Synthesis, characterization and evaluation of nanoparticles of public health larvicides for mosquito control.

or solid particles with a size in the range of 10–1000 nm. Depending upon the method of preparation, nanoparticles, nanospheres or nanocapsules can be obtained. Controlled release and particle degradation characteristics can readily be modulated by the choice of matrix constituents1. Efficacy of Chrysosporium tropicum, a pathogenic fungus mediated silver and gold nanoparticles was reported against Aedes aegypti2. The silver nanoparticles, synthesized with the leaf extract of Eclipta prostrata, were studied for their larvicidal activity against Culex quinquefasciatus and Anopheles subpictus3. Santhoshkumar et al4 also synthesized silver nanoparticles using Nelumbo nucifera leaf extract and studied their larvicidal activity against filariasis and malaria vectors. A number of liposomes (lipidic nanoparticles) currently in the market are the first nanomedicine delivery system to make the transition from concept to clinical application, and these are now on the established technology platform with considerable clinical acceptance5. Until recently, there has been no report on the development of nanoparticles for the used chemical larvicides in the mosquito control programme. The current study deals with the preparation of nanoparticles of two mosquito larvicides of organophosphorous group, viz. temephos and pirimiphos-methyl and an indigenous insect growth regulator ( IGR), DPE-28 (2,6-ditertiarybutyl phenyl-2’,4’-dinitro phenyl ether), which was reported to be effective against Cx. quinquefasciatus with an EI50 value of 2.2 × 10 -3 mg/l6 and with assessing the potential whether the nanoparticles-based formulation could improve the biological activity of the larvicides than the conventional emulsifiable concentrate formulation of the respective larvicides. Nanoparticles are generally prepared by three methods: (i) dispersion of preformed polymers; (ii) polymerization of monomers; and (iii) ionic gelation or coacervation of hydrophilic polymers. Out of these three methods, dispersion of preformed polymers is a common technique used to prepare biodegradable nanoparticles. In this method, the polymer is dissolved in an organic solvent which is also used for dissolving the hydrophobic technical grade material which may be a drug or insecticide. The mixture of polymer and insecticide solution is then emulsified in an aqueous solution containing a surfactant or emulsifying agent to form an oil in water (o/w) emulsion. After the formation of stable emulsion, the organic solvent is evaporated either by reducing the pressure or by continuous stirring. Particle size was found to be influenced by the type and concentrations of stabilizer, homogenizer speed and polymer concentration7. The nanoparticles of the larvicides, temephos, pirimiphos-methyl and the IGR, DPE-28 were obtained by the method of dispersion of preformed polymers. An aqueous solution (B) of sodium lauryl sulphate (2 g) in distilled water (20 ml) was added drop-wise with magnetic stirring to the organic phase (A) obtained by mixing the solution of polyvinylpyrrolidone (PVP) (2 g) in dichloromethane (20 ml) with the solution of technical grade larvicide (0.5 g) in dichloromethane (20 ml) to yield a stable emulsion. The emulsion was stirred for 6 h and stored at –40°C for overnight. The solvents from the freeze-dried emulsion were stripped off using a Lyophilizer at 0.1 Torr. The nanoparticles without a larvicide and with the larvicide (10%) were obtained as amorphous powder. The properties of nanoparticles vary significantly with their size and shape, and therefore, accurate measurement of these two characteristics of nanoparticles is critical to their application. The nanoparticles obtained for the larvicides, temephos and pirimiphos-methyl and the IGR, DPE28 were characterized using a scanning electron microscope (SEM Hitachi S 3400) that scanned the surface of the sample in a raster pattern, utilizing an electron beam. J Vector Borne Dis 50, September 2013, pp. 225–228