPs towards all examined microbes were in the range of 31.25–1.95 μg/ml. AgB NPs have confirmed the MIC result of 3.90 μg/ml against E. coli, and 7.81 μg/ml toward S. aureus. Finally, AgB NPs have proved the encouraging MIC result of 1.95 μg/ml against C. albicans.

AgB NPs size is not the only parameter measuring the antimicrobial features, further important points like the elemental composition (the purity), and AgB NPs shape need to be brought into attention [71].

Similar reports have explained the importance of Ag NPs as an antibacterial factor against different pathogenic bacteria. Manash Das et al., [72] synthesized Ag NPs by aqueous suspension of graphene oxide sheets and studied the antimicrobial activity. The result indicated that, by elevating the concentration of Ag NPs the growth delay of P. aeruginosa and E. coli was increased, which symbolizes that Ag NPs conc. is a choice parameter used to determine the efficacy of its as antibacterial agents.

Additionally, Amr Saeb et al., [73], produced biogenic Ag NPs from several soil isolates and investigated the antimicrobial activity against highly pathogenic and MDR bacteria. The synthesized Ag NPs were active against four of the tested pathogens, namely, K. pneumonia, S. epidermidis, S. aureus, and E. coli.

Finally, Juhi et al. [74], synthesized Ag NPs (about 75.0 ppm) by green methods for studying its activity against E. coli producing action by 15.0 mm ZOI, and for S. aureus about 14.0 mm ZOI. Further, Ag+ ions were active upon E. coli as 11.0 mm ZOI and S. aureus as 12.0 mm ZOI.

The proposed reaction mechanism of Ag NPs towards pathogenic bacteria was described in our previous studies [5]. They have included four mechanisms that qualified for the action of Ag NPs on the microbial pathogens. It starts by the adhesion of Ag NPs across the surface of the bacterial cell wall. After that, it deals with the understanding of Ag NPs inside the bacterial cell and cleavage of the intracellular organization like biological molecules (DNA and mitochondria). Then the cellular toxicity (oxidative stress) produced by the generation of Reactive Oxygen Species (ROS) occurs. Finally, Ag NPs were affects the signal transduction pathways.

On the other hand, there are various related articles [48,49,50, 75], regarding the antimicrobial activity of boron doped with different material to form boron nano-complex. The antimicrobial activity was determined against diverse pathogenic bacteria and fungi.

Antibiofilm Potential of AgB NPs

Biofilm production is recognized in different pathogenic microbes forming exopolysaccharides [42]. Biofilm maturation through E. coli, S. aureus, and C. albicans (the common sensitive bacteria-causing UTI and yeast-producing UTI giving significant antimicrobial results) were tested by inoculating into the nutrient broth medium with and without AgB NPs using tube technique.

E. coli bacteria injected in the tubes, without AgB NPs, produced a thick whitish yellow matt in the air–liquid space. It was fully adhered throughout the tube walls and presented as deep blue color as adhered bacterial cells. After dissolving the Crystal Violet by the ethanol; a dark blue solution was obtained and used for further semi quantitative estimation (Fig. 11A).

Fig. 11
figure 11

Antibiofilm activity of the synthesized AgB NPs by PVP and gamma rays at 20.0 kGy using tube method against AEscherichia coli, BStaphylococcus aureus and CCandida albicans

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Additionally, the treated tube which included with E. coli and 25.0 µg/ml AgB NPs exhibited a negative result, regarding both growth and ring formation, compared to the control (E. coli only) which was reflected on a lighter blue color after the addition of ethanol as shown in Fig. 11A. The same situations were shown in both Fig. 11B and C for the biofilm of S. aureus, and C. albicans, respectively.

To determine the repression percentage (%) of the examined bacterial and yeast biofilm, UV–Vis. spectrophotometer was adjusted at 570.0 nm. The O.D. was assessed following separating the stained bacterial and yeast biofilm by the ethanol as a potential of their generation. Table 4, presented the inhibition % of the biofilm formation. The highest repression was recorded as 87.00% for S. aureus which managed by 25 µg/ml AgB NPs, E. coli by 85.30% and C. albicans as 79.40%.

Table 4 Semi-quantitative inhibition % evaluation of the biofilm formation for untreated and treated bacterial and yeast pathogen with AgB NPs
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Biofilm inhibition is an area of fast investigation and the components involved in biofilm construction was identified as viable targets to the treatment [42]. Insufficient information is known about the inhibitors of biofilm-creating pathogens. Wood (2009) [76], noted that many non-toxic antibiofilm factors were integrated for E. coli repressions such as ursolic acid, 5-fluorouracil, and indole substances.

The resistance mechanism regarding the bacterial biofilms was still not defined but a perhaps important determinant is the creation of the glycocalyx (also known as the pericellular matrix, involves glycoprotein and glycolipid) which promotes the bacterial cell formation inside the bacterial biofilm to decrease the patient resistance and the effect of the antibacterial agents [77].

Antibacterial agents were used to reduce the bacterial biofilm through the penetration into the polysaccharide layers and subsequent to facilitate the inhibition of the bacterial cells. Nanotechnology may present antibiofilms composites which lowering a biofilm synthesis by the purpose of bio-nanotechnology surface methods [78].

The tested pathogenic bacteria developed without AgB NPs, showed a thick yellowish matt, meaning generation of exopolysaccharides, which was essential for the development of biofilm (Fig. 11A, B, and C). Whereas, after the bacteria was inserted with AgB NPs, it must be inhibited. Thus, when the exopolysaccharide synthesis is halted, bacteria cannot produce the biofilm. Similar conclusions were additionally defined by Kalishwaralal et al. (2010), [79] against P. aeruginosa and S. epidermidis biofilms and concluded that 100 nM of the synthesized Ag NPs provided 96–99% regarding biofilm restraint.

It must be mentioned that we consider the action mechanism of AgB NPs upon biofilm-producer S. aureus using SEM and EDX examinations. SEM images showed the bacterial cell appearance after the treatment with 25 µg/ml AgB NPs. S. aureus cells developed without AgB NPs, illustrated the familiar cellular shape including proper cell surfaces and the biofilm was exhibited. on the other hand, EDX elemental study of untreated S. aureus showed the common elements organized inside the bacterial cell like Na, K, Al, P, Cl, S, O, N, and C [80], as presented in Fig. 12A.

Fig. 12
figure 12

SEM images, and the corresponding EDX elemental analysis of Staphylococcus aureus where, A Normal bacterial cell without AgB NPs treatment and B The depressed, and deformed bacterial cell under the influence of AgB NPs incorporated with PVP polymer

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Additionally, S. aureus was shown a morphological modification after AgB NPs (25 µg/ml) treatment (Fig. 12B). Noticeable changes in the severity of the bacterial cell surface and the malformation in the bacterial cells indicated that it was reduced in the size and their appearances were changed following AgB NPs addition. Moreover, they showed a considerable decrease in the viable count and the biofilm was not identified which proposed the effect of AgB NPs as an antibiofilm factor. SEM examinations clearly showed that AgB NPs decreased and influenced the surface characteristics of S. aureus and there are a layer was formed around the bacterial cells due to the formation of AgB NPs-PVP nano-layer (Fig. 12B).

EDX elemental study of the treated S. aureus exhibited the appearance of Ag, B, C and N confirming the action of AgB NPs manufactured by PVP and gamma rays against the bacterial cell.

Some findings can be received from the SEM images regarding the reaction mechanism in our research. It may be due to the positively charged AgB NPs which can simply connect electro-statically with the negative charge founded in the cell wall of the tested S. aureus and damage it [81], as exhibited in Fig. 12B.

The present results are excellent conclusions which matched the earlier study regarding antibiofilm activity of Ag NPs [82]. They realized that Ag NPs strongly decreased the bacterial cell count in the studied biofilms (number of bacteria capable of forming biofilm and/or the ability to form biofilm). The external surface of E. coli was reduced by the prepared Ag NPs by 25.0% after the first day of treatment.

Conclusion

This study advances the alternative eco-friendly method for AgB NPs construction utilizing PVP polymer under the influence of gamma rays. The complete validation procedure studies the shape, crystallinity, distribution and the size of the incorporated AgB NPs, which established to be anisotropic with a common size of 85.25 nm. A proposed reaction mechanism explains the possible and continuous reduction of ions due to the oxidation of PVP caused by 20.0 kGy gamma rays. PVP ring opening which corresponds to its oxidation was identified and confirmed by FTIR analysis. Antimicrobial activity was investigated as ZOI and MIC against MDR microbes-causing UTI. AgB NPs (at low conc.; 1.95 μg/ml) inhibited the growth of C. albicans. The antibiofilm potential of the synthesized AgB NPs was examined and produces 87.0% inhibition towards S. aureus. The synthesized AgB NPs were a promising agent for the applications in industrial, pharmaceutical and medical fields, and cosmetics.