A biosensor based on self-assembled ssDNA(aptamer) and polyethylene glycol functionalized graphene oxide(GO-PEG) has been designed for sensing profenofos in food.The sensor has employed the fluorescence “on/off” switching strategy in a single step in homogeneous solution.Compared to traditional detection methods,the strategy proposed here is simple,convenient,fast and sensitive.Furthermore,compared with the general aptamer-GO structure,this aptamer-GO-PEG structure is in possession of a better detection performance,which is largely attributed to the improvement of the biocompatibility and the adjustment of the adsorption capacity of GO by grafting the blocking agent PEG onto the surface of GO.Additionally,the improved biocompatibility of GO shows better stability in salt solutions and physiological solutions,which is more conducive to its practical application in foods.Ii this project,profenofos had been detected with the proposed strategy,and the limit of detection has been controlled to be 0.21 ng/mL.This aptasensing assay has been applied to determining profenofos in (spiked)tap water,cabbage and milk with the recovery values ranging from 93.1％ to 108.5％,from 90.8％ to 113.2％ and from 105.9％ to 114.2％,respectively.