Parasitol Res (2011) 108:1541–1549 DOI 10.1007/s00436-010-2212-4
ORIGINAL PAPER
Evaluation of green synthesized silver nanoparticles against parasites Sampath Marimuthu & Abdul Abdul Rahuman & Govindasamy Rajakumar & Thirunavukkarasu Santhoshkumar & Arivarasan Vishnu Kirthi & Chidambaram Jayaseelan & Asokan Bagavan & Abdul Abduz Zahir & Gandhi Elango & Chinnaperumal Kamaraj
Received: 23 November 2010 / Accepted: 30 November 2010 / Published online: 22 December 2010 # Springer-Verlag 2010
Abstract Green nanoparticle synthesis has been achieved using environmentally acceptable plant extract and ecofriendly reducing and capping agents. The present study was based on assessments of the antiparasitic activities to determine the efficacies of synthesized silver nanoparticles (AgNPs) using aqueous leaf extract of Mimosa pudica Gaertn (Mimosaceae) against the larvae of malaria vector, Anopheles subpictus Grassi, filariasis vector Culex quinquefasciatus Say (Diptera: Culicidae), and Rhipicephalus (Boophilus) microplus Canestrini (Acari: Ixodidae). Parasite larvae were exposed to varying concentrations of aqueous extract of M. pudica and synthesized AgNPs for 24 h. AgNPs were rapidly synthesized using the leaf extract of M. pudica and the formation of nanoparticles was observed within 6 h. The results recorded from UV–vis spectrum, Fourier transform infrared, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy support the biosynthesis and characterization of AgNPs. The maximum efficacy was observed in synthesized AgNPs against the larvae of A. subpictus, C. quinquefasciatus, and R. microplus (LC50 =13.90, 11.73, and 8.98 mg/L, r2 =0.411, 0.286, and 0.479), respectively. This is the first report on antiparasitic activity of the plant extract and synthesized AgNPs.
S. Marimuthu : A. A. Rahuman (*) : G. Rajakumar : T. Santhoshkumar : A. V. Kirthi : C. Jayaseelan : A. Bagavan : A. A. Zahir : G. Elango : C. Kamaraj Unit of Nanotechnology and Bioactive Natural Products, Post Graduate and Research Department of Zoology, C.Abdul Hakeem College, Melvisharam, 632 509, Vellore District, Tamil Nadu, India e-mail:
[email protected]
Introduction Diseases transmitted by blood-feeding mosquitoes, such as dengue fever, dengue hemorrhagic fever, Japanese encephalitis, malaria, and filariasis, are increasing in prevalence, particularly in tropical and subtropical zones. To control mosquitoes and mosquito-borne diseases, which have worldwide health and economic impacts, synthetic insecticidebased interventions are still necessary, particularly in situations of epidemic outbreak and sudden increases of adult mosquitoes (Yaicharoen et al. 2005, Nathan et al. 2006). Malaria is the world’s most dreadful important tropical disease. It is prevalent in about 100 countries and around 2,400 million people are at risk (Kager 2002). In Southeast Asia alone, 100 million malaria cases occur every year and 70% of these are reported from India (WHO 2004). As reported recently, 406 million Indians were at risk of stable Plasmodium falciparum transmission in 2007 with an uncertainty point estimate of 101.5 million clinical cases (Hay et al. 2010). The World Health Assembly in its annual meeting in 2005 urged member states to establish policies and operational plans to ensure that at least 80% of those at risk of, or suffering from malaria and related vector-borne diseases, benefit by 2010 by employing major preventive and curative interventions, so as to ensure a reduction in the burden of malaria of at least 50% by 2010 and 75% by 2015 (WHO 2005). Culex quinquefasciatus, a vector of Wuchereria species causing lymphatic filariasis, is widely distributed in tropical regions with around 120 million people infected and 44 million people under clinical manifestation (Bernhard et al. 2003). In India, a total of 553 million people are at risk of infection and there are approximately 21 million people with symptomatic filariasis and 27 million microfilaria carriers. Wuchereria bancroftic is the national burden, widely distributed in 17 states and six union territories (Das et al. 2000).
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Rhipicephalus (Boophilus) microplus is responsible for losses in milk, meat, and leather production and for the death of a number of animals, which results in economic losses associated with cattle production. A recent survey on acaricide resistance conducted through a questionnaire reported a large-scale acaricide resistance in India (FAO 2004). Continuous and indiscriminate use of acaricides leads to the selection of chemical-resistant ticks along with contamination of the environment and animal products (Graf et al. 2004). The consumer’s preferences for products, such as meat and milk that do not contain chemical residues have contributed to new methods to control the parasite, among which are biological methods, such as green synthesized silver nanoparticles (AgNPs). Numerous products of botanical origin, especially essential oils, have received considerable renewed attention as potent bioactive compounds against various species of mosquitoes. Due to the fact that application of adulticides may only temporarily diminish the adult population, more efficient and attractive approach in mosquito control programs is to target the larval stage in their breeding sites with larvicides (Mehlhorn et al. 2005; Amer and Mehlhorn 2006a, b; Rahuman et al. 2009a, b). The efficacy of some of the medicinal plant extracts and oil against R. (B.) microplus has been evaluated and a potential plant has been identified (Ghosh et al. 2010; Martinez-Velazquez et al. 2010). There is an urgent need to develop new insecticides for controlling mosquitoes which are more environmentally safe and also biodegradable and target specific against parasites. AgNPs may be released into the environment from discharges at the point of production, from erosion of engineered materials in household products (antibacterial coatings and silver-impregnated water filters), and from washing or disposal of silver-containing products (Benn and Westerhoff 2008). Plants and microbes are currently used for nanoparticle synthesis. The use of plants for synthesize of nanoparticles are rapid, low cost, eco-friendly, and a single-step method for biosynthesis process (Huang et al. 2007). Among the various known synthesis methods, plant-mediated nanoparticles synthesis is preferred as it is cost-effective, environmentally friendly, and safe for human therapeutic use (Kumar and Yadav 2009). It has been reported that medicinally valuable angiosperms have the greatest potential for synthesis of metallic nanoparticles with respect to quality and quantity (Song and Kim 2009). Biosynthesized AgNPs are used in label-free colorimetric assay to detect enzymatic reactions, (Wei et al. 2008), surface plasmon resonance studies (Turney et al. 2004; Kundu et al. 2004), antimicrobial materials (Duran et al. 2005), anti-viral, and anti-HIV studies (Elechiguerra et al. 2005). Biological methods for nanoparticle synthesis using microorganisms, enzymes, and plants or plant extracts have been
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suggested as possible eco-friendly alternatives to chemical and physical methods (Mohanpuria et al. 2008). Using plants for nanoparticle synthesis can be advantageous over other biological processes because it eliminates the elaborate process of maintaining cell cultures and can also be suitably scaled up for large-scale nanoparticle synthesis (Shankar et al. 2004). Synthesis of nanoparticles using microorganisms or plants can potentially eliminate this problem by making the nanoparticles more biocompatible. Mimosa pudica (sensitive plant), is a creeping annual or perennial herb often grown for its curiosity value, the compound leaves alkaloids, steroidal sapogenins, flavonoids, tannins, unsaturated sterols, triterpenoids, and essential oils have been reported (Lozoya and Lozaya 1989). It is also applied externally to fissures, skin wounds, and ulcers. Its action on small blood vessels is implicated in its hemostatic property. It contains an alkaloid called mimosine, which has been found to have potent antiproliferative and apoptotic effects (Restivo et al. 2005). M. pudica, a plant used by the local people to treat snakebite patients, was effective to neutralize the lethality and toxic enzymes of Naja kaouthia venom. The unusual C-glycosidic flavonoid, 4"-hydroxymaysin isolated from the touch sensitive legume M. pudica could contribute to the resistance of this plant to generalist insect herbivores (Lobstein et al. 2002). In the present study, the synthesized AgNPs from M. pudica were tested for larvicidal activity against the Anopheles subpictus, C. quinquefasciatus, and R. microplus, which showed increased activity from the synthesized AgNPs, and it was also tested against bacteria and fungi.
Material and method Materials The healthy leaves of M. pudica Gaertn (Mimosaceae) (Fig.1) were collected from Pillaiyar kuppam Village, Vellore district, Tamil Nadu, India in January 2010 and the taxonomic identification was made by Dr. C. Hema, Department of Botany, Arignar Anna Government Arts College for Women, Walajapet, Vellore. The voucher specimen was numbered and kept in our research laboratory for further reference. Silver nitrate (AgNO3), analytical grade was purchased from Qualigens Fine Chemicals, Mumbai, India (99.9% pure). Parasites rearing and collection A. subpictus and C. quinquefasciatus larvae were collected from rice field and stagnant water areas of Melvisharam (12°56′23″ N, 79°14′23″ E) and identified in the Zonal Entomological Research Centre, Vellore (12°55′48″ N, 79° 7′48″ E), Tamil Nadu, to start the colony, and larvae were
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Fig. 1 Mimosa pudica Gaertn (Mimosaceae)
kept in plastic and enamel trays containing tap water. They were maintained and reared in the laboratory as per the method of (Kamaraj et al. 2009). Larvicidal bioassay During preliminary screening with the laboratory trial, the larvae of A. subpictus and C. quinquefasciatus were collected from the insect-rearing cage and identified in the Zonal Entomological Research Centre, Vellore. One gram of aqueous leaf extract was first dissolved in 100 ml of distilled water (stock solution). From the stock solution, 100 mg/L was prepared with dechlorinated tap water for bioassay test of plant extract. The larvicidal activity was assessed by the procedure of (WHO 1996) with some modifications and as per the method of Rahuman et al. (2000). For the bioassay test, larvae were taken in five batches of 20 in 249 mL of water and 1.0 mL of aqueous plant extract concentration. The control was set up with dechlorinated tap water. The numbers of dead larvae were counted after 24 h of exposure, and the percentage of mortality was reported from the average of five replicates. The experimental media in which 100% mortality of larvae occurs alone were selected for dose–response bioassay. Synthesized AgNPs toxicity test was performed by placing 20 mosquito larvae into 200 mL of sterilized double distilled water with nanoparticles into a 250-mL beaker (Borosil). The nanoparticle solutions were diluted using double distilled water as a solvent according to the desired concentrations (25, 20, 15, 10, and 5 mg/L). Each test included a set control group (silver nitrate and distilled water) with five replicates for each individual concentration. Mortality was assessed after 24 h to determine the acute toxicities on fourth instar larvae of A. subpictus and C. quinquefasciatus. Twenty mosquito larvae were placed into 250-mL glass beakers (Borosil) and set in an environmental chamber at
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25°C with a 16:8-h light/dark cycle. Each beaker containing the mosquito larvae distilled water was spiked with stock solutions of AgNPs (Sigma) in order to achieve target nominal concentrations of 25, 20, 15, 10, and 5 mg/L with a final volume of 200 mL. A negative control (no AgNPs) was used in all experiments, and all conditions were tested in five replicates. In order to compare the mortality of AgNPs to that of dissolved Ag released and the mosquito larvae were exposed to a range of dissolved Ag concentrations so as to cover the range released from all doses of AgNPs. To avoid settling of particles especially at higher doses, all treatment solutions were sonicated for an additional 5 min prior to addition of the mosquito larvae. Since this additional sonication appeared to significantly decrease the settling of particles, we tested the effects of AgNPs without sonication (stirred only) or with sonication. The newly attached larvae of Rhipicephalus microplus (Canestrini) (Acari: Ixodidae) were collected from the softer skin inside the thigh, flanks, abdomen, brisket, and forelegs of naturally infested cattle. R. microplus larvae have a short, straight capitulum and a brown to cream body. The parasites were identified in the Department of Veterinary Parasitology, Madras Veterinary College, Tamil Nadu Veterinary and Animal Sciences University, Chennai, Tamil Nadu. The applied method in the present study to verify the acaricidal activity of AgNPs against the larvae of R. microplus was developed as per the method of FAO (2004), incorporating slight modifications to improve practicality and efficiency of tested materials (Fernandes et al. 2005). From the stock solution, 100 mg/L was prepared and a series of filter paper envelopes (Whatman filter paper no.1, 125 mm diameter) with micropores were treated with each concentration of extract of M. pudica. The synthesized particles were impregnated with 20 mg/L of which 3 ml solution of the stock was uniformly distributed with a pipette on internal surfaces. Five envelopes were impregnated with each tested solution. The control papers were impregnated with distilled water only. The opening of the envelopes (treated and inoculated with larval ticks) was folded (10 mm) and re-sealed with a metallic clip, with its identification mark (tested solution and concentration) on the outside. The packets are placed in the BOD incubator at a temperature of 28–30°C and 80–90% RH for 24 h. The envelopes were opened 24 h after exposure and the number of live and mortality larvae were recorded (Fernandes and Freitas 2007). The experimental media, in which 100% mortality of larvae occurs alone, were selected for dose– response bioassay. Dose–response bioassay Based on the preliminary screening results, crude leaf extract of M. pudica and synthesized AgNPs were
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subjected to dose–response bioassay for larvicidal activity against the larvae of A. subpictus and C. quinquefasciatus. Different concentrations ranging from 20 to 100 mg/L (for aqueous plant extracts) and 5.0 to 25 mg/L (for synthesized AgNPs) were prepared for larvicidal activity of parasites. The numbers of dead larvae were counted after 24 h of exposure, and the percentage of mortality was reported from the average of five replicates. However, at the end of 24 h, the selected test samples turned out to be equal in their toxic potential. Preparation of plant extract Aqueous extract was prepared by mixing 50 g of dried leaf powder with 500 mL of water (boiled and cooled distilled water) with constant stirring on a magnetic stirrer (Minjas and Sarda 1986). The suspension of dried leaf powder in water was left for 3 h, filtered through Whatman no. 1 filter paper, and the filtrate was stored in amber colored air tight bottle at 10°C and used within a week. Synthesis of silver nanoparticles M. pudica plant leaf broth solution was prepared by taking 10 g of thoroughly washed and finely cut leaves in a 300 ml Erlenmeyer flask along with 100 ml of sterilized double distilled water and then boiling the mixture for 5 min before finally decanting it. The extract was filtered with Whatman filter paper no. 1 and stored at −15°C and could be used within 1 week. The filtrate was treated with aqueous 1 mM AgNO3 solution and incubated at room temperature. Eighty-eight milliliters aqueous solution of 1 mM of AgNO3 was reduced using 12 ml of leaves extract at room temperature for 10 min, resulting in a brown–yellow solution indicating the formation of AgNPs. The nanoparticle solution was diluted to 20 times with Millipore water to avoid errors due to high optical density of the solution. The bioreduction of AgNPs ions in solution was monitored by periodic sampling of aliquots (1.0 ml) of aqueous component and measuring UV–vis spectra of the solution (Parashar et al. 2009).
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subjected to centrifugation at 60,000×g for 40 min; resulting pellet was dissolved in deionized water and filtered through Millipore filter (0.45 μm). Fourier transform infrared (FTIR) spectra of the samples were measured using a Perkin-Elmer Spectrum One instrument in the diffuse reflectance mode at a resolution of 4 cm−1 in KBr pellets. Powder samples for the FTIR was prepared similarly as for powder diffraction measurements. The FTIR spectra of leaf extracts taken before and after synthesis of silver nanoparticles were analyzed which discussed for the possible functional groups for the formation of silver nanoparticles. An aliquot of this filtrate containing silver nanoparticles was used for X-ray diffraction (XRD), FTIR, and analysis. For XRD studies, dried nanoparticles were coated on the XRD grid, and the spectra were recorded using Phillips PW 1830 instrument operating at a voltage of 40 kV and a current of 30 mA with CuKα1 radiation. For electron microscopic studies, 25 μL of sample was sputter-coated on copper stub, and the images of nanoparticles were studied using scanning electron microscopy (SEM; JEOL, Model JFC-1600) and transmission electron microscopy (TEM; JEOL, model 1200EX) measurements were operated at an accelerating voltage of 120 kV and later with an XDL 3000 powder. Data analysis Mean percent larval mortality data were subjected to analysis of variance and compared with Duncan’s multiple range tests to determine any differences between plant species and within species and concentration (SPSS 2007). Prior to analysis, mortality in treatments was corrected for that in controls using the formula of (Abbott 1925). LC50 and their associated confidence intervals were estimated from 24-h concentration mortality data using probit analysis (Finney 1971). Lethal concentrations at the 50% and slope levels were considered significantly different if their associated confidence intervals did not overlap. All differences were considered significant if p≤0.05.
Results and discussion Characterization of the synthesized nanoparticles Synthesis of AgNPs solution with leaves extract may be easily observed by UV–vis spectroscopy. The bioreduction of the Ag+ ions in solutions was monitored by periodic sampling of aliquots (1 mL) of the aqueous component after 20 times dilution and measuring the UV–vis spectra of the solution. UV–vis spectra of these aliquots were monitored as a function of time of reaction on a Schimadzu 1601 spectrophotometer in 300–700-nm range operated at a resolution of 1 nm. Further, the reaction mixture was
In the present study, the larvicidal aqueous crude leaf extracts and synthesized AgNPs of M. pudica is noted; however, the highest mortality was found in synthesized AgNPs against the larvae of A. subpictus (LC50 =13.90 mg/L and r2 =0.411) and against the larvae of C. quinquefasciatus (LC50 = 11.73 mg/L and r2 =0.286), respectively. The chi-square value was significant at p≤0.05 level. The anti-lice activity of aqueous crude leaf extracts and synthesized AgNPs of M. pudica showed the LC50 =52.01, 8.98 mg/L; r2 =0.754 and 0.479) (Table 1).
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Table 1 Larvicidal activity of aqueous and synthesized silver nanoparticle of M. pudica leaves against larvae of A. subpictus, C. quinquefasciatus, and R. microplus Extract
Species
Aqueous extract
A. subpictus
C. quinquefasciatus
Silver AgNPs
A. subpictus
C. quinquefasciatus
Aqueous extract
Silver AgNPs
R. microplus
R. microplus
Concentrations (mg/L)
Percent mortalitya (mg/L)±SD
100 80 60 40 20 100 80 60 40 20 25 20 15 10 5 25 20 15
85±1.22 67±0.92 56±0.22 45±0.45 28±0.84 92±0.34 83±0.33 72±0.44 56±0.12 23±1.22 100±0.000 77±0.560 49±0.910 30±1.140 26±0.430 100±0.000 89±1.796 51±1.231
10 5 100 80 60 40 20 20 15 10 5
41±1.18 14±1.011 78±1.172 63±0.783 56±0.667 38±0.753 17±0.843 89±1.796 51±1.231 41±1.185 14±1.011
UCL–LCL (mg/L)
Slope
r2
45.82
54.19–38.74
45.00
0.562
35.90
40.69–31.67
56.00
0.331
13.90
16.05–12.04
77.00
0.411
11.73
12.91–10.66
14.00
0.286
52.01
59.49–46.51
38.00
0.754
8.98
10.62–7.60
51.00
0.479
LC50 ±SE (mg/L)
UCL upper confidence limit, LCL lower confidence limit
The larvicidal activity of ethyl acetate extract of M. pudica showed the LD50 =134.66, 156.55, and 112.78 ppm; LD90 =921.14, 1,214.47, and 627.80 against Culex gelidus and LD50 =134.15, 152.64, and 115.66 ppm; and LD90 =633.38, 781.63, and 485.12 against C. quinquefasciatus, respectively (Kamaraj et al.2010). Fifty percent hydroethanolic extracts of Bonninghausenia albiflora whole plant, Calotropis procera root, Citrus maxima flower, Acorus calamus rhizome, and Weidelia chinensis whole plant showed acaricidal efficacy ranging from 4% to 35% within 24 h of application on R. (B.) microplus, rhizome extract of A. calamus revealed that 79.31% of correlation with log concentration in probit mortality could be assigned to the concentration of the extract and the regression line of the extract showed the LC85 as 11.26% (Ghosh et al. 2010).
The color change was noted by visual observation in the M. pudica leaf extracts when incubated with AgNO3 solution. M. pudica leaf extract without AgNO3 did not show any change in color (Fig. 2a, b). The color of the extract changed to light brown within an hour and later it changed to dark brown during 6 h incubation period after which there was no significant change occurred. Absorption spectrum of M. pudica leaf extracts at different wavelengths ranging from 300 to 600 nm revealed a peak at 420 nm (Fig. 2c). The AgNPs produced by M. pudica leaf extract were more distinct and scattered in distribution. The FTIR spectra of AgNPs exhibited prominent peaks at 3,402; 2,359; 2,019; 1,631; 1,383; 1,076; 817 cm−1 (Fig. 3). The sharp absorption peak at 1631 cm−1 were assigned to C=O stretching vibration in carbonyl compounds which may be
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Fig. 4 XRD pattern of AgNPs synthesized using M. pudica leaf broth
Fig. 2 a Photographs showing change in color after adding AgNO3 before reaction. b After reaction time of (6 h). c UV–vis spectra of aqueous silver nitrate with M. pudica leaf extract at different time intervals
characterized by the presence of high content of terpenoids and flavonoids. The peaks at 1076 cm−1 correspond to C–N stretching vibration of aliphatic amines or alcohols/phenols, representing the presence of polyphenols. The absorption Fig. 3 FTIR spectrum of synthesized AgNPs using M. pudica leaf extract
bands at 1,076 cm−1 in the fingerprint region indicate several modes such as C–H deformation or C–O or C–C stretching, pertaining to carbohydrates. The bands at 1,383 to 1,431 cm−1 were assigned to scissoring modes of methylene tails, CH3 R (1,383 cm−1). The peak located at around 2,359 cm−1 was attributed to the N–H stretching vibrations or the C=O stretching vibrations. A broad intense band at 3,402 cm−1 in both the spectra can be assigned to the N–H stretching frequency arising from the peptide linkages present in the proteins of the extract (Mukherjee et al. 2008). The X-ray diffraction pattern of silver nanoparticles produced by leaf extract is shown in (Fig. 4). The control thin films of the leaf extract as well as the AgNO3 did not show the characteristic peaks. The XRD pattern shows four
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intense peaks in the whole spectrum of 2θ values ranging from 25 to 60. The XRD spectrum compared with the standard confirmed spectrum of silver particles formed in the present experiments were in the form of nanocrystals, as evidenced by the peaks at 2θ values of 38.14°, 53.05°, 66.04°, and 77.17° corresponding to 111, 200, 300, and 311 planes for silver, respectively. The value of the pure silver lattice constant has been estimated to be α=4.081, a value that is consistent with α=4.0862 Å reported by the JCPDS file no. 4-0783. This estimation confirmed the hypothesis of particle monocrystallinity. The sharpening of the peaks clearly indicates that the particles were in the nanoregime. Dubey et al. (2009) reported the size of silver nanocrystallites as estimated from the full width at half maximum of the (111) peak of silver using the Scherrer formula was 20–60 nm. Moreover, two small insignificant impurity peaks were observed at 60° and 70° which may be attributed to other organic substances in culture supernatant. XRD pattern clearly illustrates that the silver nanoparticles formed in this present synthesis were crystalline in nature. The shape and size of the AgNPs that were analyzed after 24 h of incubation by using TEM are depicted in Fig. 5. In general, the nanoparticles were in spherical shape with varying size ranged from 25 to 60 nm. Most of the nanoparticles were aggregates with only a few of them scattered, as observed under TEM. The particle shape of plant-mediated AgNPs were mostly spherical with exception of neem (Azaddirachita indica) which yielded polydisperse particles both with spherical and flat plate-like morphology 5–35 nm in size (Shankar et al. 2004).TEM images of silver nanoparticles from Emblica officinaris were also predominantly spherical with an average size of 16.8 nm ranging from 7.5 to 25 nm (Ankamwar et al. 2005). For the SEM studies, reaction mixtures were air-dried on silicon wafers. As a result, a coffee ring phenomenon was observed. It is well-known that when liquids that contain fine particles were evaporated on a flat surface, the particles
Fig. 5 Transmission electron microscopic image showing synthesized AgNPs from M. pudica
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accumulate along the outer edge and form typical structures (Chen and Evans 2009). Representative SEM micrographs of the reaction mixtures containing 10 mg of M. pudica leaf extract powder and 1.0 mM of silver nitrate incubated for 6 h magnified ×1,500 and ×5000, are shown in Fig. 6, respectively. The XRD and SEM analysis showed the particle size between 25 and 50 nm as well as the cubic structure of the nanoparticles (Khandelwal et al. 2010).The silver nanoparticles synthesized by treating silver nitrate solution with Eucalyptus hybrida leaf extract. The silver nanoparticles formed were predominantly cubical with uniform shape. It is known that the shape of metal nanoparticles considerably change their optical and electronic properties (Xu and Käll 2002). Mouchet et al. (2008) reported that a high mortality rate (85%) was noted at the highest double-walled carbon nanotube concentration (500 mg L−1) against the larvae of Xenopus laevis. Baun et al. (2008) indicated the toxicity of C60, carbon nanotubes, and titanium dioxide to an aquatic invertebrate, Daphnia magna. Although an attempt to develop essential oil for pesticides and insecticides has been made in a variety of water-soluble formulations such
Fig. 6 Scanning electron micrographs of AgNPs synthesized with M. pudica leaf extract and 1.0 mM AgNO3 solution and incubated at 60°C for 6 h at pH 7.0 a magnified ×1,500, inset bar represents 10 μm; b magnified ×5,000 inset bar represents 5 μm
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as nanoemulsion incorporated with β-cypermethrin (Wang et al. 2007) and essential oil-loaded microcapsules for pest control (Moretti et al. 2002). Sakulku et al. (2009) have reported the low release rate of nanoemulsion with large droplet size that resulted in prolonged mosquito repellant activity compared to the nanoemulsion with small droplet size. Recent studies demonstrated that silver nanoparticles induce embryonic injuries and reduce survival in zebrafish Danio rerio (Asharani et al. 2008; Griffitt et al. 2008). In conclusion, present green synthesis shows that the environmentally benign and renewable source of M. pudica used as an effective reducing agent for the synthesis of silver nanoparticles. This biological reduction of metal would be boon for the development of clean, nontoxic and environmentally acceptable “green approach” to produce metal nanoparticles, involving organisms even ranging higher plants. The formed silver nanoparticles are highly stable and had significant mosquito larvicidal activity, larvae of R. microplus, and show more antimicrobial activity against Escherichia coli, P. aeruginosa and Aspergillus niger. This reveals high efficacy of AgNPs as a strong antimicrobial agent. The surface reactivity facilitated by capping enables these functionalized nanoparticles as promising candidates for various pharmaceutical, biomedical, and environmental applications. References Abbott WS (1925) A method of computing the effectiveness of an insecticide. J Econ Entomol 18:265–267 Amer A, Mehlhorn H (2006a) Repellency effect of forty-one essential oils against Aedes, Anopheles, and Culex mosquitoes. Parasitol Res 99:478–490 Amer A, Mehlhorn H (2006b) Larvicidal effects of various essential oils against Aedes, Anopheles, and Culex larvae (Diptera: Culicidae). Parasitol Res 99:466–472 Ankamwar B, Damle C, Absar A, Mural S (2005) Biosynthesis of gold and silver nanoparticles using Emblica officinalis fruit extract, their phase transfer and transmetallation in an organic solution. J Nanosci Nanotechnol 10:1665–1671 Asharani PV, Wu YL, Gong ZY, Valiyaveettil S (2008) Toxicity of silver nanoparticles in zebrafish models. Nanotechnology 19:1–8 Baun A, Hartmann NB, Grieger K, Kusk KO (2008) Ecotoxicity of engineered nanoparticles to aquatic invertebrates: a brief review and recommendations for future toxicity testing. Ecotoxicology 17:387–396 Benn T, Westerhoff P (2008) Nanoparticle silver released into water from commercially available sock fabrics. Environ Sci Technol 42:4133–4139 Bernhard L, Bernhard P, Magnussen P (2003) Management of patients with lymphoedema caused by filariasis in northeastern Tanzania: alternative approaches. Physiotherapy 89:743–749 Chen L, Evans JR (2009) Arched structures created by colloidal droplets as they dry. Langmuir 25:11299–11301 Das PK, Pani SP, Krishnamoorthy K (2000) Prospects of elimination of lymphatic filariasis in India. ICMR Bulletin 32(5–6):41–54 Dubey M, Bhadauria S, Kushwah BS (2009) Green synthesis of nanosilver particles from extract of Eucalyptus hybrida (safeda) leaf. Digest J Nanomater Biostruct 4:537–543
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