Nanotechnol Rev 2016; 5(6): 601–622

Review

Agbaje Lateef*, Sunday A. Ojo and Joseph A. Elegbede The emerging roles of arthropods and their metabolites in the green synthesis of metallic nanoparticles

DOI 10.1515/ntrev-2016-0049 Received June 22, 2016; accepted August 5, 2016; previously 1 Introduction ­published online October 14, 2016 Arthropods belong to the phylum Arthropoda, and this Abstract: Nanotechnology has remained relevant as a consists of the insects, arachnids, myriapods, and crus- multifacet discipline, which cuts across different areas taceans. Arthropods possess distinct features, which of science and technology. Several successful attempts include jointed limbs and cuticle composed of calcium had been documented regarding the involvement of bio- carbonate and/or α-chitin [1]. There are several millions logical materials in the green synthesis of various metal of arthropod species varying between 1,170,000 and 5–10 nanoparticles (MeNPs) because of their eco-friendliness, million, and for this reason, they account for more than cost-effectiveness, safe handling, and ultimately less 80% of all known species of living animals and approxi- toxicity as opposed to the physical and chemical meth- mately two thirds of currently existing species [2]. There ods with their concomitant problems. Biological agents, are four major groups of arthropods: Chelicerata (horse- including bacteria, fungi, algae, enzymes, plants, and shoe, spiders, and scorpions), Crustacea (shrimps, lob- their extracts, have been implicated in most cases by sev- sters, and crabs), Tracheata (insects and myriapods), eral authors. Moreover, nanotechnology in recent times and the extinct trilobites, which were the first animals has also made an inroad for animal species, specifically whose eyes were reportedly capable of high-degree reso- arthropods and metabolites thereof to be used as excel- lution, with several other species that are well known [3]. lent candidates for the green synthesis of MeNPs. The It has been established that insects and other arthropods increasing literature on the use of metabolites of arthro- provide condiments that have been highly essential and pods for the green synthesis of nanoparticles has neces- of utmost importance in traditional medicine for many sitated the need to document a review on their relevance years, particularly in some parts of Africa, East Asia, and in nanobiotechnology. The review, which represents the South America [4]. first of its kind, seeks to underscore the importance of Natural products, which are usually secondary metab- arthropods in the multidisciplinary subject of nanosci- olites, and their derivatives constitute more than 50% of ence and nanotechnology. the drugs used clinically for the treatment of diverse ail- ments world over. Many of these products are produced Keywords: arthropods; green synthesis; nanoparticles; from plants, fungi, and bacteria [5]. However, it has been spider; wasp. reported that arthropods, being ubiquitous globally, have also played a vital role in the provision of inexpensive and abundant healing agents, most especially in coun- tries where there are economic challenges [5]. Some of the *Corresponding author: Agbaje Lateef, Laboratory of Industrial arthropods’ natural agents include bee venom contain- Microbiology and Nanobiotechnology, Nanotechnology Research ing varieties of peptides, including adolapin, mast-cell Group (NANO+), Department of Pure and Applied Biology, Ladoke Akintola University of Technology, PMB 4000, Ogbomoso, Nigeria, degrading peptide, melittin, phospholipase, and non- e-mail: [email protected]; [email protected] peptide compounds, which all have useful applications Sunday A. Ojo and Joseph A. Elegbede: Laboratory of Industrial in the treatment of cancer [6–8], control of diabetes [9], Microbiology and Nanobiotechnology, Department of Pure and treatment of neurodegenerative disease [10], treatment of Applied Biology, Ladoke Akintola University of Technology, PMB free radical-mediated disease [11], and treatment against 4000, Ogbomoso, Nigeria HIV infection [12]. 602 A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles

It was also reported that enzymes such as chymot- period without losing its viability. Its life span is esti- rypsin, serine proteases, metalloproteinase, and aspartyl mated to be 10 times more than that of the workers (i.e. proteinase produced by maggots (larvae of Lucilia sericata, 1–2 years) [47]. Lucilia cuprina, Calliphora vicina, and Phormia regina) There are a million neurons found in the honey bee play important roles in the healing of diabetic foot wound, (four times as much as that of Drosophila but five orders postoperative infections, leg ulcers, and bed sores [13–16]. of magnitude less than that of humans) according to Furthermore, defensin, an enzyme produced by house flies Witthöft et al. [48]. Honey bees have the ability to learn alongside other factors, played an important role as an abstract concept, which may be “same” or “different” antibacterial agent against the methicillin-resistant Staph- [49]. They are holometabolous organisms belonging to ylococcus aureus (MRSA) and the vancomycin-resistant the same insect order (Hymenoptera) as species of ants, enterococci [17, 18]. Cantharidin, a toxin produced from the sawflies, and wasps. The male bees arise from unfertilized bodies of several species of blister beetles, has also been haploid eggs, whereas the females arise from fertilized found as a useful therapeutic agent. It has also been used diploid eggs; hence, they exhibit haplodiploid sex deter- for the removal of warts [19], treatment of cancer [20–26], mination [50, 51]. The suggested geographical regions and prevention of apoptosis and DNA damage [27]. Polybia where A. mellifera originated are Africa [45], Middle East MPI, a novel antimicrobial peptide present in the venom of [52], and Asia [53], and these creatures were reportedly social wasp (Polybia paulista), was reported to be capable carried by humans to all other parts of the world because of cell membrane disruption and has also played a vital of their ability to make honey [53]. role in cancer therapy [28, 29]. Nanotechnology has continued to receive great attrac- tions because of its widespread applications in different aspects of life endeavors. It is a subject that cuts across 3 Bee honey different fields of science and technology. The quest for For many centuries, honey as a natural product of honey nanomaterials that are environmentally benign, cost- bee, is renowned as a sweetening agent of mankind and is effective, and nature-friendly has led to the green (bio- also considered as one of the healthiest foods ever known. logical) synthesis of metal nanoparticles (MeNPs) with the Honey is composed of fructose and glucose as well as amino size range of 1–100 nm, and it is an attractive alternative to acids that help nourish the body and has been a subject of physical and chemical protocols. Several biological agents extensive study all over the world in terms of their physico- including bacteria, fungi, plants, enzymes, and extracts chemical properties, mineral content, vitamins, and quality have been used for the biological synthesis of MeNPs control [54–58]. According to Philip [59], it was reported that [30–43]. However, there are few reports on the biological the high energy, chemical constituent, vitamins, enzymes, synthesis of MeNPs using metabolites of the arthropods. and important minerals such as potassium and magnesium This article therefore seeks to review the involvement of found in the honey help to elongate the life span of man. several arthropods in the green synthesis of MeNPs as well Honey plays an important role in the repair and regenera- as their various practical applications. tion of tissues. For instance, the 5.8-kDa of honey compo- nent isolated by Tonks et al. [60] was reported to induce the production of tumor necrosis factor-α cytokines via TLR4 in 2 Honey bee human monocyte cultures, which enhanced the repair and regeneration of damaged tissue. In this modern age, Apis mellifera, which is commonly There are also several reports on the use of honey in called western honey bee, remains one of the few species the treatment of wound infections, bedsores, and burns having a considerable social impact [44]. As one of the [61]. In addition, the boundaries of knowledge of bees and “eusocial” colonies of insects, honey bees are distin- their honey have been further extended as a result of their guished into two castes, the queen and the worker. The contributions to the advancement of nanotechnology. Fol- queen (usually one per colony) has the ability to pro- lowing the necessity for safe, ecologically benign, and create, whereas the workers amass food, take care of cost-effective natural agents in the synthesis of MeNPs, the young ones, construct the nest, and also secure the bees and bee honey have been used to mediate the bio- colony. Social evolution has provided the honey bee with synthesis of various MeNPs such as silver (Ag), gold (Au), unique characteristics [45, 46]. The queen is capable of cerium oxide (CeO), palladium (Pd), and copper oxide laying up to 2000 eggs in a day and store sperm for a long (Cu2O) nanoparticles (Table 1). A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles 603 [5] [69] [71] [74] [63] [73] [59] [62] [66] [68] [67] [65] [72] [64] [70] References

– Applications in additive antifungal, Antibacterial, improvement antibiotic paint, and – Treatment of colon cancer colon of Treatment Antibacterial activity Antibacterial – – Prevention of mild steel corrosion in corrosion steel mild of Prevention environment acidic Cross-coupling for the synthesis the synthesis for Cross-coupling of hydrogenation and biaryls of olefins conjugated – Antibacterial and antifungal and Antibacterial Antibacterial Antibacterial, antifungal, dye dye antifungal, Antibacterial, and anticoagulant, degradation, activities thrombolytic Antibacterial –

Spherical Spherical Shape Cluster with core-shell core-shell with Cluster structure Spherical – Spherical Spherical – – – Spherical – Anisotropic; sphere, 3D sphere, Anisotropic; rod, rhombus, triangle, hexagon Spherical, pyramidal, and and pyramidal, Spherical, cuboidal –

4 – – – – 10 15 23 9.9 34.5 3–50 5–40 12–18 12.5–95.5 11.16–14.52 Size (nm) Size

O) 2 Silver (Ag) Silver Silver (Ag) Silver Type of nanoparticles of Type (Ag) Silver AgNPs Silver (Ag) Silver (Cu oxide Copper AgNPs Silver (Ag) Silver Gold (Au) Gold Silver (Ag) Silver Palladium (Pd) Palladium Cerium (Ce) Cerium Gold (Au) Gold Silver (Ag) Silver Silver (Ag) Silver

3 ; 3 ; ; 3 4 : room : room 3 at pH 9–10 at glucose; + glucose; 3 3 : room : room 3 O; pH 12; solution (0.02 solution 2 3 O + NaOH 2 .H 2 C (in oil (in oil 60 ° C at O); stirred 2 C (200 rpm); 24–72 h (1:2); 37 ° C 3 . 6H 3 40 ml of 1 m AgNO of + 40 ml ) 3 (added up to 10 ml with distilled distilled with 10 ml to up (added ; pH 6.5–8.5; 1 min 4 3 40 ml of 1 m AgNO of + 40 ml O); room temperature; 2 h temperature; O); room 2 m 0.1 m of + 20 ml solution honey of 15 ml AgNO 1 ml of the honey solution (1 g/100 ml (1 g/100 ml solution the honey of 1 ml solution/1 + ammonium water) distilled m AgNO NaOH (0.1 m ) hydrolyzed of 1 ml nest 3 ml of honey + CuCl of 3 ml Aqueous SF + AgNO SF solution Aqueous 30 ml HAuCl + 30 ml solution honey 10 ml Phosphate buffer treated ground bee ground treated buffer Phosphate (pH 7, 25 m ) + 1 AgNO cerium nitrate nitrate + cerium solution honey of 50 ml (Ce(NO Camellia Camellia of honey + 50 ml of 5 ml lemon juice of + 5 ml sinensis 20 ml of AgNO of + 20 ml solution honey of 15 ml 95 ml of 0.1 m AgNO of honey + 95 ml of 5 ml + 1 m AgNO solution honey of 15 ml + AgNO silk modified PAA 1 ml of 1 m m of + 1 ml solution honey of 1–5 ml HAuCl ) hydrolyzed NaOH (0.1 m ) hydrolyzed of 1 ml cobweb temperature; 8 min temperature; Reaction conditions Reaction 8 min temperature; incubation (room temperature), 220 rpm temperature), (room incubation 30 min) temperature, (room stirred UV light (365 nm); 2 h light + UV mol/L) pH 8.5 stirred; 3 h stirred; stirred (under bright sunlight, 10 min) sunlight, bright (under stirred (1 m ); pH 6.5–8.58 50 ml of distilled H distilled of (2 g) + 50 ml bath); 6 h bath); H

Bee honey Bee honey Wasp-nest Paper extract Bee honey SF Bee honey Honey bee Honey Bee honey Honey and and Honey sinensis Camellia lemon with fortified Bee honey Bee honey Bee honey Silk fiber Silk Bee honey Cobweb extract Cobweb Green synthesis of metallic nanoparticles using metabolites of arthropods arthropods of metabolites using nanoparticles metallic of synthesis 1: Green Table Metabolites 604 A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles [79] [75] [76] [74] [80] [77] [84] [83] [81] [81] [78] [81] [81] [82] References

) 4 Antioxidant, ferric reducing antioxidant antioxidant reducing ferric Antioxidant, AuNPs of synthesis and assay, power + HAuCl (WSSF-NPs – Oxygen reduction reaction catalytic catalytic reaction reduction Oxygen activity – Applications – – – Antibacterial activities on fabric activities Antibacterial Antibacterial activity Antibacterial – – Heterogeneous catalysis of of catalysis Heterogeneous reduction p -nitrophenol activity Antibacterial inhibition biofilm and Antibacterial activity

Spherical Spherical/monodisperse Flowerlike/monodisperse Spherical/homogeneously Spherical/homogeneously disperse Shape Core-shell structure Core-shell Roughly spherical with with spherical Roughly dispersed edges/well smooth Nearly round Nearly Spherical/fairly Spherical/fairly monodisperse Round Monodisperse Monodisperse

6 5 – 40 10 29 15 20–40 2 ± 0.2 3 ± 1.0 5 ± 1.0 46–117 13 ± 2.5 12 ± 2.1 Size (nm) Size

WSSF-NPs SeNPs AuNP/RGO composite AuNPs AgNPs Type of nanoparticles of Type AuNPs AgNPs QD-CDs/SF QD-CDs/SF nanocomposite PtNPs PdNPs AgNPs AuNPs AgNPs AgNPs

3 O: 2 S : H

2 2 3 ; pH 9–10 4 solution (1, solution 3 borate in 0.1 m borate 4 O at pH 3 for 10 h pH 3 for O at 2 + Na solution 2 (25 m ); pH 7; 45 ° C; 5 4 100 ml AgNO + 100 ml solution 4 at room temperature room at 4 at 85 ° C at at room temperature room at at room temperature room at (5–80 mg) + 5 ml powder 6 4 3 3 C for approximately 1.5 h approximately for 45 ° C OH) at 5 PdCl 2 PtCl H 2 2 10 ml SF + 10 mg AgNO SF solution 10 ml + 1 m HAuCl films Silk + CdCl solution SF Aqueous SF + HAuCl SF solution Aqueous 10 ml RSF RSF + 10 ml solution oxide Graphene + HAuCl solution 2 ml SF-cysteine solution at pH 10 + 2 m at solution SF-cysteine 2 ml HAuCl SF irradiated with electron accelerator in accelerator electron with irradiated SF 30 kGy) air (1, 5, 10, 20, and 0.5 ml NaBH 0.5 ml AgNO 2 ml SF-cysteine solution at pH 10 + 2 m at solution SF-cysteine 2 ml H Selenious acid solution solution acid (0.04 wt.%) + Selenious SF (4 m ) acid (1 m ) + Ascorbic 2 ml SF-cysteine solution at pH 10 + 2 m at solution SF-cysteine 2 ml AgNO pH 10 + 2 m at solution SF-cysteine 2 ml Na + AgNO (5–20 mg/ml) SS min buffer at pH 10.5 or H at buffer ) at pH 9 and 11 at room room 11 at pH 9 and 10 m ) at 5, and stirring. constant temperature; Reaction conditions Reaction gamma radiation (10–80 kGy) radiation + gamma powder ternary solution (CaCl solution + ternary solution C SS solution (0.29 m ) + SS solution regenerated SF solution (1 wt.%) under (1 wt.%) under solution SF regenerated 2 h for bulb an incandescent with light

SF Silk films Silk SF SF RSF SF SF Table 1 (continued) Table Sericin SF SF SF SF SF Sericin Metabolites A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles 605

4 Bee and bee honey-mediated diffraction (XRD), and transmission electron microscopy (TEM). Maximum absorption at 413 nm and monodis- MeNPs persed spherical-shaped nanoparticles with an average size of 4 nm (as revealed by TEM) were observed. XRD 4.1 Silver nanoparticles (AgNPs) revealed the biosynthesized nanoparticles as nanocrystal- lites, which were 6 nm in size. Although glucose in honey Silver is a nontoxic inorganic material recognized for pos- was suspected for the reduction process, proteins present sessing an inhibitory effect toward 650 types of microbes in the honey were reportedly responsible for the stabiliza- [85], and also displays the highest electrical and thermal tion of AgNPs. conductivities among all the metals [86]. AgNPs have a El-Deeb et al. [63] investigated the involvement extract wide range of applications and the uppermost level of of dried bee in the synthesis of AgNPs. The extract of the commercialization among the nanomaterials [87]. For honey bee was reacted with 1-mm silver nitrate as a sub- instance, among different nanoparticles that have been strate for the synthesis of the nanoparticles. There was investigated, AgNPs are the most promising particles that noticeable change in color of the solution (indicating the are used in the field of nanomedicine for their antimicro- formation of AgNPs) with maximum absorption at 450 nm. bial activity against several microbes [88]. Yezhelyev et al. The nanoparticles were spherical with carbon, oxygen, [89] reported that AgNPs in the size range 1–100 nm is very and silver being the most prevalent elements according to advantageous for the diagnosis and treatment of cancers, TEM and energy-dispersive spectroscopic (EDX) analysis. which led to the new discipline of nano-oncology. AgNPs The biosynthesized AgNPs were proposed as a promising (not silver nanoclusters) became a member of antimicro- agent in drug delivery and colon cancer therapy because bial silver family because of their elevated specific surface of their anticolon cancer activities at both the cellular area and prominent fraction of surface atoms than bulk and the molecular level. In another study, Obot et al. silver. It has also been proposed that AgNPs interact with [66] reported the formation of stable AgNPs with charac- the bacterial membranes to cause structural alteration teristic yellow brown color when 5 ml of bee honey was and degradation of cells. AgNPs destroy permeability of reacted with 95 ml of 0.1 m silver nitrate after exposing outer membrane, hinder respiration and growth of cells, honey-AgNO3 solution to sunlight. The absorbance peak and obliterate the structure of membrane, leading to cell was found at 450 nm. The suggested reducing agent in decomposition and death eventually [90], and may cause the honey was fructose, whereas proteins were found to apoptosis through the arrest of G0/G1 cycle [91]. It has be responsible for the stabilization of the resulting AgNPs. become increasingly clear that nanoparticles play promi- The nanoparticles displayed a high level of corrosion inhi- nent roles in the treatment of cancer, including the use in bition of mild steel in 0.5 m HCl, producing an inhibition targeted drug delivery [92]. efficiency of 91.5%, with a treatment of 6% v/v of AgNPs. Singh et al. [5] demonstrated the biosynthesis of Different levels of local honey from Malaysia used AgNPs using bee honey. Honey was boiled in deionized for the synthesis of AgNPs were reported by Haiza et al. water and added to 1 mm concentration of silver nitrate [70]. By modulating the pH of AgNO3 and local honey as and ammonium solution. The change in the color of the well as their concentrations, AgNPs of different morphol- solution from bright yellow to dark brown (after 72 h of ogies were synthesized. The color of the AgNPs formed reaction) indicated the formation of nanoparticles. The was golden yellow. As the concentration of the honey biosynthesized AgNPs maximally absorbed at 420 nm increased, the size of the nanoparticles decreased and when subjected to UV-Vis spectroscopy. Observation of vice versa in the range of 15.63–26.05 nm. The biosynthe- this peak showed the extracellular reduction of Ag+ ions. sized AgNPs were characterized using UV-Vis spectros- The Fourier transform infrared (FTIR) spectroscopy of copy, FTIR, SEM, and field emission scanning electron the AgNP solution also revealed proteins as the biomol- microscope. The absorbance peaks of AgNPs at pH of 6.67, ecules responsible for the stabilization of the biosynthe- 7.00, 7.51, and 8.01 were 490, 482, 430, and 424 nm, respec- sized AgNPs. The AgNPs were reported to have excellent tively. The biosynthesized nanoparticles were anisotropic antimicrobial activity against MRSA. Moreover, following with polydispersed distribution. The reducing and stabi- the bioreduction of the silver ions in the solution using lizing agents in the honey-AgNO3 solution were glucose bee honey, Philip [59] reported the synthesis of AgNPs and protein, respectively. visually characterized by the formation of golden yellow The involvement of extract of plant fortified with color. The biosynthesized AgNPs were characterized using honey also mediated the synthesis AgNPs under sonica- analytical techniques such as UV-Vis spectroscopy, X-ray tion according to Kothai and Jayanthi [69]. The extract 606 A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles of Camellia sinensis fortified with lemon and honey was Sreelakshmi et al. [65] reacted different volumes of reacted with 0.001 m AgNO3. As the reaction proceeded, the honey solution (water/honey) with HAuCl4 separately, color of the solution changed from pale yellow to reddish with the color of the reaction mixtures turned pale yellow brown, indicating the formation of AgNPs. The analytical at the end of the experiment, indicating the synthesis of techniques used included UV-Vis, FTIR, EDX, and SEM. AuNPs. Absorbance peak was observed at 550 nm. The The absorbance peak was observed at 425 nm. Water-sol- AuNPs (diameter 9.9 nm) were spherical in shape and uble alkaloids, flavonoids, and phenols were reported as crystalline in nature as revealed by TEM and XRD. They the capping and stabilizing agents with elemental silver also showed an excellent growth inhibition of test Gram- being the most prevalent in the solution. The nanoparti- positive and Gram-negative bacteria, including antibiotic- cles formed were spherical in shape and polydispersed in resistant strains as well as Candida albicans. The MIC of distribution with the size range of 30.2–75.4 nm. 31.25 μg/ml was obtained against S. aureus MTCC 1144, whereas 62.5 μg/ml was obtained against Escherichia coli MTCC 739, Salmonella typi MTCC 733, Streptococcus 4.2 Gold nanoparticles (AuNPs) mutans MTCC 890, and C. albicans MTCC 183.

MeNPs, particularly AuNPs, have remarkable biocom- patibility and nontoxicity. Moreover, it is less oxidizable 4.3 Cerium oxide nanoparticles substance than silver and, thus, can be used for long-term applications. Antibodies and proteins can be conjugated Darroudi et al. [67] established the involvement of honey to AuNPs through definite thiol functionality, which bee in the synthesis of cerium oxide nanoparticles makes them significant for biochemical detection and (CeO2NPs) – a rare-earth material. The solution of honey therapeutic functions [76]. AuNPs are extensively studied was made by dissolving honey in distilled water. The solu- because of their explicit optical, catalytic, electric, and tion was well stirred under room temperature. Cerium delivery properties [93]. Uniform nanostructures with a oxide was reacted with a clear solution in a reaction vessel range of morphologies have been produced, such as wires placed in an oil bath at 60°C, and a light yellow color [94], spheres [95], plates [96], cubes [97], dendrites [98], resin was obtained after stirring and was also divided and flowers [90]. It has been described that thiol moiety into parts. Exposure to different calcinating tempera- (–SH) can capably advance the stability and dispersity of tures (200–800°C) and subsequent maintenance of the colloidal noble MeNPs, particularly to AuNPs in solution, product at specific temperatures in air led to the formation compared with other functional groups (–NH2, –COOH, of CeO2NPs. The sol-gel derived CeO2NPs with aqueous etc.), and this is mainly because thiol (–SH) groups bind honey solution as a greener capping and stabilizing agent covalently to the surface of AuNPs [99]. Several reports changed from black color to lemon and finally white as a also support the interface of thiol moiety with Ag, Pd, and result of an increase in calcinating temperature. Absorp- Pt nanoparticles [81]. tion peak was observed at 314 nm. Other analytical tech- Philip [62] demonstrated the use of honey in the niques used included field emission electron microscope, biosynthesis of AuNPs. Natural honey was dissolved in powder XRD, energy-dispersive spectrum, FTIR, and ther- deionized water, and the mixture was reacted with gold mogravimetric analysis. The biosynthesized CeO2NPs were chloride (HAuCl4) solution. The AuNPs formed after the approximately 23 nm and isotropic with CeO2 as the most − bioreduction of AuCl4 were light purple in color, and the prevalent compound in the sample. By using the neuro2A maximum absorbance of the particles was obtained at 541 cells, the nontoxicity of the synthesized CeO2NPs at con- nm. The sizes of the nanoparticles reduced as the quan- centrations lower than 25 μg/ml was demonstrated. The tity of the honey increased. The nanoparticles produced study concluded that the green method could be used for were anisotropic structures of sphere, rod, and triangle the synthesis of CeO2NPs, avoiding hazardous materials/ as revealed by TEM. Other analytical techniques used steps. were XRD (which confirmed the crystalline nature of the biosynthesized AuNPs with an average size of ~ 15 nm) and FTIR, revealing protein as the capping and stabiliza- 4.4 Palladium, copper oxide, and platinum tion biomolecule. The nanoparticles were also suggested nanoparticles for therapeutic use because of their photoluminescence potentials. The AuNPs produced photoluminescence at Reddy et al. [68] synthesized palladium nanoparticles 447 nm because of functionalization with honey. (PdNPs) by reacting bee honey solution (water/honey) A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles 607

with palladium chloride (PdCl2) in acidic medium. The of spiders in the World is 40,000 [105]. Many species of absorption bands of biosynthesized PdNPs at 223 and spiders construct webs, specifically the orb webs [106]. 280 nm confirmed the total reduction of Pd ions. XRD Many times, the production of silk evolved in arthropods pattern showed the biosynthesized nanoparticles as [107]; however, spiders are recognized as notable and crystalline solid with face-centered cubic structure. EDX excellent silk craftsmen. They use different types of silk result revealed strong Pd spectra with carbon and oxygen threads to form an array of structures, which range from as functional entities. The nanoparticles were within the simple lifelines to shelters for moulting, from egg sacs to range of 5 and 40 nm according to SEM analysis. The bio- webs, and also for ballooning (dynamic kitting) [108]. synthesized PdNPs were used in Suzuki cross coupling for the synthesis of biaryls and also for the hydrogenation of conjugated olefin because of their catalytic property. 6 Cobweb (spider silk)

Polycrystalline copper oxide (Cu2O) is a semiconduct- ing material used as one of the constituents of paints and Silk can be loosely defined as fibrous proteins that are as antitumor agent [100, 101]. Ali et al. [64] investigated extended outside an organism body and are composed the use of honey to mediate the synthesis of their nano- of semicrystalline molecular structures [107]. Spider silk particles. Solutions of edible honey, copper chloride dehy- is spun by spigots found on the spinnerets (which are drate, and NaOH in distilled water were reacted together three pairs of appendage-like organs) on the abdomen of and stirred at room temperature with pH 12. However, dif- the spiders. Spider silk has been reported to have unique ferent solvents were used to obtain the final product for chemical, molecular structure, and molecular properties comparison. The resultant Cu2O nanoparticles (Cu2ONPs) [109]. Silk fibers produced ranked among the strongest, were observed to have brick red color. The nanoparticles stretchiest, and toughest biomaterials known and are were spherical in shape and crystalline in nature with Cu therefore common subjects of behavioral and ecological (I)-O stretching according to SEM, FTIR, and XRD analy- research [110]. sis. The nanoparticles produced inhibited the growth of S. Spiders invest physiologically important compounds aureus and E. coli within 13–14 mm. in the construction of their webs. Most spider silks consist Venu et al. [102] have demonstrated the synthesis of proteins that are composed of highly repetitive amino of platinum nanoparticles (PtNPs) and nanowires using acids “motifs”, that is, short amino acid sequence mainly honey. The reaction conducted at 100°C for 2 h led to the consisting of highly repetitive glycine and alanine blocks formation of PtNPs, having the size of ~2.2 nm, whereas at [111], which is why silks are often called block copolymers. longer heating of 4–20 h, nanowires of 5–15 nm in length Pyrrolidine, a nonprotein compound that has hygroscopic were obtained through the self-assemblage of PtNPs. properties, helps to keep the silk moist and also wards off The particles absorbed maximally at 533 nm, indicating ants invasion. Potassium hydrogen phosphate found in the formation of PtNPs. The FTIR showed that particles spiders produces a photon that reduces the pH to 4, thus were formed as a result of reduction by proteins through making the silk acidic. This protects the silk from bacte- binding with carboxylate ion, whereas the XRD showed ria and fungi, which could otherwise digest the protein the formation of highly crystalline particles with face-cen- [112]. Potassium nitrate and phospholipids found in the tered cubic structure. The catalytic application of synthe- silk are believed to prevent the protein from denaturation sized PtNPs was demonstrated through the synthesis of an in the acidic milieu (surrounding) and also to prevent the organic dye, antipyrilquinoneimine, with the potential for growth of fungi and bacteria on it [113–115]. Other com- detection and removal of anilines from water and soil. ponents include phosphorylated glycoprotein, pigments, and lipids, which enhance good adhesive property of the silk fiber. They are nutritionally important, and they act as 5 Spiders a protection layer in the fiber [116, 117]. Carpathian mountain dwellers used the tubes of Spiders are creatures with four pairs of legs. They have chi- silk produced by a spider species, Atypus, to cover their tinous coverings and two body regions, which are divided wounds, and the silk reportedly facilitated the healing into cephalothorax and abdomen. The cephalothorax of the wounds because of its antiseptic properties [113]. consists of head and thorax combined together as one Also, because the silk is rich in vitamin K, it is consid- external unit [103]. Of approximately 1.7 million species ered to be effective in blood clotting [118]. It was reported of bacteria, plants, animals, fungi, and protists described that the web of Nephila was used by the fishermen in according to DMNS [104], the proximate figure of species the Indo-Pacific ocean to catch small fish [113]. The silk 608 A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles of Nephila clavipes was also used to help in mammalian The nanoparticles were crystalline in nature and spherical neuronal regeneration [119]. At one time, spider silk was in shape with polydispersed distribution, and their sizes commonly used as a thread in optical devices such as tel- ranged between 3 and 50 nm (Figure 1). The biosynthe- escopes, microscopes, and telescopic riffle sights. Several sized nanoparticles inhibited the growth of test clinical studies have also shown that some of bisphosphonate bacterial isolates and also potentiated the activities of peptides that have antibacterial activity could be found cefixime, augmentin, and ofloxacin to the tune of 3.9%– in the spider silk [120]. Roozbahani et al. [121] evaluated 100%, 6.3%–100%, and 3.1–20%, respectively, against the antimicrobial activity of the silk of the spider Pholcus multiple drug-resistant organisms, including S. aureus, phalangioides against food-borne bacterial pathogens. Klebsiella granulomatis, Pseudomonas aeruginosa, and E. Spider cobwebs have also been used for the monitoring coli (Figure 2). The AgNPs were therefore suggested as an of pollution in industrial and residential areas [122, 123], antibacterial agent for clinical applications. The nanopar- and spiders have been used as biocontrol agents in reduc- ticles were also reportedly useful as an additive in emul- ing populations of insect pests on farmlands [124]. In sion paint for quality improvement and for the prevention addition, venoms of spiders have been evaluated for the of microbial attack, through the complete obliteration of treatment of cardiac arrhythmia [125], Alzheimer’s disease deteriorating bacterial and fungal species that were inoc- [126], and erectile dysfunction [127]. ulated in to the emulsion paint (Figure 3). On the account of the combination of excellent mechanical properties, biocompatibility, and slow bio- degradability, spider silk has found tremendous appli- cations in biomedical field, such as tissue engineering 8 Paper wasps [128], and also as additives in cosmetic products, such as Paper wasps belonging to the genus Polistes have been shampoos, soaps, creams, and nail varnish, enhancing studied in details among the eusocial wasps (Hymenop- the brightness, softness, and or toughness of the products tera, Vespidae, and Polistinae), with the report of exist- [128]. Furthermore, spider silk fibers could be applied in ence of approximately 200 cosmopolitan species [129–131]. technical textiles (used, for example, in parachutes and Polistes live in groups of approximately 100 individuals bulletproof vests), which demand high toughness in per colony in nonenveloped nests. The nests are con- combination with thinness [128]. The quest for biological structed on surfaces, such as twigs, leaves, dense shrubs material that could be used in the area of nanotechnology and grass, hollow trees, and elevated natural cavities and for the synthesis of safe, eco-friendly, and cost-effective man-made structures [132, 133]. These nests, which are MeNPs has further led to the exploration of spiders for the paperlike, are derivatives of the eating habits of wasps on synthesis of nanoparticles. plant resources [134] and are used by female wasps as sites to lay eggs. The nests are rich in cellulose and proteins, with the reported occurrence of more than 20 amino acids 7 Cobweb-mediated synthesis obtained in field and laboratory nests; the most frequently occurring amino acids are glycine, serine, alanine, valine, of AgNPs and proline [135–137]. Antimicrobial metabolites, such as Dominulin A and B, have been reported from the cuticle In our laboratory, we have further extended the limits of and venom of Polistes dominulus, producing MIC of 2 and knowledge on biotechnological applications of biosynthe- 8 μg/ml against Bacillus subtilis and E. coli [138]. However, sized AgNPs through the first report of the use of spider the metabolites of paper wasps have not been adequately cobweb as a novel biomaterial to synthesize AgNPs [71]. exploited for the green synthesis of nanoparticles. The cobweb extract obtained by alkaline hydrolysis of cobweb using NaOH under appropriate conditions was reacted with 1 mm AgNO3 solution. As the reaction (extract/

AgNO3 solution) proceeded under static condition (at room temperature), a dark brown color resulting from AgNPs 9 Synthesis of AgNPs using synthesis was formed. The biosynthesized nanoparticles ­hydrolyzed nest of paper wasp were characterized using analytical techniques, including UV-Vis spectroscopy, FTIR, TEM, EDX, and selected area We have recently reported the first study on the green syn- electron diffraction (SAED) analysis. The AgNPs produced thesis of AgNPs in our laboratory using the hydrolyzed showed a maximum absorbance at wavelength of 436 nm. nest extract of Polistes sp. [72]. The nest was hydrolyzed A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles 609

Figure 1: Green synthesis of AgNPs using cobweb extract and the characteristics of biosynthesized AgNPs.

with 0.1 m NaOH at a temperature of 90°C for 1 h, and the very good blood anticoagulation and clot dissolution supernatant was used for the green synthesis of AgNPs (thrombolysis) activities in vitro (Figure 6). without further purification (Figure 4). The crystalline AgNPs (12.5–95.55 nm) had surface plasmon resonance attained at 428 nm, with the formation of anisotropic struc- tures of sphere, 3-D triangle, rhombus, hexagon, and rod 10 Silkworm and silk waste (Figure 5). FTIR data suggest that proteins and phenolic compounds were involved in the synthesis of AgNPs. The The silkworm is the larva of the domestic silk moth Bombyx nest extract-mediated AgNPs depicted good antimicrobial mori. It is an economically essential insect, being a prin- activities against K. granulomatis and P. aeruginosa in the cipal producer of silk. Silk waste is a major part of the range of 12–35 mm. Similarly, at 100 μg/ml, the AgNPs cocoons of silkworms (B. mori) [139]. Although it is inapt produced 100% against Aspergillus niger and Aspergillus for silk textile production, the composition of such silk flavus, whereas 75.61% was obtained against Aspergillus waste is comparable with that of good silk [140]. It is made fumigatus. Furthermore, the AgNPs degraded malachite up of fibroin core polymer (75%–83%) and sericin gluelike green by 64.3%–93.1% within 24 h. The biomedical appli- protein as a covering (17%–25%). The primary structure cation of AgNPs in the management of blood coagulation of silk fibroin (SF) polymers largely consists of the amino disorders was demonstrated, with the particles showing acid sequence of (Gly-Ala-Gly-Ala-Gly-Ser)n, existing in 610 A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles

Figure 2: The synergistic activities of cobweb extract-synthesized AgNPs with antibiotics on some clinical bacterial isolates.

glycine (Gly, 43%), alanine (Ala, 30%), and serine (Ser, permeable membrane, and drug release substances. It has 12%) components [84, 141]. Fibroin and sericin are the two attracted wide interest in many fields, including polymer proteins in unprocessed silk spun from the silk glands of technology, biology, materials science, medicine, sericul- adult caterpillars belonging to the species B. mori. Fibroin ture, and chemical engineering, leading to the increase is enclosed by the gumlike substance sericin, which com- in studies on silk protein [143–145]. Because of its notable poses of approximately 25% of raw silk, whereas sericin is biocompatibility with human tissue, biodegradability, typically removed as waste in the process of silk enhance- flexible morphology, drug permeability, nontoxicity, and ment [142]. Both raw silk proteins have been used in the good mechanical property [84], SF is of great significance green synthesis of various MeNPs (Table 1). in the field of biomedicine and applications in health care materials, such as food and cosmetic additive, tissue engineering [146], and drug delivery method [139, 147]. SF protein from B. mori silkworm is FDA permitted, and it has 11 Silk fibroin been used in biomedical applications, developed as scaf- fold materials and effectively used in healing of wounds Silk fibroin fiber (SFF) is a natural protein or biomaterial and in tissue engineering of bone, tendon, cartilage, and generally obtained from silkworm B. mori cocoons. It has ligament tissues [84, 148]. Also, it exhibits inflammatory been found that SF has unique properties for being used as response although less than collagen [149]. healthy foods, enzyme immobilizing materials, cosmetics, In recent times, it has been reported that SF produced cell culture medium, biosensor, artificial skin and muscle, from B. mori harbors antioxidant and hypolipidemic A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles 611

Figure 3: Antimicrobial activities of cobweb extract-synthesized AgNPs on bacteria and fungi inoculated into emulsion paint.

Figure 4: The biosynthesis of AgNPs using paper wasp nest extract. properties [150, 151]. It is of great importance as a natural interaction between silk protein and noble metal ions, antioxidant for applications in food, pharmaceutical, the silk protein has the exceptional property to prepare cosmetic, and biomedicine [152]. In investigating the nanocolloidal metal particles [153]. Water-soluble fibroin 612 A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles

4A 4B

1500 4C

1000

Count s 500

0 0246810 12 14 keV

Figure 5: Transmission electron micrograph (A), SAED pattern (B), and EDX spectrum (C) of the biosynthesized AgNPs using nest extract of paper wasp.

Microscopic view

Slide view

Microscopic view ABC

Figure 6: Anticoagulant (A) and thrombolytic activities (B and C) of biosynthesized AgNPs. FB, fresh blood; EDTA, anticoagulant; WHA, nest extract AgNPs; BC, blood clot; S, AgNO3 solution; WH, nest extract only. A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles 613 protein has 18 species of amino acid residues such as spectra showed strong emission band traversing from 500 alanine, glycine, serine, and tyrosine, and it is prepared to 700 nm under the excitation of 450 nm. Also, the images by destroying hydrogen bonds in SF and dissolving them from confocal microscope proved that the Ag nanoclus- in water [154], making them more effective in nanocolloid ters displayed the luminescence emission properties. The synthesis. This gives SFF potential to provide various reac- X-ray photoelectron spectroscopy (XPS) measurements tive sites for bioinspired processes, as well as to become showed the characteristic energy values of metallic Ag (0), possible biomaterials for the synthesis of functional nano- signifying Ag (I) ions were reduced to Ag atoms. composites under mild conditions. SF has been used in Chen et al. [74] reported the synthesis of metal nano- micro- and nanoparticles for drug delivery applications colloid by SF solution in situ reduction in which SF acted [77]. The SF nanoparticles have been produced using as both reducing agent and protector. This kind of noble emulsion-solvent evaporation/extraction, self-assembly, metal nanocolloid has a novel core-shell structure with a solvent displacement, phase separation, rapid expan- stable and highly dispersed nature. Aqueous SF solution sion of supercritical solution, and spray-drying tech- was reacted with AgNO3 solution at room temperature. niques [155]. Different inorganic materials such as silica, Ag nanocolloid synthesis was signified by the gradual magnetite, apatite, titania, silver chloride, zirconia, and change of the silver solution from a chromic into yellow MeNPs have been deposited onto or within silk matrices to after a period. The UV-Vis spectra indicated a symmetric increase mechanical and optical properties [76]. absorption band appearing at 420 nm; the colloids were SF for the synthesis of nanoparticles can be acquired monodisperse, around spherical, and size distribution by removing the outer sericin of silk fibers with anhydrous was reportedly narrow. FT-IR measurement showed peaks sodium carbonate solution at an appropriate temperature. at 1622, 1512, and 1262 cm−1 relating to amide I, amide II, SF may adapt the interface of nanoparticles, manage the and amide III bands, respectively. Also, amide IV band growth of nanoparticles, and stabilize the nanoparticles was obtained at 694 and 642 cm−1. The morphology of the solution [79]. Many potential applications of SF-noble nanocolloid was observed using TEM, which indicated metal nanocolloids, especially in biotechnology such as that the silver nanocolloid was formed as a cluster that immunoassay, DNA identification, biosensor, and inspec- has more than 10 core-shell structured silver-SF parti- tion, gene therapy, will gain prominence in research [74]. cles. The average size of the silver cores was reported as approximately 10 nm. Recently, a gamma radiation-assisted biosynthe- sis of AgNPs using SF was reported by Kumar et al. [80].

12 Synthesis of nanoparticles Silver nitrate (AgNO3) powders were added to SF solution, and the mixture was then exposed to gamma radiation with SF of different doses from 10 to 80 kGy. Color change from colorless to yellowish then to dark brown was observed, 12.1 Silver nanoclusters and nanoparticles and the formation of the Ag NPs was established by its typical surface plasmon resonance band at approximately Silk templates have been used as a matrix for the incorpo- 424 nm in UV-Vis spectra. The FTIR spectra revealed peaks ration of preformed AgNPs and also for binding metal ions indexed as belonging to amide I, amide II, and amide III from solutions and their consequent chemical reduction bands. The XRD analysis confirmed the nanocrystalline [76]. Wang et al. [73] demonstrated the in situ growth of phase of silver with fcc crystal structure. The TEM images Ag nanoclusters on silk fibers, which resulted in a novel showed that the nanoparticles were roughly spherical in composite silk fiber with luminescence and strong anti- shape. Also, the results from the dynamic light scatter- bacterial activities against E. coli and S. aureus. The syn- ing (DLS) study showed that the average size nanopar- thesis involved soaking polyacrylic acid-modified silk into ticles formed in SF ranged from 20 (at 60 kGy) to 40 nm an aqueous silver nitrate solution (0.02 mol/l) and then (at 20 kGy), indicating that increasing the radiation dose irradiating it using 365 nm ultraviolet (UV) light lamp. increases the rate of reduction and decreases the particle Under the UV light, silk fibers transformed color from size. Thus, the size of the AgNPs can be tuned by control- white to pink, signifying the formation of Ag nanoclus- ling the dose of radiation. ters. The characterization of the Ag nanocluster using the SF was also used as a biotemplate for the synthesis of UV-Vis absorption spectra indicated an absorption peak AgNPs in situ under both incandescent light and sunlight of approximately 490 nm, which is associated with Agn at room temperature in a study reported by Fei et al. [82]. nanoclusters (n = 4–9) [156]. The fluorescence emission The AgNPs showed effective antibacterial activity against 614 A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles the MRSA and consequently inhibited the biofilm forma- Flowerlike AuNP/reduced graphene oxide (RGO) com- tion caused by the same bacterium. Moreover, it was con- posites were produced by Shengjie et al. [154] in a simple, firmed that a matured biofilm created by the MRSA can one-pot, environmentally friendly method with regener- be destroyed by the SF-AgNP composite. Silver nitrate ated silk fibroin (RSF) as the reducing agent and adhesive powder was added to approximately 1 wt% regenerated for binding AuNPs and RGO. This was based on the fact SF solution, which was then exposed under the light with that RSF can be simply and firmly absorbed onto RGO an incandescent bulb and incubated at room temperature surfaces by π–π stacking and H-bonding, whereas the for 24 h for reduction and synthesis. It was believed that –NH2 and –COOH groups on RSF chains can function as SF was capable of reducing Ag+ to Ag by the redox-active nucleation sites for MeNPs. The effects of reaction time, nature of tyrosine residues in its chemical structure. Color temperature, and HAuCl4: RGO ratio on the morphology change from colorless to yellow was observed, and UV-Vis of AuNPs overloaded on RGO sheets were examined. Also, spectra showed absorption peak at 440 nm with small the flowerlike AuNP/RGO composite showed good cata- shoulder found at 347 nm, suggesting the possible exist- lytic performance for oxygen reduction reaction. AuNP/ ence of different sizes and morphology of AgNPs [157]. RGO composite was prepared by reacting 25 mm HAuCl4 The TEM micrograph showed that the average size of solution with RGO solution at 45°C for 5 min. The UV-Vis AgNPs was approximately 12 nm, and the high-resolution spectra indicated various peaks depending on the tem- transmission electron microscopy image of an individual perature of synthesis. The AuNP/RGO composite prepared nanoparticle indicated that the d-spacing of the crystal- at room temperature exhibited peak at 528 nm, 37°C at lographic plane was 0.23 nm, which agrees well with the 538 nm, and 45°C at 645 nm. The SEM image revealed that distance of (111) lattice plane of Ag [75]. Also, EDX con- the AuNPs were nearly monodispersed in a size of 200– firmed that the local elemental composition of the product 300 nm with rough surfaces. Enlarged image illustrated was Ag, and SAED confirmed the single crystal nature of that AuNPs were flowerlike and composed of some 10-nm the synthesized AgNPs. nanoparticles. The image from the TEM showed that the AuNPs were not arranged very compactly, resulting in possible relevance in catalysis. SAED showed diverse dif- 12.2 Gold nanoparticles fraction pattern, including (111), (200), and (220) faces, signifying the existence of defects and multiple crystal Silk was also found to condense metal ions from aqueous domains in the Au crystals [158]. It was ascertained that by solution without additional reducing agents, leading changing reaction parameters such as reaction time, tem- to the one-step in situ synthesis of MeNPs at ambient perature, and pH, the size, shape, and crystal aggregation conditions. This method was applied to SF solutions at of the AuNPs loaded on RGO could be regulated. alkaline conditions to attain colloidal core-shell gold- A study has also established a simple and adaptable silk nanoparticles with high monodispersity. Silk micro- strategy to generate ultrathin nanocomposite silk films fibers having diameters of 2–5 μm have also been used with evenly dispersed AuNPs at ambient conditions [76]. It as solid templates for the reduction of gold and silver was also established that both silk I and silk II forms were nano- and microparticles [76]. Chen et al. [74] synthe- capable of metal reduction, and the reduction did not alter sized gold nanocolloid by reacting aqueous SF solution the initial secondary structures of silk surface layers for with HAuCl4 solution at room temperature. The synthe- both silk I and silk II types. For synthesis, the silk films sis of nanocolloid was indicated by the gradual change were immersed into 1 mm HAuCl4 solution at room tem- in color of gold solution from yellow to purple. The perature in 0.1 m borate buffer at pH 10.5 or into water at UV-Vis absorption spectra showed an absorption peak at pH 3 for 10 h. Characterization by UV-Vis spectra showed approximately 520 nm, and pH 9–10 was observed as the peak at 547 nm, and FTIR spectra showed a typical amide I best condition for reduction. Characteristic amide bands band (1600–1700 cm−1), which is related with C=O stretch- in FTIR spectra of the gold nanocolloid were reported ing in the protein backbone joined to the N-H bending with peaks at 1621, 1515, 1262, 1232, 697, and 615 cm−1. and C=N stretching modes [159]. The major peak centered The TEM showed the morphology of the nanocolloid as at 1644 cm−1 relates with silk I spectra. There was no dif- gold colloid-SF bioconjugate of sizes ranging between ference in the spectra of both silk I and silk II before and 40 and 60 nm. The nanocolloid was a novel core-shell after mineralization, signifying that gold formation did structure with gold cores (approximately 29 nm) covered not bring about any conformational transformation in by SF. The gold colloid was very stable and dispersed in silk structures. The TEM images showed that the AuNPs nature. were evenly distributed over the surface with diameters of A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles 615 approximately 6.7 nm, and the sizes of nanoparticles were For the synthesis of QD-CdS/SF nanocolloids, a certain approximately 7.0 nm. amount of SF were dipped into CdCl2 solution, rinsed, and

Recently, Wongkrongsak et al. [78] described the syn- immersed into Na2S solution for some hours. Then it was thesis of water-soluble silk fibroin nanoparticles (WSSF- observed that the SF changed to a yellowish color. The NPs) using electron beam irradiation. The electron beam yellowish fibers were washed and dried in vacuum at irradiation reduced the molecular weight of SF from 250 room temperature. The yellowish solid sample gotten was to 37 kDa. The synthesized WSSF-NPs irradiated with immersed in the ternary solution (CaCl2:H2O:C2H5OH = 1:8:2 electron beam doses ranging from 1 to 30 kGy showed [molar ratio]) at 45°C to dissolve the SF and to obtain a effective antioxidant activities with EC50 for scavenging clear yellowish QD-CdS/SF colloid, which was steady at DPPH ranging from 0.27 to 0.98 mg/ml. Also, the ferric room temperature. The UV-Vis spectra characterization reducing antioxidant power assay indicated that rela- of the nanocolloid showed peak at 482 nm, and results of tive reducing power increased along with the increase in FTIR showed peaks at approximately 1645 and 1702 cm−1 concentration of the WSSF-NPs. Moreover, the WSSF-NPs (amide I bands) due to C=O stretching, at approximately displayed potent reducing agent for the green synthe- 1515 cm−1 (amide II bands) due to N-H bending, and at sis of gold nanocolloid. WSSF-NPs were synthesized by approximately 1230 and 1261 cm−1 (amide III bands) due irradiating the aqueous solution of SF with an electron to vibrations involving O-C-N and N-H. Also, the peak in accelerator in air at different doses of 1, 5, 10, 20, and 30 the region of 1645 cm−1 of the C=O stretching band shifted kGy. FTIR spectrum showed three major peaks at 1630 to 1657 cm−1, revealing the chelation between Cd2+ and cm−1, 1520 cm−1, and 1260 cm−1 belonging to C=O (amide C=O from peptide bonds of SFF. The photoluminescence I), N-H (amide II), and C-N and N-H (amide III), respec- spectra showed a smooth broad peak that centered at tively. The FTIR spectrum also showed the peaks at 3280 approximately 450 nm, which indicated the formation cm−1 interpreted as N-H stretching and the peaks at 2930 of energy bands that may be because of the chelation of and 2960 cm−1 belonging to C-H stretching of the amino Cd2+ with the C=O from the peptide bonds of SFF. SAED acid. SEM and TEM micrographs indicated that the WSSF- revealed that CdS has hexagonal (greenockite) structure NPs were loosely packed spherical particles and they with significant planes indexed to (101), (102), (110), and have an average diameter of approximately 40 nm. The (103) of greenockite CdS. The TEM image showed that the WSSF-NPs also mediated the synthesis of gold nanocol- QD-CDS/SF nanocolloids were nearly round spheres with loid by reacting 10-kGy irradiated WSSF-NPs with 0.1 mm an average diameter of approximately 5 nm.

HAuCl4 for 24 h. Color change from pale yellow to dark A solution-phase approach to the synthesis of sele- violet color was observed, and UV-Vis spectrum indicated nium nanoparticles by mixing appropriate amount of SF various peaks for the gold nanocolloid at 545, 550, 555, with selenious acid solution, with the addition of ascorbic and 560 nm depending on the concentration of WSSF- acid solution to initiate reaction, was reported by Xia [79]. NPs added. Color change from colorless to red was observed. The nan- oparticles were characterized by atomic force microscopy (AFM) and X-ray techniques, and the effects of tempera- 12.3 Cadmium and selenium nanoparticles ture and ultrasonication on the morphology of selenium nanoparticles were also discussed. AFM indicated that A suitable room temperature bioinspired system was the nanoparticles were monodispersed uniform spheri- developed by Su et al. [77] to synthesize hybrid quantum cal selenium colloid particles that were enveloped by SF. dot (QD)-cadmium sulphate (CdS)/SF colloid, in which SF Also, results from XRD indicated that the nanoparticles functioned as both natural biocompatibilizer and capable were amorphous. The selenium nanoparticles were also passivator of trap sites on the QD-CdS surface, which reported to be stable. could be of use in photocatalysts, novel luminescence, and photoelectron transfer devices and also for some pos- sible usage in the biological fields. QD-CdS/SF nanocol- 12.4 Silver, gold, platinum, and palladium loids consist of well-diffused QD and the substrate SFF. nanoparticles QD-CdS as typical II–VI semiconductor nanoparticles are studied widely because of their range of properties, Furthermore, Das and Dhar [81] demonstrated the use including unique optical properties, photocatalytic and of cysteine-modified SF as a reducing agent, stabiliz- tunable photoluminescence with high quantum yield, ing agent, and material matrix in the synthesis of noble and broad excitation wavelength scope [160]. MeNPs (Au, Ag, Pd, and Pt), which was done by a facile 616 A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles one-pot procedure using silk fibroin-cysteine solution as boiling [84], also by using high-temperature and high- (SF-SH). The integration of thiols (–SH) into SF led to the pressure degumming technique [162] followed by filtra- formation of almost monodispersed MeNPs. In the synthe- tion to remove fibroin fibers [83]. Sericin is gaining wide sis, the aqueous solution of SF-SH at pH 10 was added to applications in recent years for the synthesis of MeNPs an aqueous solution of 2 mm of metal precursor (HAuCl4, (Table 1).

AgNO3, and Na2PdCl4) at room temperature. The same method was followed at 85°C in the case of platinum. Color changes were observed as follows: AuNPs, yellow to light purple to purple to wine red; AgNPs, colorless to 14 Synthesis of nanoparticles using blackish brown; and PdNPs, yellow to colorless. However, sericin PtNPs were not formed at room temperature by using the same reaction procedure. The UV-Vis spectra of the syn- 14.1 Silver nanoparticles thesized Au and Ag-SF-SH conjugates showed a strong absorption band at 524 and 410 nm, respectively, which Yue et al. [161] also used sericin as both reducing agent were measured to be intact after a month. For Pd and and dispersing agent in the synthesis of AgNPs-sericin PtNPs, the absorption band of the salt vanished, and there (AgNPS-sericin) hybrid colloid, which endowed excel- was no peak generation that may validate the formation lent antibacterial activities, good moisture absorption of zero valent MeNPs. The XRD analyses show the forma- ability, smooth handle, and wrinkle-resistant properties tion of nanoparticles with strong peaks corresponding to to improve wearability when embedded on a cotton fabric. (111), (200), and (220) based on the face-centered cubic The synthesis involved addition of silver nitrate solution (fcc) structure of Au and AgNPs. For PdNPs, only peak at to sericin solution (50 g/l), the pH was adjusted to 9.5, and 200 was the major peak, and PtNPs showed 111 and 200 the mixture was placed on the heating magnetic stirrer at peaks. Also, the TEM micrograph showed that the Au and 80°C. Color change from pale yellow to brown yellow was Ag, Pd, and PtNPs had narrow distribution particle size observed, and the UV-Vis spectra showed absorption peak of approximately 13.0, 5.0, 3.0, and 2.0 nm, respectively. at 420 nm. The dynamic light scattering (DLS) showed The accessibility of catalytic site of nanoparticles in these that the hydrodynamic diameter of AgNPs in the hybrid biohybrid materials was demonstrated by 4-nitrophenol colloid was approximately 18 nm. Also, the TEM micro- reduction by using NaBH . Moreover, the 3D porous scaf- 4 graph showed good dispersion of the spherical AgNPs, fold of high mechanical strength from the Au-SF-SH and which had no apparent agglomeration after 1 month, and Pd-SF-SH conjugate materials was also obtained, which the XRD indicated four obvious strong peaks in the whole facilitated heterogeneous catalysis. The AgNPs composite spectrum, which are in accordance with 111, 200, 220, and film showed very fine antibacterial activity against E. coli. 311 crystal faces of silver microcrystal [163]. The structure Therefore, these NP-SF conjugate materials have potential and morphology of the finished cotton fabric with hybrid for applications in catalysis and biomedicine. colloid of AgNPs-sericin was studied. The FTIR spectrum showed peak at 1556 cm−1, which was attributed to the presence of C=N stretching vibration of the imine group 13 Sericin in the finished cotton. The XPS measurements revealed binding energy peaks at 368.2 and 374.2 eV, which are Silk sericin (SS) is a water-soluble protein obtained in accordance with characteristic of metallic silver. Also, through silk refinement. Presently, SS is regarded as a EDX showed strong carbon, oxygen, and gold, silver, and waste product from the textile industry. It is extremely nitrogen peaks as expected. For the antibacterial activi- hydrophilic with strong polar side chains such as ties of the finished cotton, initial bacterial reductions of hydroxyl, carboxyl, and amino groups. In recent times, SS finished cotton fabric by hybrid colloid of Ag NPS-sericin has been widely used in biomaterial applications because were 99.28% and 99.06% against S. aureus and E. coli, of its biocompatibility, biodegradability, and antioxidative respectively. After approximately 20 washing cycles, it dis- and bioactive activities [83]. It is well known that sericin played excellent laundering strength at levels higher than proteins, as the biopolymer and biocompatible materials, 95% for S. aureus and E. coli. have attracted a lot of research interests in fields, such as SS was also used as both reducing and stabilizing cosmetics, health care food, and biomaterials [161]. SS can agent in the synthesis of AgNPs, as reported by Aramwit be extracted from silkworm cocoons by easy process such et al. [83]. Prepared sericin solution was added to the A. Lateef et al.: Roles of arthropods in the green synthesis of metallic nanoparticles 617

AgNO3 solution (1, 5, and 10 mm) under constant stirring at Acknowledgments: Prof. A. Lateef is grateful to the room temperature overnight. Color change from transpar- authority of LAUTECH, Ogbomoso, Nigeria, for the provi- ent to yellow was observed, and UV-Vis spectra showed sion of some of the facilities used in some works cited in maximum absorption peak at 420 nm. The FTIR spectra this review. of the SS-capped AgNPs showed new functional groups different from the original SS, which included carboxylate (1451, 1404, and 1353 cm−1) and amine salt (830 cm−1). The References new absorptions signified the hydrolysis of amide linkage into its basic structural units [164]. The carboxylate [1] Cutler B. Arthropod cuticle features and arthropod monophyly. groups also acted as a weak reducing agent for the syn- Experientia. 1980, 36, 953. thesis of AgNPs [165–167]. The TEM micrograph showed [2] Ødegaard F. How many species of arthropods? Erwin’s estimate revised. Biol. J. Linn. 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Active Prod. Nature 2014, 4, 332–342. change from transparent to yellow was observed. The [6] Nam KW, Je KH, Lee JH, Han HJ, Lee HJ, Kang SK, Mar W. UV-Vis spectra revealed an absorption peak of 389 nm ­Inhibition of COX-2 activity and proinflammatory cytokines (TNF-α and IL-1β) production by water soluble sub-fractionated (after the synthesis) and 399 nm (after stabilization with parts from bee (Apis mellifera) venom. Arch. Pharm. Res. 2003, sericin). The TEM micrograph showed that the AgNPs 26, 383–388. were spherical particles with an average diameter of [7] Moon DO, Park SY, Heo MS, Kim KC, Park C, Ko WS. Key regula- 15 nm. SEM revealed that the AgNPs have fairly uniform tors in bee venom induced apoptosis are Bcl-2 and caspase-3 size distribution and were fairly monodispersed. The sta- in human leukemic U937 cells through down regulation of ERK bility of the colloidal nanoparticles was confirmed by zeta and Akt. Int. Immunopharmacol. 2006, 6, 1796–1807. 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Bionotes Joseph A. Elegbede obtained BTech in Science Laboratory Agbaje Lateef Technology (Biology/Microbiology option) in 2011 at Ladoke Laboratory of Industrial Microbiology and Akintola ­University of Technology, Ogbomoso, Nigeria. He is Nanobiotechnology, Nanotechnology currently on MTech program under the supervision of Prof. Research Group (NANO+), Department of A. Lateef, with research work focusing on enzyme technol- Pure and Applied Biology, Ladoke Akintola ogy and nanobiotechnology. https://scholar.google.com/ University of Technology, PMB 4000, citations?user=fctO-eMAAAAJ&hl=en. Ogbomoso, Nigeria, [email protected]; [email protected]

Agbaje Lateef obtained BTech in Pure and Applied Biology, MTech in Biotechnology, and PhD in Microbiology in 1997, 2001, and 2005, respectively. He has 18 years of teaching experience at the university with vast interests in microbiology and biotechnology, especially fermentation processes and enzyme technology. He has more than 60 publications to his credit. He is currently involved in the green synthesis of nanoparticles, and he is the head of the Nanotechnol- ogy Research Group (NANO+) at LAUTECH, Ogbomoso, Nigeria. His articles have enjoyed 695 citations, and he has an h-index of 14. https://scholar.google.com/citations?user=C388_KsAAAAJ&hl=en.