1 Introduction

Recently, nanotechnology has evolved as a promptly emerging field along with plentiful biomedical applications. Nanoparticles are established with exclusive characteristics that create them desired in biology and materials science [1,2,3,4]. Amongst numerous nanoparticles, AgNPs (silver nanoparticles) are most common for investigating in current decades. The ability to fabricate AgNPs with accurate control of their size, composition, and shape at nanoscale has opened up numerous possibilities for application across various fields [5]. From electronics and optics to catalysis and medicine, nanomaterial’s play a pivotal role in advancing technological innovations [6, 7]. They possess unique properties like nanosize as well as large ratio of surface area to volume that increases nanoparticles efficiency towards biomedical applications. Most importantly they exhibit noteworthy wide range of, antifungal, antibacterial and antiviral characteristics at even low concentration and free of adverse effects [8]. They have ability of penetrating into cell walls of microbes, altering cell membranes structure and resulting even in death of cells [9]. Additionally, they are economical with low cytotoxicity as well as immunological reaction. Hence, AgNPs have manifold potential biomedicinal applications. They are widely explored for drug delivery, medical imaging, and molecular diagnostics. Furthermore, they are employed in therapeutics, for instance assembly regarding replacement of artificial joints, surgical mesh, dressing for wounds, in addition to curative for healing of wounds [10, 11].

Currently, unconventional antimicrobial agents for overpowering MDR (multidrug resistance) are progressively attaining implication. In recent times, advancement of innovative and effective nano-based antimicrobial mediators resisting MDR bacteria is among important research areas in biomedicine [12, 13]. The most precarious chemical and physical constraints that influence antimicrobial properties of AgNPs comprise dimensions, morphology, concentration, surface charge, and colloidal state [14]. Furthermore, benefit of employing nanosilver is moderately less sensitive as compared to silver ions, and consequently, they are well-suited for therapeutic and clinical applications [15]. Because of their strong anti-inflammation and antibacterial influence, They are exploited in different biological, pharmaceutical, and physical fields, such as, ointment/cream having AgNPs for wounds and burns for inhibition of microbial infection [16, 17].

Antimicrobial action regarding AgNP is not totally comprehended; on the other hand there are some assumptions that explain antimicrobial activity. AgNPs have capability to penetrate cell or get attached to cell wall due to large surface area that results in disruption in permeability of membrane creating it porous, and ultimately it leads to more cell content leak [18]. Pores formation over membrane results in diffusion of nanoparticle in cell and get bonded to phosphorus and sulphur-enclosing proteins, that results in DNA and proteins deactivation [19]. Alternative hypothesis proposes that releasing of of silver (Ag +) via oxidation dissolution procedure is reason of antimicrobial activity of AgNPs. Oxidized Ag ions from AgNPs primarily integrate with proteins and enzymes bonded to their thiol groups, thus interfere with chain of respiratory system and distressing bacterial cell wall [20]. Ag ions also assist ROS (reactive oxygen species) generation being deliberated as foremost reason of death of cells by deactivation of DNA replication and production of ATP [21].

In this review, an inclusive overview regarding antimicrobial activity regarding AgNPs has been elaborated. Additionally several techniques to synthesize AgNPs are also mentioned herein. Numerous mechanisms that contribute to antimicrobial action of AgNPs have also been described. Furthermore some valuable uses relevant to antimicrobial characteristics have also been discussed.

2 Synthesis of silver nanoparticles

The progress and enhancement of methods to prepare nanomaterials have emerged as a rapidly growing and multidisciplinary area of research. Fabrication of AgNPs includes two primary approaches: bottom-up and top-down. These methodologies could be further categorized in three groups: chemical, physical, and biological. Among these, biological synthesis proposes several benefits over chemical and physical approaches, including high yield, improved solubility, and enhanced stability [22, 23]. Different methods for synthesis of AgNPs are given below and summarized in Table 1.

Table 1 Different methods to synthesize AgNPs with their pros and cons
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2.1 Physical methods

One important physical approach aimed at to prepare AgNPs is evaporation–condensation. This method involves the evaporation of a silver-containing material followed by the condensation of the vapor to form nanoparticles. By controlling the conditions of evaporation and condensation, nanoparticles with diameters ranging from ten to several hundred nanometers can be obtained. Another physical method for synthesizing silver nanoparticles is laser ablation. This technique involves the use of a laser to irradiate a silver target, leading to the ejection and subsequent condensation of silver atoms or clusters into nanoparticles [40, 41]. Microwave assisted preparation is another capable technique to synthesize AgNPs. Compared to conventional oil bath heating, microwave heating offers several advantages in producing nanostructures. It results in smaller particle with narrow distributions, in addition to higher crystallization degree. Additionally, heating using microwaves leads to short time of reaction with less consumption of energy and particle agglomeration [42, 43]. Various irradiation methods can be employed to synthesize AgNPs. Irradiation of silver salt with surfactant by laser results well-defined shaped and sized AgNPs. Lower laser powers and shorter irradiation times yield approximately 20 nm NPs, whereas higher powers generate nanoparticles of around five nm. Both lasers as well as mercury lamps could serve as source of light sources to produce AgNPs [40]. Ion implantation is another highly effective and extensively employed technique for creating nanoparticles within a matrix. It finds wide applications in various fields such as semiconductor device manufacturing, metal surface treatment, and materials science research. The process involves the introduction of ionized atoms propelled with sufficient energy into a target sample. These ions penetrate only the surface regions of the sample, resulting in desirable modifications and nanoparticle formation [44].

2.2 Chemical methods

Chemical reduction method comprises inorganic and organic reducing agents for converting silver ions (Ag+) into metallic silver (Ag0) through oxidation–reduction reactions [45]. Various reducing agents for instance ascorbate, sodium citrate, sodium borohydride, Tollens reagent, hydrogen, poly(ethylene glycol)-block copolymers, N, N-dimethylformamide could be employed in aqueous or non-aqueous form of solutions [46]. Reducing agents facilitate silver ions reduction and promote development of particles of metallic silver, which subsequently aggregate to form colloidal silver. Natural compounds like sodium citrate and sugars can also act as mild, inexpensive, and non-toxic reducing agents, although they often require higher temperatures and longer reaction times. In some cases, such compounds might act as both reducing as well as protective agents [47, 48]. A challenge associated with the chemical reduction method is the tendency of nanoparticles to aggregate during synthesis or storage, which can lead to the loss of their characteristic properties [46, 49]. Microemulsion technique is another method that involves the separation of reducing agents and metal precursor in 2 immiscible phases, typically an organic and aqueous phase. Interaction rate between these reactants is influenced through interface between two liquids and inter-phase transport assisted via salts of quaternary alkyl-ammonium [50]. Tollens technique is single-step process used to prepare AgNPs with controlled size. The method involves the Ag(NH3)2+ reduction (Tollens reagent) using aldehyde. By modifying this process, there is a reduction of silver by saccharides in ammonia presence, leading to silver hydrosols (20–50 nm), AgNPs films (50–200 nm), and AgNPs with various morphologies. Ammonia concentration and reducing agent are crucial in controlling shape and dimensions of AgNPs.

2.3 Biological methods

Conventional methods involve the use of Ag precursors, reducing agents, and stabilizing agents. However, biological methods utilize microorganisms like algae, yeast, fungi, and bacteria as replacements for conventional agents [51]. Biological techniques offer advantages such as cost-effectiveness, reproducibility, and lower energy consumption [52, 53]. The anaerobic bacterium Shewanella oneidensis has been successfully employed for AgNPs biosynthesis using AgNO3 (silver nitrate) as precursor. The resulting nanoparticles had a uniform size of less than fifteen nm, are spherical in shape, and displayed improved stability [54]. Similarly, the white mold fungus Chrysosporium Phanerochaete and the filamentous cyanobacterium Plectonema boryanum UTEX 485 have demonstrated the ability to synthesize silver nanoparticles through protein involvement. Marine algae such as Chlorella salina, Chaetoceros calcitrans, Tetraselmis gracilis, Isochrysis galbana also contribute to silver ions reduction with subsequent AgNPs synthesis. Using plants to prepare nanoparticles is another economical and valuable substitute to produce nanoparticles at large-scale [55, 56]. Further studies on the synthesis of AgNPs with pure bio-organics could provide a good understanding of the underlying mechanisms. Glutathione, a reducing/capping agent, has been found effective in synthesizing size-modifiable silver nanoparticles that are soluble in water readily attached to model proteins such as BSA (bovine serum albumin) [57].

Synthesis of AgNPs using green strategy is a bottom-up approach in which nanoparticles are prepared via reduction/oxidation procedure of metallic ions by organic moieties extracted from biological resources. Green synthesis of AgNPs can be explained by chemical mechanism as shown in Fig. 1. The first step during synthesis involves oxidation of biomolecules that results in release of electrons. These electrons lead of Ag+ to Ag0. After reduction, Ag0 undertakes sequence of agglomeration termed as nucleation (I) and (II) to form a nanoparticle. Nucleation of silver zero atoms results in formation of nanoparticles i.e. AgNPs as shown in Fig. 1 [58]. The biological synthesis is summarized in Table 2 by mentioning the synthesis of AgNPs using the "green route," that includes various biological methods and their outcomes for synthesis.

Fig.1
figure 1

Mechanism of green synthesis of silver nanoparticles

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Table 2 Biological synthesis of silver nanoparticles using different biological species like algae, fungi, bacteria, plants, and also biopolymers along with their characteristics
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3 Antimicrobial mechanism of silver nanoparticles

Traditionally, all kinds of silver are employed as antimicrobial agent itself and also in combined form along additional technologies [81]. They take an advantage of having capability of inhibition of growth of bacteria through incorporation of it as silver sulfadiazine or silver nitrate for dressings and creams for treating ulcers and burns, for food packaging for preventing contamination, in home utilizations such as washing machines and refrigerators, in addition to numerous industrial applications [82]. AgNPs are executed as outstanding antimicrobic agent with capability of combating bacteria that causes in vitro as well as in vivo contagions. Their antimicrobial ability shields bacteria (Gram-positive and Gram-negative) comprising MDR strains. They display simultaneous and multiple action mechanisms through in corporation with other antibacterial agents for instance antibiotics or organic compounds against pathogens bacteria [83]. Though, the particular mechanism through which AgNPs inhibits bactericidal growth or activity is not been clarified fully yet. The current investigational results supports various mechanisms against different types of bacteria (Table 3), which take into account their chemical and physical features for instance dimensions and exterior that permits their interaction or passing across cell membranes and walls with disturbance of intracellular components [84]. Presently, literature proposes mainly four mechanisms (Fig. 2) that are observed separately or together, through which AgNPs execute their antimicrobial activity.

Table 3 Antimicrobial mechanism of AgNPs against various types of bacteria
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Fig. 2
figure 2

Illustration of different antimicrobial mechanism of AgNPs (silver nanoparticles). 1-AgNPs adhesion to cell membrane, 2- AgNPs penetration into microbial cells, 3- Increase in ROS in microbial cells due to AgNPs, and 4, Modulation of cellular signal system because of AgNPs

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Biofilm are bacterial cells bonded to non-living or living surfaces and surrounded by hydrated extracellular polymeric matrix. These films are more resistant to conventional antimicrobial agents because (a) inability of antimicrobial to penetrate biofilm, (b) growth complex drug resistance features, and (c) biofilm facilitated modification or inactivation of antimicrobial enzymes [85]. AgNPs are widely used to combat biofilms due to their antibiofilm activities [86]. AgNPs displayed antimicrobial activity via disruption of cell membrane integrity of bacteria resulting in outflow of cellular content and ultimately death. Moreover, they produce ROS (reactive oxygen species) that interact with cellular constituents such as lipids, DNA, and proteins, initiating malfunctioning of bacteria and ultimately its death [84]. These nanoparticles employ their antibiofilm activity through prevention of adhesion of bacteria to surfaces or through destructing intermolecular forces [87]. They also inhibit quorum sensing [88]. AgNPs have ability to inhibit formation of biofilm and also its degradation for therapy treatments that signify a new way to efficiently treat different infectious diseases due to pathogenic microbes [89]. Their small dimensions fit into ideal range for biofilm-infection control that favour biofilm penetration [90]. Biofilms converse protection from hostile environment and could be reservoirs for pathogenic microorganisms and causes of disease epidemics, particularly in medical devices. AgNPs efficiently preclude biofilms formation and kill bacteria in developed biofilms that proposes that AgNPs can be utilized to prevent and treat biofilm-related infections [91]. Thus potential of utilizing AgNPs with enhanced bioactivity offers a promising and active alternative to traditional antimicrobial agents associated with health concerns.

3.1 Adhesion to microbial membrane

AgNPs have ability to adhere or stick to the cell wall or cell membrane causes destabilization and damage of cells, enhancing of membrane permeability, in addition to prompting leak of cellular constituent and successively cell death [92]. This adherence is because of electrostatic attraction of positive silver ions which are generated through AgNPs oxidation and negatively charged cell membrane [93]. It has been demonstrated that AgNPs could also interact with proteins containing sulphur inside bacterial cell wall. This interaction resulted in structural destruction resulting in rupture of cell wall [94]. Adhesion of AgNPs leads to irreparable morphological variations in cell membrane in addition to integrity loss of lipid bilayer. Changes in structure of cell due to AgNPs adhesion increases cell membrane permeability that in return influences the ability of cells to regulate their activity regularly. Increase in permeability also caused leak of cellular components like proteins, cytoplasm, ions, ATP, and cellular energy reservoir that could persuade ghost cell impact regarding microorganisms. This impact inside bacteria takes place on removal of microbial or cell contents that creates a hollow envelope of microorganisms [95].

3.2 Penetration into cell and disruption of cellular activity

AgNPs have ability to disrupts intercellular biomolecules and penetrate cells ultimately affecting activity of cells. They could enter into bacterial cells via water-filled channel known as porins and start binding with structures and biomolecules (DNA, protiens, and lipids) of cells, consequently destroying inner structure of bacteria. Released Ag ions into environment get bounded with negative protein that changes protein configuration leading to its deactivation [96]. Furthermore, AgNPs also interact with bacterial DNA of bacteria causing its denaturation as well as interrupt growth of microbes. AgNPs reduces DNA stability in regard to electrostatic repellence between DNA and AgNPs [97].

3.3 Generation of reactive oxygen species (ROS)

This mechanism normally causes oxidation stress inside microbe cells. These oxygenated complexes are tangled in different biological cellular events for instance hydrogen superoxide, peroxide, in addition to hydroxyl radicals [98]. AgNPs produces free radicals and ROS that ultimately enhances oxidative stress inside cells, which contributes to antimicrobial activity. Intercellular ROS generation is an imperative indicator regarding toxicity of nanoparticles that persuade damage of lipid, leak of biomolecules of cells, and finally cell death [99].

3.4 Modulation of cellular signalling system

Relay signal mechanism is essential for cellular growth and activity and has been characterized in microbes via dephosphorylation cascade and phosphorylation cycle [100]. AgNPs control signalling pathway that depends on dephosphorylation and phosphorylation cascade of enzymes or protein. AgNPs perform as modulators of transduction of signals in cells of microbes due to their extraordinary physicochemical features, thus inhibiting microbial growth [101].

4 Applications employing antimicrobial properties of silver nanoparticles

Materials based on AgNPs showed unique, demanding, as well as promising characteristics suitable for variety of life science applications. Recently they have emerged as one of the most investigated and studied nanostructures, and they are useful in diverse industries, such as biomedicines, foods, textiles, and electronic usages [105]. The improved antimicrobic activity regarding AgNPs has been valuable for healthcare and medical areas. Their integration in different products is examined, comprising food and surgical handling tools, cosmetics, clothing, catheters, dental products, and dressings [106]. Additionally, they are also applied as antimicrobic agents to disinfect to treat water [107]. Some applications have been described below exploring antimicrobial characteristic of AgNPs.

4.1 Biomedical and healthcare

Because of their unusual oxidative effect, Ag ions are recognized as antimicrobic agent and investigated for therapeutic purposes aimed at biomedical usages. Controlled dimensions along with improved stability and dispersion are main parameters concerning AgNPs designed for diagnostic and therapeutic applications [108]. They are familiar for their potential antimicrobic activity towards different bacterial strains comprising pathogenic bacterial species (gram negative as well as gram positive) [109].

They exhibited good substantivity and antimicrobial properties for inhibition of growth of bacteria of different oral biofilms separated from focuses with vigorous periodontal disease and dental caries. Primary factors related to their best efficiency of substantivity and antimicrobial activities were found in small nanoparticles (~ 10.2 nm) statistically, for short periods (1–24 h) in addition to, gender (male patients) in some cases. Consequently, solution of chlorhexidine (gold standard agent) possessed best substantivity as well as antimicrobial features. The substantivity and antimicrobial levels regarding AgNPs with two sizes towards biofilms took directly from young-adult and young patients with diseases of active periodontal and active caries were determined. This study proposed AgNPs employment as prospective antimicrobic agent in stomatology and other biomedical areas to control and prevent periodontal disease and dental caries [110]. In one of research works, AgNPs were synthesized with chitosan shell (Ch-AgNPs). Ch-AgNPs were crystalline, uniformly dispersed, and spherical, having mean diameter of 21 nm. In-vitro activity of anti-biofilms prepared from nanoparticles had been tested against pathogenic bacteria for instance Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative) that caused infection of wounds. These nanoparticles showed anti-biofilm activity, depending on dose. Confocal-laser and light scanning microscopy established noteworthy inhibition biofilms growth regarding P. aeruginosa (95%) as well as S. aureus (85%) at nanoparticle concentration of 100 μg/mL. Furthermore, Ch-AgNPs stimulated healing of wound through increasing murine macrophages (RAW 264.7) migration of cells at 75 μg/mL and 100 μg/mL after twenty-four hours. Additionally, in-vitro toxicity of developed nanoparticles towards human breast (MCF 7) cancerous cells, showed great inhibition of cell proliferation (64%) at 100 μg /mL [111].

A different type of chitosan (CS) sponge loaded with catechol-conjugated chitosan coated AgNPs (CCS-AgNPs) was established for sustained release aimed at long-term antimicrobial dressing. CCS-AgNPs were experiential to be un-aggregated and well-dispersed in compound sponges. The compound sponges showed exceptional flexibility and capability to absorb water because of interrelated multi-porous assembly that is valuable for removal of additional exudates efficiently. CCS-AgNPs/CS presented continuous release as shown by silver release tests, while control group with no catechol displayed spurt release. Hence, catechol prolonged release time of silver from one day to four days at least. This sustained release of silver provides sponges having long-term bacteriostatic influence towards bacteria (Gram negative and gram positive). Bacterial growth had been inhibited entirely for three days. Disk diffusion test further confirmed sustained release of silver. Figure 3a and b showed results of this diffusion test concerning E. coli and S. aureus, correspondingly. Inhibition zone relies upon constituent release related to antimicrobic activity. In case of CS pure sponge, there is no release from water-insoluble sponge that confirmed no inhibition zone. Solution of CCS-AgNPs (Ag-2) having similar silver amount was utilized as a control for relating with CS-Ag-2 sponge. There is more silver release for bigger inhibition zone. The zones of inhibition around CS-Ag-2 sponge have been small in comparison to solution of CCS-AgNPs, representing that only part of silver is released from CS-Ag-2 sponge during test conducted for twenty-four hours. In the meantime, CCS-AgNPs pointedly enhanced bactericidal influence. Above 99.99% of bacteria were destroyed by this sponge that meets completely antibacterial necessities for healing of wound. However, an excess of silver component persuaded cytotoxicity inside MC3T3 cells. Generally, silver content of about 0.63 in sponge is appropriate and considered as prospective candidate for dressings used for wound healing because of lasting bacteriostatic influence, dominant bactericidal activity, besides outstanding biocompatibility [112].

Fig. 3
figure 3

Adopted from Ref. [112]

Schematic representation of sponges of CCS-AgNPs/CS. Zone of inhibition regarding CS sponge, CS-Ag-2 sponge and Ag-2 solution against a E. coli and b S. aureus.

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Antimicrobial coatings comprising of PVA (polyvinyl alcohol) coated AgNPs rooted in matrix of (CS) chitosan were developed. Homogenous nanocomposite biocoatings with dissimilar PVA-coated AgNPs contents were deposited on substrates of titanium via “spread casting” followed by solvent evaporation. Test for nano-indentation in addition to antimicrobial activity were performed on bionanocomposites and CS exposed PVA-coated AgNPs integration increased overall functional characteristics of coatings, for estimating mechanical constancy and microbial activity towards Staphylococcus aureus and Escherichia coli. Samples with coatings preserved their antimicrobial activity for eight hours because of sustained and slow silver ions release. The general benefits of these coatings increase with increase of PVA-coated AgNPs contents of in bionanocomposites [113]. An antibacterial complex coating was fabricated by uniting PDA (polydopamine), CS (chitosan) along with AgNPs on to urinary catheters and surfaces of Ti (titanium). Fabrication involves CS and PDA co-deposition within solution of acid and subsequent immersion in solution of silver nitrate (AgNO3). This method permits antibacterial coating of PDA/CS/AgNPs by easy immersion procedure in friendly settings. CS plays a vital role to improve and smooth coatings showed by morphology (Fig. 4). Antibacterial tests against S. aureus had been carried out on inhibition halo measurements as well as adhered numbers of bacteria. The outcomes displayed that catheter with coatings of PDA/CS/AgNPs possess lasting firmness above thirty days in addition to antibacterial activity towards S. aureus. Anti-adhesion rate of Ti surface coated with PDA/CS/AgNPs are 85% and 91% for dead and live bacteria, correspondingly. Thus this coating has pronounced potential in real-world application to be used in antibacterial urinary catheters besides additional biomedicinal devices [114].

Fig. 4
figure 4

Adopted from Ref. [114]

Representation of fabrication of antibacterial complex coating by co-deposition of PDA (polydopamine), CS (chitosan) and AgNPs on uncoated surfaces. The microscopy (SEM) results showed the bacterial adhesion before and after coating.

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4.2 Textile

Antimicrobial nanotextiles have been fabricated by deposition or coating biocides for instance nanoparticles and organic compounds on textile fibres. The AgNPs deposition on textiles gains much attention because of their effective antimicrobial properties [115]. AgNPs deposition on textiles could be attained by two methods, post synthesis and in situ deposition. The in situ methodology offers firm advantages for instance small size of particle along with uniform distribution and therefore it is desired approach [116].

An inappropriate interior microclimate has hostile effects on protection of historic textiles organized within them, supporting growth of bacteriological microflora. One of the research works combined innovative and traditional methods for cleaning and preserving traditional hundred years old shirt from Bihor, Romania. Material of shirt had been soaked in thirty and seventy ppm nanosuspensions of AgNPs and afterwards washed with material gained out of boiling natural wood ash (lye). AgNPs antimicrobial action and lye washing applied for examining material of textile were objectives to evaluate in addition to recognize the method by which ecological factors such as light act on preservation degree of textile with AgNPs. These techniques are sustainable and cause no damage to fabrics. Results from hyperspectral imaging technique showed that infusion of AgNPs into textile, changed reflectance spectrum of textile after its treatment with them. Microbiological investigation discovered that bacterial colonies of bacteria were decreased above 95%. Antimicrobial influence of AgNPs on textile of shirt was preserved during study period, and under standard ecological conditions, influence would remain effective and long lasting [117]. AgNPs inserted/ adhered on textile have an efficient antimicrobial part. Though, the release of AgNPs because of fewer adherences besides their destiny in ordinary settings is interrogated regarding toxicity. To solve this adherence problem, in situ AgNPs formation in 5 textile fibres (sheep’s wool, cotton (chemically bleached and untreated), polyester, and polyamide) was evaluated. First textile fibres were soaked in solution of silver ions (1 gL−1 of AgNO3) at ambient temperature for twenty-four hours, after that draining and re-immersion fibres in intense chemical solution (0.25 g/L of NaBH4) for reduction at ambient temperature for twenty-four hours. This step results in in situ AgNPs formation where dimensions less than 50 nm and greater than 5 nm, concentration of coating on surface, as well as aggregation degree relies upon textile as presumed from images (FESEM). Such easy chemical laboratory technique permits immediate AgNPs in situ development on fibres with no need of additional thermal management. In addition, all textile fibres comprising AgNPs (sheep’s wool 10 mg/g > untreated cotton 2.3 mg/g > bleached cotton 1 mg/g > polyamide 0.62 mg/g > polyester 0.28 mg/g) had been subjected to intermingle in aqueous media with strong oxidants (ultrapure water as the control, 7.5% v/v of H2O2, 0.5 M and 0.05 M of HNO3). Results showed innovative curves revealing that rate of oxidative dissolution (mol/g min) regarding adhered AgNPs strongly relies on nature of fibre, as well as concentration and nature concerning oxidative solution. The presented study proposed successful adherence of AgNPs inside natural fibres (cotton and wool) with safe perception along effective biocide features established via consuming Bacillus subtilis [118].

Cotton fibres with biogenic impregnated AgNPs were prepared from solution of Fusarium oxysporum fungal filtrate (FF). It opens opportunity for AgNPs utilization in medicinal situation as well as agriculture wear for avoiding spreading of microbes. Their intense activity against Xanthomonas axonopodis pv. citri (Xac) and Candida parapsilosis, categorized morphologically, indicates robust influence of AgNPs upon membranes of microorganisms. Then AgNPs were impregnated onto cotton fibres. This preserved intense antimicrobic actions after repetitive washing automated cycles up to ten. The textile after repetitive cycles of washing using suds and water caused in vanishing of colour (Fig. 5). These biogenic AgNPs can be used as strong agrochemicals, in addition of their usage within textiles aimed at antiseptic wear aimed at agronomic besides medical uses [119].

Fig. 5
figure 5

Adopted from Ref. [119]

An illustration of farication of antiseptic plastic. Photographs of cotton fabric with biogenic impregnated AgNPs using padding approach. In sequence: a impregnated fabric with no wash, b one wash, c two washes, d three washes, e four washes, f five washes, g six washes, h seven washes, i eight washes, j nine washes, k ten washes and l textile with no impregnation and wash.

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Biogenic AgNPs were synthesized utilizing extracellular filtrate extracted from epiphytic fungus B. ochroleuca. Impregnation technique was used to incorporate these nanoparticles in fabric of polyester and cotton via typical, recurring once, two-fold or 4 times. Fabrics loaded with AgNPs displayed effective antimicrobic activity on Escherichia coli and Staphylococcus aureus as well as clinically related Candida glabrata, Candida albicans, and Candida parapsilosis, representing that impregnation of AgNPs on polyester and cotton fabrics was proficient. AgNPs efficiently inhibited formation of biofilm via Pseudomonas aeruginosa showing no toxicity to Galleria mellonella larvae specifying hopeful possibility of biotechnological use [120]. A different, rapid, plus single-step sonochemical method with deposition procedure was developed for preparation AgNPs coated cotton fabrics. Hydrodynamic diameter of AgNPs increases from 32 to 144 nm along with increase of irradiation time from thirty to ninety minutes. Electron microscopy regarding cotton fabrics with AgNPs deposition displayed their homogenous deposition on cotton. Cotton fabric with deposited AgNPs exhibited moderate antimicrobial activities towards Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) as well as exceptional antibacterial actions towards Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) [121].

4.3 Water treatment

Antimicrobial activity against microorganisms is also beneficial for dye removal, water purification, and wastewater treatments [122]. The positive consumption of AgNPs against pollutants (organic materials and heavy metals) of water as plasmonic sensors functions as photocatalysts, which encouraged oxidation (degradation) of dyes and pesticides, increasing ecological functions [123].

The inventive and multipurpose hydrogel beads based on chitosan were restrained with AgNPs through polydopamine (PDA) coating for enhancing adsorption and antimicrobial activity simultaneously. The covalent linkage between silver and carboxylate with Van der Waals and hydrophobic forces confirmed in situ AgNPs synthesis on beads surface, evidenced by FTIR. The performance of adsorption regarding hydrogel beads was explored to remove metal ion (Cu (II)) and anionic dye. AgNPs presence increased capacity of adsorption of beads for aforesaid adsorbates. Antimicrobial activities had been estimated against conceivable pathogens of humans counting Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Antimicrobic action concerning these beads on Gram-negative bacteria was greater in comparison with activity on Gram-positive bacteria. These hydrogel beads can be employed to control biological and chemical contaminants simultaneously within wastewater [124]. In another work, biological method was employed for preparing AgNPs by Helichrysum graveolens. They possess spherical shape having11 nm as mean diameter. These biosynthesized nanoparticles exhibited antimicrobic features against leading pathogenic microbes (Staphylococcus epidermis, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa). Furthermore they displayed anticancerous activity against colon (C26) cancer ouscell line, depending on concentrations and time. Additionally, they function as a green catalyst because they quicken decomposition of stable and organic dye (Methylene Orange) so advantageous for water treatment [125].

Resources of natural water are being rapidly polluted due to inappropriate sewage treatment from industries. AgNPs were synthesized employing MOS (Moringa oleifera seed) as reducing/capping agent and AgNPs use for photocatalytic oxidation as well as antimicrobial activity to treat water was investigated. MOS-AgNPs displayed tremendous antimicrobial activity towards Gram negative bacteria (Salmonella enterica typhimurium (29 mm), Escherichia coli; 30.6 mm) and Gram positive bacteria (Staphylococcus aureus; 14.6 mm, Pseudomonas aeruginosa; 22.8 mm). Furthermore, MOS-AgNPs displayed extraordinary photocatalytic action against organic dyes (methylene blue (> 81%), orange red (> 82%), and 4-nitrophenol (> 75%)) under sunlight irradiation. Additionally, greater than 80% of toxic metal ions of lead was expunged from water after MOS-AgNPs treatment. MOS-AgNPs also reserved their photocatalytic competence in same conditions even after ten photocatalytic cycles (Fig. 6). Generally, MOS-AgNPs found to be influential antimicrobial agent towards water borne pathogens in addition to be talented and cost-effective agent to be used to treat waste produced by dyeing procedures in industries [126].

Fig. 6
figure 6

Adopted from Ref. [126]

Schematics of synthesis of MOS-AgNPs and using their photocatalytic oxidation and antimicrobial activity to detoxify water.

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AgNPs were prepared from extract from MOF (Moringa oleifera flower) and their sensing as well as antimicrobial features were explored. They are monodispersed with size of 8 nm having FCC (Face-Centered Cubic) lattice, perceived in spectrum of XRD. Spectroscopic (FTIR) results showed phenolic and proteins constituents within MOF that are accountable for depletion. They are stable up to 6 months. They possess generated maximum zone of inhibition zone of 29 mm and 17 mm towards Staphylococcus aureus and Klebsiella pneumonia, respectively. Additionally, AgNPs efficiently noticed copper ions presence at concentration of 1 mM to 12 mM. Sensitiveness regarding copper using such AgNPs had been performed by optical sensors. Thus acquired optical and antimicrobial characteristics of AgNPs, proposed their usage to purify water [127]. A novel process was established to develop FAgNPs via AgNO3 reductions. The fraction of flavonoids of PGL (Psidium guajava leaves) has been utilized as reducing and green capping agent. The mean size of FAgNPs was found to be fifteen to twenty nm, along maximal wavelength for absorbance of 420 nm. Furthermore, they demonstrated an intense inhibition against selected microbes, particularly Escherichia coli, Alcaligenes faecalis, and Aspergillus niger. Prominently, they also exhibited worthy catalytic degradation strength for organic dyes, specifically, methyl orange and Coomassie brilliant blue G-250, under solar and UV irradiation. Generally, they have outstanding potential to develop anti-microbial constituents as well as for photo-catalytic chemicals and poisonous dyes decomposition, thus paving approach to treat waste water besides ecological bio-remediation [128].

4.4 Food packaging

AgNPs are nanostructures with superlative antimicrobial activity and consequently, with pronounced potential to be used in food packing and processing. However, increased assimilation of AgNPs in consumables marks it crucial to report their possible hazard for human wellbeing [129]. For food processing, AgNPs are effective to reduce pathogenic microbes that ultimately decreases antibiotics usage in livestock. Furthermore, few AgNPs also displayed operative antiparasitic activity [130]. The use of AgNPs for packaging of food is categorized in 3 classes: (a) ecological, (b) active, as well as (c) smart packaging. Though combinations of packing are imaginable also (for instance ecological and active packing) [131]. AgNPs protect plants against pathogens by inhibition of microbial growth, encouraging innate plant immunity, and providing micronutrients and pesticides [132].

Iturin A possesses fascinating antifungal activity however less antibacterial activity, whereas AgNPs possess noteworthy antibacterial activities however exhibited possible threat to human well-being. For overcoming these restrictions, AgNPs were prepared using iturin and develop iturin-AgNPs. They are monodispersed having mean diameter of 20 nm. In vitro antimicrobial activities regarding iturin-AgNPs in addition to AgNPs coated with PVP (polyvinyl pyrrolidone)—AgNPs were estimated towards distinctive food borne microbes including fungi and bacteria. Iturin-AgNPs have also been used for paper packaging for protecting oranges from contagion by fungus alone as well as preventing chicken from contagion due to bacteria as compared to PVP-AgNPs. Iturin-AgNPs presented broader spectrum regarding antimicrobial activity, a low concentration of silver, with higher antifungal and antibacterial activities as compared to PVP-AgNPs. Thus a different agent was developed for food protection from fungal and bacterial contamination in time of storage [133]. Influence of dextran-coated AgNPs loading on barrier, mechanical, in addition to antimicrobial characteristics of thin films made of cellulose nanofibrils using solvent casting process were investigated as recyclable and material or food packaging materials. Dextran functions as dispersing medium for AgNPs and regulates its release. Additionally dextran also acts as a sealable additive that is resistant to moisture, collectively with decreased permeability for oxygen, might preserve food against growth of bacteria. Therefore, considerably decreased hydrophilicity and rates of transmission of oxygen (from 2.07 to 1.40–0.78 cm3 m−2d−1), resulting in 99.9% Escherichia coli inhibition after repetitive 5 cycles comprising twenty-four exposition to solution of NaCl (0.9%) was demonstrated, maintained through regulated release of Ag+ ions. These outcomes specify that these hybrid films served as a supportable and last day discarding man-made counterparts replacement within food-contact or multilayer food packing [134].

Extremely efficient, harmless, and less-drug resistant AgNPs were synthesized as antibacterial agents to be used in food packaging. AgNPs were synthesized consuming extract of mango peel (MPE) as reducing agent and stabilizer. Furthermore, a preservative film was fabricated using PLA (polylactic acid) as substrate and shield. Dimensions of AgNPs ranges from 2.5 to 6.5 nm. AgNPs addition enhanced mechanical features of film along with barrier capability to oxygen and water vapour. The film showed outstanding antibacterial characteristics, and rate of inhibition towards Staphylococcus aureus and Escherichia coli were more than 95%. Also, in respect of safety, Ag migration besides cytotoxicity of film found applicable ideas, and strawberries shelf-life was prolonged considerably (Fig. 7) [135].

Fig. 7
figure 7

Adopted from Ref. [135]

An illustration of synthesis of PLA/MPE/AgNPS films utilized for food packing besides to elongate strawberries shelf-life.

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Stable AgNPs were prepared using green path consuming fruit peel of Vitis vinifera (black grapes), and assessed for antimicrobial action towards Staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa, and Escherichia coli. Prepared nanoparticles are spherical with mean dimensions of 30 nm. A hybrid inorganic–organic nanofibres (AgNPs-PVA (poly (vinyl alcohol)) were fabricated via electrospinning process, by integrating prepared AgNPs in matrix of PVA, to preserve food. AgPVA nanofibers and AgNPs both demonstrated better antibacterial action towards tested pathogenic strains of bacteria for food. Nanofibres verified an improved shelf-life when coated over fruit surface, Fragaria ananassa (strawberry) and Citrus limon (lemon), by avoiding decomposing instigated because of pathogens of food. Results specified that prepared nanofibres could possibly be consumed as antimicrobial packaging to preserve food [136]. Releasing of Ag ions out of packing and their dispersion within food hydrogel, along with influence upon Pseudomonas fluorescent production was investigated. Biosorbed- AgNPs (BSNPs) were prepared using extract of plant and were integrated in PVA or CS polymer for fabricating biocomposite films. BSNPs addition enhanced antimicrobial and physical features of films demonstrated by inhibition of P. fluorescent and tensile strength in hydrogels, correspondingly. BSNPs films based on PVA exhibited strong antimicrobial influence, in contrast with BSNPs films based on chitosan. This can be relevant to Ag ions release in higher amount from PVA film in hydrogel. Results propose that interaction strength between film polymer and BSNPs is key parameter resulting in difference in releasing behaviour of antimicrobials that determines antimicrobial activity regarding active food packaging [137].

4.5 Agricultural uses

The usage of AgNPs against different pathogens is well acknowledged in agriculture sector. AgNPs have been extensively reported to control disease in numerous agricultural crops. The efficiency of AgNPs is controlled through regulating size and concentration of nanoparticles in formulation [138]. In numerous circumstances, AgNPs showed more effectiveness towards phytopathogens inside plant tissues itself as compared to in vitro conditions [139]. AgNPs has noticeable importance in agricultural field because of its antimicrobial activity besides slight deviancy from understanding its effect on insecticidal features and germination [140].

AgNPs were synthesized using green method as a hopeful substitute to synthetic pesticides for overcoming pest hazard to increase agricultural productivity. AgNPs had been prepared from extracts of Solanum torvum fruit and their bactericidal characteristics towards phytobacteria were investigated. They are nearly sphere with average size of 27 nm. AgNPs showed minimal concentrations of 6.25 μg/mL and 12.5 μg/mL for inhibition towards plant bacterial pathogens Xanthomonas axonopodis pv. and Punicae and Ralstonia solanacearum. In vitro analysis using disk-diffusion displayed zones for inhibition of 18.1 ± 1 mm regarding X. axonopodis pv. punicae and 11.4 ± 1 mm regarding R. solanacearum after treatment with AgNPs with concentration of 50 μg /mL. These nanoparticles produced intracellular ROS within microbes. Inhibition investigations concerning destruction as well as replication of DNA presented genotoxicity regarding AgNPs to bacterial cells. Studies about plant toxicity established nontoxicity of AgNPs. Thus, AgNPs could be possibly employed as feasible, safe, and active strategy to overcome diseases caused by bacteria in crops [141]. In one of research works, AgNPs were prepared using aqueous Ocimum gratissimum leaf extract. Impact of different parameters for instance AgNO3 concentration, ratio of extract to AgNO3, incubation time, and pH were investigated to optimize synthetic process. The prepared AgNPs exhibited high antimicrobic action towards Gram negative bacteria (Escherichia coli, Klebsiella pneumonia) compared with Gram positive bacteria (Bacillus subtilis, Staphylococcus aureus, plus Micrococcus luteus). Additionally, solution containing AgNPs was forced to toxicity assay utilising Vigna radiata (Moong Bea seeds). It was observed that AgNPs treated seeds exhibited better germination rates and enzyme activity regarding oxidative stress had been at equivalence with control levels. This validates that leaf extracts of O. gratissimum could be consumed for AgNPs production with prospective antibacterial activity [142].

AgNPs were exogenously synthesized using living plant system (Tephrosia apollinea) simulated by PEG (Polyethylene glycol). Cell death, biomass, and H2O2 component were assessed for determining toxic impact on plant after treatments. Additional severe impact was perceived in sixth day plants in comparison with third day plants, and at high levels of drought. Different techniques for instance energy dispersive X-ray spectroscopy, UV (ulta-violet)-visible spectrum, SEM (scanning electron microscopy), XRD (X-ray diffraction), and FTIR (Fourier transform infrared spectroscopy) were employed for characterizing T. apollinea synthesized AgNPs. The Ag NPs were of cubic and spherical shape with dissimilar phytochemicals as conceivable capping agents. Antimicrobic action about AgNPs towards Staphylococcus aureus and also Escherichia coli had been determined through broth microdilution (Fig. 8). Antimicrobial activity got enhanced at high concentrations of PEG. Bactericidal impacts were perceived towards E. coli, whereas only bacteriostatic impact was sensed towards S. aureus [143].

Fig. 8
figure 8

Adopted from Ref [143]

Impact of treatment of polyethylene glycol (PEG) and AgNO3 on phenotypes of plants.

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A novel method was established to prepare magnetic nanocatalyst comprising of magnetite (Fe3O4) with active AgNPs doped with chitosan. The prepared nanocomposite has average size of 8 ± 2 nm. These nanocomposites are utilized as an efficient catalyst to reduce anthropogenic contaminant p-nitrophenol into p-aminophenol. One advantage is to separate them with magnet. This nanocatalyst stays stable and active after even recycled for 15 times. Similarly, an exceptional antifungal activity was perceived resisting agricultural microbes for instance, Colletotrichum coccodes, Aspergillus niger, and Pyricularia sp. Consequently, modified nanostructures Fe3O4@Chitosan-AgNP nanocomposite could possibly grip better prospective in catalysis as well as agriculture uses [144]. Potential impact of AgNPs having various sizes (three, five, eight, and ten nm) and with various concentrations (12.5–100 ppm) towards phytopathogenic Fusarium oxysporum f. sp. radicis-lycopersici (FORL) strains was determined. Extreme antifungal action had been obtained via reducing size along with growing AgNPs concentration. Capabilities in respect to growth of Mycelium got reduced to 50%, 75% and 90% by AgNPs treatment utilizing 3 nm sizes at concentrations of 25 ppm, 37.5 ppm and 50 ppm, correspondingly. Fungal biomass yield inside liquid medium for growth has been limited at concentration of 25–37.5 ppm of AgNPs using all dimensions. Additionally, dimensions and separation number of macro- in addition to microconidia progressively reduced with usage of AgNPs. This research presented that AgNPs at low concentration can be exploited for possible antifungal activity in addition to be used to regulate phytopathogens [145].

5 Conclusions

Silver nanoparticles gained considerable interest due to their exclusive features and demonstrated uses in miscellaneous sectors for instance medicine, textile engineering, catalysis, nanobiotechnology, biotechnology, electronics, bio-engineering sciences, water treatment, and optics. Various methods have been established for synthesizing AgNPs of different sizes, including, chemical, physical, and biological methods. These nanoparticles possess noteworthy inhibitory impact resisting microbial pathogens and have been broadly consumed as antimicrobic agents in variety of products. AgNPs are in usage as an effective antimicrobial agent for discouraging growth of bacteria. AgNPs also exhibited anti-biofilm properties that could be exploited in treatment of biofilm based persistent infections. This review elaborates various applications in various fields of AgNPs attributed to their antimicrobial activity along with its mechanisms. The suggested mechanisms intended for AgNPs antimicrobial activity include destruction of cell wall structure, persuading ROS generation, and DNA impairment. AgNPs signify a tremendous antimicrobial agent and possess an extraordinary antibacterial ability. Various applications exploiting antimicrobial activity of AgNPs have been discussed with examples in biomedicine, agriculture, treatment of water, food packaging, as well as textile industry.