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RESEARCH ARTICLE
Year : 2022 | Volume
: 59
| Issue : 3 | Page : 216-227
Mosquito larvicidal potential of Solanum xanthocarpum leaf extract derived silver nanoparticles and its bio-toxicity on non-target aquatic organism
Pawan Kumar1, Dinesh Kumar1, Vikram Kumar1, RPS Chauhan2, Himmat Singh1
1 ICMR-National Institute of Malaria Research, New Delhi, India
2 Department of Biochemistry, Magadh University, Bodh Gaya Bihar, India
Correspondence Address:
Dr. Himmat Singh
Vector Biology, ICMR-National Institute of Malaria Research, Delhi 110077
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/0972-9062.325635
Background & objectives: Mosquitoes are insects of public health importance that act as a vector to transmit various vector-borne diseases in humans including dengue, malaria, filariasis and yellow fever. The continually employed synthetic insecticides have developed resistance in mosquitoes. Nano-based botanical insecticides can be considered as the best alternative due to several advantages like being simple, non-pathogenic, biodegradable and safe to the environment. The present work reported the maximum larvicidal potential of green synthesized silver nanoparticles (AgNPs) derived from the leaf extract of Solanum xanthoearpum against the third instar larvae of Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus over its crude leaf extract.
Methods: The synthesis of AgNPs was done by adding leaf extract into silver nitrate solution in a conical flask. The characterization of AgNPs was done using different techniques such as UV-Vis, SEM, TEM, XRD, DLS and SAED. FT-IR analysis was done to find out the compound responsible for bio-reduction of silver nitrate. Larvicidal activity of AgNPs was checked against An. stephensi, Ae. aegypti, and Cx. quinquefasciatus according to WHO standard protocol and toxicity was evaluated against Poecilia reticulate.
Results: A change in colour was observed indicating the synthesis of AgNPs which was further confirmed by a strong surface plasmon resonance peak at 421nm under the UV-Vis spectrum. SEM and TEM micrographs exhibited that the most common shape of AgNPs was spherical. XRD spectrum showed crystalline nature of silver nanoparticles. FT-IR spectrum showed the presence of various functional groups such as carboxyl and hydroxyl which might be responsible for bio-reduction and capping of silver nanoparticles. Further, silver nanoparticles were very effective against An. stephensi, Ae. aegypti, and Cx. quinquefasciatus with LC50 and LC90 values of 1.90, 2.36, 2.93, 3.82, 4.31 and 7.63 ppm, respectively, as compared to aqueous leaf extract after 72 h of exposure and were non-toxic against non-target organism P. retieulata.
Interpretation & eonelusion: From the above finding, it can be concluded that fabricated AgNPs can be promising eco-friendly tools for controlling mosquito vectors.
Keywords: AgNPs; UV-Visible; FT-IR; XRD; SEM
Mosquitoes belonging to phylum Arthropoda and class Insecta, act as vectors for many pathogens, microbes and parasites[1]. These microbes transmit several diseases, including malaria, dengue, chikungunya, Zika, Japanese encephalitis and lymphatic filariasis, which are a significant public health concern[2]. Anopheles is a genus of mosquito that acts as a vector of several Plasmodium species and is responsible for malaria disease transmission[3]. Malaria is one of the largest tropical diseases and it is endemic in 109 countries. Most are situated in the African, Asian and Latin American based on cross region[4]. Though drug prophylaxis is available for malaria but it still faces significant challenges. There are reports of parasite strains developing resistance to artemisinin drug[5]. The vaccines RTS,S discovered are not found to be effective in the case of malaria[6]. The inadequate health infrastructure and poor socioeconomic conditions have further worsened the control measures of malaria for the low, marginalized population in tropical and subtropical countries of the world. Therefore, vector control can play an essential role in reducing the incidence of vector-borne diseases such as malaria, dengue, Zika, and filariasis[7]. The application of synthetic larvicides is one of the common approaches used in vector population control. Consequently, nonjudicious usage of insecticides has resulted in insecticide resistance in mosquitoes and negative effects on the environment, including persistent residues and toxicity towards non-target organisms including humans[8]. In addition to this, insecticides have high operational cost[8]. The rapid development of insecticide resistance in vectors and limitations of insecticidal agents has prompted the need for novel insecticides, biological tools and alternative methods to supplement vector control[9],[10]. Insecticides from natural sources such as plants are preferred because they are target-specific, biodegradable, and ecofriendly[11]. Insecticides from plant origins have different mechanisms of action, which reduces the chances of developing resistance in mosquito populations[12]. In the present scenario, nanomaterials like green synthesized silver nanoparticles (AgNPs) offer a sustainable and eco-friendly tool for vector control. Silver nanoparticles are most important among nanomaterials due to their unique chemical and physical properties. They are used in many applications, including medicine, electronic devices, and catalysis, anti-microbial agent, inks, sensors, and pest management[7],[13],[14]. Synthesis of silver nanoparticles using chemical methods generates many hazardous byproducts[15]. In this context, the green combination of silver nanoparticles is an economical and biodegradable process as it does not involve high pressure, energy, temperature, surfactants, and toxic chemicals[16],[17]. Moreover, green synthesized silver nanoparticles (AgNPs) are preferred as safe eco-friendly larvicidal on account of lesser toxicity towards non-target organism and novel mode of action[6]. Fabrication of Ag-NPs using various plants leaves extracts such as Oxalis stricta, Curcuma zedoaria, Aquilaria sinensis and Pogostemon, and Barleria cristata are well-acknowledged in literature[18],[19],[20],[21]. S. xanthocarpum is prevalent in the tropics and warm temperate regions of the world as a weed and is known to be associated with various properties such as anti-cancer, anti-oxidant, anti-HIV, anti-bacterial and insecticidal[22],[23],[24],[25]. In this article, an attempt has been made to develop AgNPs using S. xanthocarpum leaves extract and evaluate its potential role as a larvicidal activity to explore its mode of action further.
Material & MethodsCollection of plant material and leaf extract preparation
The green leaves of Solanum xanthocarpum (L.) were collected from a plant growing near the recreational area (latitude 28.56°N; longitude 77.06°E) of Dwarka, Sector-8, New Delhi, India [Figure 1]A and washed with running tap water to remove soil particles and other contaminants. The leaves were shade dried at 26±5°C RT, for one week before they were ready to use. The leaves become rigid and then smashed into a fine powder using pestle and mortar. Subsequently, 10g of fine powder was mixed in 100ml water and kept incubator shaker for continuous stirring in a 250ml conical flask for 25 min. The mixture or extract was filtered through Whatman filter paper No.1. The filtrate was collected and residue was discarded. The filtrate was concentrated and stored at 4°C for further experiments.
Figure 1: (A) In vivo grown plant of Solanum xanthocarpum collect from Dwarka Sector-8, New Delhi, India; (B) Chromatic variation of the S. xanthocarpum leaves extract after adding 1 mM silver nitrate solution; (C) UV–visible spectrum S. xanthocarpum derived silver nanoparticles showing strong absorption bands at 421nm; (D) XRD spectrum of S. xanthocarpum leave derived AgNPs using 1 mM AgNO3; (E & F) SEM images of S. xanthocarpum derived AgNPs showing spherical in shape with the range of 10-20 nm.Synthesis of silver nanoparticles
For silver nanoparticles synthesis, 5g powder of S. xanthocarpum was mixed with 50 ml of double distilled water and heated at 50°C for 30 min to obtained bioactive compound present in leaf extract. The mixture was filtered through Whatman filter paper No.1. and 3.5 ml of above filtrate was added into 46.5ml solution of 1mM silver nitrate (AgNO3) in a 250 ml conical flask and was heated at 60±5°C with continuous stirring for 25min. Slowly, colour change of the solution observed through reduction of silver ions to metallic silver, which depicts the synthesis of silver nanoparticles. Primarily, the light yellowish colour changes to dark brown indicate initial development of silver nanoparticles (AgNPs). The solution was centrifuged at 8000 rpm for 20 min and the pallet was collected and dehydrated overnight at 50°C in an oven. The pellet was stored at 4°C for characterization and bioassay analysis.
Characterization of silver nanoparticles
Silver nanoparticles synthesis was determined by the change in colour of the reaction mixture i.e., from pale yellowish to dark brown. UV-V spectrum analysis is one of the most efficient methods to find out AgNPs production at the initial stage. It was also verified by a specific peak measured in the solution’s spectrum using UV-Visible spectrophotometer analysis (Double beam spectrophotometer model no BRI-2700). The operating range of wavelength was from 350 to 700 nm. Silver nanoparticles prepared under standard condition was centrifuged, residue was collected and freeze dried in order to obtain its powder form, 5-6 mg of silver nanoparticles powder was subject to X-ray diffraction (XRD) analysis. XRD analysis was used for characterization of crystalline form of the AgNPs. XRD was done through Philips Xpert pro-XRD System working under given conditions current 40 mA with Cu ka radiation of 0.1541 nm voltage 40 kV; step size, 0.02/h, 2θ range 20°–80° at Instrumentation Research Facility (AIRF)’ Jawahar Lal Nehru University (JNU), New Delhi, India. Further, analysis of surface morphology, distribution and elemental nature of AgNPs silver nanoparticles subjected to scanning electron microscopy (SEM) and transmission electron microscopy analysis. SEM coupled with energy dispersive X-ray’ processing unit used to analyze topology and shape of silver nanoparticles. EDX spectrum was used to confirm the elemental nature of AgNPs. A very small amount of silver nanoparticles was dropped on carbon coated grid and subjected to SEM analysis by using TM-1000 (SEM, Carl Zeiss EVO 40, München, Germany). The scanning was performed with a voltage of 20 kV. Transmission electron microscopy and selected area electron diffraction was done using TEM (Tecnai G20 FEI, Oregon, USA) in order to characterize the size, shape, and distribution of biosynthesis silver nanoparticles AgNPs. The accelerating voltage was 50–300 kV for the silver nanoparticles. Stability of silver nanoparticles was determined through Dynamic light scattering (DLS) analysis. DLS analysis was used to determine the size and stability of silver nanoparticles through Zetasizer Nano-ZEN3600, Malvern Instruments Pvt. Ltd., UK at 25°C in AIIMS, New Delhi, India. To find out bio-molecule involved bioreduction, AgNPs solution was subjected to Fourier transforms infrared spectroscopy (FT-IR) analysis. Aqueous leaf extract of S. xanthocarpum was analyzed using FT-IR for the determination of functional group responsible for biosynthesis of AgNPs. The analysis was done in ATR mode (Perkin-Elmer 1600 series FT-IR spectrometer) in Advanced Instrumentation Research Facility’ JNU, New Delhi, India.
Mosquito culture
Cyclic colonies of An. stephensi, Ae. aegypti, and Cx. quinquefasciatus were maintained in ICMR-National Institute of Malaria Research (NIMR), Delhi, India, retained under a photoperiod of 14:10 (day/light) at 27±5°C, for a comparative humidity of 75–85%. Mosquitoes were kept in 30 cm3 organdy cloth cages tied on iron frame and 10% glucose solution was given as energy source. Mosquito feeding was carried out in insectary. Small plastic container lined with filter paper on water surface was used by gravid females for oviposition of their eggs. Eggs were undisturbed for 48 h for hatching. The hatched larvae fed on powdered of dog biscuit and fish food (6:4) ratio.
Bio-assay study of aqueous leaf extract and AgNPs derived from S. xanthocarpum
The third stage larvae of An. stephensi, Ae. aegypti and Cx. quinquefasciatus were reared at insectary of ICMR-NIMR, New Delhi, India and were exposed to various concentrations of leaf extract and silver nanoparticles synthesized from S. xanthocarpum to assess lethal dose using WHO protocol[26]. Stock solutions of crude leaf extact and AgNPs were prepared, individually by dissolving 1g of sample in 500 ml of water and further dilutions were made using de-chlorinated water in order to test concentrations. Different concentrations of aqueous leaf extract (250, 500, 750, 1000, 1250 and 1500 ppm) and AgNPs (2.5, 5, 10, 15, 20 and 25 ppm) were made in triplicate from stocks concentrations using double distilled water. Twenty-five larvae of above said vectors were exposed to different concentrations of aqueous leaf extract and AgNPs in a beaker containing 1 ml solution and 249 ml of water and experiments were run in triplicate with dechlorinated water and 1 mM silver nitrate as a control. All bioassays were conducted at room temperature and no food was provided to larvae during exposure period. Larvae were provided with larval food after 24 h of observations.
Bioassay study against non-target organism P. reticulata
The poisonous effects of AgNPs were checked against a non-target organism, P. reticulata which was collected from the cemented pools of ICMR-NIMR, Delhi and brought to the laboratory for further experiments. Patil et al.,[27] procedure was followed for the evaluation of toxic effect against non-target organism. P. reticulata species 25 in number were kept within (500 ml) competence of the plastic little bowls and exposed to 200 ml of experiment concentrations (LC concentrations) of AgNPs for 72 h at 28°C RT.
Data analysis
Larvicidal mortality was calculated after 24 h, 48 h, and 72 h of AgNPs treatments, as well as the resulting lethal dosage (LC50 and LC90 values), high and low confidence limit (UCL-LCL), chi-square value, and regressions equation calculated according to Probitanalysis[28]using the SPSS software 20, windows 16. Comparative efficacy was also evaluated between aqueous leaf extract and AgNPs.
Ethical statement: Not applicable
ResultsA colour transition of the reaction mixture from the pale yellowish to dark brown showed complete reduction of silver nitrate by addition of leaf extract which depicted the synthesis of silver nanoparticles [Figure 1]B. The Ultraviolet–visible spectroscopy showed significant bands at (421nm) which confirmed [Figure 1]C the synthesis of silver nanoparticles. No colour change was observed in silver nitrate without addition of plant extract, indicating that the plants have different compounds which might be involved in the reduction of silver nitrate. Further, XRD analysis of AgNPs depicted crystalline nature of AgNPs synthesized using S. xanthocarpum leaves extracts. The crystalline character of nanoparticles in terms of cubic closest packed structure was clearly demonstrated by Bragg reflection values of 38.46 (111), 44.64 (200), 64.71 (220), and 77.38 (311) at 2Θ angles in the lattice planes [Figure 1]D. The presence of different bio-molecules in aqueous leaves extracts that serve as capping and reducing agents is indicated by the sharp peaks found in XRD patterns. There are also several unassigned small peaks in the XRD pattern that may appear because of bio-compound interactions over the AgNPs surface. SEM image of S. xanthocarpum leaf extract derived silver nanoparticles showed individual as well as aggregated nanoparticles, [Figure 1]E & [Figure]F. The particles were primarily spherical, and they combine into larger particles with no specific and measurable morphology. The size of the AgNPs nanoparticles can be seen in the SEM image, which was in the range of 10 to 20 nm. The TEM micrograph of S. xanthocarpum derived Ag-NPs showed that the major nanoparticles were spherical shaped and formed in the range of 10–20nm [Figure 2]A & [Figure 2]B. The synthesized nanoparticles are fine, dispersing through small agglomerations. The S. xanthocarpum synthesized silver nanoparticles showed the presence of elemental nature of silver which was measured through TEM-EDAX analysis and confirmed by presence of heavy absorption band at 3keV [Figure 2]C. The absorption band across the spectrum 0.1-0.5keV in EDAX is due to the presence of carbon, nitrogen, and oxygen in leaf extract. The SAED of AgNPs showed single crystalline nature of AgNPs which indicates the spot type pattern of nanoparticles [Figure 2]D. DLS analysis revealed a highly negative zeta potential of S. xanthocarpum synthesized AgNPs (-19.7 mV), which confirmed that the biosynthesized Ag-NPs in the solvent were extremely stable [Figure 2]E. FT-IR studies have shown the presence of different functional groups in leaves extracts of S. xanthocarpum which might be involved in bio-reduction of AgNPs. FT-IR spectrum of AgNPs indicated strong magnification peaks at 3212, 2976, 2378,1640,1408,1380,1239,1094,1054, 1046 and 895cm-1, corresponding to functional groups (O–H phenol), (C-H), (O=C=O), (C=C), (S=O), (O-H alcohol), (CN), (C-O), (S=O), (CO-O-CO) and (C=C) and represent following compounds carboxylic acid, alkenes, carbon dioxide, sulfonyl chloride, phenolic, amine, anhydride and sulfoxide, respectively [Table 1], [Figure 3].
Table 1: FT-IR profile of plant extract shows the functional groups responsible for AgNO3 reduction
Figure 2: (A & B) TEM images of S. xanthocarpum synthesized AgNPs with the size of 5–20 nm. (scale bar; E=20 nm, F=10 nm); (C) EDAX spectrum of S. xanthocarpum synthesized AgNPs showing absorption band at 3 keV; (D) SAED spectrum of S. xanthocarpum synthesized AgNPs showing single crystalline nature of particles; (E) Zeta potential of S. xanthocarpum leaf derived AgNPs.
Figure 3: FT-IR spectrum of S. xanthocarpum derived AgNPs prepared using 1mM AgNO3.The bio-efficacy of silver nanoparticles derived from leaf extract S. xanthocarpum and its aqueous leaf extract were evaluated against 3rd instar larvae of An. stephensi, Ae. aegypti and Cx. quinquefasciatus. The AgNPs exhibited strong larvicidal activity against An. stephensi (LC50-1.90 and LC90-3.82 ppm) followed by Ae. aegypti (LC50-2.36 and LC90-4.31ppm) and Cx. Quinquefasciatus (LC50-2.93 and LC90-7.63 ppm) as compared to aqueous leaves extract having LC50 and LC90 values were 1089.341, 1239.173, 999.265, 2057.65, 2007.178 and 1850.382 ppm, respectively, after 72 h of treatment [Figure 4] & [Table 2]. More than 100 times reduction in concentration was found to be reported in case of AgNPs compared to its crude extract. Zero percent mortality was recorded in controls (1mM AgNO3 solution, de-chlorinated water). S. xanthocarpum biosynthesized AgNPs prove to be non-toxic against non-target organisms, P. reticulata at concentrations (LC50 and LC90) that exhibited toxicity on the larvae of Ae. aegypti, An. stephensi and Cx. quinquefasciatus.
Table 2: Log probit and regression analysis of Solanum xanthocarpum leaf extracts against the 3rd instar larvae of Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus
Figure 4: Graphical representation of lethal doses (LC50/90) causing mortality against Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus larvae using crude leaf extract and AgNPs synthesized using S. xanthocarpum. (A) A. stephensi, (B) A. aegypti (C) C. quinquefasciatus; (AE=aqueous leaf extract; AgNPs=Silver nanoparticles). Discussion Nanoparticles synthesis has gained much attention due to its wide range of application in various fields such as pharmaceuticals, optronics, sensing and catalysis. Synthesis of AgNPs using plants has more advantage over other methods including non-pathogenic, single procedure and non-toxic to non-target organism[6]. Green synthesis means simply adding of aqueous solution of metal salt into plant extract which produced AgNPs. In the present study, the colour change of solution from yellow to dark brown was observed after adding S. xanthocarpum leaf extract in silver nitrate solution. The colour change of the solution was due to surface plasmon resonance excitation (SPR) which arises by combined vibration of free electrons in resonance with light wave[29]. In Atropa belladonna a similar result was reported where positive correlation was found between change in color as well as the AgNPs synthesis[30]. The SPR vibrations also confirmed the silver existence of AgNPs by showing strong absorption peak at 421nm. A prominent absorption peak was seen at 320 nm Origanum vulgare derived silver nanoparticles[31]. Similar UV-V is spectrum peak (420nm) in Holarrhena antidysenterica bark extract prepared AgNPs[32]. Plants have different compounds such as terpenoids, chlorophyll pigments, alcoholic compounds, alkaloids, phenolics, amino acids, polysaccharides, proteins, caffeine, theophylline, flavones, methylchavicol, linalool, ascorbic acid, quinol and enzymes which participated in bio-reduction of silver nitrate and synthesis of AgNPs[33],[34],[35]. In the present study, it was also seen that crude leaf extract of S. xanthocarpum has various compounds such as phenol, terpenoid, alkaloid, tannins and amino acids which might be involved in bioreduction of silver nitrate. S. xanthocarpum synthesized silver nanoparticles were crystalline in nature as observed in XRD spectrum. Crystalline nature was also observed in Salvia officinalis derived AgNPs[36]. Several authors have reported similar findings in various plants[37],[38]. Individual or aggregated with average size of 10–20nm of S. xanthocarpum derived AgNPs were reported through SEM images. AgNPs spherical in shape and somewhere they combine into large particles without showing any specific morphology. As a high-energy electron beam interacts with a compound’s constituents, it produces signals that reveal valuable details about the compound’s structure, particle size, and other properties such as electrical conductivity[30]. Clustered and irregular shape AgNPs were reported in Salvia officinalis synthesized AgNPs through SEM analysis[36]. Hypnea musciformis synthesized AgNPs were also spherical in shape[39]. The TEM micrograph of S. xanthocarpum derived AgNPs were small agglomeration, fine and agglomerated or dispersed. The results of the study were comparable with the findings of other studies, where spherical well distributed nanoparticles were reported in Atropa belladonna with an average size 15–20 nm[30]. Similarly, spherical shapes AgNPs were reported in case of Cullen corylifolium aqueous seed extract[40].
EDAX spectrum confirmed silver elemental nature of AgNPs. In A. belladonna similar findings were obtained by researchers where absorption peak at 3keV was found in EDAX spectrum confirmed elemental silver presence in AgNPs[30]. SAED analysis confirms crystalline nature with spot type pattern of AgNPs. Polycrystalline and monodispersed silver nanoparticles were reported from Cullen corylifolium seed extract as depicted by SAED analysis[40]. The zeta potential is associated with the net surface charge that nanoparticles have. The magnitude of electrostatic repulsion between nanoparticles in a solution is measured by zeta potential. Nanoparticles with zeta potentials of just under 15mV or more than 15mV in colloidal solution have a higher degree of stability[41]. This analysis revealed a highly negative zeta potential of synthesized AgNPs (-19.7 mV), confirmed that the biosynthesized AgNPs in the solvent were extremely stable. Comparable negative zeta potential -28.1mV was also reported in Rhynchosiasuaveolens mediated AgNPs which was highly stable[42]. Zeta potential of S. xanthocarpum derived AgNPs was highly negative which confirmed extremely stable Ag-NPs. Several functional groups have been reported in the leaf aqueous extract of S. xanthocarpum through FT-IR analysis which might be involved in capping and reduction of AgNPs. The results of this study are comparable with the results of other studies which reported few strong peaks at 3311, 1637 and 1047 cm–1, corresponding to N-H, H-O-H and C-O functional groups in belladonna mother tincture derived AgNPs[30]. FT-IR spectrum showed the presence of carboxylic acid, alkane, phenol, alcohols, amines, sulfonyl chloride, anhydride group and sulfoxide compounds, among other biomolecule, definitely involved in reduction, capping and stabilization of AgNPs[43]. These bio-molecules are efficiently involved in binding as well as stabilization of nanoparticles. This capping stops nanoparticles from integration and allopathic in the colloidal system to produce highly stable AgNPs.
In recent times, green synthesized silver nanoparticles have great potential to control vector borne diseases[44],[45]. It has been reported that silver nanoparticles have strong larvicidal activity as compared to the plant extract itself. In this study, maximum larvicidal activity was reported in S. xanthocarpum leaf extract derived silver nanoparticles as compared to leaf extract. Silver nanoparticles showed strong larvicidal activity against An. stephensi, Ae. aegypti, Cx. quinquefasciatus having LC50 and LC90 values 1.90, 2.36, 2.93, 3.82, 4.31 and 7.63 ppm, respectively, as compared to aqueous leaves extract having LC50 and LC90 value were 1089.341, 1239.173, 999.265, 2057.65, 2007.178 and 1850.382 ppm, respectively, after 72 h of treatment. Comparable findings were also observed and reported in Piper longum derived silver nanoparticles against An. stephensi, Ae. aegypti, and Cx. quinquefasciatus, with LC50 and LC90 values of 8.96, 14.79, 18.66 and 16.10, 28.53, 40.90 ppm, respectively, after 72 h of exposure[46]. Similarly, Aganosma cymosa leaf extract derived silver nanoparticles have strong larvicidal efficacy against An. stephensi, Ae. aegypti and Cx. quinquefasciatus having LC50 values 12.45, 13.58 and 14.79 μg/mL, respectively[47]. A strong larvicidal activity was observed in case of Blumea mollis derived silver nanoparticles against Anopheles subpictus, Aedes vittatus and Culex vishnui with LC50/LC90 values 18.17/39.56, 21.82/40.431 and 23.45/42.49, μg/ml, respectively[48]. Similarly, minimum LC50 (0.28 ppm) and LC90 (0.43 ppm) values were reported in Ambrosia arborescens leaf derived AgNPs against Ae. aegypti over its aqueous leaf extract having LC50 and LC90 values 1844.61 and 6043.95 ppm, respectively[49]. Sutthanont et al[50], while working on Curcuma zedoaria synthesized silver nanoparticles reported strong larvicidal activity having LC50 and LC90 values 0.64 and 8.88 ppm, respectively, against the larvae of Cx. quinquefasciatus. Likewise, LC50 (1.02 and 1.04 ppm) and LC90 (2.49 and 2.85 ppm) values were exhibited in silver nanoparticles derived from Aquilaria sinensis and Pogostemon cablin, respectively, against Ae. albopictus larvae[51].
AgNPs have strong larvicidal activity due to small dimension, which helps them move throughout the cuticle of insect’s larvae. Within the membrane AgNPs can bind to sulphur and phosphorus groups, causing abnormal cell activity, resulting in death of mosquito larvae[49],[50]. Several research papers are available but the exact mechanism for the toxic behavior of silver nanoparticles towards mosquito is still unknown. Shahzad and Manzoor[52] mentioned that AgNPs induced toxicity in insect through necrosis, depigmentation, and cellular disorganization, breakdown of endo and exocuticle and loss of hair. Death of the larvae was reported due to creation of dark pots in the body of Ae. aegypti due to the dissemination of AgNPs[53]. When the larvae Ae. albopictus and Cx. pipiens pallens were exposed to Cassia fistula synthesized silver nanoparticles at 1.7 to 3.6 mg/L concentrations, a significant reduction of total protein content, acetylcholinesteras and carboxylesterase activities was observed[54]. Few authors also mentioned that AgNPs disrupt body temperature regulation and molting process in insect[55]. Degradation of membrane and nuclei, disintegration of epithelial cells, vacuolization of cell and cytopathological variations was also observed in the larvae of Ae. albopictus when exposed to different concentrations of AgNPs[51]. A significant CAT and SOD activity was increased and GPX activity was decreased when An. stephensi larvae was treated with AgNPs. Ag-NPs induced ROS production through over expression CAT and SOD and ROS production is directly linked to cytochrome c and programmed cell death in mosquito[56]. S. xanthocarpum derived silver nanoparticles were nontoxic towards non-target organisms, P. reticulata when exposed at concentrations (LC50 and LC90) that exhibited toxicity on the larvae of Ae. aegypti, An. stephensi and Cx. quinquefasciatus. The findings of the present study directly corroborated with the findings of other studies in which researchers have synthesized AgNPs using Plumeria rubra and Pergularia daemia and reported that AgNPs do not show any poisonous effect against P. reticulata fish and other organisms[57],[58],[59]. The current research work highlights the simple, economical and environmentally sustainable approach for silver nanoparticles synthesis using leaf extract of S. xanthocarpum and its strong larvicidal activity against different mosquito vectors. Many authors have reported that plants derived silver nanoparticles are quick, simple, environmentally sound and economical[60],[61].
ConclusionCurrently there is an urgent requirement to provide an efficient synthesis of AgNPs which are environment friendly, less expensive, non-toxic and biodegradable in nature. In the present study, non-toxic, cheap and ecofriendly AgNPs were synthesized using S. xanthocarpum leaf extract. Silver nanoparticles were synthesized by adding aqueous leaf extract S. xanthocarpum into silver nitrate solution; change in colour was observed confirming AgNPs synthesis. SEM, TEM and XRD analysis showed that AgNPs were spherical in shape with crystalline nature. The FT-IR analysis of AgNPs extract indicated the presence of different functional groups that might be responsible for bio-reduction, capping and stabilization of AgNPs. Leaves extracts can be used as a strong reducing and binding agents for large-scale production of AgNPs that are small in size and have excellent stability. AgNPs synthesized in the present study showed outstanding larvicidal potency against 3rd star larvae of the An. stephensi (LC50-1.90 and LC90-3.82ppm), Ae. aegypti (LC50-2.36 and LC90-4.31ppm) and Cx. quinquefasciatus (LC50-2.93 and LC90-7.63ppm) without harming the non-target organism P. reticulata (guppy) after 72 h of treatment.
Conflict of interest: None
AcknowledgementsThe authors are grateful to the Director of ICMR-National Institute of Malaria Research, Dwarka, Sector-8, New Delhi, India for providing necessary infrastructure and support during the research work of this study. DK is indebted to Indian Council of Medical Research, India for awarding Post-Doctoral Research Fellowship.
References
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