Nazia Tarannum*a,
Divyaa and
Yogendra K. Gautamb
aDepartment of Chemistry, Chaudhary Charan Singh University, Meerut 250004, India. E-mail: naz1012@gmail.com
bSmart Materials and Sensor Laboratory, Department of Physics, Chaudhary Charan Singh University, Meerut 250004, India
First published on 29th October 2019
In the field of nanotechnology, the development of reliable and eco-friendly methods for the synthesis of NPs is crucial. The conventional methods for the synthesis of NPs are costly, toxic, and not ecofriendly. To overcome these issues, natural sources such as plant, bacteria, fungi, and biopolymers have been used to synthesize AgNPs. These natural sources act as reducing and capping agents. The shape, size, and applications of AgNPs are prominently affected by the reaction parameters under which they are synthesized. Accessible distributed data on the synthesis of AgNPs include the impact of different parameters (temperature and pH), characterization techniques (DLS, UV-vis, FTIR, XRD, SEM, TEM and EDX), properties and their applications. This review paper discusses all the natural sources such as plants, bacteria, fungi, and biopolymers that have been used for the synthesis of AgNPs in the last ten years. AgNPs synthesized by green methods have found potential applications in a wide spectrum of areas including drug delivery, DNA analysis and gene therapy, cancer treatment, antimicrobial agents, biosensors, catalysis, SERS and magnetic resonance imaging (MRI). The current limitations and future prospects for the synthesis of inorganic nanoparticles by green methods are also discussed herein.
Around 5000 years back, numerous Egyptians, Persians, Greeks and Romans utilized silver in several structures to store nourishment items.4 During ancient periods, silverware was used in household daily activity due to its antimicrobial activity. There are records regarding the therapeutic applications of silver in the literature as early as 300 BC. Until the revelation of antimicrobials by Alexander Flemming, silver was ordinarily utilized as an antimicrobial specialist. In the Hindu religion, to date, silverware is favored for making the “panchamrit” utilizing Ocimum sanctum, curd, and different ingredients. The restorative properties of different metals are referenced in the old Indian Ayurvedic prescription book named “Charak Samhita5”.
In the past, AgNPs have attracted considerable attention from analysts. Due to the uncommon attributes of AgNPs, they are used in different fields such as biomedical (fast diagnosis, imaging, tissue regeneration and drug delivery, and development of new medical products),7 textile industry,8 food packaging,9 cosmetic industry,10 catalysis,11 sensors,12 biology, coatings,13 plasmonics (SERS),14 optoelectronics,15 antimicrobial activities,16 DNA sequencing,17 SERS,18 climate change and contamination control,19 clean water technology,20 energy generation, and information storage. Also, due to their remarkable protection against a wide scope of microorganisms and medicinal properties, AgNPs are utilized as anti-infection agents, tranquilizers conveyance agents, water treatment, farming, etc.21 Furthermore, due to their high conductivity, AgNPs have found application in electronic devices, inks, adhesives, pastes, etc.22 Generally, the synthesis of AgNPs is carried out using physiochemical techniques such as autoclaving, gamma-ray radiation, use of microemulsions, electrochemical techniques, chemical reduction, laser ablation, microwave irradiation, and photochemical reduction.23–33 Fig. 1 presents the various techniques used for the synthesis of NPs.
Fig. 1 Representation of various techniques for the synthesis of NPs.6 |
The above methods have a high yield, but simultaneously they have limitations such as the use of toxic chemicals, and high functional cost and energy requirement. To overcome the limitations of physiochemical methods, alternative cost-effective methods involving plant extracts, microorganisms and natural polymers have been used for the synthesis of AgNPs. The combination of green chemistry and nanotechnology has extended the range of cytogenetically and biologically compatible metallic NPs.4
Over the previous decade, few review concentrating on the green synthesis of AgNPs have been published.34 The majority of them concentrated on a few plants (aloe leaf,35 cherry extract,36 Coffea arabica seed,37 Trianthema decandra,38 Macrotyloma uniflorum,39 and Rosa rugosa40), biopolymers41 (chitosan42,43) and microbial sources44 for the synthesis of AgNPs. Several characterization procedures (DLS, UV-vis, FTIR, XRD, SEM, TEM and EDX) have been employed to investigate information regarding the source, shape, size and properties of AgNPs with respect to different applications. The present review, in contrast to the prior reviews, focuses on the synthetic methods, parameters, characterization techniques, applications, and anticipated antibacterial components from different green ways for the synthesis of AgNPs.
Source | Components responsible for the reduction of silver nitrate | Mechanism for the synthesis |
---|---|---|
Plants | Flavanoids, terpenoids, alkaloids, polyphenols, alcohol, phenolic acids, antioxidants, vitamins | Electrostatic interaction between the functional groups of respective constituent of plant extract and Ag+ ion |
Fungi | Proteins, enzymes, NADH, NADPH, peptides, nitrogenous biomacromolecules, napthoquinones, anthraquinones | Intracellular and extracellular synthesis of AgNPs |
Biopolymers | Chitosan, lignin, polypeptides, alginate, cellulose, protein | Electrostatic interaction between Ag+ ion and polar groups attached to polymer |
Prem Jose Vazhacharickal et al. (2015) synthesized AgNPs using Curry leaf (Murraya koenigii) as the reducing and capping agent, which exhibited good antibacterial activity.62 M. Firdaus et al. (2017) reported the synthesis of AgNPs using aqueous fruit extract from (Carica papaya) papaya as the reductant under sunlight irradiation without additional capping agents. The AgNPs were characterized via UV-vis spectrophotometry and FTIR spectroscopy. A green environmental sensor was developed due to the good selectivity of AgNPs towards the hazardous heavy metal mercury in aqueous solution.63 Jerushka S. Moodley et al. (2018) reported the antimicrobial potential of synthesized AgNPs using leaf extracts of Moringa oleifera and utilized sunlight irradiation as the primary source of energy.64 Yu C. et al. (2019) synthesized AgNPs from the leaf extract of Eriobotrya japonica (Thunb) and utilized them in the catalytic degradation of reactive dyes.65 The most suitable choice to synthesize AgNPs is plant-like angiosperms. Medicinally important plants such as Boerhaaviadiffusa,66 Tinosporacordifolia,67 Terminalia chebula,68 aloe vera69, Ocimumtenuiflorum,70 Catharanthus roseus,71 Emblica officinalis72, Azadirachtaindica,73 common spices Piper nigrum,74 Cocos nucifera75, Cinnamon zeylanicum76 and some tropical weeds such as Partheniumhystero-phorus77 have been utilized to synthesize AgNPs. Plants that produce essential oils (Mentha piperita) and alkaloids (Papaver somniferum) have also been used to synthesize AgNPs. The have been a few cases in which chemicals such as sodium-dodecyl sulfate were used externally to stabilize AgNPs.78 All the plant extracts act as both reducing agents and capping agents. The proteins metabolites79 and chlorophyll80 present in the extract of plants act as stabilizing agents to synthesize AgNPs. Fig. 2 presents the mechanism for the synthesis of AgNPs from plants. Other synthetic procedures, conditions, characterization and application of AgNPs are discussed below (Table 2).
S. no. | Reducing agents (green sources) | Applications | Operating conditions | Characterization techniques used | Particle characteristics | Reference |
---|---|---|---|---|---|---|
1 | Aqueous leaf extract of aloe vera | Antibacterial activity | AgNO3 (1 mM), extract: AgNO3 (1:10), stir 20 min, incubated for 24 h | UV-vis, FTIR, TEM, | Size: (36.61 ± 4.88 nm), shape: spherical | 35 |
2 | Cherry extract | Antioxidant | AgNO3 (1 mM), extract: AgNO3 (1:10) | FTIR, UV-vis, DLS, TEM, XRD, TGA and DTA | Size: (61.1 ± 39.2 nm) (for blue light), shape: spherical, crystal - FCC | 36 |
3 | Coffea arabica seed extract | Antibacterial activity on E. coli and S. aureus | AgNO3 (0.02 M, 0.05 M, and 0.1 M), volume of extract kept constant for each solution | SEM-EDX, TEM, XRD, UV-vis, DLS | Size: (20 to 30 nm), shape: spherical and ellipsoidal | 37 |
4 | Plant extract of Trianthema decandra | Antimicrobial activity | AgNO3 (1 mM), extract: AgNO3 (1:5, 1:10, 1:15) | EDX, FTIR, UV-vis, SEM | Size: (36 to 74 nm) | 38 |
5 | Seed extract of Macrotyloma uniflorum | AgNO3 (0.59 mM), extract: AgNO3 (1:60) | TEM, XRD, UV-vis, FTIR | Size: (12 nm) | 39 | |
6 | Fruit extract of Tanacetum vulgare | AgNO3 (1 mM), extract: AgNO3 (1.8:50) | TEM, XRD, EDX, FTIR, zeta potential, UV-vis, FTIR | Size: (16 nm), shape: spherical | 40 | |
7 | Leaf extracts of Rosa rugosa | AgNO3 (1 mM), extract: AgNO3 (2.5:60) | UV-vis, TEM, XRD, FTIR, zeta potential, EDX | Size: (12 nm), shape: spherical | 40 | |
8 | Saccharum officinarum | High antimicrobial activity against biofilm-forming bacteria and fungi. Reduce cytotoxicity on mammalian somatic and tumoral cells | AgNO3 (14, 24, 52, and 104 mM), CS:AgNO3:VC (5:1:1), stirred for 12–15 h with heat | UV-vis, TEM, EDS | Size: (<10 nm) | 42 |
9 | Seed extract of Nelumbo nucifera | Antibacterial and antifungal | AgNO3 (1 mM), seed extract: AgNO3 (1:19) | UV-vis, FTIR, TEM, XRD, SEM | Size: (5.03 to 16.62 nm), shape: spherical | 43 |
10 | Eriobotrya japonica (Thunb.) leaf extract | Catalytic degradation of reactive dyes | Different ratios of leaf extract and silver salt solution (1:1, 1:2, and 1:10, v/v) | UV-vis, XRD, TEM, SEM, FTIR, EDX | Size at different temperatures: 20 °C: 9.26 ± 2.72, 50 °C: 13.09 ± 3.66, 80 °C: 17.28 ± 5.78 nm | 65 |
11 | Sapota pomace extract (Manilkara zapota) | Good antibacterial activity against Gram-positive and Gram-negative bacteria | AgNO3 (7 mM), mixed with extract in ratio 1:0.5 (v/v), temperature 20 °C | UV-vis, XRD, FTIR, DLS, TEM, zeta potential | Size: (8 to 16 nm), shape: spherical, moderate stability (zeta potential of −13.41) | 81 |
12 | Pomegranate peel extract (Punica granatum) | Antibacterial activity against Staphylococcus, Pseudomonas aeruginosa and Escherichia coli pathogens | AgNO3 (1 mM), mixed with extract (incubated for 24 h) | UV-vis, FTIR, SEM | Size: (5 to 50 nm), UV-vis: 371 nm | 82 |
13 | Saccharum officinarum extract and chitosan | Antibacterial against Bacillus subtilis, Klebsiella planticola, Streptococcus faecalis, Pseudomonas aeruginosa and Escherichia coli | AgNO3 (1 mM), extract: AgNO3 (9:1), incubated at 37 °C, till change in color | UV-vis, TEM, SEM, EDS, FTIR | Size: (10 to 60 nm), UV-vis: 460 nm | 83 |
14 | Arbutus unedo (strawberry) leaf extract | Cost effectiveness, medical and pharmaceutical applications | AgNO3 (1 mM), AgNO3:extract (1:1); temperature 80 °C, stir at 1000 rpm | UV-vis, EDS, TEM, XRD | Size: (2 to 20 nm), shape: spherical, geometry: FCC | 84 |
15 | Pomegranate leaf extract | Antibacterial, anticancer activity on human cervical cancer cells86 | AgNO3 (1 mM), AgNO3:extract (9:1) | UV-vis, FTIR, SEM, XRD, EDX | Size: (10 to 30 nm), geometry cubic | 85 |
16 | Walnut seed extract | Used in photocatalytic degradation of effluent dye | AgNO3 (1 mM), AgNO3:Extract (10:1) | UV-vis, XRD, FTIR, TEM | Size: (80 to 90 nm), shape: spherical, UV-vis: 420 nm, crystalline | 87 |
17 | Cinnamomum camphora leaf extract | AgNO3 (1 mM), heat: 30 °C, stir: 150 rpm | UV-vis, XRD, TEM, SEM, AFM, FTIR | Size: (55 to 80 nm), shape: spherical and triangular | 88 | |
18 | Pomegranate peel extract | Photocatalytic degradation of methylene blue | AgNO3 (1 mM), pH: 8, temperature: (21 ± 5 °C) | UV-vis, XRD, FTIR, EDS | Size: (57.7 to 142.4 nm) | 89 |
19 | Azadirachta indica aqueous leaf extract | Antibacterial activity against Staphylococcus aureus and Escherichia coli | AgNO3 (1 mM to 5 mM) (1–5 mL) of extract was added to 10 mL of AgNO3 solution | FTIR, UV-vis, DLS, photoluminescence, TEM | Size: (34 nm), shape: spherical and irregular | 90 |
20 | Grape (Vitis vinifera) fruit extract | Antibacterial activity against Bacillus subtilis and Escherichia coli | AgNO3 (20 mM) extract: AgNO3 solution (1:1) | UV-vis, DLS, EDX, TEM | Size: (19 nm), shape: spherical | 91 |
21 | Alpinia katsumadai seed extract | Free radical scavenging, antibacterial and antioxidant | AgNO3 (10 mM) extract: AgNO3 (1:10) pH: 10, stir: 200 rpm for 90 min | UV-vis, FETEM, EDX, SAED, XRD, FTIR | Size: (12.6 nm), shape: spherical | 92 |
22 | Apple extract | Antibacterial against Gram-negative and Gram-positive bacteria with MIC of 125 mg mL−1 | AgNO3 (0.1 M) extract: AgNO3 (1:9) stir and heat at 80 °C | XRD, DLS, FTIR, UV-vis | Size: (30.25 ± 5.26 nm), crystalline | 93 |
23 | Berberis vulgaris leaf and root extract | Antibacterial activity against Escherichia coli and Staphylococcus bacteria | AgNO3 (0.5, 1, 3, 10 mM) extract: (3, 5, 10, 15, 30 mL) contact time: (1, 2, 6, 12, 24 h) | XRD, TEM, UV-vis, DLS, | Size: (30 to 70 nm), shape: spherical | 94 |
24 | Cinnamon zeylanicum bark extract and powder | Bactericidal activity | 100, 500 and 1000 mg of CBP added to 50 mL of 1 mM aqueous AgNO3 solution and incubated in the dark at 25 °C and shaken at 160 rpm. For CBPE, 1, 2.5 and 5 mL extract added to 50 mL of 1 mM aqueous AgNO3 solution | UV-vis, TEM, EDX, XRD, zeta potential | Size: (31 and 40 nm), quasi-spherical, and small, rod-shaped | 95 |
25 | Lippia nodiflora aerial extract | Antioxidant and antibacterial against human pathogenic bacteria, cytotoxic against MCF-7 breast cancer cell lines | AgNO3 (1 mM), extract: AgNO3 solution (1:19), heat from 30 °C to 95 °C for 10 min | UV-vis, FTIR, XRD, SEM-EDX, TEM, zeta potential | Size: (30 to 60 nm) | 96 |
26 | Andean blackberry fruit extract | Antioxidant | AgNO3 (1 mM), extract: AgNO3 solution (1:10), keep at 25 °C | UV-vis, TEM, DLS, XRD, FTIR | Size: (12 to 50 nm), shape: crystalline and spherical | 97 |
27 | Aqueous broccoli extract | High toxicity against MCF-7 cell line | AgNO3 (1 mM), extract: AgNO3 solution (1:19), pH: (6 to 7) | UV-vis, FTIR, XRD, SEM, TEM, EDAX | Size: (40 to 50 nm), FCC structure | 98 |
28 | Pinus merkusii cone flower extract | AgNO3 (0.1 M), extract: AgNO3 solution (2:1), heated at 60 °C | FTIR, UV-vis, TEM | Size: (9 to 23 nm), shape: spherical | 99 | |
29 | Curcuma longa tuber (turmeric) powder and extract | Immobilization on cotton cloth for bactericidal activity | 100, 500 and 1000 mg of CLP added to 50 mL of 1 mM aqueous AgNO3 solution and incubated in the dark at 25 °C in a rotary shaker at 160 rpm. 1, 2.5 and 5 mL extract added to 50 mL of 1 mM aqueous AgNO3 solution | UV-vis, TEM, XRD | Size: (21 and 30 nm) | 100 |
30 | Garlic extract (Allium sativum) | Nontoxic to VSMCs and NIH 3T3 fibroblasts | AgNO3 (0.98 mM), extract solution (1.0 mL to 2.5 mL) added to 51 mL of AgNO3 solution | TEM, UV-vis, EDX, ATR-FTIR, zeta potential, HPLC | Size: (4 to 6 nm) | 101 |
31 | Ginger extract (Zingiber officinale) | Antibacterial activity against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Bacillus cereus and Proteus vulgaris | AgNO3 (1 mM) extract (20%): AgNO3 solution (1:9), temperature (27 ± 2 °C) | UV-vis, XRD | Size: (2.89 nm), shape: spherical | 102 |
32 | Aqueous seed extract of Manilkara zapota (L.) | Antimicrobial activity against Candida species | 10% concentration of MZSE was added to 0.01 M AgNO3, heated at 80 °C | EDX, DLS, TEM, XRD, UV-vis | Size: (40 to 100 nm) | 103 |
33 | Leaf extract of avocado | Antibacterial activity | AgNO3 (5 mM), extract: AgNO3 solution (1:9), kept in the dark for 24 h | FTIR, XRD, SEM, UV-vis | Size: (35.6 nm), shape: spherical | 104 |
34 | Origanum vulgare L. plant extract | Antimicrobial activity | AgNO3 (0.5 mM), 1 mL of plant extract added to 49 mL of AgNO3 solution and stirred for 2 h at 85–90 °C | FTIR, UV-vis, XRD, TEM, EDX | Size: (12 nm), FCC structure | 105 |
35 | Root extract of Croton sparsiflorus | Antimicrobial activity | AgNO3 (1 M) | UV-vis, SEM | Size: (30 to 50 nm), shape spherical | 106 |
36 | Roots extract of Coleus forskohlii | Antimicrobial activity | AgNO3 (1 mM), extract: AgNO3 solution (1:20), incubated for 24 h at 28 °C | UV-vis, EDS, FTIR, SEM, XRD | Size: (82.46 nm), shape: needle | 107 |
37 | Lemon leaf extract | Antimicrobial activity | AgNO3 (2 mM), extract: AgNO3 solution (1:9), keep in the dark at room temp | FTIR, UV-vis, TEM, SEM, AFM | Size: (Smaller than 100 nm range), shape: multi-shaped | 109 |
38 | Banana peel extract | Antimicrobial activity | AgNO3 (1.75 mM), extract: AgNO3 (1:50 (v/v)) | UV-vis, XRD, SEM, EDX | Size: (23.7 nm), crystalline | 110 |
39 | Valerian officinalis aqueous extract | AgNO3 (5 mM), plant powder (0.25, 0.50, 0.75 and 1.0 g) 50 mL distilled water | UV-vis, XRD, SEM, TEM | Size: (22 nm), shape: spherical, crystalline | 111 | |
40 | Tectona grandis seed extract | Antimicrobial activity against microorganisms | AgNO3 (1 mM), AgNO3:seed extract (1:9) | UV-visible XRD, FTIR SEM/EDS, FESEM, TEM | Size: (10 to 30 nm), shape: spherical, crystalline | 112 |
41 | Extracts of Ananas comosus | AgNO3 (10 mM), pineapple juice: AgNO3 (1:10) | XRD, UV-vis, EDAX, TEM | Size: (12 nm), FCC crystalline | 113 | |
42 | Extract of saffron (Crocus sativus L.) | Antibacterial activity | AgNO3 (2 mM), extract: AgNO3 solution (1:4) | UV-vis, FTIR, XRD, TEM | Size: (15 nm), shape: spherical | 114 |
43 | Onion (Allium cepa) extract | Antibacterial activity | AgNO3 (0.1 mM), extract: AgNO3 solution (1:10), constant stirring at 50–60 °C | UV-vis, DLS, TEM | Size: (33.6 nm), shape: spherical | 115 |
44 | Thymus kotschyanus plant extract | Antioxidant, antibacterial and cytotoxic effects | AgNO3 (1 mM), extract: AgNO3 (1:10), stir for 30 min in the dark | UV-vis, FTIR, EDX, XRD, TGA, SEM, TEM, AFM | Size: (50 to 60 nm) | 116 |
45 | D. carota (carrot) extract | AgNO3 (0.5 mM), extract: AgNO3 (1:6) | XRD, UV-visible FTIR, TEM | Size: (20 nm), shape: spherical | 117 | |
46 | Garcinia mangostana stem aqueous extract | Antimicrobial activity | AgNO3 (1 mM), extract: AgNO3 (3:17) | UV-vis, XRD, SEM, EDX | Size: (30 nm) | 118 |
47 | Olive leaf extract | Antibacterial activity | AgNO3 (1 mM), extract (2–9 mL) added to AgNO3 solution | TEM, UV-vis, FTIR, TG, XRD | Size: (20 to 25 nm), shape: spherical | 119 |
48 | Extract ofChenopodium ambrosioides | AgNO3 (1 mM and 10 mM), extract: AgNO3 (0.5, 1, 2, 3 and 5 mL:5) | UV-vis, TEM, FTIR | Size: (4.9 ± 3.4 nm), FCC | 120 | |
49 | Aqueous leaf extract of Acalypha indica | Antifungal effect against Phytopathogen Colletotrichum capsici | AgNO3 (1 mM), extract: AgNO3 (1:9), incubate at 37 °C | UV-vis, antifungal | 121 | |
50 | Ficus benghalensis leaf extract | Antibacterial activity | UV-vis, TEM-EDX, XRD | 122 | ||
51 | Litchi chinensis leaf methanolic extract | Strong muscle relaxant, analgesic and anti-inflammatory activities | AgNO3 (1 M), extract: AgNO3 (1:1 and 1:10) | UV-vis | 123 | |
52 | Salvia leriifolia leaf extract | Antibacterial activity against 9 bacteria | AgNO3 (1 mM), extract: AgNO3 (1:24) | SEM, AFM, XRD, FTIR | Size: (27 nm), shape: pherical | 124 |
53 | Glycyrrhiza glabra root extract | Treatment of gastric ulcer | AgNO3 (1 mM), extract: AgNO3 (1:49) | UV-vis, TEM, XRD, FTIR | Size: (19 nm), crystalline | 125 |
54 | Pimpinella anisum seed extract | Antimicrobial activity and cytotoxicity on human neonatal skin stromal cells and colon cancer cells | AgNO3 (3 mM), extract: AgNO3 (1:100) | UV-vis, FTIR, XRD, EDX, TEM | Size: (15 nm) | 126 |
55 | Glycyrrhiza uralensis root extract | Antimicrobial agent against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella enterica | AgNO3 (1 mM), extract: AgNO3 (1:1), heated in oil bath at 80 °C, change in color is observed | UV-vis, TEM, SAED, XRD, DLS, FTIR | Size: (5 to 15 nm), shape: spherical | 127 |
56 | Orange peel | Antimicrobial activity | AgNO3 (1 mM), AgNO3:orange peel extract (1:1), pH above 7 | UV-vis, FTIR, DLS, XRD, zeta potential, TEM | Size: (48.1 ± 20.5 nm) | 128 |
57 | Citrus recticulata fruit peel extract | Antibacterial activity against Streptococcus pyogenes, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Salmonella Paratyphi and Klebsiella pneumoniae | AgNO3 (1 mM), extract: AgNO3 (1:20) | UV-vis, FTIR, XRD, SEM, EDX | Size: (24 nm) | 129 |
The choice of bacteria in the green synthesis of AgNPs and an appropriate method are important for their large scale production.138 Mokhtari et al. (2009) reported the synthesis of AgNPs via photosynthesis by adding a solution of silver nitrate to the culture supernatant of Klebsiella pneumonia, and showed visible-light irradiation prompted the synthesis of AgNPs with a size of 3 nm139. According to reports by Lee and Shehata and Marr (Lee 1996; Shehata and Marr 1971), AgNPs were also produced via the reduction of silver ions using culture supernatants of bacteria. It should be noted that the growth of bacteria depends on the nutrients in the culture medium (glucose, phosphate or tryptophan).140 Shahverdi et al. (2007) reported the use of Enterobacter cloacae (Enterobacteriaceae), Escherichia coli and Klebsiella pneumonia for the fast synthesis of AgNPs, which formed AgNPs within a few minutes of Ag ions reacting with the cell filtrate.141 Kharissova et al. (2013) highlighted that bacteria kept on growing after the synthesis of AgNPs. However, compared to conventional methods, the utilization of bacteria for the reduction of Ag+ ions leads to a slow formation rate and limited range of shapes and sizes of AgNPs.142 Therefore, fungi-based NPs and reducing agents involving plants and plant extracts have been investigated for the synthesis of AgNPs (Table 3).
S. no. | Bacteria | Application | Conditions | Characterization | Size | Reference |
---|---|---|---|---|---|---|
1 | Psychrophilic bacteria | Stable for 8 months in the dark | 1 mL of 1 mM AgNO3 was added to 25 mg of the washed cell, and incubated under a fluorescent lamp (CFL) of 9 W | UV-vis spectroscopy, transmission electron microscopy, atomic force microscopy | Size: (6 to 13 nm) | 136 |
2 | Endophytic bacterium, Pantoea ananatis | Antimicrobial against multi-drug resistant bacteria | Reaction mixture of cell free extract and 100 mL of 0.1 mM AgNO3 solution (2%, v/v) exposed to bright sunlight, pH (7) | UV-vis, TEM, SEM, FTIR, zeta potential | Size: (8.06 to 91.32 nm) | 137 |
3 | Culture supernatant of Klebsiella pneumonia | AgNO3 (1 mM), supernatant 1% (v/v) | XRD, UV-vis, TEM, EDS | Size: (3 nm) | 139 | |
4 | Culture supernatants of Enterobacteriaceae | AgNO3 (1 mM), supernatant (1%, v/v) | UV-vis, EDS, TEM | Size: (52.5 nm) | 141 | |
5 | Biomass of bacterial exopolysaccharide | Used in degradation of azo dye | AgNO3, (9 mM) | UV-vis, TEM, SEM, AFM, XRD, TGA-DTA, Raman spectroscopy | Size: (35 nm), shape: spherical | 143 |
Fungi can synthesize metal NPs since they secrete enzymes and proteins, which are used to reduce metal salts. The large-scale synthesis of NPs from distinct fungal strains has been implied due to their growth even in vitro145. Xue B. et al. (2016) reported morphological and molecular methods to synthesize AgNPs under optimized conditions, i.e., the substrate concentration of 1.5 mM, alkaline pH, reaction temperature of 55 °C, and reaction time of 10 h, utilizing the fungal strain of Arthroderma fulvum. The synthesized AgNPs were found to be crystalline in nature and the particle size was optimized to be ∼15.5 ± 2.5 nm. Antifungal activity was observed against fungal strains, including Candida, Fusarium, and Aspergillus.146 Honary S. et al. (2013) evaluated a green synthetic method for the extracellular production of AgNPs using Penicillium citrinum isolated from soil. The synthesized NPs were found to be spherical in shape with an average diameter of 109 nm.147 A controlled and up-scalable green method for the synthesis of AgNPs with a well-defined morphology utilizing the cell-free aqueous filtrate of a non-pathogenic and suitable biocontrol agent Trichoderma asperellum was reported for the first time.148 Verma VC et al. (2010) prepared AgNPs utilizing Aspergillus clavatus and demonstrated their antimicrobial potential.149 AgNPs were synthesized by Li G. et al. (2012) using culture supernatants of Aspergillus terreus for the reduction of Ag ions.150
Subashini G. and Bhuvaneswari S. (2018) reported the synthesis of AgNPs from fungi and their applications in various fields of biology.151 AgNPs synthesized using Fusarium oxysporum were optimized by Birla SS et al. (2013) using different media, pH, temperature, light intensity, filtrate volume, salt concentration, and quantity of biomass.152 Neethu S. et al. (2018) reported the extracellular green synthesis of AgNPs utilizing the biomass of Penicillium polonium.153 Khan MN et al. (2015) utilized aqueous Raphanussativus root extract as a reducing and capping agent for the synthesis of silver nanomaterials for the first time.154 Ma L. et al. (2017) utilized the supernatant of the fungus strain Penicillium aculeatum Su1 to synthesize extracellular AgNPs.155 Al-Bahrani R. et al. (2017) reported the green synthesis of AgNPs utilizing the aqueous extract of basidiocarps of oyster mushroom, Pleurotus stratus156. Jalal M. et al. (2018) studied the extracellular green synthesis of AgNPs using the supernatant of Candida glabrata isolated from oropharyngeal mucosa of human immunodeficiency virus (HIV) patients and evaluated them for antibacterial and antifungal potential against human pathogenic bacteria and fungi.157 Eugenio M. et al. (2016) reported the biosynthesis of Ag NPs using yeast strains.158 Otari SV et al. (2014) synthesized AgNPs utilizing the culture supernatant of phenol degraded broth as the reducing agent.159 Ishida K. et al. (2014) studied the synthesis and antifungal activity of AgNPs synthesized utilizing the aqueous extract of the fungus Fusarium oxysporum.160 More details on the synthesis of AgNPs from fungi and yeast are discussed in Table 4.
S. no. | Reducing fungus | Application | Optimization conditions | Characterization techniques | Shape and size | Reference |
---|---|---|---|---|---|---|
1 | Arthroderma fulvum | Antifungal against Candida, Aspergillus spp., and Fusarium spp. | AgNO3 (1.5 mM) alkaline pH, reaction temperature 55 °C, and reaction time of 10 h | UV-vis, XRD, TEM | Size: (15.5 ± 2.5 nm) crystalline | 146 |
2 | Penicillium citrinum isolated from soil | Presence of amide linkage groups found in the fungal extract | Dark compartment at 28 °C, 24 h, membrane filter (0.45 fÊ) | FTIR, photon correlation spectroscopy (PCS), SEM, fluorescence spectroscopy, UV-vis | Size: (109 nm), shape: spherical | 147 |
3 | Trichoderma asperellum | AgNPs formed were highly stable for 6 months | AgNO3 (1 mM), 5 days incubated at 25 °C with biomass of Trichoderma asperellum | UV-vis, FTIR, TEM, XRD, SERS | Size: (13–18 nm) | 148 |
4 | Aspergillus clavatus (AzS-275), an endophytic fungus | Antimicrobial against Candida albicans, Pseudomonas fluorescens and Escherichia coli | AgNO3 (1 mM), cell biomass: AgNO3 (1:9), incubated at 25 °C on a rotary shaker (150 rpm) for 72 h | UV-vis, FTIR, XRD, TEM, AFM | Size: (10 to 25 nm) extracellular, polydispersed spherical or hexagonal | 149 |
5 | Biomass of Aspergillus terreus | Antifungal and antibacterial | AgNO3 10 mM, NADH, biomass: AgNO3 solution (5:1), incubated for 24 h at 28 °C | XRD, TEM, UV-vis | Size: (1 to 20 nm), shape: spherical | 150 |
6 | Raphanus sativus | Antimicrobial activity | Raphanus sativus root extract, (1.0–6.0 mL) added to AgNO3 solution | DLS, TEM, EDX, XRD, FTIR, SEM | Size: (3.2 to 6 nm) | 154 |
7 | Cell-free filtrate of the fungus strain penicillium aculeatum Su1 | Antimicrobial activity, drug delivery vehicle or anticancer drug for clinical treatment. | AgNO3 (10 mM) | TEM, XRD, FTIR | Size: (4 to 55 nm), FCC crystalline | 155 |
8 | Pleurotus ostreatus | Inhibitory activity against pathogenic bacteria | (1–6 mg mL−1) of aqueous extract of P. ostreatus was added to 5 mL, of 1 mM aqueous silver nitrate, kept at 28 ± 2 °C in the dark and incubated for 6, 12, 18, 24, 30, 36 and 40 h | SEM, TEM, EDX, FTIR | Size: (<40 nm) | 156 |
9 | Candida glabrata | Antimicrobial activity against clinical strains of bacteria and fungi | AgNO3 (1 mM) supernatant (20 mL) kept at room temperature overnight | FTIR, UV-vis, TEM | Size: (2 to 15 nm) | 157 |
10 | Biomass of Trichoderma viride (fungi) | Antibacterial activity against human pathogenic bacteria | AgNO3 (10 mM), biomass: AgNO3 (5:1), incubated for 24 h at 25 °C | UV-vis, TEM, SEM, | Size: (1 to 50 nm), shape: globular | 158 |
11 | Biomass of thermophilic Bacillus sp. AZ1 | Antimicrobial activity against human pathogenetic bacteria | AgNO3 (1 mM) | SEM, EDX, TEM, UV-vis | Size: (7 to 31 nm), shape: spherical | 161 |
12 | Biomass of Aspergillus niger | Antimicrobial activity | AgNO3 (10 mM), biomass of fungi:AgNO3 (5:1), incubated for 24 h at 28 °C | UV-vis, XRD, TEM | Size: (1 to 20 nm), shape: spherical | 162 |
Atta A et al. (2014) reported a green synthetic method involving the reduction of Ag+ ions in aqueous acidic solution in the presence of polyvinyl alcohol modified with thiol groups (PVA-SH). AgNPs were stabilized by coating different types of citrate-reduced AgNPs with different weight ratios of PVSH derivatives (1–3 wt%). The as-prepared AgNPs were characterized via UV-vis spectroscopy, TEM/EDS, DLS and XRD combined with Rietveld analysis. The changes in the particle size, shape and hydrodynamic diameter of the AgNPs were determined using TEM, XRD and UV-visible spectroscopy after different durations of exposure to synthetic stomach fluid (SSF) and 1 M HCl. The data showed that for more than 90 days, these AgNPs were highly stable against SSF, which was not previously reported in the literature.169 Wu Q. et al. (2008) synthesized glutathione-capped AgNPs with adjustable sizes. These particles could be bound covalently to other functional molecules and displayed sensitive optical properties to particle size and surface modification. The AgNPs with a diameter of ∼6 nm prevented the proliferation of human K562 cells with leukemia, implying their potential cancer activity.170 The procedure for the synthesis of AgNPs using biopolymers is shown in Fig. 5.
Si S. et al. (2007) synthesized AgNPs at pH 11 utilizing synthetic oligopeptides containing tryptophan residue at the C-terminus. The tryptophan residue in the peptides, possibly through electron transfer, is responsible for reducing metal ions to the respective metals.171 Oligopeptides based on L-valine with the chemical structure Z–(L-Val) 3–OMe and Z–(L-Val) 2–L-Cys(S-Bzl)–OMe formed stable organogels in butanol. Both peptides are effective gelators, but they crystallize more readily than Z–(L-Val) 2–L-Cys(S-Bzl)–OMe. These two peptides are capable of forming mixed fibers, including gel butanol. The fibers can be mineralized using DMF as a reducing agent with AgNPs. The Z–(L-Val) 2–L-Cys(S-Bzl)–OMe fraction of the sulfur-containing peptide controlled the shape and size of the resulting NPs. Small spherical particles were distributed throughout the fiber at a high Z–(L-Val) 2–L-Cys(S-Bzl)–OMe content. A lower Z–(L-Val) 2–L-Cys(S-Bzl)–OMe content led to an increase in particle size and more complex forms such as plate-like and silver-like raspberry particles. The interactions between peptide and silver ions or silver particles occur through the complexation of silver ions to the sulfur atom of the thioether moiety and were shown to be the key interaction in controlling the formation of the particles.172
Kasthuri J. et al. (2009) reported the synthesis of quasi-sphere AgNPs using apiine as the reduction and stabilization agent. The size and shape of the NPs could be controlled by varying the ratio of metal salts to apiine compound in the reaction medium. UV-vis-NIR, TEM, FTIR spectroscopy, XRD and TGA were used to characterize the synthesized NPs. The interaction between the NPs and the carbonyl group of the apiine compound was confirmed using FT-IR spectroscopy. The average size of the AgNPs was found to be 39 nm via TEM invetigation.173 Safaepour M. et al. (2009) synthesized evenly dispersed AgNPs with a uniform size and shape in the range of 1 to 10 nm using geraniol. The cytotoxicity analysis of the AgNPs showed a direct dose–response relationship, where higher concentrations resulted in increased cytotoxicity. The AgNPs were able to inhibit the growth of the Fibrosarcoma-Wehi 164 cell line by less than 30% at a concentration of 1 μg mL−1.174 The aqueous solution of AgNPs exhibited different SPR when prepared at different pH values. PEG was used as a reducing and stabilizing agent to synthesize AgNPs since it is ecofriendly, which produced monodispersed particles with a diameter of less than 10 nm. The colloids exhibited activity against Gram-positive and Gram-negative bacteria and fungi. Biodegradable starch played the role of a capping agent in the synthesis of AgNPs. The analysis showed that a starch layer was coated on NPs. The diameters of the particles ranged from 5–20 nm. XRD analysis showed the face-centered cubic structure of the NPs. In many fields of science, ion-exchangeable polymers act as capping agents. These often-used polymers contain phosphonic acid groups with a low molecular weight. Polymer complexation to Ag+ occurs, and then the metal ions are reduced to NPs. In the presence of an ion-exchange polymer, AgNPs were stabilized. The morphology of the surface indicated the formation of cubes and rectangular prism structures. Copolymers such as CD, grafted with PAA, helped to synthesize AgNPs initiated by potassium persulfate.175
Maity D. et al. (2011) used poly(methyl vinyl ether co maleic anhydride) (PVM/MA) as a reducing and capping agent. The synthesized NPs were stable for a month at room temperature and surrounded by 5–8 nm sheath of PVM/MA.176 A variety of factors influenced the formation of NPs, such as acidity, initial concentration of starting materials, and molar ratio of reactants. Some dispersing agents prevented the accumulation of NPs and helped in the analysis of morphology, particle size, composition of elements, etc. The NPs were non-aggregated, and possessed a face-centered cubic (FCC) structure, and spherical shape. Ascorbic acid or citrate was used to reduce ions, which resulted in an average particle size of approximately 10.2–13.7 nm. The zeta potential ranged from 40–42 mV and was primarily influenced by the acidity and size of the NPs.177 When reacted with ammonium hydroxide, formaldehyde produced a polymer that affected the way silver was bound to the substrate. In unfavorable conditions for the synthesis of the polymer, the NPs formed were concentrated and possessed a gold-silver plasmon resonance (498 nm).177
Fig. 6 (a) Reaction mechanism for the synthesis of AgNPs due to the flavanoids92 present in plant extract. (b) Reaction mechanism for the synthesis of AgNPs due to NADH present in fungi and bacteria. |
Fig. 7 SEM images of AgNPs synthesized from different sources.4 |
Chen Yu et al. reported the application of AgNPs in catalysis, which enhanced the reduction rate of NaBH4 in the reduction of azo dye.65,186 Due to the enhanced electromagnetic field on the surface of AgNPs, AgNPs are broadly used in nanomedicine including diagnostics, biomedicines, nanoelectronics and molecular imaging. AgNPs act as nanoantennas due to the increase in their resonant SPR peak with an increase in the intensity of the electromagnetic field. AgNPs act as sensors with Raman spectroscopy to identify any molecule due specific vibrational modes.50,187 Due to the antimicrobial action of AgNPs they are used in food packaging to prevent microbial infections.188,191 AgNPs are used in nanosensors to analyze contaminations, colors or flavors, drinking water and for clinical diagnostics.189 AgNPs have found application in agriculture also. Plant productivity can be enhanced via the communication of nanotechnology-based smart plant sensors with actuate electronic device, where these sensors optimize and automate water and agrochemical allocation, and enable high-throughput plant chemical phenotyping. Ag NPs are used in plant nutrition and defense against diseases,192 where AgNPs can be delivered with pesticides to crops to enhance the production of crops in agriculture.190 AgNPs are extensively used as therapeutic agents as antifungal, antimicrobial, anti-inflammatory and antiviral agents. Due to the antimicrobial action of AgNPs, they can be used in drug delivery to reduce the dose of drugs, improve specificity and decrease toxicity.88,193
AgNPs | Silver nanoparticles |
NPs | Nanoparticles |
PEG | Polyethylene glycol |
SERS | Surface-enhanced Raman scattering |
DLS | Dynamic light scattering |
TEM | Transmission electron microscopy |
SEM | Scanning electron microscopy |
XRD | X-ray diffraction spectroscopy |
EDAX | Energy-dispersive X-ray spectroscopy |
FTIR | Fourier transform infrared spectroscopy |
CD | Cyclodextrin |
PAA | Polyacrylic acid |
CMC | Carboxy methyl cellulose |
NTA | NP tracking analysis |
PCS | Photon correlation spectroscopy |
SPR | Surface plasmon resonance |
TGA | Thermo-gravimetric analysis |
This journal is © The Royal Society of Chemistry 2019 |