Herein, the preparation of gold nanoparticles-silk fibroin (SF-AuNPs) dispersion and its label-free colorimetric detection of the organophosphate pesticide, namely chlorpyrifos, at ppb level are reported. The silk fibroin solution was extracted from B. mori silk after performing degumming, dissolving and dialysis steps. This fibroin solution was used for synthesis of gold nanoparticles in-situ without using any external reducing and capping agent. X-ray Diffractometry (XRD), Field Emission Transmission Electron Microscopy (FETEM) along with Surface Plasmon Resonance based optical evaluation confirmed generation of gold nanoparticles within SF matrix. The resultant SF-AuNPs dispersion exhibited rapid and excellent colorimetric pesticide sensing response even at 10 ppb concentration. Effect of additional parameters viz. pH, ionic concentration and interference from other pesticide samples was also studied. Notably, SF-AuNPs dispersion exhibited selective colorimetric pesticide sensing response which can be calibrated. Furthermore, this method was extended to various simulated real life samples such as tap water, soil and agricultural products including plant residues to successfully detect the presence of chlorpyrifos pesticide. The proposed colorimetric sensor system is facile yet effective and can be employed by novice rural population and expert researchers alike. It can be exploited as preliminary tool for label-free colorimetric chlorpyrifos pesticide sensing in water and agricultural products. Pesticides act as toxic compounds to all living organisms and hence used to control the insects, weeds, nematodes and other various pests. The pesticides can be carcinogenic in nature, which can produce disorders in bone marrow and nervous system and can sometimes cause infertility and respiratory diseases. Organophosphates (OPs) are among the major pesticides that are largely used in agriculture owing to their relatively low persistence and high effectiveness in insect and pest eradication 1. They are synthetic esters, amides, or thiol derivatives of the phosphoric, phosphonic, phosphorothioic, or phosphonothioic acids 2,3 and are used all over the world to control agricultural, household and structural pests. They are usually considered as safe for agricultural applications due to their relatively faster degradation rates 4. Over the past several years, organophosphate turned out to be an important parameter for water quality evaluation 5. Pesticides in residual form can enter into humans through the food chain (fishes, raw vegetables, fruits and water) 6. As insecticidal mechanism, OPs inhibit acetylcholine-esterase (AChE) activity in insects providing the pesticide action 4,7,8. However, they can also affect the nervous system of other organisms as well as humans imparting toxicity and number of environmental and health issues associated with them have not only provoked the public concern but also research activities for
