Facile formulation of starch–silver-nanoparticle encapsulated dichlorvos and chlorpyrifos for enhanced insecticide delivery
The facile formulation of starch–silver nanoparticle encapsulated dichlorvos and chlorpyrifos, respectively, was explored in this study with the view to develop a safer and more economical insecticide delivery system. The nanoparticle matrices were synthesized and the insecticides encapsulated in situ during the chemical reduction of silver nitrate by glucose employing direct heating. The starch–silver nanoparticle encapsulation of dichlorvos (ST–AgNP–VOS) and chlorpyrifos (ST–AgNP–FOS) was confirmed by UV-Vis spectroscopy and characterized by HR-TEM, EDX, SAED, FTIR, XRD and FESEM. The characteristic colour of AgNPs was observed and surface plasmon resonance (SPR) of the materials was found to be in the range of 418–422 nm. In addition, the XRD results revealed the silver identification diffraction peaks at 2θ angles in each formulation. The insecticide encapsulation efficiency was about 95% for ST–AgNP–VOS and 98% for ST–AgNP–FOS. Compared to control having no silver (NDVOS), both materials showed better insecticide loading. Their HR-TEM images indicated spherical natures of the materials with an average particle size range of 23–35 nm. The FESEM image showed spheres as well and a size close to that indicated by HR-TEM analysis. FTIR also confirmed the loading of dichlorvos and chlorpyrifos with additional peaks corresponding to them, compared to the insecticide-free starch. These nano-insecticide formulations were subjected to aqueous release studies. The result showed an enhanced release over the formulation without silver nanoparticles. It was concluded that this approach could be used to prepare slow release formulations of these insecticides, with the advantage of the silver nanoparticles also acting as an anti-microbial agent. This current synthetic/encapsulation process can be readily applied to large-scale production.